Solar Hydrogen Fuel Cell Water Heater (Educational Stand)

Cairo University Faculty of Engineering Mechanical Power Dept.

Solar Hydrogen Fuel Cell Water Heater Educational Stand B.Sc. B.S c. Gra Gradua duation tion Pro ect 201 20100

Ahmed Ali Ali El-Beltagy Khaled Ali Ali El-Beltagy Mahmoud Mohamed Emam

Radia M. Fekry El-Deeb Tarek Mahmoud El-Gammal

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The existence of energy was never a problem as much as how to extract, transform, and store it into a useful form. form. Human history tells us stories about fights over energy sources from the simplest food fights, which is the source of energy for the body, to the world wars over the sources of fossil fuels in modern time. Therefore, energy is the soul of life and existence. Human civilization is based on the use of energy in more effective ways to increase the industrial production and human comfort.

One of the most important trends of energy sources in the 21st century is Solar Energy. Solar Energy is a clean, renewable and cheap, actually free-cost, energy source. But the main disadvantages are that it is not available at night, in addition to the high utilization cost. Consequently storing energy is an important issue in order to provide the continuous availability of energy.

Fuel cells offer cleaner, more-efficient alternatives to the combustion of gasoline and other fossil fuels. They have the potential to replace the internal combustion engines in vehicles and provide power in stationary and portable power applications because they are energy-efficient, clean, and fuel-flexible. Hydrogen or any hydrogen-rich fuel can be used by this emerging technology. It is visualized that as fossil fuels run out, hydrogen will become the major world fuel and energy vector.

Cairo University Faculty of Engineering Mechanical Power Dept.

Solar Hydrogen Fuel Cell Water Heater

(Educational Stand) B.Sc. Graduation Project ( 2010 )

Ahmed Ali Ali El-Beltagy Khaled Ali Ali El-Beltagy Mahmoud Mohamed Emam

Radia M. Fekry El-Deeb Tarek Mahmoud El-Gammal

American Society of Heating, Refrigerating, and Air-Conditioning Engineers

“The title of your project is very challenging and demonstrates an exciting approach in teaching. I wish you very successful project realization on the benefit of Cairo students, and in addition might be as an advanced Educational Stand it could become a model for broader world-wide implementation. With the very best wishes and regards”

MarijaTodorovic, Regional Vice Chair, Student Activities Committee, RAL

Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

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CONTENTS

LIST OF FIGURES....................................... FIGURES............................................................. ............................................ ............................................ ........................... ..... viii LIST OF TABLES..................................... TABLES........................................................... ............................................ ............................................ ............................... ......... xiv NOMENCLATURE ......................................... ............................................................... ............................................ ............................................ ......................... ... xv ACKNOWLEDGMENT.......................................... ................................................................ ............................................ .................................... ..............xviii PREFACE ........................................... ................................................................. ............................................ ............................................ ...................................... ................ xix Chapter 1: INTRODUCTION ........................................... ................................................................. ............................................ .............................. ........ 1 Chapter 2: LITERATURE REVIEW ........................................................ .............................................................................. ........................... ..... 4

2.1. Introduction ......................................... ............................................................... ............................................ ............................................ ........................... ..... 5 2.2. Solar Panels ......................................... ............................................................... ............................................ ............................................ ........................... ..... 5 2.2.1. Standing Seam Metal Roofing ............................................ .................................................................. ........................... ..... 5 2.2.2. Vision Glass .................................... .......................................................... ............................................ ......................................... ................... 5 2.2.3. MIT’s Solar Concentrator Window ............................................ ............................................................... ................... 5 2.3. Electrolysis............................................................. ................................................................................... ............................................ .............................. ........ 7 2.3.1. Sea water (Brine) Electrolysis ......................................... ............................................................... .............................. ........ 7 2.4. Fuel Cells …………………………………………………………………………….8 2.4.1. Stationary Systems............................................ .................................................................. ............................................ ........................ 8 2.4.2. Transportation (Automotives) ............................................ .................................................................. ........................... ..... 8 2.4.3. Portable Micro-Power........................................... ................................................................. ......................................... ................... 9 2.5. Commercial Applications........................................... ................................................................. ............................................ ........................ .. 10 2.5.1. Home Energy Station............................................ .................................................................. ....................................... ................. 10 2.6. Experimental Applications .............................. .................................................... ............................................ ................................... ............. 11 2.6.1. Dr FuelCell Science Kit ............................................ .................................................................. ................................... ............. 11 2.6.2. Dr FuelCell Model Car ..................................... ........................................................... ........................................... ..................... 14 2.6.3. Fuel Cell Kit, Green Utility Utilit y House .................................. ........................................................ ............................ ...... 14


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2.6.4. Fuel Cell Car Science Kit ............................................................... ............................................................................ ............. 18 2.7. Conclusion........................................ .............................................................. ............................................ ............................................ ............................ ...... 19 2.8. References.............................................................. .................................................................................... ............................................ ............................ ......20 Chapter 3: PREPARATION .............................................. .................................................................... ............................................ ............................ ...... 21

3.1. Electrolysers........................................................... ................................................................................. ............................................ ............................ ...... 22 3.1.1. Esperanza....................................................... ............................................................................. ............................................ ........................ .. 22 3.1.2. The Fuel Cell Store Electrolysers ........................................... ................................................................ ..................... 22 3.2. Fuel Cells 24 3.2.1. Convection fuel cell stack............................................ .................................................................. ................................ .......... 24 3.2.2. H-Series Fuel Cells .................................... .......................................................... ............................................ ............................ ...... 26 3.3. Further Details .............................. .................................................... ............................................ ............................................ ................................ .......... 29 3.4. Our Choice ........................................... ................................................................. ............................................ ............................................ ........................ .. 31 3.5. Steps towards Purchasing........................................... ................................................................. ............................................ ........................ .. 31 3.6. References.............................................................. .................................................................................... ............................................ ............................ ......34 Chapter 4: COMPONENTS ......................... ............................................... ............................................ ............................................ ............................ ...... 35 ................................................................ ............................................ ............................................ ............................ ...... 36 4.1. SOLAR CELL ..........................................

4.1.1. Brief History ..................................................... ........................................................................... ........................................... ..................... 37 4.1.2. Solar Radiation .......................................... ................................................................ ............................................ ............................ ...... 37 4.1.3. Photovoltaic Solar Cell Systems.......................................... ................................................................ ........................ .. 44 4.1.4. Solar Energy in Egypt........................................... ................................................................. ....................................... ................. 53 4.1.5. References................................... ......................................................... ............................................ ........................................... .....................56 4.2. ELECTROLYSER .......................................... ................................................................ ............................................ ................................... ............. 57 4.2.1. Water Electrolysis Technology............................................ .................................................................. ........................ .. 58 4.2.2. Types of Electrolysers ......................................................... ............................................................................... ........................ .. 59 4.2.3. Elecrolyser and Fuel Cell.......................................... ................................................................ ................................... ............. 61 4.3. FUEL CELL ..................................... ........................................................... ............................................ ............................................ ............................ ...... 62 4.3.1. Introduction...................... Introduction............................................ ............................................ ............................................ ................................ .......... 63 4.3.2. History ............................................ .................................................................. ............................................ ....................................... ................. 63 Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

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4.3.3. Components and their functions .................................. ........................................................ ................................ .......... 64 4.3.4. Operation ............................................ .................................................................. ............................................ ................................... ............. 65 4.3.5. Types of fuel cell .................................................. ........................................................................ ....................................... ................. 66 4.3.6. PEM Fuel Cell (PEMFC).......................................... ................................................................ ................................... ............. 68 4.3.7. References................................... ......................................................... ............................................ ........................................... .....................77 4.4. ELECTRIC LOADS .......................................... ................................................................ ............................................ ................................ .......... 78 4.4.1. The first load: Light Emitting Diode (LED) .......................................... ................................................ ...... 79 4.4.2. The second load: Fan ................................. ....................................................... ............................................ ............................ ...... 79 4.4.3. The third load: Electric Heater ....................................................... .................................................................... ............. 84 4.4.4. References................................... ......................................................... ............................................ ........................................... .....................92 Chapter 5: MODELLING AND TESTING............................................ .................................................................. ............................ ...... 93

5.1. Solar Radiation ................................. ....................................................... ............................................ ............................................ ............................ ...... 94 5.1.1. Definitions .......................................... ................................................................ ............................................ ................................... ............. 94 5.1.2. Modeling Results .............................................. .................................................................... ........................................... ..................... 97 5.2. Photovoltaic Panel ............................ .................................................. ............................................ ............................................ ............................ ...... 99 5.2.1. Technical Data ............................................... ..................................................................... ............................................ ........................ .. 99 5.2.2 Modeling of Photovoltaic cell .......................................... ................................................................ ............................ ...... 99 5.2.3. PV Modelling Results ........................................... ................................................................. ..................................... ............... 104 104 5.3. PEM Electrolyser .............................................................. .................................................................................... ..................................... ............... 107 5.3.1. Technical Data ............................................... ..................................................................... ............................................ ...................... 107 107 5.3.2. Modelling of the PEM Electrolyser ............................................ ........................................................... ............... 108 5.3.3. PEM Modelling Results............................................ .................................................................. ................................. ........... 112 5.4. PEM Fuel Cell .............................. .................................................... ............................................ ............................................ .............................. ........ 117 5.4.1. Technical Data ............................................... ..................................................................... ............................................ ...................... 117 117 5.4.2. Modeling of the PEM Fuel Cell........................................... ................................................................. ...................... 118 5.4.3. PEM Fuel Cell Modelling Results .......................................... ............................................................. ................... 122 5.5. References.............................................................. .................................................................................... ............................................ .......................... .... 127 Chapter 6: MEASURING DEVICES AND CONTROL ......................................... ................................................. ........ 130 130 Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

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6.1. Introduction .......................................... ................................................................ ............................................ ............................................ ......................131 6.2. Measurements ......................................... ............................................................... ............................................ ......................................... ................... 132 6.2.1. General................................................ ...................................................................... ............................................ ................................. ........... 132 6.2.2. Electricity Measurements ........................................................... .......................................................................... ............... 132 132 6.2.3. Thermal Measurements ........................................... ................................................................. .................................. ............ 133 133 6.3. Programming and Control ........................... ................................................. ............................................ ..................................... ............... 135 135 6.3.1. Control of Lamp Position ................................................... ......................................................................... ........................ 135 135 6.3.2. Testing and Assurance ....................... ............................................. ............................................ .................................. ............ 141 6.3.3. Programming ......................................... ............................................................... ............................................ .............................. ........ 143 6.4. References.............................................................. .................................................................................... ............................................ .......................... .... 156 Chapter 7: BILL OF MATERIALS AND COST...................................... COST............................................................ ........................ 157 157 Chapter 8: FABRICATION AND ASSEMBLY ........................................... .............................................................. ................... 161

8.1. Educational Stand Fabrication ......................................................... ............................................................................... ...................... 162 8.1.1. Bench Fabrication ...................................... ............................................................ ............................................ .......................... .... 162 8.1.2. Solar Lamp Movement Fabrication ............................. ................................................... .............................. ........ 169 8.2. Educational Stand Assembly......................................... ............................................................... ......................................... ................... 171 Chapter 9: OPERATING PROCEDURE OF THE EDUCATIONAL STAND ........... 174

9.1. Experiment 1: Investigating the Solar Panel ........................................... .......................................................... ............... 175 9.1.1. Procedure ........................................... ................................................................. ............................................ .................................. ............ 175 9.1.2. Evaluation ............................................................. ................................................................................... ..................................... ............... 176 9.2. Experiment 2: Investigating the characteristic curve of the electrolyser ............... ............... 177 9.2.1. Procedure ........................................... ................................................................. ............................................ .................................. ............ 177 9.2.2. Evaluation ............................................................. ................................................................................... ..................................... ............... 178 9.3. Experiment 3: Investigating the characteristic curve of a fuel cell ........................ ........................ 179 9.3.1. Procedure ........................................... ................................................................. ............................................ .................................. ............ 179 9.3.2. Evaluation ............................................................. ................................................................................... ..................................... ............... 180 9.4. Experiment 4: Solar Heater ......................... ............................................... ............................................ ..................................... ............... 181 9.4.1. Instructions ............................................ .................................................................. ............................................ .............................. ........ 181 Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

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9.4.2. Evaluation ............................................................. ................................................................................... ..................................... ............... 182 9.5. Experiment 5: Fuel Cell Heater......................................... ............................................................... ..................................... ............... 183 9.5.1. Procedure ............................................ .................................................................. ............................................ ................................. ........... 183 9.5.2. Evaluation ............................................................. ................................................................................... ..................................... ............... 183 9.6. Other Experiments .......................................... ................................................................ ............................................ ................................. ........... 184 Chapter 10: TESTS AND RESULTS ................................ ...................................................... ............................................ .......................... .... 185

10.1. Introduction ........................................... ................................................................. ............................................ ......................................... ...................186 10.2. Results and Discussion......................................... ............................................................... ............................................ .......................... .... 186 10.2.1. Electrolyser Characteristics .................................................. ..................................................................... ................... 186 10.2.2. Single Fuel Cell ........................................... ................................................................. ............................................ ...................... 187 10.2.3. Fuel Cells in connection ............................................ .................................................................. .............................. ........ 189 10.2.4. Heaters .......................................... ................................................................ ............................................ ..................................... ............... 192 10.2.5. Solar Cell performance ............................ .................................................. ............................................ .......................... .... 195 10.3. Further Interpretation ............................................................. ................................................................................... .............................. ........ 205 10.3.1. Solar Cell .......................................... ................................................................ ............................................ ................................. ........... 205 10.3.2. Electrolyser .......................................... ................................................................ ............................................ .............................. ........ 205 10.3.3. Fuel Cell ......................... ............................................... ............................................ ............................................ .............................. ........ 206 APPENDICES ........................................... ................................................................. ............................................ ............................................ .............................. ........ 208

Appendix A: THERMOPHYSICAL PROPERTIES OF MATTERS .................................. .................................. 209 Appendix B: FREE CONVECTION HEAT TRANSFER CORRELATIONS .................... .................... 215 215 Appendix C: SOLAR CELL ACTUAL CHARACTERISTIC CURVEINVESTIGATION 219 Appendix D: NI USB-6008 DATA SHEET ........................................... ................................................................. .............................. ........ 230 Appendix E: PT100 TEMPERATURE SENSOR DATA SHEET ....................................... ....................................... 263 Appendix F: EWTR 910 TEMPERATURE PANEL DATA SHEET .................................. .................................. 265 Appendix G: MATLAB CODE ............................................ .................................................................. ............................................ .......................... .... 270 Appendix H: HEATER EXPERIMENTS ........................................... ................................................................. .................................. ............ 294


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LIST OF FIGURES Figure 1.1: Solar Hydrogen Fuel Cell Electric Heater Educational Stand ................................ ........................................ ........ 2

Figure 2.1: MMU solar roof ............................................... ..................................................................... ............................................ ......................................... ................... 6 Figure 2.2: Organic solar concentrators collect and focus diff erent colors of sunlight. Solar cells can be attached to the edges of the plates. By collecting light over their full surface and concentrating it at their edges, these devices reduce the required area of solar cells and consequently, the cost of solar power. Stacking multiple concentrators allows the optimization of solar cells at each wavelength, increasing the overall power output. ................................. ....................................................... ............................................ ...................... 7 Figure 2.3: Toshiba ‘Dynario’ mobile charger ......................................... ............................................................... ......................................... ................... 9 Figure 2.4: From left NEC, Toshiba, Samsung laptops........................................... ................................................................. ........................ .. 10 Figure 2.5: Home Energy Station (HES III) .......................................... ................................................................ .......................................... .................... 10 Figure 2.6: Dr Fuel cell science kit ......................................... ............................................................... ............................................ ................................... ............. 11 Figure 2.7: Dr Fuel cell model Car ......................................... ............................................................... ............................................ ................................... ............. 14 14 Figure 2.8: Fuel Cell Kit, Green Utility House ........................................ .............................................................. ....................................... ................. 17 Figure 2.9: Fuel cell car science kit .................................... .......................................................... ............................................ ....................................... ................. 18

Figure 3.1: Purchase Invoice ...................................................... ............................................................................ ............................................ ............................... ......... 32

Figure 4.1: Variation of extraterrestrial solar radiation with time of year ..................................... ..................................... 38 Figure 4.2: Angles ........................................... ................................................................. ............................................ ............................................ ................................... ............. 40 40 Figure 4.3: Declination angle δ ......................................... ............................................................... ............................................ ....................................... ................. 41 Figure 4.4: Latitude angle ф ........................................... ................................................................. ............................................ .......................................... .................... 41 Figure 4.5: Hour angle ω ............................................ .................................................................. ............................................ ............................................ ........................ .. 4 2 Figure 4.6: Beam radiation on horizontal and tilted surface ......................................... .......................................................... ................. 43


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Figure 4.7: Behaviour of light shining on a solar cell. (1) Reflection and absorption at top contact. (2) Reflection at cell surface. (3) Desired absorption. (4) Reflection from rear out of cell—weakly absorbed light only. (5) Absorption after reflection. (6) Absorption in rear contact..................... contact ....................... .. 46 Figure 4.8: The effect of light on the current-voltage characteristics of a p-n junction .................. 47 Figure 4.9: Typical representation of an I-V curve, showing short-circuit current (Isc and opencircuit voltage (Voc) points, as well as the maximum power point (Vmp, ( Vmp, Imp) ............................ ............................ 47 Figure 4.10: The effect of temperature t emperature on the I-V characteristics of a solar cell .......................... ............................ .. 49 Figure 4.11: Parasitic series and shunt resistances in a solar cell circuit ........................................ ........................................ 50 Figure 4.12: The effect of series resistance on fill factor ......................... ............................................... ....................................... ................. 50 Figure 4.13: A typical laminated module structure (EVA stands for Ethylene Vinyl Acetate) ...... 52 Figure 4.14: Solar radiation world map ........................................... ................................................................. ............................................ ........................ .. 53 Figure 4.15: The average annual direct solar radiation (normal incidence) in Egypt in kWh/d .... 54 Figure 4.16: Kuraymat power station site ............................................ .................................................................. .......................................... .................... 55 Figure 4.17: Water Electrolysis principle .......................................... ................................................................ ............................................ ........................ .. 58 Figure 4.18: Schematic drawing of a PEM cell with cell reactions .......................................... ................................................ ...... 60 Figure 4.19: Schematic drawing of a Solid Oxide Electrolyser ..................................... ...................................................... ................. 61 Figure 4.20: Fuel cell ........................................... ................................................................. ............................................ ............................................ ............................... ......... 63 Figure 4.21: Schematic diagrams for the PEMFC basic components and the reactants/ions/products flow ............................................ .................................................................. ............................................ ............................................ ............................................ ................................... ............. 65 Figure 4.22: An example of a membrane electrode assembly assembly (MEA). The membrane is a little larger than the electrodes that are attached. These electrodes have the gas diffusion layer attached, which gives it a ‘grainy’ texture. The membrane is typically 0.05 to 0.1mm thick, the electrodes are about 0.03mm thick, and the gas diffusion layer is between 0.2 and 0.5-mm thick. .............................. ................................ .. 69 Figure 4.23: Cathode–electrolyte–anode construction of a fuel cell ........................... ............................................... .................... 70 Figure 4.24: Electrode reactions and charge flow for an acid electrolyte fuel cell. Note that although the negative electrons flow from anode to cathode, the ‘conventional current’ flows from cathode to anode. ......................................... ............................................................... ............................................ ............................................ ............................................ ................................... ............. 70 Figure 4.25: Simple edge connections of three cells in series ........................................... ........................................................ ............. 71 Figure 4.26: Single cell with end plates for taking current from all over the face of the electrodes and also supplying gas to the whole electrode. …………………………………………………..72 Figure 4.27: Two bipolar plates of very simple design. There are horizontal grooves on one side and vertical grooves on the other. ............................................ .................................................................. ............................................ ....................................... ................. 73 Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

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Figure 4.28: Voltage-current curve ideal & actual .......................................... ................................................................ ............................... ......... 74 Figure 4.29: Chart to summarize the applications and main advantages of fuel cells of different types, and in different applications. ………………………………………………………………76 Figure 4.30: Red LED .......................................... ................................................................ ............................................ ............................................ ............................... ......... 79 Figure 4.31: LED symbol ............................................ .................................................................. ............................................ ............................................ ........................ .. 79 Figure 4.32: Left -Hand-Rule for current-carrying ..................................................... ......................................................................... .................... 80 Figure 4.33: Current-Carrying Conductor in a Magnetic Field .......................................... ....................................................... ............. 81 Figure 4.34: PMDC Motor .......................................... ................................................................ ............................................ ............................................ ........................ .. 82 Figure 4.35: Schematic view for PMDC .......................................... ................................................................ ............................................ ........................ .. 82 82 Figure 4.36: Right-Hand Rule for Motors .......................... ................................................ ............................................ ....................................... ................. 83 Figure 4.37 :DC motor operation .......................................... ................................................................ ............................................ ................................... ............. 83 Figure 4.38: Theory of operation of PMDC Motor ............................................ .................................................................. ............................ ...... 84 Figure 4.39: Conduction in a solid cylinder with uniform heat generation..................................... ..................................... 85 Figure 4.40: Free convection boundary layer l ayer transition on a vertical plate .................................... .................................... 89 Figure 4.41: Hollow cylinder with convective surface conditions ............................................ .................................................. ...... 91

Figure 5.1 : Variation of percentage of diffuse radiation with clearness index………………….…97 index………………….…97 Figure 5.2: Variation of total hourly radiation with solar hour……………………………… hour……………………………………..98 ……..98 Figure 5.3: Single-diode model of the theoretical PV cell and equivalent circuit of a practical PV device including the series and parallel resistances……………………………………………….100 Figure 5.4: Characteristic I–V curve of the PV cell. The net cell current I is composed of the lightgenerated current I pv and the diode current I d……………………………………………………..101 Figure 5.6: Variation of PV maximum power through sunlight duration……………………… duration…………………………104 …104 Figure 5.6: PV Power-Voltage curve at maximum intensity of the specific day………………….105 day………………….105 Figure 5.7: Variation of optimum voltage through sunlight duration……………………………. duration……………………………..105 .105 Figure 5.8: PV I-V I- V curve at maximum iintensity ntensity of the specific day………………………………106 day………………………………106 Figure 5.9: Variation of photovoltaic efficiency through sunlight duration………………………10 duration………………………106 6 Figure 5.10: Variation of Electrolyser voltage with the solar hour………………………… hour………………………………..112 ……..112 Figure 5.11: Variation of Electrolyser current with the solar hour……………………………… hour………………………………..113 ..113 Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

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Figure 5.12: Variation of Electrolyser hydrogen production with the solar hour…………………113 hour…………………113 Figure 5.13: Variation of Electrolyser power with the solar hour……………………………… hour…………………………………114 …114 Figure 5.14: Variation of Electrolyser efficiency with the solar hour…………………………….115 hour…………………………….115 Figure 5.15: Variation of Electrolyser heats with the solar hour……………………………… hour………………………………….116 ….116 Figure 5.16: Electrolyser characteristic curves at noon……………………… noon……………………………………… ……………………117 ……117 Figure 5.17: Variation of Fuel cell current with the solar hour……………………… hour…………………………………… ……………122 122 F Figure 5.18: Variation of Fuel cell voltage with the solar hour……………………… hour…………………………………123 …………123 Figure 5.19: Variation of Fuel cell power with the solar hour…………………………………….1 hour…………………………………….123 23 Figure 5.20: Variation of Fuel cell efficiency with the solar hour angle………………………….123 angle………………………….123 Figures 5.21: Characteristic curves of single fuel cell operating with all hydrogen flow………..124 flow………..124 Figures 5.22: Characteristic curves of single fuel cell operating with half hydrogen flow in parallel and series connections…………………………………………………………………………….125 Figures 5.23: Characteristic curves of two fuel cells operating with all hydrogen flow (parallel and series connections)………………………………………………………………………………..126

Figure 6.1: Voltmeter and Ammeter Circuits………………………… Circuits………………………………………… …………………………..1 …………..132 32 Figure 6.2: Thermistors Temperature ranges……………………………………………………...134 Figure 6.3: non-terminated wires………………………………………………………………….134 Figure 6.4: Electric lamp fixed perpendicular to solar panel………………………………… panel……………………………………..135 …..135 Figure 6.5: H-Bridge circuit………………………………………………………………………136 Figure 6.6: On the left: The lamp motor and on the right: The power screw which drives the lamp up and down………………………………………………………………………………………136 Figure 6.7: Manual Control of Lamp……………………………………………………………..137 Figure 6.8: Transistor BC107……………………………………………………………………..137 Figure 6.9: The final Manual and DAQ control circuit…………………………… circuit………………………………………….. ……………..138 138 Figure 6.10: Circuit connections views…………………………………………………………..139 Figure 6.11: The circuit drawn and marked on the board…………………………………………140 Figure 6.12: The fabricated board…………………………………………………………………140 Figure 6.13: The final connected board top view…………………………………………………140 Figure 6.14: 36V Motor……………………………………………………………………………142 Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

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Figure 6.16: The H bridge lamp l amp position control experimental circuit………………………… circuit……………………………143 …143 Figure 6.17: LabVIEW® Block Diagrams………………………………………………………..145 Figure 6.18: Lamp Controller……………………………………………………………………..146 Figure 6.19: Front Panel of Measurement recorder……………………………………………….147 Figure 6.20: Measurement recorder Block Diagram………………………………………………148 Figure 6.21: Characteristic Curve Drawer Front Panel……………………………………………150 Figure 6.22: Characteristic Drawer Block Diagram (part 1)…………………………… 1)………………………………………15 …………154 4 Figure 6.23: Characteristic Drawer Block Diagram (part 2)…………………………… 2)………………………………………15 …………155 5

Figure 8.1: Early bench designs…………………………………………………………………...162 Figure 8.2: Third bench design…………………………………………………………………….163 Figure 8.3: AutoCAD bench isometric drawing…………………………………………………...164 Figure 8.4: Solidworks bench and table 3D drawing……………………………………………...165 Figure 8.5: Solidworks bench and table 2D drawing……………………………………………...166 Figure 8.6: Fabricated bench and table…………………………………………………………….168 Figure 8.7: The photovoltaic placed on the inclined roof and the lamp is perpendicular on its face as the Sun……………………………………………………………………………………………..170 Figure 8.8: Lamp stand installation………………………………………………………………..170 Figure 8.9: The bench with the assembled components…………………………………………...171 Figure 8.10: Back of the bench…………………………………………………………………….172 Figure 8.11: Monitor and DAQ Card……………………………………………………………...172 Figure 8.12: Different components assembled to the bench………………………………… bench………………………………………172 ……172

Figure 9.1: Solar Cell investigation………………………………………………………………..175 Figure 9.2: Electrolyser investigation……………………………………………………………..177 Figure 9.3: Single Fuel Cell investigation…………………………………………………………179 Figure 9.4: The fuel cells connected in series……………………………………………………..180 Figure 9.5: The fuel cells connected in parallel…………………………………………………...180


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Figure 9.6: Solar heater experiment……………………………………………………………….181 Figure 9.7: Fuel cell heater experiment……………………………………………………………182

Figure 10.1: Electrolyser voltage-current curve……………………… curve……………………………………… …………………………..1 …………..186 86 Figure 10.2: Electrolyser P-I characteristic curve……………………………… curve…………………………………………… …………………187 ……187 Figure 10.3: Single Fuel cell characteristic curve…………………………………………………188 Figure 10.4: Single Fuel Cell power - current characteristic curve……………………… curve……………………………….189 ……….189 Figure 10.5: V-I curve of a fuel cell in a set of cell……………………………………… cell…………………………………………….….190 …….….190 Figure 10.6: P-I curve of a fuel cell in a set of cells………………………………… cells……………………………………………….1 …………….191 91 3

Figure 10.7: Temperature change of 10 cm of water heated by a Heater powered by PV cell…..192 Figure 10.8: Efficiency change of 10 cm3 water heated by a Heater powered by PV cell………..193 3

Figure 10.9: Temperature change of 10 cm of water heated by a Heater powered by fuel cell….194 3

Figure 10.10: Efficiency change of 10 cm water heated by a Heater powered by PV cell……….194 Figure 10.11: Theoretical and Experimental Voltage corresponding to maximum power through the day…………………………………………………………………………………………………204


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LIST OF TABLES Table 4. 1: Number of days (n) .......................................... ................................................................ ............................................ ....................................... ................. 38 Table 4. 2: Angles description ........................................... ................................................................. ............................................ ....................................... ................. 39

Table 4. 3: Fuel cell types t ypes and specifications .......................................... ................................................................ ....................................... ................. 67 Table 4. 4: Components Materials and Advantages ........................................... ................................................................. ............................ ...... 68

Table 4.5: One-Dimentional, Steady-state Solutions to the Heat Equation for Uniform Heat Generation in a Solid Cylinder ....................................... ............................................................. ............................................ ........................................... ..................... 87 87

Table 5.1: Monthly fraction of sunshine hours ......................................... ............................................................... ....................................... ................. 95 Table 5.2: Solar panel technical data ......................................... ............................................................... ............................................ ................................ .......... 99 Table 5.3: PEM Electrolyser technical t echnical data ......................................... ............................................................... ......................................... ................... 107 Table 5.4: Constants used to calculate potential losses for low temperature PEMFC. ................. ................. 120

Table 6.1: Truth Table ......................................... ............................................................... ............................................ ............................................ .............................. ........ 139 Table 6.2: Block Diagram Main Components.......................................... ................................................................ ..................................... ............... 149 149 Table 6.3: Block Diagram Main Components.......................................... ................................................................ ..................................... ............... 152 152


xiv

NOMENCLATURE Symbol A B Cp E⁰ E F

G Go Gon Gsc GT g H Ho �o H h h hx

I IL Isc Imp

Description Surface area Magnetic field strength Specific heat at constant pressure Standard Nernst potential Potential Faraday constant

Unit 2

m Tesla J/kg.K V V C mol

-1

2

Irradiance

W/m

Extraterrestrial radiation Extraterrestrial radiation

W/m

Solar constant

W/m2

solar radiation on the solar cell array

W/m2

2 2

W/m

2

Gravitational acceleration Irradiation or Radiant Exposure (Insolation ) in day

m/s

Daily extraterrestrial radiation

J/m

Monthly extraterrestrial radiation

J/m

Convective heat transfer coefficient Average convective heat transfer coefficient Local convective heat transfer coefficient

Current

2

J/m

2 2

2

W/m .K W/m2.K 2 W/m .K Amp

The light-generated current

Amp

Cell short circuit current

Amp

Cell maximum power current

Amp

i io iL

Current density Exchange current density Limiting current

A/m 2 A/m 2 A/m

k

Boltzmann’s constant Lenght Power Total heat transfer Charge

L

P Q

q qo qr q′′r q′′x

R r ro

volumetric generation rate Heat transfer rate in the radial direction heat flux in the radial direction Local heat flux

Resistance radius Outer radius


2

J/K M Watt W C W/m3

W W/m2 W/m2

Ω m m xv

T Ts T∞ Tf ∆T

U V Voc Vmp

Temperature Surface temperature Fluid temperature Film temperature

Temperature difference Overall heat transfer coefficient

O

C or K o

C, K C, K o C, K °C,K o

W/m2K

Voltage.

V

Cell open circuit volt

V

Cell maximum power volt

V

Greek Letters

α

Absorption coefficient

αs αp ф δ β γ γs ω ωs θ θz

Solar altitude angle

λ

Wave length (m) 3 Density (kg/m )

ρ μ

Profile angle Latitude angle Declination angle Slope angle Surface azimuth angle Solar azimuth angle Hour angle Sunset or Sunrise hour angle Incident angle Zenith angle

Dynamic viscosity or Viscosity (kg/s.m)

Chemical Symbols H2 + H O2 OH H2O CO2 LiAlO2 -2 CO3 CO

Hydrogen molecule Hydrogen ion Oxygen molecule Hydroxyl ion Water molecule Carbon dioxide lithium aluminum oxide Carbon trioxide (ion) Carbon monoxide


xvi

Dimensionless groups Nu Nu Gr Pr Ra

Nusselt No. Nusselt No. based on average heat transfer coefficient Grashof No. Prandtl No. Rayleigh No.


xvii

ACKNOWLEDGMENT The Graduation Project Team would like to express their gratitude and appreciation to the moral and financial support provided by The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). We would specially like to thank them for their interest in the topic of our project so that they selected it as the only non-American project funded this year. Progress made in our project would not have been possible without the direct guidance and persistent help of our supervisors Prof. Dr. Hany Khater, Prof. Dr. Adel Khalil and Dr. Galal Mostafa. Individually, we would like to express our gratitude and appreciation for our classmate and friend Mohamed Ahmed Youssef Ahmed for his great participation and deep working in the first part of the project. We would also like to express our gratitude to everybody who helped us with editorial, presentational, instrumental/technical, instrumental/technical, conceptual conceptual and peer interactive communication communication supports in preparing or doing our practical experiments so far, specially Prof. Dr. Hassan Rakh (NREA's Advisor for PV activities), Prof. Dr. Abd El-Wahed Eldeeb, Dr. Abd Almaged Ebraheem, Dr. Ahmed Kamel, Dr. Ahmed Attia (Shoubra Faculty of Engineering, Banha University), Eng. Abbas R. Rady (System Eng. Dept Manager and Solar Energy Projects Manager, Arab Org. for Industrialization, Arab British Dynamics), Eng. Osama Mowafaq, Teaching Assistants Assistants in Faculty of Engineering, Cairo University (Eng. Mohamed Beshr, Eng. Nadim M. Arafa, Eng. Ahmed Yehia, Eng. Mohamed Yafia, Eng. Rania Eldeeb ‘Biomedical Engineering Dept’, Eng, Ahmed Hassan ‘Biomedical Engineering Dept’, Eng. Yasser ‘Electric Power Dept’ and Eng. Mohamed Shouka ‘B.Sc. year, Electric Power Engineering Dept’). Special gratitude also for the technicians in the Heat research lab (Mr. Abd Elrazek, Mr. Ali, Mr. Abbas, Mr. Tarek and Mr. Magdy Kamel) and Electric Power research lab, Faculty of Engineering, Cairo University.


xviii

PREFACE The whole world is directing its efforts to get over the end of the non-renewable fuel era by introducing renewable and clean sources of energy. Electrolyser Fuel Cellsystems are one of the efficient ways of storing and producing energy which have great demands in engineering applications. Fuel Cells need Hydrogen and Oxygen to work. So, we can use Solar Energy. Solar energy is the greatest and free renewable source of energy as it is supplied by the sun. A Photovoltaic Solar Cell is a special type of solar cells in which solar energy is converted into an electric voltage (or current). The current will be used to produce hydrogen and Oxygen in an electrolyser using water electrolysis process. The hydrogen and Oxygen produced will first be stored and then be used by a fuel cell to produce current, heat and water. In large scale applications, the water vapor possessing the heat can then be passed through a countercurrent heat exchanger to heat water. Thus, hot water will be available for household, companies…etc companies…etc using a natural everlasting source of energy. On a small scale water vapor cannot be used as it is too little for a 1.7Watt Fuel cell. Thus, in our project, only the current produced by the fuel cell will be used to heat water in a small heater or to run a simple load. A study of the characteristic curves of each of the photovoltaic cell, the electrolyser and the fuel cell will be performed by varying the input light intensity through varying the distance of an electric lamp from the solar panel. The knowledge of different heat and mass transfer mechanisms, system process design, equipment selection, material selection, instrumentation, data acquisition, data analysis, and performance tests are the required qualities to be gained by our team and passing it to junior students at the mechanical department. This is in addition to comparing between theoretical and actual experimental data which gives more sense of the difference between paper work and reality.


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Chapter 1

Introduction

Chapter 1

INTRODUCTION


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Chapter 1

Introduction

The existence of energy was never a problem as much as how to extract, transform and store it into a useful form. Human history tells us stories about fights over energy energy sources from the simplest food fights, which is the source of energy for the body, to the world wars over the sources of fossil fuels in modern time. Therefore, energy is the soul of life and existence. Human civilization is based on the use of energy in more effective ways to increase i ncrease the industrial production and human comfort. st

One of the most important trends of energy sources in the 21 century is Solar Energy. Solar Energy is a clean, renewable and cheap, actually free-cost, energy source. But the main disadvantages are that it is not available at night, in addition to the high utilization cost. Consequently storing energy is an important issue in order to provide the continuous availability of energy. Fuel cells offer cleaner, more-efficient alternatives to the combustion of gasoline and other fossil fuels. They have the potential to replace the internal combustion engines in vehicles and provide power in stationary and portable power applications because they are energy-efficient, clean, and fuel-flexible. Hydrogen or any hydrogen-rich fuel can be used by this emerging technology. It is visualized that as fossil fuels run out, hydrogen will become the major world fuel and energy vector.

Figure 1.1: Solar Hydrogen Fuel Cell Electric Heater Educational Stand

Solar-Hydrogen Fuel Cell Water Heater Educational Stand shown in Figure 4.1 is an educational kit that demonstrates the idea of the use of renewable energy in a power system module that enables the generation, use and instantaneous storage of energy. The Sun is a main source of vast amount of radiation energy that can be used in an economical way. Photovoltaic (PV) panels are now commercially available and considered as a permanent source of energy. Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

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Solar-Hydrogen Fuel Cell system is the 'Giant leap' for renewable and clean energy storage: ‘Solar-Hydrogen Fuel Cell System will allow the sun's energy to be used to split water into hydrogen and oxygen gases. Later, the oxygen and hydrogen may be recombined inside a fuel cell, creating carbon-free electricity to power your house or your electric car, day or night. This unprecedented process for energy storage has been developed by Nocera and Matthew Kanan, a postdoctoral fellow in Nocera's lab, MIT.’

This system could be applied as a “Home Refueling Station” in residential homes, as shown in Nocera’s system on the cover page of this chapter, factories and a wide range of applications. PV panels, an electrolyser and a fuel cell can form a power system assembled to undergo the generation, storage and continuous supply of clean energy. In our project the objective is to demonstrate this system to students and introduce the idea in the form of a laboratory experiment. They will understand, analyze and be able to study how the system works. They will be required to record different points on the characteristic curves of each of the solar cell, the electrolyser and the fuel cell by changing the input light intensity of an electric lamp by varying its distance from the solar cell. They will then, of course, be required to draw these curves. They will also study the two fuel cells first a single cell, then series and parallel connections curves. They will be required to compare them. The components of the experiment bench are: 1. Electric lamp 2. Photovoltaic solar cell 3. Single electrolyser 4. Two fuel cells 5. Variable resistance 6. Fan 7. Lamp 8. Two Electric heater

Theory of operation

Light intensity produced by the electric lamp demonstrates the sun giving enough energy for the photovoltaic cell to produce enough current for water electrolysis that takes place in the electrolyser. Hydrogen produced by the electrolyser during the electrolysis process is used in the fuel cell membrane to be recombined with oxygen again and produce the required current according to the connected load. The fuel cell acts as a battery supplying the current according to load. Thus, by varying the load connected to the fuel cell, we can get different points on the characteristic curve and be able to draw it.


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Chapter 2 LITERATURE REVIEW

Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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2.1.Introduction 2.1. Introduction In this section we will spotlight the latest technology and applications related to our solar-hydrogen electric system. As our system mainly deals with solar panels (photovoltaics), electrolysers and fuel cells, we will trace each component alone followed by the whole system.

2.2.Solar 2.2. Solar Panels The actual development of the efficiency of the photovoltaic (PV) panels and the start of its commercializing has run rapidly in the last few decades. Now the PV technology is spreading and replacing the fossil fuel shortage. However, it has the problem of high installing and operating costs as compared to conventional fossil fuel. The following are examples of some of the PV applications developing:

2.2.1. Standing Seam Metal Roofing Standing Seam Metal (SSM) roofing is a traditional roofing material that uses long, vertically sloped metal trays with raised edges. The trays are snapped together along the long axis to build the roof. Thinfilm, amorphous-silicon, triple-junction photovoltaic (PV) modules can be glued or laminated to the tray surface. The material produces electricity as well as performs its traditional weather-sealing function.

2.2.2.Vision Glass PV vision glass technology substitutes a thin-film, semi-transparent photovoltaic panel for the exterior glass face in a traditional double-pane glass window. Electric wires extend from the sides of each glass unit are connected to wires from other windows, building up the entire system. Many Universities install these types of PVs to efficiently operate their buildings and an adoption of their studies about the efficient, clean, inexpensive renewable energy.

2.2.2.1. Manchester Metropolitan University (MMU) Complete Solar Panel Project

[1]

MMU has invested almost half a million pounds in the installation of 400 photovoltaic (PV) panels covering 524 square meters – one of the largest solar arrays of any UK university. The shiny PV panels have been successfully installed on the roof of MMU's Student Union. The conversion of sunlight to electricity by the cells will generate 40,900 kWh of energy per year enough power to light 7,200,100-watt light bulbs, power 960 student laptops, boil 40 kettles or supply electricity to 10 houses.


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Figure 2.1: MMU solar roof

2.2.2.2.University 2.2.2.2. University of Wisconsin-Green Bay

[2]

It integrates two Building Integrated Photovoltaic (BIPV) sections with separate photovoltaic (PV) technologies. One is Standing Seam Metal roofing that is used commercially, available roofing product and used commonly throughout Wisconsin. The other section incorporates a thin-film BIPV vision glass product. In total, about 4,300 square feet of (BIPV) material were installed, which will generate approximately 27,500 kWh annually.

2.2.3. MIT’s Solar Concentrator Window

[3] [4]

MIT engineers introduced a new approach to harnessing the sun's energy that could use sunlight to efficiently help power buildings. Light is collected over a large area (like a window) and gathered, or concentrated, at the edges. As a result, rather than covering a roof with expensive photovoltaic, the cells will only need to be around the edges of a flat glass pane. In addition, the focused light increases the electrical power obtained from each solar cell by a factor of over 40, without the need for solar tracking. That, in turn, would substantially reduce the cost of solar electricity. The MIT solar concentrator involves a mixture of two or more dyes that is essentially painted onto a pane of glass or plastic as shown in Figure 2.2. The dyes work together to absorb light across a range of wavelengths, which is then re-emitted at a different wavelength and transported across the pane to waiting solar cells at the edges.


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Figure 2.2: Organic solar concentrators collect and focus different colors of sunlight. Solar cells can be attached to the edges of the plates. By collecting light over their full surface and concentrating it at their edges, these devices reduce the required area of solar cells and consequently, the cost of solar power. Stacking multiple concentrators allows the optimization of solar cells at each wavelength, increasing the overall power output.

2.3.Electrolysis 2.3. Electrolysis Water electrolysis is essentially a conventional electrolysis process constantly under development. Other industrial electrolysis processes may include the electrolysis of Al 2O3 for pure aluminum production and electroplating of iron surfaces. Applications of water electrolysis may include:

2.3.1.Sea Water (Brine) Electrolysis A) NaOH and Cl2 production : for many industrial purposes. B) H2 production: About 4% of H 2 gas produced worldwide is created by electrolysis. The majority of this hydrogen produced through sea water (Brine water) electrolysis where it is a side product in the production of chlorine . 2 NaCl

+

2 H 2O

→

Cl2

+ H 2 +

2 NaOH

The hydrogen produced from this process is either burned, used for the production of specialty [5] chemicals or various other small scale applications and of course for fuel cells. [6]

Bayer Technology Services , Chlorine Engineers corp., Ltd. [8] are examples of the companies using this technology.

[7]

and Han Su Technical Service Co., Ltd.


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2.4.Fuel 2.4. Fuel Cells st

In the 21 century, fuel cells have been at the forefront of cutting edge science, with many people now viewing them as the only alternative to fossil fuels for generating power. Fuel cell vehicles can reduce emissions to zero if the hydrogen is produced from renewable electricity, which greatly improves local air quality. They also significantly reduce noise pollution as well. The numerous applications of fuel cells may include:

2.4.1. Stationary Systems More than 2500 fuel cell systems have been installed all over the world: In hospitals, nursing homes, hotels, office buildings, schools, utility power plants. They are either connected to the electric grid to provide supplemental power and backup assurance for critical areas, or installed as a grid-independent [9] generator for on-site service in areas that are inaccessible by power lines. In Europe, there is a great direction towards the Fuel Cell and Hydrogen technologies to the domestic stationary market, in the form of Combined Heating and Power (CHP) systems due to its benefits of high efficiency (approximately 85%) and low pollution (Chemical and Acoustic).

2.4.2. Transportation (Automotives) 2.4.2.1. Cars All the major automotive manufacturers have a fuel cell vehicle either in development or in testing right now and several have begun leasing and testing in larger quantities. Commercialization is a little further down the line (some automakers say 2012, others later), but every demonstration helps bring that date [9] closer. As an example of the demonstrated cars: 

BMW (series 7-745 h-Sedan): showed in 2000 with (UTC PEM FC 5 KW) ICE.



Daihatsu (MOVE FCV-K II): showed in 2001 with (Toyota PEM FC 30KW)/battery hybrid engine.



Daimler (A-Class F-Cell): showed in 2002 with (Ballard Mark 9000 series PEM FC 85KW)/battery hybrid



Ford Motor Company (Explorer): showed in 2006 with (Ballard PEM FC 60KW)/battery hybrid engine.



Honda (FCX Clarity): showed in 2007 with (Honda PEM FC 100KW) Engine.


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2.4.2.2.Buses 2.4.2.2. Buses Over the last four years, more than 50 fuel cell buses have been demonstrated in North and South [9] America, Europe, Asia and Australia and manufactured by Honda, DaimlerChrysler, Toyota and [12] Ballard power systems.

2.4.2.3. Scooters (Small Motor Cycles) In spite of their small size, many scooters are pollution powerhouses especially those with two-stroke engines. This is a great application for fuel cells. The most outstanding models are MOJITO FC Scooter (known as Habana in Europe) which was produced by Manhattan Scientifics and Aprilia in 2007 but the production was stopped. Another one is Suzuki Burgman Fuel Cell Scooter which is manufactured by [13][14] Intelligent Energy Energy in partnership with Suzuki and announced in 2009.

2.4.2.4. Others Like airplanes, marine and trains. They are under development to be operated by the fuel cells which give better efficiency, durability and lifetime than the batteries. Boeing is developing its first fuel cell plane.

2.4.3.Portable Micro-Power Like mobiles and laptops, companies have already demonstrated fuel cells that can power cell phones for 30 days without recharging and laptops for 20 hours. These miniature fuel cells generally run on [9] methanol, an inexpensive wood alcohol. Toshiba has developed a mobile charger Dynario. It has a methanol fueled fuel cell which causes a [13] reaction between H 2 in methanol and O 2 to produce the charging electricity.

Figure 2.3: Toshiba ‘Dynario’ mobile charger

[16][ 17]

In the beginning of 2004, Japanese electronics company NEC has shown the prototype of a laptop with built-in fuel cell, claiming the prototype has 10 hours life, extending the life of the traditional battery [14] powered laptop by up to 50%. In 2006 Toshiba and Samsung has shown off their fuel cell laptops. [16][17][18][19]


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Figure 2.4: From left NEC, Toshiba, Samsung laptops

[10][16]

2.5.Commercia 2.5. Commerciall Applications 2.5.1. Home Energy Station In 2003, Honda has established an experimental Home Energy Station (HES) that generates hydrogen from natural gas for use in fuel cell vehicles and can also supply electricity and hot water to the home. Part of ongoing research by Honda into hydrogen energy sources, the new system can currently produce enough hydrogen to refill the tank of a Honda FCX hydrogen fuel cell vehicle taking just a few minutes once a day. Honda is also applying newly developed solar panel technology to its hydrogen-refueling R&D by using the energy generated by the panels mounted on the refueling station to improve its overall efficiency other [20] than Home Energy Station (HES III) which is using natural gas.

Figure 2.5: Home Energy Station (HES III)


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2.6.Experimental 2.6. Experimental Applications 2.6.1. Dr FuelCell Science Kit

[21]

Figure 2.6: Dr Fuel cell science kit

2.6.1.1. Overview The Dr FuelCell Science Kit, shown in Figure 2.6, is an extensive experiment set for the subject of renewable energies for students. The Dr FuelCell Science Kit reproduces a complete solar hydrogen energy cycle. It makes it possible to approach the subject of renewable energies both as a complete cycle and at the level of the single technologies of photovoltaics and the fuel cell.

2.6.1.2. Components The components of the Dr FuelCell Science Kit can be used in various ways for instruction. Solar panel

The 5-cell photovoltaic module is used for experiments in solar energy and for generating electric energy for the hydrogen generator. The practical base facilitates alignment to the light source.

Electrolyser

The electrolyser separates water into hydrogen and oxygen. It is operated with distilled water and requires no caustic solutions or acids. The integrated graduated hydrogen storage cylinders visualize the classic hydrogen separation experiment, as in the Hoffmann apparatus.


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Fuel cell

The fuel cell generates electrical energy from hydrogen and oxygen. It is based on PEM technology, which is the most widespread technology used in the development of fuel cell applications, e.g. for motor vehicles or stationary power supply systems.

Load measurement box

The convenient and compact load measurement box is used for recording data during experiments. Integrated consumers, such as a motor, a lamp and 7 selectable resistors, enable numerous experiments, e.g. recording characteristic curves, or current and voltage.

Take-apart fuel cell

The take-apart fuel cell makes it possible to examine the functions and the t he design of a fuel cell in detail. A plug-in resistor, an electrode with reduced catalyst quantity and an air panel for air instead of oxygen operation enable in-depth experiments.

Methanol cell

The methanol fuel cell uses methanol instead of hydrogen to generate electrical energy. This makes it possible to conduct more extensive experiments. The package includes storage cylinders for storage of the methanol solutions.

fuel

2.6.1.3. Technical Details Dr FuelCell Science Kit Complete Dimensions

(W x H x D):430 x 150 x 310 mm Weight: ca. 10.1 kg

Solar panel Dimensions (W x H x D): 80 x 130 x 52 mm Voltage: 2.0 V Current: 180 mA Output: 0.36 W Electrolyser Dimensions (W x H x D): 80 x 195 x 85 mm Storage volume for hydrogen and oxygen: 10 ml each Operating voltage: voltage: 1.4 ... 1.8 V Electric current: max. 500 mA Hydrogen production: max. 3.5 ml / min (at 500 mA) Fuel cell Dimensions (W x H x D): 65 x 85 x 38 mm Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Rated output: 0.25 W Voltage: 0.4 ... 0.9 V Current: max. 1000 mA Load measurement box

Dimensions (W x H x D): 190 x 110 x 60 mm Ammeter: 0 ... 2 A Voltmeter: Voltmeter: 0 ... 20 V DC Measured resistance (in ohm): 1, 3, 5, 10, 50, 100, 200, open and short circuit

Take-apart fuel cell

Dimensions (W x H x D): 85 x 65 x 65 mm Rated output for oxygen mode: 0.3 W Voltage: 0.4 ... 0.9 V Current in oxygen mode: max. 1500 mA Current in air mode: max. 800 mA

Methanol fuel cell

Dimensions (W x H x D): 65 x 85 x 34 mm Rated output: 0.1 W (with 1 M methanol solution) Voltage: 0.1 ... 0.6 V Current: max. 100 mA

Dr FuelCell Professional manufactured by Heliocentris Inc. www.heliocentris.com


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2.6.2. Dr FuelCell Model Car

[22]

Figure 2.7: Dr Fuel cell model Car

2.6.2.1. Overview Model Car with reversible Fuel Cell

The Dr FuelCell Model Car integrates the subject of renewable energies in the instruction for the lower secondary level in an uncomplicated manner. Hands-on teaching of renewable energies

The Dr FuelCell Model Car can be operated with energy from a fuel cell or a solar panel. A reversible fuel cell makes it possible to generate and store hydrogen wherever it is needed. Practical experiments help students easily understand the relationships between energy conversion, storage and consumption. Extensive features

The package includes a reversible fuel cell, which functions both as a hydrogen generator and fuel cell. The fuel cell uses the energy supplied by the solar panel or the hand generator to separate water into oxygen and hydrogen. In fuel cell mode, the stored hydrogen is converted into electric power to operate the car. The load measurement box makes it possible to measure the current and voltage.


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Time-tested quality

Developed for daily use in the classroom, the model car is user-friendly and features a flexible and robust design, making it suitable for both group and individual instruction.

2.6.2.2. Components The single components of the Dr FuelCell Model Car can be used in various ways for instruction. Solar panel

The 5-cell photovoltaic module is used for experiments in solar energy and for generating electric energy for hydrogen production. The practical base facilitates alignment to the light source. The module can easily be mounted on the car chassis to make a solar vehicle.

Reversible fuel cell with integrated gas storage cylinders

This component is a fuel cell and hydrogen generator in one. It is operated with distilled water and requires no caustic solutions or acids. The generated hydrogen is stored in integrated gas storage cylinders, safely and directly.

Car chassis

The car chassis is designed both for fuel cell operation and solar operation. A single click and two cable connectors are all you need to make the switch. The front axis is steerable and lockable, so the car chassis can also be used where space is limited.

Load measurement box

The load measurement box for recording data is used for advanced experiments. Integrated consumers, such as a motor, a lamp and 7 selectable resistors, enable numerous experiments, e.g. recording characteristic curves, or current and voltage.

Hand generator

The high-quality hand generator, which simulates wind power, is an alternative to the solar panel. Muscle power is used to generate electrical energy for the separation of water in the reversible fuel cell.


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2.6.2.3. Technical Details Dr FuelCell Model Car Complete

Erection

Dimensions (W x H x D): 345 x 160 x 280 mm Weight: ca. 2.9 kg Language versions: German, English, French, Spanish, Italian, Turkish, Japanese, Korean and Arabic

Solar panel

Dimensions (W x H x D): 80 x 130 x 52 mm Voltage: 2 V Current: 180 mA Output: 0.36 W

Reversible fuel cell

Dimensions (W x H x D): 80 x 80 x 70 mm Operating voltage: voltage: 0.5 ... 0.9 V DC Rated output: 0.25 W Operating current: 0 ... 500 mA Hydrogen production: max. 3.5 ml / min

Car chassis electric motor

with

Dimensions (L x W x H): 195 x 110 x 50 mm Operating voltage of motor: 0.5 ... 3.0 V Hydrogen consumption: 3 ... 5 ml / min Running time with full gas storage cylinders: 3 ... 5 min

Load box:

measurement

Dimensions (W x H x D): 190 x 110 x 60 mm Ammeter: 0 ... 2 A Voltmeter: 0 ... 20 V DC

Hand generator

Dimensions (W x H x D): 55 x 137 x 55 mm No-load voltage: 2.1 V Typical operating voltage with electrolyser: ca. 1.7 V

Dr FuelCell Model Car manufactured by Heliocentris Inc. www.heliocentris.com


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2.6.3. Fuel Cell Kit, Green Utility House

[23]

Figure 2.8: Fuel Cell Kit, Green Utility House

With this fuel cell kit, you can build your own experimental green utility house and install wind energy, solar energy, and fuel cell home power generator. • • • •

Fuel Cell Kit: shows energy conversion and storage demonstrates the application of renewable and non-pollutant energies in daily lives teaches electrochemical experiments and new technology appreciation lets us discover principles of fuel cells, wind energy, solar energy, electrolyser, and hybrid systems

Solar and wind energy are not reliable sources of energy. During nighttime or at times of reduced or no sunlight or wind, these systems are not able to generate electricity. Fuel Cell Kit, Green Utility House shows how this problem can be overcome if the extra electricity produced by solar cells during sunny days or by wind turbines during windy days can be stored (Fuel Cell Kit green utility house can only store solar energy not wind energy). In this fuel cell kit, the electrolyser is able to use the extra electricity to convert water into hydrogen and oxygen gases that can be stored. During the night time or at times of a reduced or absent sunlight and wind, the fuel cells consume stored hydrogen to generate electricity. In the hybrid system, such a Fuel Cell Kit Green Utility House fuel cells and hydrogen technology cover the short-coming of solar and wind energy to provide continuous, reliable, and independent power supplies.


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These educational kits are all about energy conversions. When light is emitted and reaches the solar cells (1), the cells convert the energy of light to electricity (electric energy). The electrolyser (2) then uses this electricity, to decompose the water to produce hydrogen and oxygen gas. These gas products enter a fuel cell (3) and within an electrochemical reaction, water and electricity are produced. As the endproduct of the 2 fuel cell, electric energy will power the electric motor (4). In the Green Utility House and Solar House products when air pushes the wind turbine blade (5), the electric shaft of the electric motor rotates. The electric motor acts as a generator and converts the kinetic energy of wind to electricity. The generated electricity then will be used in the ceiling fan (4). Fuel Cell Kit, Green Utility House manufactured by Hydrogen and Fuel Cell Inc. www.h-fc.com

2.6.4.Fuel Cell Car Science Kit

[24]

Figure 2.9: Fuel cell car science kit


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Fuel Cell Car Science Kit uses a reversible PEM fuel cell that combines electrolysis and power conversion into one single device. Watch as oxygen and hydrogen gases are formed in two transparent water containers. The car steers independently of the user once in operation: when the car hits a barrier, it will automatically find its way by reversing away 90 degrees. Fuel Cell Car Science Kit manufactured by Horizon Fuel Cell Inc. www.horizonfuelcell.com

2.7. Conclusion Our project essentially aims to build a Solar-Hydrogen Fuel Cell Educational Stand that demonstrates the idea of “Home Refueling Station” or “Solar-Hydrogen House” which is the major technique required for Solar Energy continuous availability. In addition our educational stand makes student aware of •

•

•

establishing an educational stand that students in the mechanical power department will learn from, understanding the operation of each device and studying its performance and characteristics as an individual device and when working as a Home Refueling Station and building the ability of measuring different quantities and analyzing the results by using digital measuring devices and computer programs.

In one word we can say that: “Solar-Hydrogen House: No More Power Bills—Ever”


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Chapter 2

Literature Review

2.8.References 2.8. References [1] http://www.mmu.ac.uk/news/ http://www.mmu.ac.uk/news/articles/1098/ articles/1098/ [2] http://www.p3xcel.com/ http://www.p3xcel.com/project12.html project12.html [3] http://web.mit.edu/newsoffice/2008/sola http://web.mit.edu/newsoffice/2008/solarcells-0710.html rcells-0710.html [4] http://www.domain-b.com http://www.domain-b.com/technology/20080711_windo /technology/20080711_window.html w.html [5] http://en.wikipedia.org/wiki/Electrolysis [6] http://www.bayertechnol http://www.bayertechnology.com/en/products/c ogy.com/en/products/chlorine-electroly hlorine-electrolysis/chlorine-elect sis/chlorine-electrolysis/is-yourrolysis/is-your-gain.html gain.html [7] http://www.chlorine-eng.co.jp/ http://www.chlorine-eng.co.jp/en/product/elect en/product/electrolysis/brine-ele rolysis/brine-electrolysis.html ctrolysis.html [8] http://www.tradekorea.com http://www.tradekorea.com/product-detail/ /product-detail/P00157657/Brine_treatm P00157657/Brine_treatment_system.html ent_system.html [9] http://www.fuelcells.or http://www.fuelcells.org/basics/apps.html g/basics/apps.html [10] http://www.engadget.com http://www.engadget.com/2006/06/01/toshiba-s /2006/06/01/toshiba-shows-off-latest-la hows-off-latest-laptop-fuel-cell-p ptop-fuel-cell-prototype/ rototype/ [11] http://www.fuelcells.org/info/charts/ http://www.fuelcells.org/info/charts/carchart.pdf carchart.pdf [12] http://www.fuelcells.org/info/charts/ http://www.fuelcells.org/info/charts/buses.pdf buses.pdf [13] http://www.varsitycycle.com/aprilia_m http://www.varsitycycle.com/aprilia_mojito_retro.shtml ojito_retro.shtml [14] http://www.reuters.com http://www.reuters.com/article/idUSTRE6123FY2010020 /article/idUSTRE6123FY20100203 3 [15] http://www.crunchgear.com http://www.crunchgear.com/2009/10/22/dynario-toshi /2009/10/22/dynario-toshiba-finally-comm ba-finally-commercializes-fuel ercializes-fuel-cell-for-mobil -cell-for-mobile-devices/ e-devices/ [16] http://www.gizmag.com http://www.gizmag.com/go/3354/ /go/3354/ [18] http://www.engadget.com/ http://www.engadget.com/2006/06/01/toshiba-sh 2006/06/01/toshiba-shows-off-latest-la ows-off-latest-laptop-fuel-cell-p ptop-fuel-cell-prototype/ rototype/ [19] http://www.gizmag.com http://www.gizmag.com/go/6666/ /go/6666/ [20] http://automobiles.honda.com/fcx-clari http://automobiles.honda.com/fcx-clarity/home-energy-sta ty/home-energy-station.aspx tion.aspx [21] http://www.heliocentris.com/en/custom http://www.heliocentris.com/en/customers/education/pro ers/education/products/science-educati ducts/science-education/dr-fuelcell-sci on/dr-fuelcell-science-kit.html ence-kit.html [22] http://www.heliocentris.com/en/custom http://www.heliocentris.com/en/customers/education/pro ers/education/products/science-educati ducts/science-education/dr-fuelcell-m on/dr-fuelcell-model-car.html odel-car.html [23] http://www.h-fc.com/ [24] http://www.horizonfuelc http://www.horizonfuelcell.com/education_ki ell.com/education_kits.htm ts.htm


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21

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In order to convert the idea into reality, a complete design of the system needed to be studied and implied. We started brain storming to put the preliminary shape of the system. We agreed that in order to identify the required sizes of the different components, the required load should be first determined. The final load was the electric heater. We realized that electric heaters can have a wide range of sizes starting from 0.1W to whatever we can imagine. On the other hand, the sizes of each of the fuel cell, electrolyser and PV cells available commercially are limited. Thus, our mission was to identify commercially available electrolyser-fuel cell system that is compatible. The next step is to find the suitable PV size to supply the required voltage and current to the electrolyser. This is a summary of the available fuel cells and electrolysers at the time.

3.1. Electrolysers 3.1.1. Esperanza (Heliocentris, www.heliocentris.com) www.heliocentris.com) We contacted Esperanza and also Heliocentris and they both told us the same information. They produce hydrogen generators which work at 230V, produce large quantity (15-60 liters per hour). That’s very professional while we are looking for something more educational. So, we started to contact Fuel Cell Store (www.fuelcellstore.com) for the electrolyser and the fuel cell.

3.1.2. The Fuel Cell Store Electrolysers Among a variety of electrolysers, we found two suitable ones, which are:

3.1.2.1. AS1 Electrolyser

[1][2]

The AS1 Stack on Electrolyser is an Alkaline Electrolyser capable of producing 0.25 Liters of hydrogen a minute at a fraction of the cost for comparable PEM Electrolysers. Using an alkaline chemistry with a 30% KOH electrolyte the AS1 can produce 360 Liters of hydrogen for only $.36 and the upfront cost is 3% the cost of a PEM electrolyser. The smallest unit can generate 15 Liters per hour but the system is stackable to suit any system size and operating requirements. Gas purities are greater than 99.6% and with additional catalytic recombiner purities over 99.9999% hydrogen can be achieved. It has a built-in ECM (Electronic Control Module) that fully automates and maintains the optimum level of water to the Electrolyser and the Double Bubbler. The hydrogen and oxygen can be collected safely in a low pressure tank for use later. Great for powering an alkaline or PEM fuel cell to generate electricity that can power electrical appliances even the entire home or hydrogen stove for cooking. A 90 watt Solar Panel will give ample power to run one electrolyser to make an unlimited amount of hydrogen.


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Electrolyser

Dimensions:

3 x 4 x 7.5in

Electrodes:

Nickel Plated 316SS

Electolyte:

30% KOH

No. of cells:

5 (2.5 volts/ cell)

Voltage:

12 volts

Current:

7 Amps.

Hydrogen Output:

15 liters/hr. (30 liters/hr @ 15 Amps.) = (500 ml/ min)

Oxygen Output:

7.5 liters/hr. (15 liters/hr @ 15 Amps.)

Pressure:

Non-Pressurized

Hydrogen Purity: 99.6%** Recirculator:

Double Tube

1.5in. Diameter

Material:

304 SS (or ABS)

Height:

11in.

Electronic Control Module:

Epoxy encased integrated with electrolyser body Start up tubing purge cycle Automatic sensing water level Automatic water refill.


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3.1.2.2. AS15 Electrolyser

Preparation

[3]

[4]

(LAB H2 SUPPLY )

Alkaline type with higher efficiency: up to 70% and generates more H2 gas compared to PEM

electrolyser for the same amount of electric current. Pressure up to 30 psi: meets most fuel cell requirements. Four minute auto purge at startup, safety

pressure relief at 40 psi. 99.9% Purity H2 gas with optional O2 collection capability 7 Amps produces 15 liters of H2 per hour: Maximum allowable current of 15 Amps makes 30 liters

of Hydrogen per hour.

3.2. Fuel Cells We contacted fuel cell store about two types of fuel cell:

3.2.1. Convection fuel cell stack 3.2.1.1. 30W 6.5V, 36W 6V Fuel Cell Stack

[5]

Product Overview

The 30-36 W Convection fuel cell stack is a 10 cell stack that does not require external humidification or pressurization. Gold-plated current collectors ensure that this stack achiev es maximum performance for precision experiments. The stack comes complete with instruction manual, I/R plot, shade for assisting the convection air flow and a six-month warranty. Possible sources of hydrogen for the 30-36 W convection fuel cell stack include electrolysers (PEM- and alkaline technologies), gas bottles, metal hydride tanks and hydrogen from chemical reactions. In order to use the fuel cell in both operating modes a control unit is required The control unit for this fuel cell performs three functions. It includes a regulator to control the inlet pressure to the stack. It monitors the temperature and operates the cooling fans as necessary and it also regulates the purging cycle for hydrogen in the dead-ended mode of operation of the fuel cell. The control unit regulates the back pressure to make sure that too much pressure does not build up inside the stack. It is a dead ended fuel cell and over pressure can damage the membranes. These stacks are "Air-Breathing", Convection style stacks with self-humidified Membrane Electrode Assemblies. Hydrogen can be kept dead-ended and water is removed continuously from the stack. The maximum operating temperature can be from 65-70 °C and at pressures from 1 to 10 psi. No special


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startup procedure or forced flow of air is required; however much higher power densities can be obtained utilizing forced air flow.

Technical Specifications

Number of cells

10

Membrane Area

25 cm2

Power

30W at 6.5V,36W at 6V

Reactant

H2/air

Temperature

Ambient-70°C

Pressure

0-2 psi (hydrogen)

Humidification

Self-humidified

Cooling

Air (cooling fans supplied and attached to the side)

Weight

3.5 pounds

Dimension

10 cm x 8.2 cm x 11 cm (LxWxH)

Hydrogen Flow Rate

About .35 Liters per minute at full power

Type of fuel cell

PEM

Start up time

Instantaneous, load following capability

Efficiency of stack

50% at full power


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3.2.1.2. 20W 13V, 25-30W 12V Fuel Cell

[6]

Has the same information for 30W 6.5V, 36W 6V 6 V Fuel Cell Stack Technical Specifications

Number of cells

20

Membrane Area

10 cm2

Power

20W at 13V, 25-30W at 12V

Reactant

H2/air

Temperature

Ambient-70°C

Pressure

0-2 psi (hydrogen)

Humidification

Self-humidified

Cooling

Air (cooling fans supplied and attached to side)

Weight

2.25 pounds

Dimension

14 cm x 5.7 cm x 8.8 cm (LxWxH)

Type of fuel cell

PEM

Start up time

Instantaneous, load following capability

Efficiency of stack

50% at full power

3.2.2. H-Series Fuel Cells 3.2.2.1. H-20 (20W Fuel Cell Stack)

[7][8]

Product Overview

The H-series Polymer Electrolyte Membrane (PEM) fuel cells, design by Horizon, are semi-integrated, efficient, reliable systems that minimize the use of peripherals. As such, they are the most compact and lightweight air-cooled, self-humidified fuel Cells around the world. The fans and purge value on the H-20 do not require an additional power source they are run by the fuel cell. H-20 includes the following items Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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*Electronic and Gas Connections *Miniature electronic valve: This is the purging value to purge hydrogen in the event of overpressure of the fuel cell *Control electronics: To regulate the purge value and fans *Integrated fan and casing: The fan is for cooling the casing is to protect p rotect the fuel cell *Low pressure protection: There is no low pressure protection on the fuel cell, the high p ressure protection would start around 6 psi. Technical Specifications

Type of Fuel Cell

PEM

Number of cells

11

Rated power

20W

Performance

6.6V @ 3A

Purging Valve Voltage

6V

Blower Voltage

5V

Reactants

Hydrogen and air

External temperature

5-40ºC

Stack operation temperature

55ºC

Composition

99.999% Dry H2

Hydrogen pressure

2.9-4 PSI

Humidification

Self humidified

Cooling

Air (integrated cooling fan)

Weight (with fan and casing)

230g

Dimensions

7.6cm x 5.6cm x 4.7cm

Hydrogen flow rate

280ml/min of hydrogen at maximum power

Start up time

Immediate

Stack efficiency

45% at maximum power


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Preparation

3.2.2.2. H-30 (30W Fuel Cell Stack)

[9][10]

Product Overview

The H-series Polymer Electrolyte Membrane (PEM) fuel cells design by Horizon are semi-integrated, efficient, reliable systems that minimize the use of peripherals. As such, they are the most compact and lightweight air-cooled, self-humidified fuel Cells around the world. The fans and purge value on the H-30 do not require an additional power source they are run by the fuel cell. Details H-30 includes the following items

*Electronic and Gas Connections *Miniature electronic valve This is the purging value to purge hydrogen in the event of overpressure of the fuel cell *Control electronics To regulate the purge value and fans *Integrated fan and casing The fan is for cooling the casing ca sing is to protect the fuel cell *Low pressure protection There is no low pressure protection on the fuel cell, the high pressure protection would start around 6 PSI

Technical Specifications

Type of Fuel Cell

PEM

Number of cells

12

Rated power

30W

Performance

[email protected]

Purging Valve Voltage

6V

Blower Voltage

5V

Reactants

Hydrogen and air


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Preparation

External temperature

5-40ºC

Stack operation temperature

55ºC

Composition

99.999% Dry H2

Hydrogen pressure

4.3-5.8 PSI

Humidification

Self humidified

Cooling

Air (integrated cooling fan)

Weight (with fan and casing)

235g

Dimensions

8.0cm x 5.4cm x 4.6cm

Hydrogen flow rate

420 ml/min of hydrogen at maximum power

Start up time

Immediate

Stack efficiency

45% at maximum power

3.3. Further Details The two types of the fuel cells are dead-ended. That means there is no hydrogen outlet on these cells; the hydrogen put into the cell is all used in the reaction and output as water and heat. The H-20 and H-30 fuel cells c ells require a small amount of pressure for operation and would not work with the AS1 electrolyser. In order to use the electrolyser to directly fuel the H-20 or H-30 we will need a low pressure storage cylinder to capture the excess gas produced. The AS15 system produces pressurized gas at 30 PSI and this requires regulation before being fed into the fuel cell. It must also be allowed to produce hydrogen and store it if not being used directly. This will keep the cell safe from over pressurization and keep the electrolyser producing gas without venting the excess hydrogen into the air. The cathode side of the fuel cell where the water will be generated is open to air. Any liquid water formed would fall out the bottom of the cell. The heat is removed by the attached fans which operate to cool the cell. There is no blower on the H-30. The Fans can be considered a blower but are listed as fans. Both of these fuel cells are a "convection" type. They both use the oxygen from the air in the environment and do not require a pure oxygen flow. The fans do serve to both remove heat and keep a constant flow of air over the cathode side of the fuel cells. Neither of these cells have the capability to use a pure oxygen flow for the operation of the fuel cell. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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The output of the fuel cell connections are 8 gauge wires which can be connected in any way we choose (no special electrical cables). Characteristic curve is not available for the convection stack fuel cells but is contained in the user manual for the H-30 fuel cell. Current vs. hydrogen production curve for the AS15 electrolyser:

There is a linear increase between the hydrogen product and current increase of the AS15 from 7 amps up to 15 amps compared to a production increase of 15 l/hr to 30 l/hr. The pressurized versions of the AS15 include holding tanks which will allow us to properly store excess hydrogen during a continuous operation of the electrolyser powering the fuel cell. We would need to maintain the proper voltage so as not to fill up the holding tanks but they will provide enough storage to make the direct operation of a fuel cell possible. The small internal storage of the pressurized AS15 is at 30 psi. The internal storage on the AS15 can be stated to have hav e 0 storage capacity. This is an a n internal reservoir for pressurizing the hydrogen for release. Hydrogen cannot be stored inside the electrolyser elec trolyser for a sustained period of time. Other questions and answers

* What is the preferred electrolyser which will work with (30W 6.5V, 36W 6V Fuel Cell Stack) and (20W 13V, 25-30W 12V Fuel Cell Stack)? The AS15 is the preferred electrolyser for all of our smaller fuel cell stacks. It will work the same with these cells as with the H-20 and H-30. * If the electrolyser produced excess hydrogen over the required to operate the fuel cell and no storage, what will happen? If the fuel cell is dead ended and the electrolyser is constantly producing gas with no outlet it will put a hole in the membranes in order for the rising pressure to escape. This would permanently damage the fuel cell and make for a very costly repair. If there is an outlet for the hydrogen to escape then it will instead release the pressure through that outlet, this is the function of the hydrogen purge valve on the H-20 and H-30 fuel cells. * What will happen for the remaining rates produced from the electrolysers & not used by fuel cell? In order to use the electrolyser to directly fuel the H-20 or H-30 you will need a low pressure storage cylinder to capture the excess gas produced. The AS15 system produces pressurized gas at 30 PSI and this need to be regulated before being fed into the fuel cell. It must also be allowed to produce hydrogen


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and store it if not being used directly. This will keep the cell safe from over pressurization and keep the electrolyser producing gas without venting the excess hydrogen into the air. * What is the difference between the convection fuel cell stack and the H-series fuel cell? Very little is different between these cells. They all operate as convection stacks, not requiring pure oxygen. They operate at very similar hydrogen pressures and use very similar amounts of hydrogen. The H-series cells are manufactured by a large company with a high production volume which allows them to lower the cost, which is the biggest bigge st difference between the different stacks.

3.4. Our Choice After requesting all the information we needed, we decided on the 30W Fuel cell and the AS15 electrolyser for the following reasons: 1. A 30W Fuel cell gives enough measurable power 2. Their prices are suitable for our budget 3. They are the most compatible couple in the choices we had with the pressurization problem being solved as well as the hydrogen purity

3.5. Steps towards Purchasing After we decided on the electrolyser-fuel cell couple we immediately put a company in charge in contacting and purchasing the components. The process of communication was first drawing some success and they promised the fuel cell will be shipped from the states within 2 weeks while the electrolyser will be shipped after a month due to slow fabrication process. Figure 3.1 shows the con tract.


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Figure 3.1: Purchase Invoice


Chapter 3

32

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Preparation

During the time we waited, we began our search for the PV. This was much easier as we have local producers. We visited all present producers, collected information and decided on a 200W solar panel as well as the shape of our bench which was a house. The details of the bench shape are in chapter 8. However, the month passed and none of the components was delivered. We began to be disappointed. We started contacting the company again to contact them and we figured out that for some reason they stopped producing the electrolyser. That happened after two months from purchasing. We tried to search for other companies in countries of far Asia and Europe but we didn’t find something educational and we had no time to waste, so we had to take a quick decision. In the USA they say if you can’t shoot the moon, shoot the stars, so we had no choice but to work on a smaller scale. The new system was 1.7W Fuel cells and we had a big challenge to design a suitable heater, which we did. Perhaps the project we had in mind did not exactly come true, but at least we delivered our aim of demonstrating the new system which will change the world to junior and senior students in our department, no matter how small it is.


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3.6. References [1]. http://fuelcellstore.com/en/pc/viewPrd.asp?idcategory=0&idproduct=1405, [2]. http://peoplesnewenergy.com/ [3]. http://www.fuelcellstore.com/en/pc/viewPrd.asp?idcategory=39&idproduct=1412 [4]. http://peoplesnewenergy.com/ [5]. http://www.fuelcellstore.com/en/pc/viewPrd.asp?idcategory=46&idproduct=369#details [6]. http://www.fuelcellstore.com/en/pc/viewPrd.asp?idcategory=46&idproduct=1389 [7]. http://www.fuelcellstore.com/en/pc/viewPrd.asp?idcategory=46&idproduct=1104 [8]. http://www.horizonfuelcell.com/fuel_cell_stacks.htm [9]. http://www.fuelcellstore.com/en/pc/viewPrd.asp?idcategory=46&idproduct=1105 [10]. http://www.horizonfuelcell.com/fuel_cell_stacks.htm


34

Chapter 4, Part 1

Solar Cell

Chapter 4

COMPONENTS


35

Chapter 4: Part 1

Solar Cell

Chapter 4: Part 1

SOLAR CELL


36

Chapter 4: Part 1

Solar Cell

4.1.1. Brief History [16] Solar energy was never a new invention, however converting this energy to mechanical or electrical energy was the invention. Nature of materials that convert light into energy was observed since the 1830s by Edmund Becquerel. Several scientists followed researching like Auguste Mouchout, the first to patent a design for a motor running on solar energy. Also others are Willoughby Smith, William Adams, Richard Day, Charles Fritz, Charles Tellier, John Ericsson and a lot others. In the 1970s, after the OPEC embargo, suddenly it became important to find an alternative form of energy as the world realized just how reliant we really are on non-renewable, finite resources like coal, oil and gas for our existence. Solar energy history was made as the price of solar cells dropped dramatically to about $20 per watt. Today, there is a renewed focus as more and more people see the advantages of solar energy and as it becomes more and more affordable. Governments across the world offer financial assistance. Solar electric systems are now used to power many homes, businesses, holiday cottages, even villages in Africa.

4.1.2. Solar Radiation The solar constant Gsc is the energy from the sun per unit time on a unit area of surface perpendicular to the direction of propagation of the radiation at mean earth-sun distance outside the atmosphere. Gsc = 1367 W/m2 [1]. Its value changed due to the altitudes it measured from such as mountains, aircraft, spacecrafts and balloons. Solar radiation incident outside the earth's atmosphere is called extraterrestrial radiation Gon [4]. Variation of the earth-sun distance does lead the variation of extraterrestrial solar radiation flux in the range of ±3.3%. Figure 4.1 shows the variation of extraterrestrial solar radiation with time of year. A simple equation with accuracy adequate for most engineering calculations is given by Equation 4.1. Equation 4.2 is more accurate in the range of ±0.01%. [1] Gon

=

G sc (1 +

0.033 cos

360n 365

)

G on = G sc (1.000110 + 0.034221co sB + 0.001280si nB + 0.000719co s2B + 0.000077si n2B)

Where:

B = (n - 1)

360

(4.1) (4.2) (4.3)

365

n: number of the day in the year (from Table 4.1)


Chapter 4: Part 1

37

Solar Cell

Chapter 4: Part 1

Solar Cell

Table 4. 1: Number of days (n)

[1]

Mont h

Januar y

Februar y

Marc h

Apri l

May

June

July

Augus t

Septembe r

Octobe r

Novembe r

Decembe r

n

I

31+i

59+i

90+i

120+ i

151+ i

181+ i

212+i

243+i

273+i

304+i

334+i

Where: i is number of days in the month

Figure 4.1: Variation of extraterrestrial solar radiation with time of year

4.1.2.1. Definitions

[1]

[1]

Beam radiation

The solar radiation received from the sun without having been scattered by the atmosphere. Diffuse radiation

The solar radiation received from the sun after its direction has been changed by scattering by the atmosphere. Total solar radiation

It is the sum of the beam and the diffuse solar radiation on a surface.


Chapter 4: Part 1

38

Solar Cell

Chapter 4: Part 1

Solar Cell

2

Irradiance (G) (W/m )

It is the rate at which radiant energy is incident on a surface per unit area of surface. 2

Irradiation or Radiant Exposure (J/m )

It is the incident energy per unit area on a surface. Insolation is a term applying specifically to solar energy radiation. The symbol H is used for insolation for a day and symbol I is used for insolation for an hour or other period. 2

Radiosity or Radiant Exitance (W/m )

It is the rate at which radiant energy leaves a surface per unit area by combined emission, reflection and transmission. 2

Emissive Power or Radiant Self-Exitance (W/m )

It is the rate at which radiant energy leaves a surface per unit u nit area by emission only. Solar Time

Time based on the apparent angular motion of the sun across the sky.

4.1.2.2. Direction of Beam Radiation

[1]

The geometric relation between a plane of any particular orientation relative to the earth at any time and the incoming beam solar radiation can be described in terms of several angles. Figure 4.2 to 4.4 indicates the angles of the earth. ea rth. Also, Table 4.2 gives angles definitions. Table 4. 2: Angles description

Angle

[1]

Symbol

Description

Latitude

ф

The angular location north or south of the equator in Figure 4.4

Declination

δ

The angular position of the sun at solar noon with respect to the plane p lane of the equator in Figure 4.3

Slope

β

The angle between the plane and the horizontal in Figure 4.4

Surface azimuth

γ

The deviation of the projection on a horizontal plane of the normal to the surface from the local meridian.


Chapter 4: Part 1

39

Solar Cell

Chapter 4: Part 1

Solar Cell

γs

The angular displacement from south of the projection of beam radiation on the horizontal plane in Figure 4.2

Hour

ω

The angular displacement of the sun east or west of the local meridian due to rotation of the earth ea rth on its axis at 15o per 1 hour in Figure 4.5

Sunset hour

ωs

The angle of the sun form the noon to the sunset.

Sunrise hour

-ωs

The angle of the sun form the sunrise to the noon.

Solar azimuth

Incident

θ

The angle between the beam radiation on a surface and the normal to the tilted surface in Figure 4.2

Zenith

θz

The angle between the vertical and the line to the sun incidence on horizontal surface in Figure 4.2

Solar altitude

αs

The angle between the horizontal and the line to the sun in Figure 4.2

Normal to

θ

the plane Plane

Figure 4.2: Angles

[1]


Chapter 4: Part 1

40

Solar Cell

Chapter 4: Part 1

Solar Cell

Figure 4.3: Declination angle δ

[7]

ф

Figure 4.4: Latitude angle ф

[5]


Chapter 4: Part 1

41

Solar Cell

Chapter 4: Part 1

Solar Cell

ω

Figure 4.5: Hour angle ω

[6]

The declination angle δ can be found from Equation 4.4 δ = 23.45 sin(360

284 + n 365

)

(4.4)

ℎ:  .    ℎ  The Incident angle θ can be found from Equation 4.3 cosθ = sin δ sin φ cos β − sin δ cos φ sin β cos γ + cos δ cos φ cos β cos ω +

cos δ sin φ sin β cos γ cos ω + cos δ sin β sin γ sin ω

(4.5)

 =  ℎ  = 0 The Solar azimuth angle γs can be found from Equation 4.6 Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

Chapter 4: Part 1

42

Solar Cell

Chapter 4: Part 1

Solar Cell

γ s

=

1

−

sign (ω ) cos (

cos θ z sin φ − sin δ sin θ z cos φ

(4.6)

)

Where: sign = +1 when ω is positive po sitive and = -1 if ω is negative

The Sunset hour angle ωs can be found from Equation 4.7 cos ω s

= −

tan δ tan φ

(4.7)

The number of day light hours (sunshine) N is given by Equation 4.8 N =

2 15

(4.8)

1

−

cos ( − tan δ tan φ )

4.1.2.3. Ratio of Beam Radiation on Tilted Surface to That on Horizontal Surface ( R R b). Figure 4.6 shows the beam radiation radia tion on horizontal and tilted surface.

Figure 4.6: Beam radiation on horizontal and tilted surface

[1]

Rb calculated from Equation 4.9 Rb

=

Gb ,t Gb

=

Gb ,n cosθ Gb ,n cosθ z

=

cosθ cosθ z


Chapter 4: Part 1

(4.9)

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4.1.2.4. Extraterrestrial Radiation on a Horizontal Surface. Extraterrestrial radiation G o at any time is given by Equation 4.10 G0

=

Gsc (1 + 0.033 cos

360 n 365

(4.10)

) cos θ z

The hourly extraterrestrial radiation I o is given by Equation 4.11 I 0

=

24 × 3600 × Gsc

π

Where:

(1 + 0.033 cos

360 n 365

) × (cos φ sin δ (sin ω 2

−

sin ω 1 ) +

π (ω 2 − ω 1 ) 180

sin φ sin δ )

(4.11)

    ℎ    ℎ ( >  ) 1

2

2

1

The daily extraterrestrial radiation H o is given by Equation 4.12 H 0

=

24 × 3600 × Gsc

π

(1 + 0.033 cos

The monthly extraterrestrial radiation H 0

=

24 × 3600 × Gsc

π

H o

(1 + 0.033 cos

360 n 365

) × (cos φ sin δ sin ω s

+

πω s 180

sin φ sin δ )

(4.12)

is given by Equation 4.13 360 n 365

) × (cos φ sin δ sin ω s

+

πω s 180

sin φ sin δ )

(4.13)

ℎ:        ℎ ℎ 4.1.3. Photovoltaic Solar Cell Systems [9] 4.1.3.1. Introduction In 1839 it was observed that certain materials, when exposed to light, produced an electric current. This is now known as the photovoltaic effect, and is the basis of the operation of photovoltaic or solar cells. Solar cells are manufactured from semiconductor materials; that is, materials that act as insulators at low temperatures, but as conductors when energy or heat is available. At present, most solar cells are siliconbased, since this is the most mature technology.


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4.1.3.2. Semiconductors Types Silicon and other semiconductor materials used for solar cells can be crystalline, multicrystalline, polycrystalline, microcrystalline or amorphous. Microcrystalline material has grains smaller than 1 µm, polycrystalline smaller than 1 mm and multicrystalline smaller than 10 cm.

i. Crystalline Silicon Crystalline silicon has an ordered crystal structure, with each atom ideally lying in a pre-ordained position. It therefore allows ready application of the theories and techniques developed for crystalline material and exhibits predictable and uniform behaviour. It is, however, the most expensive type of silicon, because of the careful and slow manufacturing processes required. The cheaper che aper multicrystalline or polycrystalline silicon (poly-silicon), and amorphous silicon are therefore increasingly being used for solar cells, despite their less ideal qualities.

ii. Multicrystalline Silicon The techniques for production of multicrystalline or polycrystalline silicon are less critical, and hence cheaper, than those required for single crystal material. The grain boundaries reduce the cell performance by blocking carrier flows, allowing extra energy levels in the forbidden gap, thereby providing effective recombination sites, and providing shunting paths for current flow a cross the p-n junction. To avoid significant recombination losses at grain boundaries, grain sizes in the order of a few millimeters are required. This also allows single grains to extend from the front to the back of a cell, providing less resistance to carrier flow and generally decreasing the length of grain boundaries per unit of cell. Such Multicrystalline material is widely used for commercial solar cell production.

iii. Amorphous Silicon Amorphous silicon can be produced even more cheaply than polysilicon. With amorphous silicon, there is no long-range order in the structural arrangement of the atoms, resulting in areas within the material containing unsatisfied or ‘dangling’ bonds. These in turn result in extra energy levels within the forbidden gap, making it to obtain reasonable current flows in a solar cell configuration.

4.1.3.3. The Behavior of Solar Cell i. Effect of Light A silicon solar cell is a diode formed by joining p-type (typically boron doped) and n-type (typically phosphorous doped) silicon. Light shining on such a cell can behave in a number of ways, as illustrated in Figure 4.7. To maximise the power rating of a solar cell, it must be designed so as to maximise desired absorption (3) and absorption after reflection (5). Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Figure 4.7: Behaviour of light shining on a solar cell. (1) Reflection and absorption at top contact. (2) Reflection at cell surface. (3) Desired absorption. (4) Reflection from rear out of cell—weakly absorbed light only. (5) Absorption after reflection. (6) Absorption in rear contact.

    =  �  − 1 − 

(4.14)

Where IL: is the light-generated current. The light has the effect of shifting the I-V curve down into the fourth quadrant where power can be extracted from the diode, as shown in Figure 4.8.


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Figure 4.8: The effect of light on the current-voltage characteristics of a p-n junction

The I-V curve characterizes the cell, with its power output being equal to the area of the rectangle in the bottom right-hand quadrant of Figure 4.8 (a). This I-V curve is most often shown reversed, as in Figure 4.9, with the output curve in the first quadrant, and represented by

    =  − �  − 1

(4.15)

Figure 4.9: Typical representation of an I-V curve, showing short-circuit current (Isc and open-circuit voltage (Voc) points, as well as the maximum power point (Vmp, Imp)


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The two limiting parameters used to characterize the output of solar cells for given irradiance, operating temperature and area are: 1. Short circuit current (Isc)—the maximum current, at zero voltage. Ideally, if V = 0, I sc = IL. Note that Isc is directly proportional to the available sunlight. 2. Open circuit voltage (Voc)—the maximum voltage, at zero current. The value of Voc increases logarithmically with increased sunlight. This characteristic makes solar cells ideally suited to battery charging. Note that at I = 0,

 + 1  =      

(4.16)

For each point on the I-V curve, the product of the current and voltage represents the power output for that operating condition. A solar cell can also be characterized by its maximum power point, when the product Vmp × I mp is at its maximum value. The maximum power output of a cell is graphically given by the largest rectangle that can be fitted under the I-V curve. That is,

 + 1  =  −      /

(4.17)

For example, if n = 1.3 and Voc = 600 mV, as for a typical silicon cell, Vmp is about 93 mV smaller than Voc. The power output at the maximum power point under strong sunlight (1 kW/m2) is known as the ‘peak power’ of the cell. Hence photovoltaic panels are usually rated in terms of their ‘pea k’ watts (Wp). The fill factor (FF), is a measure of the junction quality and series resistance of a cell. It is defined as

 =  

(4.18)

 =   

(4.19)

Hence maximum point power is:


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Obviously, the nearer the fill factor is to unity, the higher the quality of the cell. Ideally, it is a function only of the open circuit voltage and can be calculated using the approximate empirical expression 0.72)  =  − (+ 1+ 0.72

(4.20)

Where νoc is defined as a ‘normalised Voc’; that is

 = /

(4.21)

The above expression applies to ideal cases only, with no parasitic resistance losses, and is accurate to about one digit in the fourth decimal place for these cases.

ii. Effect of Temperature The operating temperature of a solar cell is determined by the ambient air temperature, by the characteristics of the module in which it is encapsulated, by the intensity of sunlight falling on the module, and by other variables such as wind velocity. The main effect of increasing temperature for silicon solar cells is a reduction in open circuit volt (Voc), the fill factor and hence the cell output. These effects are illustrated in Figure 4.10.

Figure 4.10: The effect of temperature on the I-V characteristics of a solar cell


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iii. Effect of Parasitic Resistances Solar cells generally have a parasitic series and shunt resistance associated with them, as shown in Figure 4.11. Both types of parasitic resistance act to reduce the fill-factor.

Figure 4.11: Parasitic series and shunt resistances in a solar cell circuit

The major contributors to the series resistance (R s) are the bulk resistance of the semiconductor material, the metallic contacts and interconnections, carrier transport through the top diffused layer, and contact resistance between the metallic contacts and the semiconductor. The effect of series resistance is shown in Figure 4.12.

Figure 4.12: The effect of series resistance on fill factor


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4.1.3.4. Cell Properties and Design i. Efficiencies Under laboratory conditions, it is possible to produce single-crystal silicon solar cells with efficiencies in excess of 24%. However, commercially mass-produced cells are typically only 13–14% efficient. There are many reasons for this; the over-riding one being that, while efficiency can be the major aim for laboratory produced cells, irrespective of cost, complexity of processing or throughput, in general, laboratory techniques are unsuited to industry. The maximum power point efficiency of a module is given by [1]

    =  

(4.22)

Where: I mp and V mp are current and volt at maximum power point, A c is array area and GT solar radiation on the array.

ii. Module Structure Solar arrays are often used in harsh and remote environments, where supplying power by central grid or fuel-dependent systems is not feasible. Hence, modules must be capable of extended, maintenance-free operation. Module lifetimes of around 20 years are normally quoted by manufacturers, although the industry is seeking 30-year lifetimes. Encapsulation is the main factor affecting solar cell life expectancy. A typical encapsulation scheme is shown in Figure 4.13.


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Figure 4.13: A typical laminated module structure (EVA stands for Ethylene Vinyl Acetate)

iii. Environmental Protection The module must be able to withstand such environmental conditions as dust, salt, sand, wind, snow, humidity, rain, hail, birds, condensation and evaporation of moisture, atmospheric gases and pollutants, and seasonal temperature variations, as well as maintaining performance under prolonged exposure to UV light. The top cover must have, and maintain, high transmission in the waveband 350– 1200 nm. It must have good impact resistance and a hard, smooth, flat, abrasion-resistant, non-staining surface, which promotes self-cleaning by wind, rain or spray. Moisture penetration is responsible for the majority of long-term module failures, with condensation on the cells and circuitry causing shorting or corrosion. Hence, the encapsulation system must be highly resistant to the permeation or of gases, vapours or liquids. The most vulnerable sites are at the interface between the cells and the encapsulating materials, and at all other interfaces between different materials. The materials used for bonding must also be carefully chosen to be able to maintain adhesion under extreme operating conditions. Common encapsulants are ethylene vinyl acetate (EVA), Teflon and casting resin. EVA is commonly used for standard modules and is applied in a vacuum chamber, as is Teflon, which is used for small scale special modules and which does not require a front cover glass. Resin encapsulation is sometimes used for large modules intended for building integration.


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4.1.4. Solar Energy in Egypt It is common knowledge that solar radiation is unevenly distributed, and that it varies in intensity from one geographic location to another depending upon the latitude, season, and time of day. Until recently, valid records for solar radiation have been very scanty in the vast majority of the developing countries. In the absence of such useful information as a guide for the proper exploitation of solar energy, only general hints can be offered regarding the geographic areas with favorable conditions for solar energy applications [13]. Figure 4.14 shows solar radiation word map.

Figure 4.14: Solar radiation radiation world map

[14]

The average annual direct solar radiation (normal incidence) in Egypt in kWh/d is depicted in Figure 4.15. According to this map, the Nile Delta and Cairo region have an average daily direct insolation of between 5.5 and 7.0 kWh/m²/day, or, 2000 to 2550 kWh/m²/yr. Along the Nile river and the Red Sea coast, the annual average is between 7.0 and 9.0 kWh/m²/d, or between 2550 and 3285 kWh/m²/yr. Most of the values have been estimated from global and diffuse radiation measurements and should be verified by ground measurements at the selected sites. Nevertheless, it gives an indication of the outstanding insolation potential of Egypt [11].


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Figure 4.15: The average annual direct solar radiation (normal incidence) in Egypt in kWh/d

Solar Cell

[11]

4.1.4.1. Kuraymat Solar Thermal Power Plant (140 MW) [12]. The project site at Kuraymat nearly 90km South Cairo, has been selected due to 1. An uninhabited flat desert land. 2. High intensity direct solar radiation reaches to 24 00 kWh /m2 / year 3. An extended unified power grid and expanded natural gas pipelines . 4. Near to the sources of water (the River Nile). See Figure 4.16.


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Figure 4.16: Kuraymat power station site

[15]


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4.1.5. References [1]. Solar Engineering of thermal processes by John A. Duffie and William Beckman. Third Edition. Ed ition. [2]. http://home.tkug.tartu.ee/~zolki/html06prak http://home.tkug.tartu.ee/~zolki/html06prakt/rainarkruus/ t/rainarkruus/ [3]. http://www.nasa.gov/mission_pages/ http://www.nasa.gov/mission_pages/hinode/solar_020.ht hinode/solar_020.html ml [4]. http://solardat.uoregon.edu/SolarRadiationBasics.html [5]. http://geographyworldonline.com/tut http://geographyworldonline.com/tutorial/latitude2.jpg orial/latitude2.jpg [6]. http://geographyworldonline.com/tut http://geographyworldonline.com/tutorial/longitude orial/longitude2.jpg 2.jpg [7]. http://www.powerfromthesun.net/chapter3/Image60.jpg

[8]. Principles of Solar Engineering by D. Yogi Goswami , Frank Kreith and Jan F. Kreider. [9]. APPLIED PHOTOVOLTAICS Second Edition by Sturat R. Wenham, Matin A. Green, Muriel E. Watt and Richard Cokish. [10]. http://en.wikipedia.org/wiki/Crystalline_silicon [11]. http://www.solarpaces.org/News/Projects/Egypt.htm [12]. http://www.nrea.gov.eg/english/page121e.htm [13]. http://almashriq.hiof.no/lebanon/600/61 http://almashriq.hiof.no/lebanon/600/610/614/solar-w 0/614/solar-water/unesco/24-26.ht ater/unesco/24-26.html ml [14]. http://www.greenrhinoenergy.com/solar/radia http://www.greenrhinoenergy.com/solar/radiation/images/World% tion/images/World%20Insolation%20D 20Insolation%20Direct.jpg irect.jpg [15]. http://www.modernpowersystems.com/story.asp http://www.modernpowersystems.com/story.asp?sectionCode=88&sto ?sectionCode=88&storyCode=2050538 ryCode=2050538 [16]. http://www.facts-about-solar-energy.com/sol http://www.facts-about-solar-energy.com/solar-energy-history.html ar-energy-history.html


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ELECRTOLYSER


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4.2.1. Water Electrolysis Technology Electrolysis of water is the decomposition of water (H 2O) into oxygen (O 2) and hydrogen gas (H 2) due to an electric current being passed through the water. The electrodes submerged in a conductive medium (electrolyte) form the electrolysis cell as shown in Figure 1 below.

Figure 4.17: Water Electrolysis principle

Principle

An electrical power source is connected to two electrodes which are placed in the water. Hydrogen appears at the cathode (the negatively charged electrode), and oxygen appears at the anode (the positively charged electrode). Assuming ideal Faraday efficiency ( the efficiency with which charge or electrons are transferred in a system facilitating an electrochemical reaction ) the generated amount (moles) of hydrogen is twice that of oxygen, and both are proportional to the total electrical charge that was sent through the solution. However, in many cells competing side reactions dominate, resulting in different products and less than ideal Faraday efficiency. Electrolysis of pure of pure water requires excess energy in the form of over potential to overcome various activation barriers. Without the excess energy the electrolysis of pure water occurs very slowly if at all. This is in part due to the limited self-ionization of water. Pure water has an electrical conductivity about one millionth that of seawater. Many electrolytic cells may also lack the requisite electro catalysts. The effectiveness of electrolysis is increased through the addition of an electrolyte (such as a salt, an acid or a base) and the use of electro of electro catalysts.


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The following reduction-oxidation chemical reactions represent the water decomposition process: 2H2O + electric energy

→

2H2 + O2

(4.23)

-

Oxidation describes the electrons (e ) loss (or the protons gain) by a molecule, atom or ion. In water electrolysis, at the anode electrode (positive) where oxygen is produced, the oxidation equation is: 2 H 2 O → O2 + 4 H 2OH

−

→

1 2

O2

+

+

4e

−

+ H 2 O +

(PEM electrolyser)

2e

−

(Alkaline electrolyser)

(4.24a)

(4.25b)

-

Reduction describes the electrons (e ) gain (or the protons loss) by a molecule, atom or ion. In water electrolysis, at the cathode electrode (negative) where hydrogen is produced, the reduction equation is: 4 H

+

+

4e

−

→

−

2 H 2 (PEM electrolyser)

2 H 2O + 2e → H 2 + 2OH

−

(Alkaline electrolyser)

(4.26a) (4.26b)

4.2.2. Types of Electrolysers 4.2.2.1. Proton-exchange membrane (PEM) electrolysers The operation of a PEM electrolyser depends on the use of precious metal catalysts (Platinum, Platinum/Ruthenium) and a solid polymeric electrolyte for transferring protons. As applies for PEM fuel cells, Dupont’s fluorocarbon-based ionomer, Nafion, dominates most designs of PEM electrolyser. PEM electrolysers have achieved >100,000 hours continuous operation without failure in critical environments (e.g. O2 provision for nuclear submarines). They can operate at much higher current densities than 2 alkaline electrolysers (1-2 A/cm ), with conversion efficiencies ranging from 50-90%, but cannot yet achieve high efficiencies at high current densities. Without auxiliary purification equipment, gas purity is typically 99.999% both for H 2 and O2. Operation at high pressure (including high differential pressure between the hydrogen and oxygen side at up to 200bar) is proven and the need for auxiliary gas compression is then considerably less than for the alkaline electrolyser.


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Figure 4.18: Schematic drawing of a PEM cell with cell reactions

The key factors favoring the PEM electrolyser are that it avoids the requirement to circulate a liquid electrolyte, it operates at a high current density, and it has the intrinsic ability to cope with transient variations in electrical power input (hence it has outstanding applications flexibility with respect to capturing intermittent renewable electricity supplies, such as wind and solar power).

4.2.2.2. Alkaline Electrolysers The operation of an alkaline electrolyser depends on the use of a circulating electrolyte solution (usually potassium hydroxide) for transferring hydroxyl ions. Alkaline electrolysers operate at relatively low 2 current densities of <0.4 A/cm and conversion efficiencies range from 60-90%. Without auxiliary purification equipment, gas purities are typically 99.8% and 99.2% for H 2 and O2 respectively. Several large alkaline electrolysers of >100MW have been applied (e.g. in Egypt and Congo to utilize hydropower to generate ‘renewable hydrogen’). A modern alkaline electrolyser will achieve an efficiency 3 of ~ 90% (consuming about 4kWh of electricity per m of H2 generated at NTP ‘Normal Temperature and Pressure’) and deliver gas at up to 30bar without auxiliary compression. However, significant postelectrolysis electricity consumption is incurred for gas compression to deliver H 2 and O2 at the pressures required by industry and for storage on-board hydrogen vehicles (350-700 bar). The key factors favoring the alkaline electrolyser are that it obviates the need for expensive Platinumbased catalysts, it is well proven at large scale and it is usually of lower unit cost than a PEM electrolyser. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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4.2.2.3. The Solid Oxide Electrolyser The operation of a solid-oxide electrolyser depends on a solid ceramic electrolyte (zirconia/ceria), which o 2at temperatures of 800-1000 C transfers oxygen ions (O ). The solid oxide electrolyser requires a source of high-temperature heat. By operating at elevated temperatures, the heat input meets some of the 3 energetic requirement for electrolysis and so less electricity is required per m of H2 generated, compared with the other electrolyser technologies.

Figure 4.19: Schematic drawing of a Solid Oxide Electrolyser

However, to date, prototype solid-oxide electrolyser units have not achieved useful operational lives and substantial engineering problems exist with respect to thermal cycling and gas sealing. Accordingly, it is premature to make comparisons with alkaline and PEM electrolysers.

4.2.3. Elecrolyser and Fuel Cell The electrolyser is the reverse of the fuel cell, so the theory of operation and design is similar. Also the electrolyser is one of the energy sources used to generate hydrogen to be used in fuel cells. The recent researches in the world are directed to develop and improve the fuel cell performance with minimal capital costs. More detailed information about different types of fuel cells is discussed in section 4.3.


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4.3.1. Introduction Fuel cells are devices convert fuel and air directly to electricity, heat and water in an electrochemical process. Unlike conventional engines, they do not burn the fuel and run pistons or shafts, and so have [1] fewer efficiency losses, low emissions and no moving parts. A fuel cell, although having components and characteristics similar to those of a typical battery, differs in several respects. The battery is an energy storage device. The maximum energy available is determined by the amount of chemical reactant stored within the battery itself (i.e., closed system). The battery will cease to produce electrical energy when the chemical reactants are consumed (i.e., discharged). In a secondary battery, the reactants are regenerated by recharging, which involves putting energy into the battery from an external source. The fuel cell, on the other hand, is an energy conversion device that theoretically has the capability of producing electrical energy for as long as the fuel and oxidant are [2] supplied to the electrodes (i.e. open system).

Figure 4.20: Fuel cell

[3] [4]

4.3.2. History It's a common misconception that fuel cells are a modern invention, born in the 21st century era of professional design and complicated science. Fuel cells have actually been around since the 1800s when the railways were first being built. In 1800, William Nicholson and Anthony Carlisle described the process of using electricity to break water into hydrogen and oxygen.


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William Grove is credited with the first known demonstration of the fuel cell in 1839. Grove saw notes from Nicholson and Carlisle and thought he might “recompose water” by combining electrodes in a series circuit, and soon accomplished this with a device called a “gas battery”. th

Fuel cells were neglected for the rest of the 19th century, and for most of the 20 . Although independent scientists carried out a lot of experiments on fuel cells in the early 20th century, it wasn’t until the late 1950s that fuel cells really came into use when two scientists, Thomas Grubb and Leonard Niedrach both did research on fuel cells, which finished with a new type of fuel cell, commonly referred to as the GrubbNiedrach fuel cell. The General Electric Company, who employed both Grubb and Niedrach, saw the potential in this new cell, and teamed up with NASA to develop the idea further, and saw the fuel cell put to its first ever commercial use on board NASA’s Project Gemini.

4.3.3. Components and their functions The basic physical structure or building block of a fuel cell circuit consists of: An Electrolyte layer (membrane)

a) Transports dissolved reactants to the electrode b) Conducts ionic charge between the electrodes and thereby completes the cell electric circuit. c) Also provides a physical barrier to prevent the fuel and oxidant gas streams from directly mixing which cause a problem called ‘gas crossover’. Porous charged electrodes (Anode and Cathode):

a) Provide a surface site where gas/liquid ionization or de-ionization reactions can take place. b) Conduct ions away from or into the three-phase interface once they are formed (so an electrode must be made of materials that have good electrical conductance). c)

Provide a physical barrier that separates the bulk gas phase and the electrolyte.

[2]

Catalyst layer on both anode and cathode:

a) Speeds up the electrochemical processes.

[2]

A schematic representation of a fuel cell with the reactant/product gases and the ion conduction flow directions through the cell is shown below.


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Figure 4.21: Schematic diagrams for the PEMFC basic components and the reactants/ions/products flow

Fuel Cell

[5]

4.3.4. Operation In a typical fuel cell, gaseous fuels (like Hydrogen) are fed continuously to the anode (negative electrode) compartment and an oxidant (i.e. oxygen) is fed continuously to the cathode (positive electrode) compartment; the electrochemical reactions take place at the ‘three-phase interface’ which is established among the reactants, electrolyte, and catalyst in the region of the porous electrode. Hydrogen is oxidized on the anode and oxygen is reduced on the cathode. Protons are transported from the anode to the cathode through the electrolyte membrane and the electrons are carried to the cathode over the external circuit. In nature, molecules cannot stay in an ionic state; therefore they immediately recombine with other molecules in order to return to the neutral state. Hydrogen protons in fuel cells stay in the ionic state by traveling from molecule to molecule through the use of special materials (Electrolyte).The electrons are attracted to conductive materials and travel to the load when needed. On [6] the cathode, oxygen reacts with protons and electrons, forming water and producing heat.


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4.3.5. Types of fuel cell 4.3.5.1. Alkaline Fuel Cell (AFC) AFCs' high performance is due to the rate at which chemical reactions take place in the cell. They have also demonstrated efficiencies near 60% in space applications.

4.3.5.2. Phosphoric Acid Fuel Cell (PAFC) The PAFC is considered the "first generation" of modern fuel cells. It is one of the most mature cell types and the first to be used commercially. This type of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large vehicles such as city buses. They are 85% efficient when used for the co-generation of electricity and heat but less efficient at generating electricity alone (37%–42%). This is only slightly more efficient than combustion-based power plants, which typically operate at 33%–35% efficiency. PAFCs are also less powerful than other fuel cells, given the same weight and volume. As a result, these fuel cells are typically large and heavy. PAFCs are also expensive. PAFCs require an expensive platinum catalyst, which raises the cost of the [7] fuel cell.

4.3.5.3. Molten Carbonate Fuel Cell (MCFC) Improved efficiency is another reason MCFCs offer significant cost reductions over phosphoric acid fuel cells (PAFCs). Molten carbonate fuel cells can reach efficiencies approaching 60%, considerably higher than the 37%–42% efficiencies of a phosphoric acid fuel cell plant. When the waste heat is captured and used, overall fuel efficiencies can be as high as 85%. MCFCs do not require an external reformer to convert more energy-dense fuels to hydrogen. Due to the high temperatures at which MCFCs operate, these fuels are converted to hydrogen within the fuel cell itself by a process called internal reforming, which also reduces cost. The primary disadvantage of current MCFC technology is durability. The high temperatures at which these cells operate and the corrosive electrolyte used accelerate component breakdown and corrosion, decreasing cell life. Scientists are currently exploring corrosion-resistant materials for components as well [7] as fuel cell designs that increase cell life without decreasing performance.

4.3.5.4. Solid Oxide Fuel Cell (SOFC) Solid oxide fuel cells (SOFCs) use a hard, non-porous ceramic compound as the electrolyte. Because the electrolyte is a solid, the cells do not have to be constructed in the plate-like configuration typical of other fuel cell types. SOFCs are expected to be around 50%–60% efficient at converting fuel to electricity. In applications designed to capture and utilize the system's waste heat (co-generation), overall fuel use efficiencies could top 80%–85%. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Solid oxide fuel cells operate at very high temperatures—around 1,000°C. High-temperature operation removes the need for precious-metal catalyst, thereby reducing cost. It also allows SOFCs to reform fuels internally, which enables the use of a variety of fuels and reduces the cost associated with adding a [7] reformer to the system.

4.3.5.5. Polymer Electrolyte Membrane Fuel Cell (PEMFC) This type is discussed in details in section 4.3.6. The following table shows the main types of fuel cells and their characteristics Table 4.3: Fuel cell types and specifications

[2]


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4.3.6. PEM Fuel Cell (PEMFC) 4.3.6.1. Overview The polymer electrolyte membrane fuel cell (PEMFC) also known as Proton Exchange Membrane Fuel Cell, also called the Solid Polymer Fuel Cell (SPFC), was first developed by General Electric in the United States in the 1960s for use by NASA on their first manned space vehicles.

4.3.6.2. Fuel and Oxidizer Gaseous hydrogen has become the fuel of choice for most applications because of 1) Its high reactivity when suitable catalysts are used. 2) Its ability to be produced from hydrocarbons or Electrolysis in a high amounts for terrestrial applications. 3) Its high energy density when stored cryogenically for closed environment applications, such as in space. Similarly, the most common oxidant is gaseous oxygen, which is readily and economically available [2] from air for terrestrial applications, and again easily stored in a closed environment.

4.3.6.3. Basic construction, Main components and Materials The electrolyte is an ion conduction polymer so it should be fabricated from a material of good conduction for protons which is ‘fluorinated sulfonic acid polymer’ (FSAP) or other similar polymer. Onto each side is bonded a catalyzed porous electrode where the catalyst is made of ‘platinum’ (Pt) for higher reaction rates (Oxidation and Reduction) while the electrode made of black carbon and ‘polytetrafluoroethylene’ (PTFE) which is hydrophobic (acts as a wet proofing Agent) and serves as the gas permeable phase, and carbon black is an electron conductor that provides a high surface area to support the electrocatalyst. The anode–electrolyte– cathode assembly is thus one item, and is very thin, as shown in Figure 4.22. These ‘membrane electrode assemblies’ (or MEAs) are connected in series, usually [2], [8] by using bipolar plates. Table 2 shows components material and its advantages. Table 4.4: Components Materials and Advantages

Component Electrolyte Electrode (Anode /Cathode)

Material FSAP Black Carbon and PTFE

Catalyst

Pt

Advantages Proton Conduction Electron conduction and gas diffusion Higher Reactions


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Figure 4.22: An example of a membrane electrode assembly (MEA). The membrane is a little larger than the electrodes that are attached. These electrodes have the gas diffusion layer attached, which gives it a ‘grainy’ texture. The membrane is typically 0.05 to 0.1mm thick, thi ck, the electrodes are about 0.03mm thick, and the gas diffusion layer is [8] between 0.2 and 0.5-mm thick.

4.3.6.4. Characteristics The polymer electrolytes work at low temperatures, which have the advantage that a PEMFC can start quickly. The thinness of the MEAs means that compact fuel cells can be made. Further advantages are that there are no corrosive fluid hazards and that the cell can work in any orientation. This means that the [8] PEMFC is particularly suitable for use in vehicles and in portable applications.

4.3.6.5. Reactions However, to understand how the 69reaction between hydrogen and oxygen produces an electric current, and where the electrons come from, we need to consider the separate reactions taking place at each electrode. These important details vary for different types of fuel cells, but if we start with a cell based around an acid electrolyte, as used by Grove, we shall start with the simplest and still the most common type. At the anode of an acid electrolyte fuel cell, the hydrogen gas ionizes, releasing electrons and creating H+ ions (or protons). −

+

2H2 → 4H + 4e

(Er=0 V)

(4.27)

This reaction releases energy. At the cathode, oxygen reacts with electrons taken from the electrode, and + H ions from the electrolyte, to form water. −

+

O2 + 4e + 4H → 2H2O

(Er=1.23 V)

(4.28)

Clearly, for both these reactions to proceed continuously, electrons produced at the anode must pass + through an electrical circuit to the cathode. Also, H ions must pass through the electrolyte (proton + exchange membrane) which is a medium with free H ions, and so serves this purpose very well.


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Comparing the two equations, we can see that two hydrogen molecules will be needed for each oxygen molecule if the system is to be kept in balance. This is shown in Figure 4.24. It should be noted that the + electrolyte must only allow H ions to pass through it, and not electrons. Otherwise, the electrons would [8] go through the electrolyte, not around the external circuit.

Figure 4.23: Cathode–electrolyte–anode construction construction of a fuel cell.

[8]

Figure 4.24: Electrode reactions and charge flow for an acid electrolyte fuel cell. Note that although the negative [8] electrons flow from anode to cathode, the ‘conventional current’ flows from cathode to anode.


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4.3.6.6. Multi-cell Construction (Fuel cell stack) i. Connecting Cells in Series – the Bipolar Plate a. Series by wiring like battery

The voltage of a fuel cell is quite small, about 0.7V when drawing a useful current. This means that to produce a useful voltage many cells have to be connected in series. Such a collection of fuel cells in series is known as a ‘stack’. The most obvious way to do this is by simply connecting the edge of each anode to the cathode of the next cell, all along the line, as in Figure 4.25 (For simplicity, this diagram ignores the problem of supplying gas to the electrodes.)

Figure 4.25: Simple edge connections of three cells in series

[8]

The problem with this method is that the electrons have to flow across the face of the electrode to the current collection point at the edge (wiring point). The electrodes might be quite good conductors, but if each cell is only operating at about 0.7V, even a small voltage drop is important. Unless the current flows [8] are very low and the electrode is a particularly good conductor, or very small, this method is not used. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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b. Bipolar plates (Anode/Cathode Electrode)

A much better method of cell interconnection is to use a ‘bipolar plate’. This makes connections all over the surface of one cathode and the anode of the next cell (hence ‘bipolar’); at the same time, the bipolar plate serves as a means of feeding oxygen to the cathode and fuel gas to the anode. Although a good electrical connection must be made between the two electrodes, the two gas supplies must be strictly separated. The method of connecting to a single cell, all over the electrode surfaces, while at the same time feeding hydrogen to the anode and oxygen to the cathode, is shown in Figure 4.26. The grooved plates are made of a good conductor such as graphite, or stainless steel. To connect several cells in series, ‘bipolar plates’ are made. These plates – or cell interconnects – have channels cut in them so that the gases can flow over the face of the electrodes. At the same time, they are made in such a way that they make a good electrical contact with the surface of each alternate electrode. [8] A simple design of a bipolar plate is shown in Figure 4.27.

Figure 4.26: Single cell with end plates for taking current from all over the face of the electrodes and also supplying gas [8] to the whole electrode.


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Figure 4.27: Two bipolar plates of very simple design. There are horizontal grooves on one side and vertical grooves on [8] the other.

4.3.6.7. Performance When comparing fuel cells with each other, and with other electric power generators, certain standard key figures are used. For comparing fuel cell electrodes and electrolytes, the key figure is the current per 2 unit area, always known as the current density. This is usually given in mA/cm . This figure should be given at a specific operating voltage, typically about 0.6 or 0.7 V. These two 2 numbers can then be multiplied to give the power per unit area, typically given in mW/cm . Electrodes frequently do not ‘scale up’ properly. That is, if the area is doubled, the current will often not double. The reasons for this are varied and often not well understood, but relate to issues such as the even delivery of reactants and removal of products from all over the face of the electrode. Bipolar plates will be used to connect many cells in series. These figures give the key figures of merit for comparing [8] electrical generators – specific power and power density. Power Density =

Power Volume

Specific Power =

Power Mass

(4.29)

Useful work (electrical energy) is obtained from a fuel cell only when a reasonable current is drawn, but the actual cell potential is decreased from its equilibrium potential because of irreversible losses as shown in the figure. Several sources contribute to irreversible losses in a practical fuel cell. The losses, which are often called polarization, overpotential, or overvoltage (η), originate primarily from three sources: (1) activation polarization (ηact), (2) ohmic polarization polarizat ion (ηohm) and (3) concentration polarization (ηconc). These losses result in a cell voltage (V) for a fuel cell that is less than its ideal potential, E (V = E [2] Losses). Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Figure 4.28: Voltage-current curve ideal and actual

[2]

The activation polarization loss is dominant at low current density. At this point, electronic barriers have to be overcome prior to current and ion flow. Activation losses show some increase as current increases. Ohmic polarization (loss) varies directly with current, increasing over the whole range of current because cell resistance remains essentially constant. Gas transport losses occur over the entire range of current density, but these losses become prominent at high limiting currents where it becomes difficult to provide enough reactant flow to the cell reaction sites.

Activation Polarization

Activation polarization is present when the rate of an electrochemical reaction at an electrode surface is controlled by sluggish electrode kinetics. In other words, activation polarization is directly related to the rates of electrochemical reactions. There is a close similarity between electrochemical and chemical reactions in that both involve an activation barrier that must be overcome by the reacting species.

Ohmic Polarization

Ohmic losses occur because of resistance to the flow of ions in the electrolyte and resistance to flow of electrons through the electrode materials. The dominant ohmic losses, through the electrolyte, are reduced by decreasing the electrode separation and enhancing the ionic conductivity of the electrolyte. Concentration Polarization

As a reactant is consumed at the electrode by electrochemical reaction, there is a loss of potential due to the inability of the surrounding material to maintain the initial concentration of the bulk fluid. That is, a concentration gradient is formed. Several processes may contribute to concentration polarization: slow Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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diffusion in the gas phase in the electrode pores, solution/dissolution of reactants/products into/out of the electrolyte, or diffusion of reactants/products through the electrolyte to/from the electrochemical reaction site.

4.3.6.8. Advantages and Applications i. Advantages The most important disadvantage of fuel cells at the present time is the same for all types – the cost. However, there are varied advantages, which feature more or less strongly for different types and lead to different applications (Figure 28). These include the following: Efficiency

Fuel cells are generally more efficient than combustion engines whether piston or turbine based. A further feature of this is that small systems can be just as efficient as large ones. This is very important in the case of the small local power generating systems needed for combined heat and power systems. Simplicity

The essentials of a fuel cell are very simple, with few if any moving parts. This can lead to highly reliable and long-lasting systems. Low emissions

The by-product of the main fuel cell reaction, when hydrogen is the fuel, is pure water, which means a fuel cell can be essentially ‘zero emission’. This is their main advantage when used in vehicles, as there is a requirement to reduce vehicle emissions, and even eliminate them within cities. However, it should be noted that, at present, emissions of CO2 are nearly always involved in the production of hydrogen that is needed as the fuel. Silence

Fuel cells are very quiet, even those with extensive extra fuel processing equipment. This is very important in both portable power applications and for local power generation in combined heat and power schemes. The fact that hydrogen is the preferred fuel in fuel cells is, in the main, one of their principal disadvantages. However, there are those who hold that this is a major advantage. It is envisaged that as fossil fuels run out, hydrogen will become the major world fuel and energy vector. It would be generated, [8] for example, by massive arrays of solar cells electrolysing water.


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ii. Applications The following figure summarizes the applications and main advantages of fuel cells of different types.

Figure 4.29: Chart to summarize the applications and main advantages of fuel cells of different types, and in different [8] applications.


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4.3.7. References [1] http://ec.europa.eu/research/energy/nn/nn_rt/nn_rt_fc/article_1137_en.htm th

[2] Fuel cell Handbook 5 edition, EG and G Services and Parsons, Inc. and Science Applications International Corporation [3] http://greenenergysolutionsinc.com/green_university_hydrogen.php [4] http://comenius-store.eu/article.php3?id_article=51 [5] http://www.sbg.ac.at/ipk/avstudio/pierofun/fuelcell/fuelcell.html [6] Profiting from Clean Energy (A Complete Guide to Trading Green in Solar, Wind, Ethanol, Fuel Cell, Power Efficiency, Carbon Credit Industries, and More) By RICHARD W. ASPLUND PEM Fuel Cell Modeling and Simulation Using MATLAB® (Colleen Spiegel) [7] http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html [8] Fuel Cell Systems Explained, Second Edition James Larminie (Oxford Brookes University, UK), and Andrew Dicks (University of Queensland, Australia) © 2003 John Wiley and Sons, Ltd ISBN: 0-47084857-X Recent Trends in Fuel Cell Science and Technology Edited by S. Basu Anamaya Publishers, New Delhi, India 2007 PEM Fuel Cell Electrocatalysts and Catalyst Layers: Fundamentals and Applications Edited by (Jiujun Zhang) Canada May 2008 http://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cell http://en.wikipedia.org/wiki/Fuel_cell#Efficiency [9] http://www.britannica.com/EBchecked/topic/221374/fuel-cell [10] "Fuel cell Technology handbook" Edited by (Gregor Hoogers) [11] http://en.wikipedia.org/wiki/Nernst_equation [12] http://www2.aream.pt/greenhotel/fuelcell.htm


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Chapter 4: Part 4

Electric Loads

Chapter 4: Part 4

ELECTRIC LOADS


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Electric Loads

Several industrial and residential applications require electric energy. Solar-Hydrogen-Fuel Cell Educational Stand is the demonstration for Home-Refueling-Station which will be the new era for power generation. In your home you need electric power for lightgni (lamps), fans, air conditioners, electrical devices and of course the water heater. Thus, the experiment includes simple electrical loads such as lamp, fan and heater to demonstrate the electrical power utilization.

4.4.1. The first load: Light Emitting Diode (LED) The light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high [1] brightness. Figures 4.30 and 4.31 show LED and its electrical symbol.

+

Figure 4.30: Red LED

[2]

Figure 4.31: LED symbol

-

[13]

The LED is based on the semiconductor diode. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called (Electroluminescence) and the color of the light (corresponding to the energy of the photon) is [1] determined by the energy gap of the semiconductor.

4.4.2. The second load: Fan A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing objects from contacting the fan blades. Most fans are powered by electric motors, but other sources of power may be used, including hydraulic motors and internal combustion engines. [3] A standalone fan is typically powered with an electric motor. Fans are often attached directly to the motor's output, with no need for gears or belts. The electric motor is either hidden in the fan's center hub or extends behind it. For big industrial fans, three-phase asynchronous motors are commonly used, placed near the fan and driving it through a belt and pulleys. Smaller fans are often powered by shaded pole AC Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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motors or brushed bru shed or brushless DC motors. AC-powered AC-pow ered fans usually usual ly use mains voltage, v oltage, while whi le DC[3] powered fans use low voltage, typically 24 V, 12 V or 5 V.

4.4.2.1.

DC Electric Motors

When a conductor carries current and located in magnetic field, a force will generate and moves the conductor in a direction perpendicular to the magnetic field. That is the basic theory by which all DC electric motors operate. [4] Every conductor carries current has magnetic field around it. The direction for the field is determined by the Left-Hand-Rule. The thumb indicates the current flow direction and the fingers point to the magnetic field direction as shown in Figure 4.32. [4] If a current-carrying conductor is placed in a magnetic field, the combined fields will be similar to those shown in Figure 4.33. The direction of current flow through the conductor is indicated with an "x" or a "·". The "x" indicates the current flow is away from the reader, or into the page. The "·" indicates the current flow is towards the reader, or out of the page. [4]

Figure 4.32: Left -Hand-Rule for current-carrying [4] Conductor

Figure 4.33: Current-Carrying Conductor in a Magnetic Field

[4]


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Above the conductor on the left, the field caused by the conductor is in the opposite direction of the main field, and therefore, opposes the main field. Below the conductor on the left, the field caused by the conductor is in the same direction as the main field, and therefore, aids the main field. The net result is that above the conductor the main field is weakened, or flux density is decreased; below the conductor the field is strengthened, or flux density is increased. A force is developed on the conductor that moves the [4] conductor in the direction of the weakened field (upward). Above the conductor on the right, the field caused by the conductor is in the same direction as the main field, and therefore, aids the main field. Below the conductor on the right, the field caused by the conductor is in the opposite direction of the main field, and therefore, opposes the main field. The net result is that above the conductor the field is strengthened, or flux density is increased, and below the conductor, the field is weakened, or flux density is decreased. A force is developed on the conductor that (4) moves the conductor in the direction of the weakened field (downward). In a DC motor, the conductor will be formed in a loop such that two parts (two-pole motor) of the conductor are in the magnetic field at the same time, as shown in Figure 4.34. This combines the effects of both conductors to distort the main magnetic field and produce a force on each part of the conductor. When the conductor is placed on a rotor, the force exerted on the conductors will cause the rotor to rotate clockwise, as shown on Figure 4.35.


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4.4.2.2.

Electric Loads

Permanent Magnet Brushed DC Motor-PMDC

The specific type of motor we are addressing is the permanent magnet brushed DC motor (PMDC), Figure 4. These motors have two terminals. Applying a voltage across the terminals results in a proportional speed of the output shaft in steady state. There are two pieces to the motor: 1) stator and 2) rotor. The stator includes the housing, permanent magnets, and brushes. The rotor, the armature, consists of windings, which were wounded around the output shaft, and commutator, Figure 4.34 and Figure 4.35.

Figure 4.34: PMDC Motor

Figure 4.35: Schematic view for PMDC

[5]

[6]

When a current passes through the coil wound around a soft iron core (current-carrying conductor), the side of the positive pole is acted upon by an upwards force, while the other side is acted upon by a downward force. According to right-hand rule for motors Figure 4.36, the forces cause a turning effect on the coil, making it rotate. To make the motor rotate in a constant direction, "direct current" commutators make the current reverse in direction every half a cycle (in a two-pole motor) thus causing the motor to [11] continue to rotate in the same direction see Figure 4.35 and Figure 4.37. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Figure 4.36: Right-Hand Rule for Motors

Figure 4.37 :DC motor operation

[4]

[7]


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A simple DC electric motor. When the coil is powered, a magnetic field is generated around the armature. The left side of the armature is pushed away from the left magnet and drawn toward the right, causing rotation.

The armature continues to rotate.

When the armature becomes horizontally aligned, the commutator reverses the direction of current through the coil, reversing the magnetic field. The process then repeats.

Figure 4.38: Theory of operation of PMDC Motor

[11]

4.4.3. The third load: Electric Heater Electric heating is any process in which electrical energy is converted to heat. Common applications include heating of water, buildings, cooking, and industrial processes. this part ,Electric Loads, is a fuel cell heater

[8]

The picture on the cover page for

[12]

An electric heater is an electrical appliance that converts electrical energy into heat. The heating element inside every electric heater is simply an electrical resistor, and works on the principle of Joule heating: an electric current through a resistor converts electrical energy into heat energy.

4.4.3.1.

[8]

Joule's first law

Joule's first law, also known as Joule heating, ohmic heating and resistive heating, is the process by (9) which the passage of an electric current through a conductor releases heat.

   =

Q is

2

.


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the 84

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heat generated through the wire [W], I is the current passing through the wire [A] and R e is the wire electrical resistance [ Ω]



If this heat generation [W] occurs uniformly throughout the medium of volume , the volumetric 3 generation rate [W/m ]



    =

=

2

.

(4.28)

The heat generated from the electric wire causes temperature difference between wire temperature and fluid temperature (water).This heat transfers from the wire to the fluid by one-dimensional steady-state conduction heat transfer with uniform thermal energy generation and within the fluid itself by free convection heat transfer. Also heat losses take place through the heater casing (glass) by one-dimensional, steady-state conduction heat transfer.

4.4.3.2.

One-Dimensional, Steady-State Conduction Heat Transfer with [10] Uniform Thermal Energy Generation

A common thermal energy generation process involves the conversion from electrical to thermal energy in a current-carrying medium (see section 4.4.3.1. Joule's first law). Heat transfer with thermal energy generation is divided into two sections; the plane wall and radial (cylindrical and spherical) systems. Our concerning is on the cylindrical systems.

a. Cylindrical Systems Heat generation may occur in a variety of radial geometries. Consider the long, solid cylinder of Figure 4.39 which could represent a current-carrying wire.

 

−

+



( )

Figure 4.39: Conduction in a solid cylinder with uniform heat generation


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For steady-state conditions the rate at which heat is generated within the cylinder must equal the rate at which heat is convected from the surface of the cylinder to a moving fluid. This condition allows the surface temperature to be maintained at s fixed value of T s. To determine the temperature distribution in the cylinder, we begin with the appropriate form of the heat equation for constant thermal conductivity k is

       

1

+

=0

(4.29)

With some mathematical calculations and assumptions at appropriate boundary conditions the temperature distribution within solid cylinder is calculated from the following equation (for more details see reference no.10):

       −    2

( )=

2

4

1

+

2

(4.30)

The heat rate at any radius in the cylinder may, of course, be evaluated by using Equation 4.30 with Fourier’s law Equation 4.31.

 −  −    ′′  −  =

=

(4.31)

=

Where

 

is the heat transfer rate in the radial direction [W],



is the thermal conductivity for the wire [W/m.k],

is the wire surface area, which is the area normal to the direction of heat transfer,

the temperature gradient form the centerline to the outer surface or any radius 3 [k/m] and is the heat flux in the radial direction [W/m ].

′′





  =2

2

[m ],

 is 

(in the radial direction)

∞

To relate the surface temperature, , to the temperature of the cold fluid, , either a surface energy balance or an overall energy balance may be used. Choosing the second approach, we obtain

   ℎ    − ∞ (

2

) = (2

)(

)

(4.32)

or


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    ∞ ℎ =

ℎ

+

(4.33)

2

where is the convective heat transfer coefficient for the cold fluid A convenient and systematic procedure for treating the different combinations of surface conditions, which may be applied to one-dimensional solid cylindrical geometry with uniform thermal energy generation (current-carrying conductor), is provided in Table 4.6. From the tabulated results of this table, it is a simple matter to obtain distributions of the temperature, heat flux and heat rate for boundary conditions of a uniform surface heat flux .

Table 4.5: One-Dimentional, Steady-state Solutions to the Heat Equation for Uniform Heat Generation in a Solid Cylinder

Temperature Distribution

       −    2

( )=

2

1

4

+

2

(4.34)

Heat Flux

.   ′′  () =

(4.35)

2

Heat Rate

    ( )=

2

    − ∞ =

(

(4.36)

)


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4.4.3.3.

Electric Loads

Free Convection Heat Transfer

[10]

We consider situations for which there is no forced velocity, yet convection currents exist within the fluid. Such situations are referred to as free or natural convection, and they originate when a body force acts on a fluid in which there are density gradients. The net effect is a buoyancy force, which induced free convection currents. In the most case, density gradient is due to a temperature gradient, and the body force is due to the gravitational field. Heat transfer by convection is calculated from the following equation

 ℎ   − ∞  (

=



)=

ℎ

(4.38)



Where is heat transferred by convection, is the average convective heat transfer coefficient, is the surface temperature, is the surface temperature, is the fluid temperature and is the heat flux (heat per unit surface area)



∞



From dimensional analysis and experimental tests the general form of free convection relation is

ℎ∗  ∗ ∆ �     3

=

ℎ

(4.39)

2

2

∗



Where is a local convective heat transfer coefficient [W/m .k], is s characteristic length [m], is 2 the fluid thermal conductivity [W/m.k], is the gravitational acceleration[m/s ], is coefficient of -1 ) [k], is the kinematic viscosity [m 2 /s], is the specific heat at thermal expansion [k ], =(



∆  − ∞  

costant pressure [J/kg.k] and

is the dynamic viscosity or viscosity [kg/s.m]

ℎ∗     ∗ ∆ ℎ               ℎ  ℎ    ∴     =

.=





(4.40)

3

=

2

.=

=

=

.=

=

,

=

 

where ,

and

(4.41)

(4.42)

(4.43)

(4.44)

are constants obtained from experiments.


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a. Free Convection Heat Transfer on a Vertical Flat Plate or Vertical Cylinder

•

• •

 ∞

When > , a free convection boundary layer is formed. The initial development is laminar. At critical distance (depends on and fluid properties) eddies are formed and transition to turbulent boundary layer occurs.



 ℎ    = =

∆

(4.45)

.

.

Figure 4.40: Free convection boundary layer transition on a vertical plate

Local and Average Heat Transfer Coefficient Since flow conditions vary from point to point on the surface,

ℎ

varies.

′′  ℎ   ℎ ∆   ′′  ∆  ℎ  ℎ  ∆∆ =

=

=

=

=





(4.46)

(4.47)

wherehx and h are local and average heat transfer coefficient respectively.

 1

ℎ   ℎ  =

(4.48)

0

Empirical Formula


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∗ ℎ     =

=

The properties are evaluated at film temperature

  

    ∞ =

  ∗

(

(4.49)

+

)

(4.50)

2

 

, and provided in Table 7-1 in Appendix B [ and at different ranges for Ra number for isothermal surfaces ( = )]. xidneppA B also provides more complicated free convective heat transfer correlations.

4.4.3.4.

 

One-Dimensional, Steady-State Conduction Heat Transfer on a Cylindrical Tube without Heat Generation (Heat losses from the [10] heater casing)

Acommonexample is the hollow cylinder, whose inner and outer surfaces are exposed to fluid at different temperatures (Figure 4.41). For steady-state conditions with no heat generation, the appropriate form of the heat equation is (compare it with Equation 4.29)

     

1

=0

(4.51)

where, for the moment, k is treated as a variable. The physical significance of this result becomes evident if we also consider the appropriate form of Fourier’s law (Equation 4.31). The rate at which energy is conducted across any cylinder surface in the solid may be expressed


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Figure 4.41: Hollow cylinder with convective surface conditions

 −  −   −   =

    ′′ 

where

=2

quantity

=

(2

)

(4.52)

is the area normal to the direction of heat transfer. Since Equation 4.51 dictates that the



is independent of , it follows from Equation 33 that the conduction heat transfer rate

(not the heat flux

) is a constant in the radial direction.



We may determine the temperature distribution in the cylinder by solving Equation 4.50 and applying appropriate boundary conditions. Assume the value of to be constant, the temperature distribution within hollow cylinder is calculated from the following equation (for more details see reference no.10):



   −      ( )=

.1

ln

.2

1

ln

1

2

+

.2

(4.53)

2

Note that the temperature distribution associated with radial conduction through a cylindrical wall is logarithmic, not linear, as it is for the plane wall under the same conditions. The logarithmic distribution is sketched in the inset of Figure 4.41. If the temperature distribution, Equation 4.53, is now used with Fourier’s law, Equation 4.52, we obtain the following expression for that heat transfer rate:


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   −   2

=

(

.1

.2 )

1

ln

(4.54)

2

From this result it is evident that, for radial conduction in a cylinder wall, thermal resistance (shown in the series circuit in Figure 4.41) is of the form

  ,

  

ln =

1 2

(4.55)

2

4.4.4. References [1]. Wikipedia, the free encyclopedia. [Online] 2001.

http://en.wikipedia.org/wiki/Light-emitting_diode [2]. http://commons.wikimedia.org/wiki/File:Red_led_x5.jpg [3]. Wikipedia, the free encyclopedia. [Online] 2001. http://en.wikipedia.org/wiki/Elect http://en.wikipedia.org/wiki/Electric_fan#History. ric_fan#History. [4]. DOE fundamentals handbook. Electrical science volume 2 of 4. Washington, D.C. 20585 : U.S. Dept. of Energy, June 1992. [5]. DK, dorling kindersley books. [Online] Penguin Publishing Group, 1974. http://www.dorlingkindersleyhttp://www.dorlingkindersleyuk.co.uk/static/clipart/uk/dk/sci_elect uk.co.uk/static/clipart/uk/dk/sci_electricity/image_sci_e ricity/image_sci_elec024.jpg. lec024.jpg. [6]. Physics at Works. [Online] Oxford University Press (China) Ltd., 2003. http://sciencecity.oupchina.com.hk/npaw http://sciencecity.oupchina.com.hk/npaw/student/gloss /student/glossary/commutator.htm ary/commutator.htm#topbar. #topbar. [7]. HyperPhysics. [Online] Georgia State University, Department of Physics and Astronomy, 2006. http://hyperphysics.phy-astr.gsu.edu/h http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/m base/magnetic/motdc.html#c1. otdc.html#c1. [8]. Wikipedia, the free encyclopedia. [Online] 2001. http://en.wikipedia.org/wiki/Elect http://en.wikipedia.org/wiki/Electric_heating. ric_heating. [9]. Wikipedia, the free encyclopedia. [Online] 2001. http://en.wikipedia.org/wiki/Joule http://en.wikipedia.org/wiki/Joule_heating. _heating. [10]. Frank P. Incropera, David P. dewitt, Theodore L. Bergman, Adrienne S. Lavine. Fundamentals of Heat and Mass Transfer 6th Edition. Hoboken, New Jersey, ISBN/ASIN: 0470055545 : John Wiley & Sons, 2007. [11]. Wikipedia, the free encyclopedia. [Online] 2001. http://en.wikipedia.org/wiki/Brush http://en.wikipedia.org/wiki/Brushed_DC_electric_motor#Si ed_DC_electric_motor#Simple_two-pol mple_two-pole_DC_motor. e_DC_motor.

[12].http://www.geeksugar.com/Portable-Beverage-Heater-226483 [13]. http://www.dtic.upf.edu/~jlozano/interfaces/interfaces1.html


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5.1. Solar Radiation 5.1.1. Definitions 5.1.1.1. Clearness Index (KT)

In the previous chapter, section 4.1., the daily extraterrestrial irradiance on a clear day was calculated. However, the obtained result can’t be used when making a practical design. This is simply because of the presence of clouds and other atmospheric factors that reduce the actual available irradiance. The clearness index is defined as the ratio of a particular day’s irradiation to the extraterrestrial irradiation irradiation for that day. K T =

H

(5.1 a)

H o

Also, the monthly average daily clearness index ( K ) is the ratio of the monthly average daily irradiation on a horizontal surface to the monthly average daily extraterrestrial irradiation. irradiation. T

K T =

H

(5.1 b)

H o

An hourly clearness index kT can also be used. k T =

G

(5.1 c)

Go

Some authors such as Duffie and Beckman [1] state the values of the monthly average clearness index measured for many cities including Cairo. Another method to obtain the value of the clearness index is through the Ångström-type regression equation. The Ångström-type regression equation [2] relates the monthly average daily irradiation ( H ) to H o at the location in question and the average fraction of possible sunshine hours (i.e. the actual duration of daylight divided by the calculated duration). H H o

H H o

= a +b(

= a + b(

S So

S So

)

)

(5.2a)

(5.2 b)

where a�, b� , a and b are empirical constants. Kamel et al. [3], Ibrahim [4] and El-Sebaii et al. [5]and others have presented different values of a�and b� . The accuracy of their correlations are performed in terms of the two widely used statistical indicators, mean bias and root mean square errors, as well as the absolute percentage error of the estimated values of Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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the global solar radiation. However, Khalil et al. [6] provided values of a� and b� which will be used in our design as these values yield estimated values of solar irradiation with good agreement with the measured values of solar irradiation at Cairo. These values were a� = 0.461

� = 0.259 b Also, the values of S/So were provided by Khalil et al. [6] and El Massah[7]. However, to maintain consistency, the values provided by [6] will be used in our calculations and are showed in Table 5.1 below. Table 5.1:Monthly fraction of sunshine hours

Month

Jan.

Feb.

Mar.

Apr.

May

Jun. Jun.

Jul.

Aug.

Sep.

Oct.

Nov.

Dec. Dec.

S/So

0.598 0.647 0.689 0.771 0.815 0.859 0.883 0.809 0.731 0.702 0.693 0.645

The measured value of H can be obtained directly from the data provided by Robaa [8]. However, the Ångström-type regression equation will be used here to get the monthly average daily clearness index. It is assumed that this monthly index is available everyday among this month. Hence, using the values of the extraterrestrial irradiation irradiation available per day (H o), the irradiation for that day (H) is calculated. 5.1.1.2. Diffuse Radiation

The solar radiation reaching the Earth is divided into two main components: the beam (direct) radiation which represents the radiation reaching the surface directly without any change in their direction, and the diffuse radiation which results from the scattering of some Sun rays by atmospheric constituents (e.g. clouds, particulates, aerosols). There are several relations available to obtain the diffuse radiation as a fraction of the total irradiation. One of these relations, was provided by Ibrahim [4], relates this fraction to the fraction of sunshine hours. Other models such as the one provided by Khalil et al. [6], and Ruth and Chant [9]uses the clearness index to determine the diffuse radiation. In our calculations, the CollaresPereira correlation [10] is used and presented graphically in Figure 5.1 below. H d = 1.188 − 2.272 K T + 9.473 K T 2 − 21.865 K T 3 + 14.648 K T 4 ,for 0.17 < K T < 0.75 H


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1 0.9 H /

d

H , n o i t a i d a r e s u f f i d f o o i t a R

0.8 0.7 0.6 0.5 0.4 0.3 0.2

0.2

0.3

0.4 0.5 Clearness index, K

0.6

0.7

T

Figure 5.1 : Variation of percentage of diffuse radiation with clearness index.

5.1.1.3. Estimation of Hourly Radiation from Daily Data

Statistical studies of the time distribution of total radiation on horizontal surfaces through the day using monthly average data for a number of stations have led to generalized charts of r t, the ratio of hourly total to daily total radiation, as a function of day length and the hour in question [1]. r t =

G H

(5.4 a)

Collares et al. [10] have provided the following relation for r t r t =

π 24

(a + b cos(ω ))

cos(ω ) − cos(ω s ) πω sin(ω s ) − s cos(ω s ) 180

(5.4 b)

Where a = 0.409 + 0.5016 sin(ω s − 60)


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b = 0.6609 − 0.4767 sin(ω s − 60)

Also, Liu et al. [11] provides the following relation for rd, the ratio of hourly diffuse to daily diffuse radiation, as a function of day length and the hour in question. r d =

cos(ω ) − cos(ω s ) πω s 24 sin(ω s ) − cos(ω s ) 180

π

(5.5)

5.1.1.4. Radiation on Sloped Surfaces

It was suggested by Liu et al. [12] that the radiation on the tilted surface (G g,t)was considered to include three components: beam (Gb,t), isotropic diffuse (G d,t), and solar radiation diffusely reflected from the ground (Gr). The radiation on the tilted surface is expressed as 1 + cos( β ) 1 − cos( β ) 2 G g ,t =G b Rb + Gd ( ) + G ρ g ( ) (W/m ) 2 2

(5.6)

Where Gb = G-Gd

Rb =

ρ g

cos(φ − β ) cos(δ ) cos(ω ) + sin(φ − β ) sin(δ ) cos(φ ) cos(δ ) cos(ω ) + sin(φ ) sin(δ )

(5.7 a)

(5.7 b)

is the diffuse reflectance of the surroundings = 0.3 [13]

5.1.2. Modelling Results In our modelling we tried to simulate the performances of our devices (PV, Electrolyser, Fuel cell) and study the effect of changing variables (Day, hour angle, PV position and inclination-etc…) on these performance characteristics. We compared these results with experimental results under similar conditions as will be shown in chapter 10 to determine how close they are. It should be noted that these results are calculated for the day 20/5/2010 (The day we carried out the experimental study for the PV performance during the sunshine period) with n=140. Using equation defined in section 4.1 and in section 5.1.1 equation 5.6 as shown in Figure 5.2.


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Figure 5.2: Variation of total hourly radiation with solar hour

This curve is showing the variation of the total radiation in Cairo. We should notice that it’s less than the actual total radiation due to the global warming phenomena; also it’s less than the laboratory lamp’s light intensity during our experiments (this will be discussed later).


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5.2. Photovoltaic Panel 5.2.1. Technical Data

[43]

Table 5.2: Solar panel technical data

Solar panel Dimensions (W x H x D)

80 mm x 130 mm x 52 mm

Terminal voltage

2.5 V (*)

Short circuit current

200 mA (*)

In the operating point with a load resistance of 10 Ω Current

180 mA (*)

Voltage

2.0 V (*)

Output

0.36 W (*)

(*) Typical measured values with a 120 watt PAR lamp from Heliocentris, at a distance of 20 cm.

The tilt angle in the model was set equal to the latitude angle = 30° to give the best collection of solar radiation on the surface.

5.2.2 Modelling of Photovoltaic cell There are several models available for modelling of a practical photovoltaic cell. The general model consists of a current source, a parallel diode, a parallel resistor expressing leakage current, and series resistor describing an internal resistance to the current flow. In an ideal photovoltaic cell, as shown in Figure 5.3, there is no series loss and there is no leakage to the ground. That is, the series resistor has a value of zero while the parallel resistor has a value of infinity.


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Figure 5.3: Single-diode model of the theoretical PV cell and equivalent circuit of a practical PV device including the series and parallel resistances.

Some authors have proposed more sophisticated models that present better accuracy and serve for different purposes. For example, Gow et al. [18] used an extra diode to represent the effect of the recombination of carriers. A three-diode model is proposed by Nishioka et al. [19] to include the influence of effects that are not considered by the previous models. For simplicity, the single diode model will be studied in this thesis. This model offers a good compromise between simplicity and accuracy [20]. The current obtained from a photovoltaic module consisting of a number of o f cells (Ns) connected in series is represented by the following equation. 

I = I pv − I 0 exp(

q (V + IR s ) akTN

 V + R s I

) − 1 −

s       

R p

(5.8)

I d

Where Ipv is the current generated by the incident light (it is directly proportional to the Sun irradiation) Id is the Shockley diode equation I0 is the reverse saturation or leakage current of the diode q is the electron charge and equal to 1.60217646 × 10−19 C k is the Boltzmann constant and equal to 1.3806503 × 10−23 J/K T is the temperature of the p–n junction in Kelvin a is the diode ideality constant. The ideality factor of a diode is a measure of how closely the diode follows the ideal diode equation. Rs is the series resistance in Ω Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Rp is the shunt resistance in Ω Vt =

kT q

is the thermal voltage of the module

Figure 5.4 below represents the characteristic I-V curve of the PV cell

[21]

.

Figure 5.4: Characteristic I–V curve of the PV cell. The net cell current I is composed of the light-generated current I pv and the diode current Id.

In the case of a number of modules connected in parallel (N p), the current obtained from equation. 5.8 is multiplied by Np. All PV array datasheets bring basically the following information: the nominal open-circuit voltage (Voc,n), the nominal short-circuit current (I sc,n), the voltage at the maximum power point (Vmp), the current at the maximum power point (I mp), the open-circuit voltage temperature coefficient (K V), the short circuit current temperature coefficient (K I), and the maximum experimental peak output power (P max,e). This information is always provided with reference to the nominal condition or standard test conditions (STCs) of temperature (25 °C) and solar irradiation (1000 W/m2). Some manufacturers provide I–V curves for several irradiation and temperature conditions [21]. The photovoltaic module used for the calculations in this chapter is the multi-crystalline multi-crystalline silicon of Dr. Fuel cell professional [22]. The Rs resistance is the sum of several structural resistances of the device. R s basically depends on the contact resistance of the metal base with the p semiconductor layer, the resistances of the p and n bodies, the contact resistance of the n layer with the top metal grid, and the resistance of the grid [23]. The Rp resistance exists mainly due to the leakage current of the p–n junction and depends on the fabrication method of the PV cell [23]. Tsai et al. [24], as well as other authors [25] assume that Isc=IPV because the series resistance is low and the parallel resistance is high. However, this assumption will not be used in this part. Instead, we will use the two separate equations below 5.9 a and 5.10.[21] I PV = ( I PV ,n + K I (T − T n ))

G Gn


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(5.9 a)

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 R p + Rs  I PV ,n =   I sc,n R   p

I sc = ( I sc ,n + K I (T − T n ))

(5.9. b) G

(5.10)

Gn

Where G = Gg,t which was obtained from equation 5.6 Gn = 1000 W/m2 (nominal solar radiation) Tn= 298.15 K (nominal temperature) KI = 3.18×10-4 A/°C (assumed) Isc,n= 1 A (assumed) King et al. [44] found that there is typically less than a 5 % change in the voltage coefficients over a tenfold change in irradiance—100 W/m2 to 1000 W/m2. The temperature of the module can be obtained ob tained from the following equation [17]. T − T a = (219 + 832K )

NOCT − 20

(5.11)

800

Where Ta is the ambient temperature which can be obtained from the weather data available for Cairo

[26]

NOCT = 50 °C (nominal cell operating temperature, assumed) K is the monthly clearness index

evaluated from equations 5.1 b and 5.2 a.

The equation above is valid when the array’s tilt is equal to the latitude minus the declination. If the angle differs from this value the right side of equation 5.11 has to be multiplied by a correction factor C f defined by 4

−

C f = 1 − 1.17 *10 ( S M − S )

2

(5.12)

Where SM is the optimum tilt angle and S is the actual tilt angle, both expressed in degrees. The diode saturation current I0 and its dependence on the temperature may be expressed by the following equation [27]


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3  qE g  1 1    Tn   −  I 0 = I 0 ,n   exp  T ak    T n T   

(5.13)

Where Eg is the bandgap energy of the semiconductor (silicon) = 1.12 eV. The bandgap energy generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band. That is, it is the amount of energy required to free an outer shell electron from its orbit about the nucleus to become a mobile charge carrier, able to move freely within the solid material. The bandgap energy for the polycrystalline Si at 25 °C is 1.12 eV[27]. The nominal saturation current I 0,nis indirectly from equation 5.8 obtained from the experimental data, which is obtained by evaluating 5.8 at the nominal open-circuit condition, with V = Voc,n, I = 0, and Ipv≈ Isc,n. I 0,n =

Where Vt,n =

I sc ,n

 V oc ,n  exp  −1 aV  t ,n 

(5.14)

kT n a

The value of a is stated by Tsai et al. [24] for different types of PV and depends on the applied PV technology. For the calculations in this thesis, the value of o f a will be taken equal to 1.3. Some authors such as Glass et al. [28] neglect the shunt resistance to simplify the model. The value of R s is very low, and sometimes this parameter is neglected too [28]. A few authors have proposed ways to mathematically determine these resistances. Although it may be useful to have a mathematical formula to determine these unknown parameters, any expression for R s and Rp will always rely on experimental data. Some authors propose varying Rs in an iterative process, incrementing R s until the I–V curve visually fits the experimental data and then vary R p in the same fashion. This is a quite poor and inaccurate fitting method, mainly because Rs and Rp may not be adjusted separately if a good go od I–V model is desired [21]. The method used here to get Rs and Rp is very simple. The first iterative value of R s is 0. Then the value of Rp will be calculated from the following equation [21] using the values at the nominal conditions which are obtained from the module data sheet.   V mp + I mp Rs a  + − R p = V mp (V mp + I mp Rs ) / V mp I PV − V mp I 0 exp V I P max,e   mp 0 kT   N s a  


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The value of the maximum power is then obtained from the graph (P max,m, using a computer code) and compared with the experimental maximum power (Pmax,e). This process is then repeated while increasing the value of Rs by small increment (e.g. 0.01 Ω) until the value of the calculated maximum power and the experimental one are equal (or close to each other within a certain tolerance, e.g. 0.001 W). It is worth noting that the values of both Rs and Rp obtained are for the nominal conditions. However, the changes in their values due to the temperature changes are small and can be neglected.

5.2.3. PV Modelling Results On n=140, the Power-Voltage curve of the PV panel was recorded at each value of solar hour, ω, with a step of 0.001 hr and recorded inside the Matlab. The change of the maximum power with ω is shown in Figure 5.5. Then it was required to give the P-V curve at maximum intensity on that day. The result is shown in Figure 5.6.

Figure 5.5: Variation of PV maximum power through sunlight duration

The value of the voltage corresponding to each maximum power, optimum voltage, at every ω was recorded and its variation with ω is shown in Figure 5.7.The Current-Voltage curve at maximum intensity is shown in Figure 5.8.


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Figure 5.6: Variation of optimum voltage through sunlight duration

Figure 5.7: PV I-V curve at maximum intensity of the specific day


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Figure 5.8: PV Power-Voltagecurve at maximum intensity of the specific day

Figures 5.7 and 5.8 show the normal expected P-V and I-V curves that characterize any PV. It should be noted that on that day the maximum power reached was slightly more than 1.2W and the open circuit voltage was slightly above 0.92V. The PV can give up to 2.3V though with higher intensities. Finally, the maximum efficiency was plotted against ω as shown in Figure 5.9.

Figure 5.9: Variation of photovoltaic efficiency through sunlight duration


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Although it’s a surprise to get this efficiency, but it becomes more logic when we know that the maximum power is about 2.15 W while for the same same Ig,t other PV with larger areas areas and number of cells can generate power of max 200 W (you may say that is because the no. of cells and the area is bigger but also the material and manufacturing affect the efficiency).

5.3. PEM Electrolyser The electrolyser was defined previously in section 4.2. However, the definition can be demonstrated by the following reactions: +

Anode

H 2 → 2 H +

Cathode

2 H

Net Reaction

+

+

2e

−

→

H 2 O → H 2 +

1

E rev ,@ 25°C = 1.229V

(5.15)

H 2

E rev ,@ 25°C = 0V

(5.16)

1

E rev ,@ 25°C = 1.229V

(5.17)

2

2

O2 + 2e

−

O2

5.3.1. Technical Data It operates at atmospheric pressure and ambient temperature (which differs according to the month). Its specifications are: [43] Table 5.3: PEM Electrolyser technical data

PEM Electrolyser Dimensions (W x H x D)

200 mm x 297 mm x 125 mm

Storage volume for Hydrogen and Oxygen

64 ml each

Operating voltage

1.4 ... 1.8 V

Electric current max.

4,000 mA

Hydrogen production max.

28 ml / min

5.3.2. Modelling of the PEM Electrolyser The voltage of the PEM Electrolyser in (volts) is defined by the following equation: Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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V = E rev + η act + η ohm + η diff

(5.18)

Where, 1. Erev is the open-circuit (Nernst) voltage of the electrolyser when operated in reversible conditions. It’s the minimum voltage required for the cell to start operation. It’s calculated from the empirical equation [29] relative to the electrolyser absolute temperature in (K):

E rev = 1.5184 - 1.5421× 10 -3 T + 9.523 × 10-5 T × lnT + 9.84 × 10-8 T 2

(5.19)

2. ηact is the activation loss at both electrodes due to the kinetics of the charge transfer reaction. It’s expressed from the modification of Butler-Volmer [29] expression relates the current density to the activation overpotential at each electrode [29]:

η act ,a =

RT

η act ,c =

1 i Sinh −1[ ( a )] 2 ia , o F

(5.20)

1 i Sinh −1[ ( c )] 2 ic ,o F

(5.21)

RT

η act = η act ,a + η act ,c

(5.22)

Such that, R is the universal gas constant = 8.314 kJ/kmol.k, F is the faraday constant =96485 C/mol, i is the cell current density in A/m 2, i0 exchange current density = 10-3 A/cm2 for Pt based catalysts cathode and10 -7A/cm2 for Pt and Pt–Fe based catalysts anode.

3. ηohm is the flow resistance imposed by the electrodes, bipolar plates and the membrane to the electrons and protons respectively. It’s expressed as:

η ohm = R cell I Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Where Rcell is the Ohmic resistance of each cell inside the stack in (Ω) and I is the stack current in (A). The cell is made up of the series connection of the electrodes, the plates and the membrane. The Ohmic resistance opposed by each of these elements has to be evaluated, although the resistance due to the membrane is usually predominant[30] . Rcell = Req , a + Rm + Req ,c

(5.23 b)

Therefore

η ohm = η ohm ,eη ohm , m

(5.24)

In our modelling we neglect the resistance of the electrodes with respect to membrane resistance (due to small size and unavailable information).The membrane resistance is calculated from [31]: η m = δ m

I

(5.25)

Aσ m

Where δm is the membrane thickness in (m), A is its effective area in (m 2) andσm is its conductivity in (s/m). The area is estimated at 0.018 m2 from the given data sheet (approximate not accurate) while the conductivity is estimated from the following equation which assumes totally hydrated membrane made of Nafion 117 at reference temp. 80 °C: [29]

σ m = σ m , ref e

(1268 (

1

1

− ))

353 T

(5.26)

Where σ m , ref is 0.14 s/cm 4. ηdiff is the diffusion overpotential (or concentration overpotential) which takes into consideration the mass transport limitations that can occur especially at high current densities.The flow encounters of course a resistance when flowing through the electrode, and this resistance increases with increasing increasing flow. It is clear that some energy is lost so that the resistance is overcome, and this is the cause of diffusion over-voltages. The cell voltage to be imposed is higher because of the mass transport limitations. As our electrolyser is of very small current (i.e. low current density) and is operated at the atmospheric pressure. It’s assumed that ηdiff is directly proportional with current such that: η diff

= 0.155 * I

(5.27)

Where 0.155 is a constant calculated from the boundary conditions (at 1.4 V, I=0 and at 1.8V, I=1) and the others overpotentials. It should be noted that this method isn’t accurate but an approximate one. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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The hydrogen molar flow rate (mol/s) produced by the electrolyser is calculated according to Faraday’s law:

N H 2 =

nc I 2 F

(5.28)

η f

Where nc is the number of electrolysers = 1, ηf is the Faraday’s efficiency which is defined asthe relation between the real hydrogen flow rate and the theoretical one (It’s assumed to be about 99% for PEM Electrolyser)[29]. So the volume flow rate inNm3 /h is:

Q H 2 = N H 2 * 3600 * 0.022414

(5.29)

The rate of the electrolyser electrolyser temperature increase is a function of the generated heat due to the exothermic reaction, lost heat to the surroundings and the absorbed heat by cooling. Such that:

C t

dT dt

= Q gen + Q loss + Q cool

(5.30)

Where the Ct is the thermal heat capacitance in (J/kg.k) of the lumped electrolyser according to the ̇ , Qloss ̇ , Qcool ̇  are the rates of heat generated, lost reasoning developed by Ulleberg, (t) is time in (s), Qgen and cooled in (J/kg) The rate of generated heat:

Q gen = nc IV (1 − Where

vtn v

is the electrolyser efficiency ηelec

vtn v

)

(5.31)

while vtn is the thermoneutral potential in (volts) at which

the water electrolysis reaction starts to be an exothermic reaction and cooling must be used in the electrolyser[30]and it‘s calculated from:

V tn =

δ h zF

(5.32)

Where δ h is the enthalpy difference for the total reaction of water splitting. At standard conditions:


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V tn =

δ h

(5.33)

zF

vtn = 286000 /(2 * 96485) = 1.482V

(5.34)

But for different conditions it’s calculated from the equation:

V tn = V HHV +

φ Y

(5.35)

F

Where VHHV is the higher heating value voltage and calculated as a function of the reaction temperature: V HHV = 1.4756 + 2.252 × 10 −4 t + 1.52 × 10 −8 t 2

While

φ Y F

(5.36)

is the voltage corresponding to the energy required for saturation of hydrogen and oxygen

with water vapour. It’s calculated as temperature variable such that:

φ =

1.5 p wsat

p − p

(5.37)

sat w

Y = 42960 + 40.762t − 0.06682t

2

p

sat w

= 1.01325 × e

(13.669 −

5096.28

T

(5.38)

, [mgw /kgd.a]

)

(5.39)

, [bar]

The rate of lost heat: Q loss =

1 Rt

(T − T amb )

(5.40)

Where Rt is the thermal resistance (K/W) But the electrolyser is operated at constant temperature which equals the ambient temperature, so:

Q gen = Q cool


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5.3.3. PEM Modelling Results The modelling equations, in section 5.3.2, were used to construct a Matlab program to get the following results.

Figure 5.10: Variation of Electrolyser voltage with the solar hour

As we see in Figure 5.10, the electrolyser voltage jumps from zero at the early minutes of the day to 1.4 V (The minimum electrolyser voltage to operate). This means that the PV became capable of generating the power required for hydrogen production in the electrolyser. The voltage increase with the solar hour angle increase till a maximum (about 1.79 V) at the noon (ω=0), then decreases again till 1.4 V and down to zero at the last minutes of the sunset. This is due du e to the increase of the overpotentials (depending on the current) over the Nernst voltage.


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Figure 5.11: Variation of Electrolyser current with the solar hour

For the same reasons mentioned in the voltage curve, the electrolyser current starts at the same time (about 5:50 a.m.) and increases to a maximum maximum at the noon then decreases to zero before the sun set by few minutes. It should be noted that the maximum current of that day isn’t the maximum of the electrolyser (1 A) as the solar radiation of this day is lower than the maximum for the PV to power the electrolyser with maximum current (See Figure 5.2) and the assumptions taken as a substitute for the missing data of the components (PV and Electrolyser).

Figure 5.12: Variation of Electrolyser hydrogen production with the solar hour


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The hydrogen production is changing with current change as they are directly proportional. Because of the above reasons, there is a difference between the maximum hydrogen production shown in Figure 5.12 (4.75 ml/min) in this day and the maximum of the electrolyser (28 ml/min).

Figure 5.13: Variation of Electrolyser power with the solar hour

The electrolyser power is the product of the current and the voltage, so it’s increasing (in a pattern similar to the current as the voltage is almost constant) with the ω till a max then decreases at the sunset

as shown in Figure 5.13. This power isn’t the maximum PV power because the electrolyser depends on the current it draws from the PV (which changes with PV power) which results in a specific electrolyser voltage (according to the voltage-current equations in section 5.3.2) and consequently a specific electrolyser power (It will be a coincidence if they are equal).


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Figure 5.14: Variation of Electrolyser efficiency with the solar hour

The efficiency of the electrolyser depends on the thermoneutral voltage ( V tn ) which depends on the constant electrolyser temperature (reactions temperature) and reversely proportional with the electrolyser voltage. As the voltage of the cell increases with the ω, the efficiency decreases and the reaction becomes

more exothermic (heat generated increases which needs equivalent cooling to fix the cell temperature constant). Note that in the early production of hydrogen the voltage is lower than the V tn because of high ambient temperature of the day which results in higher V tn than the experimental atmosphere provided by its data sheet[43], so the efficiency is very high as the reaction is considered neutral (neither exothermic nor endothermic).


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Figure 5.15: Variation of Electrolyser heats with the solar hour

The generated heat inside the electrolyser is a function of the electrolyser efficiency and current, so it increases with ω as the current increases and the efficiency decrease. For the same reason, the generated heat doesn’t start from the same ω when the electrolyser starts to operate. While the lost heat is zero as

the electrolyser temperature is the ambient temperature. So the generated heat (which is a neglected quantity) is removed by cooling (water).


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Figure 5.16: Electrolyser characteristic curves at noon

As an example, we calculated the characteristic curves (V-I and P-I) at the noon (maximum power) to see how the modelling curves is similar to the actual measured ones. As we see, there is a high increase of voltage with the increased current due to the mentioned overpotentials (which have logarithmic and exponential responses with current) while the power is almost linear with the current.

5.4. PEM Fuel Cell 5.4.1. Technical Data It operates at atmospheric pressure and ambient temperature (which differs according to the month). They are two identical fuel cells that can be connected in series or parallel connection. Each cell has the following specifications: [43] Dimensions (W x H x D): 200 x 297 29 7 x 115 mm Voltage in parallel connection: 0.4 ... 0.9 V Voltage in series connection: 0.8 ... 1.8 V Current in parallel connection: max. 3 A Rated power in series connection: 1.7 W


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5.4.2. Modelling of the PEM Fuel Cell An analytical simulation model of the PEMFC is presented in this part. Assuming in this model that the fuel is pure hydrogen at inlet to the anode and the oxidant is pure oxygen at inlet to the cathode. The fuel cell model implemented in this work, known as the Generalized Steady State Electrochemical Model (GSSEM), is zero dimensional, semi-empirical and static in nature, thus the parameters of the equations are determined experimentally to provide the time-independent polarization curves, power curves and efficiencies at various operating conditions and the model is applicable to an entire fuel cell. The voltage of the fuel cell is modeled as [36]: V cell = E Nernst − V act − V ohm − V conc

(5.42)

here ENernst is the Nernst voltage, which is the expression for the electromotive force (emf) for given product and reactant activities; V act is the activation overvoltage, which is the amount of voltage used to drive the reaction; V ohm is the ohmic overvoltage, which is the amount of voltage lost due to the resistance to electron flow in the electrodes and the resistance to ion flow in the electrolyte; V conc is the concentration overvoltage, which is the voltage lost when the concentration of reactant at the electrode is diminished. Mann et al. [30] have expressed the Nernst voltage by the following equation as a function of operating temperature and pressure of the cell: int erface ) E Nernst = 1.229 − 0.85 *10 −3 (T cell − 298 .15) + 4.3085 *10 −5 * T cell (ln( p H 2

(5.43)

+ 0.5 ln( pOint erface )) 2

Where Tcell is the stack temperature (in K), and are the hydrogen and oxygen partial gas pressures (in atmospheres) at the surface of the catalyst at the anode cathode, int erface int erface and p H p O2 2 respectively. It should be noted that there is no term for the partial pressure of the water product in equation 5.43. The assumption has been made that the water product is in pure liquid form and that a thin film of liquid water covers the catalyst and allows the reactants to diffuse through the water. It is further noted that the expression in equation 5.43for the Nernst voltage incorporates the voltage loss due to fuel crossover(where H 2 passes through the electrolyte without reacting)and internal current (where electrons pass through themembrane rather than through the electrodes). Thepartial pressures at the catalyst surface are assumed to bethe b ethe same across the entire cell [38], = 2 / 3 * pcell

(5.44 a)

pO2 erface = 1 / 3 * p cell

(5.44 b)

int erface

p H 2 int

Pcell is the operating pressure of the fuel cell. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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The reaction would produce a maximum amount of useful work if all the free energy is directed to transfer electrons from one electrode to the other. The value of maximum obtainable work from a fuel cell is given by [39] : W max,elec = − ∆G = z * F * E Nernst

(5.45)

Deviation from the ideal values of cell voltage is due du e to the losses one would experience when current is to be induced between cell electrodes. There are three types of losses as mentioned earlier and as detailed below: Activation losses that are caused by the slowness of the reactions taking place on the surface of the electrodes (the activation of the anode and the cathode). A proportion of the voltage generated is lost in driving the chemical reaction that transfers the electrons to or from the electrodes. This voltage drop is highly nonlinear. For most values of overvoltage, one may use the following equation [41]: V act = AT * ln[(i + in ) / i0 ]

(5.46)

Where ATis the slope of the Tafel line {AT = Rgc*Tcell /(2*0.5*F)} /(2*0.5*F)} (Volt). i is the current density (mA/cm 2). inisthe internal and fuel crossover equivalent current density (mA/cm 2) i0 is either the exchange current density at the cathode if the cathodicovervoltage is much greater than the anodic, or it is a function of bothexchange current densities (mA/cm2). Ohmic losses are due to the electrical resistance (electrons) of the electrodes, and the resistance to the flow of ions (protons) in the electrolyte. To be consistent with the other equations for voltage loss the equation should be expressed in terms of current density. The equation for the voltage drop then becomes [41] : V ohm = (i + in ) * r

(5.47) 2

Where ris the area specific resistance (ASR) (kΩ.cm

)

Concentration losses are the result of the pressure drop of the reactant gases. The overvoltage depends on the amount of current drawn from the cell, as well as the physical characteristics of the gas supply systems. In general, the concentration or mass transport losses are given by the equation [41] : V conc = m * e ( n*i )

(5.48)

Where m and n are the constants in the mass transfer overvoltage The constant values used in this work are given in Table 3-7 below [36]. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Table 5.4: Constants used to calculate potential losses for low temperature PEMFC.

Constant

Units

Value

in

mA.cm-2

r

kΩ. .cm

2.54 2.54 × 10−4

io

mA.cm-2

0.1

m

Volts

n

Cm2 /mA

3

-2

2.11 2.11 × 10−5 8 × 10−3

The main outputs of the fuel cell operation are power, water and heat production. The power output ou tput of a fuel cell is the most important measure of its performance. Much of the current research in the area of fuel cells is focused on attempts to increase the power output while decreasing the manufacturing costs. The gross output of the fuel cell stack (in W) is given by: W cell = I * V cell

(5.49)

Where I is the total direct current (DC) generated by the fuel cell A power conditioning unit is required to convert the DC current into alternating current (AC) current. The net power output in AC of the fuel cell stack is a more important consideration when assessing its performance, and is given by: Pnet ,cell = W cell *η pc

(5.50)

Where ηpc is the power conditioning efficiency (assumed to be 0.99).

As well, in this model of the stand alone PEMFC, the cell electrical efficiency efficiency was calculated as the cell gross power output divided by the heating value of the hydrogen inlet to the cell (η cell): η pc

 H = W cell /( m

2 , in

(5.51)

* HHV )

Where HHV is the lower heating value of hydrogen (141900 kJ/kg) The amount of hydrogen and oxygen required to provide a certain current I at the cell voltage V cellfor one hour is obtained from the following relation m H 2 =

I

*

2.0158

z * F 1000 *U H 2

* 3600

, [kg]


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Q H 2 =

m H 2

m3 at STP

0.08988

mO 2 =

QO2 =

m H 2

*

32

2.0158 * 2 1000 *U O 2 mO2

1.429

* 3600

kg

, m3 at STP

(5.52 b)

(5.52 c) (5.52 d)

Where U and U are the utilization factors of hydrogen and oxygen respectively. A lot of research is being conducted on the PEM fuel cells. The primary focus of ongoing research has been to improve performance and reduce cost. The principal areas of development are improved cell membranes, CO removal from the fuel stream, and improved electrode design. This of course leads to improvement in the utilization actor to values up to 0.96 [36]. Also, a recirculation mode may be utilized so that the unused gas is returned to the inlet by a compressor, or sometimes a passive device such as an ejector (based on a Venturi tube) may be employed. Thus, both utilization factors are assumed to have a value of 0.96 in this study. H 2

O2

Heat will be generated by the operation of the fuel cell since the enthalpy that is not converted to electrical energy will instead be converted to thermal energy. In order to operate the PEMFC at constant temperature a cooling system must be added to absorb this heat and use it for co-generation purposes [42]. That is, the heat output of the fuel cell will be utilized in the form of hot water which can also be used for heating purposes. A fuel cell stack will generate the following amount of heat during operation  total = ( E max − V cell ) * I Q

(5.53)

whereEmax is the maximum EMF of the fuel cell


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5.4.3. PEM Fuel Cell Modelling Results 5.4.3.1. One Cell

Figure 5.17: Variation of Fuel cell current with the solar hour

The current of the fuel cell is directly proportional with the mass flow rate of the hydrogen produced from the electrolyser (we assumed equal flow rates of consumption and production of hydrogen for a steady state process). The produced current takes the same trend of hydrogen production (consumption). It should be noted that the current of the electrolyser isn’t equal the current of the fuel cell due to the efficiencies and utilization utilization of the two components and the different modelling methods.


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Figure 5.18: Variation of Fuel cell voltage with the solar hour

Unlike the electrolyser, the fuel cell has no minimum voltage (i.e. the cell starts is at 0V) which means that it generates power to loads when the hydrogen and oxygen reach the reaction site. But the voltage decreases towards the noon as the current increases due to hydrogen production increase and consequently the overpotentials (voltage losses) increase which lower the Nernst voltage.

Figure 5.19: Variation of Fuel cell power with the solar hour

Figure 5.20: Variation of Fuel cell efficiency with the solar hour angle

As the voltage is changing in a narrow range, as shown in Figure 5.18, the cell power will be in a direct response to the cell current, so the shape is similar to Figure 5.17. The power is lower than the electrolyser power curve as mentioned before. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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The efficiency decreases with the hour angle, as shown in Figure 5.19, although the power increases because of the voltage decrease which increases the heat generated and lost with the water produced. There is also another efficiency called (Cogeneration efficiency) which is the sum of the electric power and the released heat over the hydrogen energy but it isn’t calculated in our case as we don’t use cogeneration due to the neglected heat quantity.

Figures 5.21: Characteristic curves of single fuel cell operating with all hydrogen flow

For a single cell consuming all the hydrogen to generate power, the V-I curve illustrates the decrease of the voltage with the current increase due to the losses. The P-I curve gives the almost linear relation between the power and current. Note that as the cell current is high, the overpotentials highly increase and the power become lower.

5.4.3.2. Two Cells (Parallel and Series connections)

The target of these curves is to show how the voltage responds at the lower currents and the power produced in these types of connections. These V-I and P-I curves are the same in both connections and equal the half of the curves of the single cell operating with the full hydrogen flow (as the current is the same and the losses are are the same). Thus, V-I and P-I curves of one fuel fuel cell in parallel and series connections are typical. In the V-I curves, shown in Figure 5.23, we calculated the change in cell voltage with the total current (The sum of the two currents in parallel connection) and the total voltage (The sum of the two voltages in the series connection) with the cell current. In the P-I curves, the power is the same as it’s the sum of the two cells’ powers while the currents are different as shown.


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Figures 5.22: Characteristic curves of single fuel cell operating with half hydrogen flow in parallel and series connections

The two cells response is similar to the single cell response but they aren’t actually the same because the losses in the two cells are the sum of the loss of one cell operating in either connection. While in the single cell the losses are generated nonlinearly (logarithmic change) with the current which is double the one cell current. This affects the cells voltages and consequently the power. It should be mentioned that these differences are very small and can be neglected because the fuel cell is very small in size and range.


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Figures 5.23: Characteristic curves of two fuel cells operating with all hydrogen flow (parallel and series connections)


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5.5. References [1]

Duffie, J.A., Beckman, W.A., “Solar engineering of thermal processes”, Third edition, Wiley, 2006.

[2] Angstrom, A., “Solar and terrestrial terrestrial radiation”, Quart J Roy Met Soc50, pp. 121–125, 1924. [3] Kamel, M.A., Shalaby, S.A., Mostafa, S.S., “Solar radiation over Egypt: comparison of predicted and measured meteorological meteorological data”, Solar Energy, Vol. 50, Issue 6, pp. 463–467, 1993. [4] Ibrahim, S.M.A., “Diffuse solar radiation in Cairo, Egypt”, Energy Conversion and Management, Vol. 25, Issue 1, pp. 69-72, 1983. [5] El-Sebaii, A.A., Trabea, A.A., “Estimation of horizontal diffuse solar radiationin Egypt”, Energy Conversion and Management, Vol. 44, Issue 15, pp. 2471-2482, 2003. [6] Khalil, S.A., Fathy, A. M., “An empirical method for estimating global solar radiation over Egypt”, ActaPolytechnica, ActaPolytechnica, Vol. 48, No. 5, 2008. [7]

El Massah, S.A., “Modelling and simulation of terrestrial solar radiation”, Interbuild Egypt, 2000.

[8] Robaa, S.M., “Evaluation of sunshine duration from cloud data in Egypt”, Energy, Vol. 33, Issue 5, pp. 785-795, 2008. [9] Ruth, D.W., Chant, R.E., “The relationship of diffuse radiation to total radiation in Canada”, Solar Energy, Vol. 18, Issue 2, pp. 153–154, 1976. [10] Collares-Pereira, M., Rabl, A., “The average distribution of solar radiation-correlations between diffuse and hemispherical and between daily and hourly insolation values”, Solar Energy, Vol. 23, Issue 2, 1979. [11] Liu, B.Y.H., Jordan, R.C., “The interrelationship and characteristic distribution of direct, diffuse and total solar radiation”, Solar Energy, Vol. 4, Issue 1, pp. 1-19, 1960. [12] Liu, B.Y.H., Jordan, R.C., The long-term average performance of flat plate solar energy collectors, Solar Energy, Vol. 7, Issue 2, pp. 53-74, 1963. [13] Yudovsky D., Pilon, L., “Simple and accurate expressions for diffuse reflectance of semi-infinite and two-layer absorbing and scattering media”, media”, Applied Optics, Vol. 48, Issue 35, pp. 6670-6683, 2009. [14] www.solar-is-future.com/index.php www.solar-is-future.com/index.php [15] Lorenzo, E., “Solar Electricity Engineering of Photovoltaic Systems”, ArtesGraficas Gala, S.L., Spain. 1994. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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[16] González-Longatt, F.M., “Model of Photovoltaic Module in Matlab™”, 2do CongresoIberoamericano CongresoIberoamericano de Estudiantes de IngenieríaEléctrica, IngenieríaEléctrica, Electrónica y Computación (II CIBELEC 2005), 2005. [17] RETScreen® International, “Clean Energy Project Analysis: RETSCREEN® Engineering and Cases Textbook”, Photovoltaic Project Analysis Chapter, 2004. [18] Gow, J.A., Manning, C. D., “Development of a photovoltaic array model for use in powerelectronics simulation studies”, Proceedings of IEE Electric Power Applications, Vol. 146, No. 2, pp. 193–200, 1999. [19] Nishioka, K., Sakitani, N., Uraoka, Y., Fuyuki, T., “Analysis of multicrystalline silicon solar cells by modified 3-diode equivalent circuit model taking leakage current through periphery into consideration”, Solar Energy Materials and Solar Cells, Cells, Vol. 91, No. 13, pp. p p. 1222–1227, 2007. [20] Carrero, C., Amador, J., Arnaltes, S., “A single procedure for helping PV designers to select silicon PV module and evaluate the loss resistances”, Renewable Energy, Vol. 32, No. 15, pp. 2579–2589, Dec. 2007. [21] Villalva, M.G., Gazoli, J.F., Filho, E.R., “Comprehensive Approach to Modelling and Simulation of Photovoltaic Arrays”, IEEE Transactions on power electronics, Vol. 24, No. 5, 2009. [22] Kyocera, “KC200GT manual”. [23] Lasnier, F., Ang, T. G., “Photovoltaic Engineering Handbook”, New York: Adam Hilger, 1990. [24] Tsai, H.L., Tu, C.S., Su, Y.J., “Development of Generalized Photovoltaic Model Using MATLAB/SIMULINK”, Proceedings of the World Congress on Engineering and Computer Science, 2008. [25] King, D. L., Kratochvil, J. A., Boyson, W. E., “Temperature Coefficients for PV Modules and Arrays: Measurement Methods, Difficulties, and Results”, Proceedings of 26 th IEEE Photovoltaic Specialists Conference, Conference, Anaheim, CA, pp. 1183–1186, 1997. [26] BBC, "Weather Centre - World Weather - Average Conditions - Cairo", Retrieved 22-01-2010. [27] De Soto, W., Klein, S. A., Beckman, W. A., “Improvement and validation of a model for photovoltaic array performance”, performance”, Solar Energy, Vol. 80, No. 1, pp. 78–88, 2006. [28] Glass, M.C., “Improved solar array power point model with SPICE realization”, Proceedings of Intersociety Energy Conversion Engineering Conference Conference (IECEC), Vol. 1, pp. 286–291, 1996. [29]Roy A,Watson S, Infield D. Comparison of electrical energy efficiency of atmospheric and highpressure electrolysers. electrolysers. International Journal of Hydrogen Energy 2006;31(14):1964-79. 20 06;31(14):1964-79.


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[30] Li X. Principles of fuel cells. Taylor and Francis Group; 2006.Prentice G. Electrochemical engineering principles.Prenticeprinciples.Prentice- Hall International Editions; 1991. [31] Choi P, Bessarabov DG, Datta R. A simple model for solid polymer electrolyte (SPE) water electrolysis. Solid State Ionics 2004;175(1-4):535-9. Bockris JO, Reddy AK. Modern electrochemistry, vol. 2.Macdonald and Co.; 1970.Londres. [32] Scott K, Taama W, Cruickshank J. Performance and modelling of a direct methanol solid polymer electrolyte fuel cell. Journal of Power Sources 1997;65(1-2):159-71. [33] Barbir F. PEM electrolysis electrolysis for production of hydrogen from renewable energy sources. sources. Solar Energy 2005;78(5):661-9. [34] G o ̈ rg u ̈ n H. Dynamic modelling of a proton exchange membrane (PEM) electrolyser. International Journal of Hydrogen Energy 2006;31(1):29-38. [35] LeRoy RL, Bowen CT, LeRoyDJ.The thermodynamics of aqueous water electrolysis. Journal of the Electrochemical Society 1980;9:1954-62. [36] US Department of Energy, “Fuel Cell Handbook”, 7th edition, National Energy Technology Laboratory, 2004. [37] Thirumalai, D., White, R.E., “Mathematical Modelling of Proton Exchange Membrane Fuel Cell Stacks”, Journal of the Electrochemical Society, Vol. 144, pp. 1717-1723, 1717-172 3, 1997. [38] Mann, R.F., Amphlett, J.C., Hooper, M.A.I., Jensen, H.M., Peppley, B.A., Roberge, P.R., “Development and Application of a Generalised Steady State Electrochemical Model for a PEM Fuel Cell”, Journal of Power Sources, Vol. 86, pp.173-180, 2000. [39] Wishart, J., Secanell, M., Dong, Z., “optimization of a fuel cell system based on empirical data of a PEM fuel cell stack and the generalized electrochemical model”, Proceedings of the International Green Energy Conference, Waterloo, Ontario, Canada, Paper No. 126, 2005. 20 05. [40] Gurau, V., Kakac, S., Liu, H., “Mathematical Model for Proton Exchange Membrane Fuel Cells”, AES Vol. 38, Proceedings of the ASME Advanced Energy Systems Division, pp. 205-214, ASME, 1998. [41] Kim, J., Lee, S.M., Srinivasan, S., Chamberlin, C.E., “Modelling of proton exchange membrane fuel cell performance with an empirical equation”, Journal of the Electrochemical Society, Vol. 142, No. 8, pp. 2670–2674, 1995. [42] Yammoto, O., “Solid Oxide Fuel Cells: Fundamental Aspects and Prospects”, EletcrochemicaActa, Vol. 45, pp. 2423-2435, 2000. [43] Heliocentris, Student Science Kit for Solar Hydrogen Technology, DrFuelCell® Science Kit.


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6.1. Introduction Experimental science data is a main source of knowledge. Theories, analytical analysis, scientific models, etc. must be proved by the measurements. Very complicated phenomena can usually be described and modeled using equations derived only from simulation measurements. Measurements entered a new era by introducing the electronic means. Computers and microprocessors enabled measurements to be done, and the data to be processed in a higher rate and increasing accuracy. Dependence on electronic means has been increasing in the past few decades. Nowadays, it is more common to find industrial processes with measurements done electronically than the old indication and calculation ways that consumes time and effort which are the most important factors in industry. Automation is now very common in industry and life. Most factories possess automated processes that are moderated and controlled using different software. Machines can be assigned new tasks, modify their tasks, time the task procedure, and even response to emergency cases with no human interference. In this project, a very basic idea about automation and data acquisition is introduced to the students. Measurements in the experiments are made by sensors connected to data acquisition hardware, and then collected and processed by a computer. The information is then indicated on a user interface. Automation is introduced in the way of controlling the motion of a DC motor using a program that gives a signal using the hardware device to control direction of motion. The user-friendly interface shows the method of controlling and the idea of using software to control a device without any direct human mechanical interaction.


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6.2. Measurements 6.2.1. General The Educational Stand Data is collected by measuring energy indicating variables in the main stages of the system, Voltage and current for electricity, temperature for heat, and intensity for solar radiation. The Data is collected using sensors with electrical analog output that is transmitted to the Data acquisition device.

6.2.2. Electricity Measurements 6.2.2.1. Voltmeter A voltmeter is used to measure voltage. As such it is a two terminal device (since it must measure potential difference between two different points). Recall that voltage is measured across a circuit component. As such, a voltmeter is placed in parallel with the component(s) it is measuring the voltage across. Since it is placed in parallel an ideal voltmeter would draw no current through it (i.e., it would have infinite resistance). Since this is impossible, it must draw some current, but we would like to minimize the amount. To do this, a real Figure 6.1: Voltmeter and Ammeter voltmeter would have a high resistance (recall the current divider Circuits rule). This is accomplished by adding a series resistor inside the voltmeter to increase the internal resistance. A by-product of this is that through the appropriate choice of series resistance, a voltmeter can be made to measure different ranges of voltage (i.e., 1mV, 10mV, 100mV, 1V, 10V, etc.). The value of the series resistance can be calculated using the Voltage Divider Rule (VDR). Note that in the case of a voltmeter current flowing through the PMMC causes a deflection of the needle. This is necessary to “calibrate” the scale so that it reads voltage instead of current.

6.2.2.2. Ammeter An ammeter is used to measure current. As such it is a two terminal device (since it must have an input and an output). Recall that current is measured through a circuit component. As such an ammeter is placed in series with the component(s) it is measuring the current through. Since it is placed in series an ideal ammeter would have no voltage across it (i.e., it would have zero resistance). Since this is impossible, it must have some voltage across it, but we would like to minimize the amount. To do this, a real ammeter would have a low resistance (recall the voltage divider rule). This is accomplished by adding a parallel resistor (the shunt resistor) across the meter mechanism inside the ammeter to decrease the internal resistance. A by-product of this is that through the appropriate choice of shunt resistance, an ammeter can be made to measure different ranges of current (i.e., 1mA, 10mA, 100mA, 1A, 10A, etc.). The value of the shunt resistance can be calculated using the Current Divider Rule (CDR).


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6.2.3. Thermal Measurements Measurements Temperature of water heater by the electric heater is measured by a Pt100 thermistor. Refer to appendix E for more technical information.

Thermistors Resistance thermometers work on the principle that the resistance of a metal varies with temperature. When accurate laboratory measurements are required, only standard platinum resistance thermometers (SPRTs) are used. There are two reasons for this: 1. Platinum is not only a noble metal but also the most electrically stable metal known to man. 2. The platinum resistance thermometer, PRT, is the reference on which the international definition of temperature is based. So long as the international temperature scale, ITS-90, is valid, the PRT is the most accurate means of measuring temperature. Industrial platinum resistance thermometers are known as IPRTs, the most widely used of which is the Pt100, which has a resistance of 100 ohms at 0 °C.

Protective tubes Detectors usually need to be enclosed in a protective tube before being used. Tubes are of two types, depending on the temperature range. They can be seamless tubes of stainless, acid-proof steel. They measure up to 250–300°C. A steel tube with PTFE or polyimid-insulated leads is generally used. The temperature limit is determined by the insulation. The heat-transfer properties are greatly enhanced, which means shorter response times and smaller reading errors caused by heat losses through the protective tube. They can also pack the Pt100 sensing element in powder, which has inferior heat-transfer properties and can be dispersed by vibration, allowing air gaps to form below. These measure up to 600°C. Thermistors have the following advantages:   

High-temperature tolerance Provides excellent moisture protection and can be immersed, eg, in water. Mechanically strong and pliant.

Output signal connections Sensors are equipped with one of the following types of connection: 

Non-terminated wires


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    


Extension fitting (sleeve connector) with lead and optional armour Fitted connector Probe-mounted terminal block Probe-mounted transmitter Probe with provision for retrofitting of terminal block or transmitter

Figure 6.2: Thermistors Temperature ranges

Temperature ranges Pt100 sensors can usually be used to measure temperatures up to approximately 250 °C. For higher temperatures, protective tubes, e.g. with mineral-oxide insulation, are required.

Figure 6.3: non-terminated wires


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Hysteresis All IPRTs exhibit hysteresis, i.e. give different readings depending on whether the temperature is rising or falling. The best design is an expensive special sensor element, closely followed by the wire-wound Pt100. Filmtype thermometer detectors and bobbin-wound elements exhibited errors 5–10 times higher. The following error values are percentages of the measuring range:  



Wire-wound Pt100 0.008% Bobbin-wound Pt100 0.08% Film-type Pt100 0.04–0.08%

6.3. Programming and Control 6.3.1. Control of Lamp Position Since the main target of our educational student is to serve enhancing student’s knowledge, it was a must to make the stand as user friendly as possible. As the lamp resembles the sun, it must be characterized by varying intensity similar to what happens outdoors from sun rise to sun set. To make this possible we had two options. The first was to use a dimmer. This idea was not preferred by the project team as the variance in light intensity will not be distinctly different. It was believed that it will give close values of light intensity. The second idea was to vary the lamp distance. To apply this and still keep the light distribution on the solar panel the same, we decided to put the way shown in Figure 6.4.

Figure 6.4: Electric lamp fixed perpendicular to solar panel


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The idea was accepted by everyone and the challenge was how to create a control to this lamp. We realized our need to form an electric circuit. We needed this circuit to let the lamp normally static in its position while in one direction or polarity makes the lamp moves in a certain direction, while in the reverse polarity makes it moves the other direction. We started or research and came up with the H-bridge shown in Figure 6.5.

Relay 1 contact

A

Fuse 1A

Relay 1 contact

D

C

Relay 2 contact

DC 36 V

M

B

Relay 2 contact

Figure 6.5: H-Bridge circuit

In the circuit shown in Figure 6.5, M is the electric motor which will be used to lift the lamp up or down. The motor is shown in Figure 6.6.

Figure 6.6: On the left: The lamp motor and on the right: The power screw which drives the lamp up and down

So, when the 36V power supply is initiated no current will flow as there are two normally opened relays. In one direction, we need C to be closed and B to be opened in the same instant to avoid any possibility of short circuiting. This will make the current flows from the positive to the negative terminals of the power Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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supply passing through C and D and the motor to move. In the other direction, A will be closed and D will be opened. This will make current flow through A and B and thus the motor moves to the other direction. However, that was just the primarily idea of the control circuit. We wanted the circuit to be controlled by LAB VIEW computer program beside the manual control. The manual control is intended to mean the push buttons shown in Figure 6.7.

Figure 6.7: Manual Control of Lamp

A series of circuits were suggested, drawn and tested using various circuit components. The main problem was in the signal produced by the NI 6008 card. It gave 5V with around 8.5 mA. The details of the NI 6008 card are in appendix D. This current was not enough to activate the relays. We solved the problem by adding an amplifier. A series of amplifiers were tried including BC182, LM741 and others. After several experiments, we used a low power transistor which is BC107 as shown in Figure 6.8 .Also we changed the direction of the manual switch diodes and the polarity of the 5 V power supply relative to the manual switch and its diodes.

Collector

Base

Emitter

Figure 6.8: Transistor BC107

We connected the circuit which contains 2 relays R1 and R2, 2 octocouplers with 2 resistances in series R=1kΩ, switch, 5 power terminals and a 5volt power supply on a copper board used for these purposes.


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We also made a small circuit with parallel resistances (R eq=25Ω) for a model motor (2*1.5 battery motor) to be operated by the 5V power supply. We also added a stop valve to in series with the relays in the manual control circuit in order to have two limits (maximum and minimum positions) at which the circuit is cut off; motor stops and the manual position switch (Up and Down) doesn’t work to save the motor from burn up. A fuse was added in series with the motor to save the current. The final circuit diagram is shown in Figure 6.9.

Figure 6.9: The final Manual and DAQ control control circuit


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As shown from Figure 6.8 the motor can be operated either by the manual circuit drawn in blue or using a computer signal converted to 5V signal by the DAQ (data acquisition card). As such we started to imply the circuit into a workable board. The following is the truth table of the circuit mission. Table 6.1: Truth Table

DAC1 0 1

DAC2 0 0

A 0 1

B 1 1

C 0 0

D 0 0

0

1

0

0

1

1

1

1

1

0

1

0

Response Stops Moves right Moves left Stops

All the experiments we undertaken on the circuit were in the department’s lab with our own tools. First we used simple copper boards as shown in Figure 6.10 with lead welding and low quality wires.

Figure 6.10: Circuit connections connections views

When we were sure the circuit worked we made a good circuit board ourselves. We bought the components which are 15x15 cm copper board, special marker, solution that reacts with the copper. After that the circuit was drawn on the board as shown in Figure 6.11.


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Figure 6.11: The circuit drawn and marked on the board

Figure 6.12 shows the circuit after it was putted in the solution and the copper removed.

Figure 6.12: The fabricated board.


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Then we connected the circuit components to the board as shown in Figure 6.13.

Figure 6.13: The final connected board top view

6.3.2. Testing and Assurance The different components of the educational stand passed through tests and experiments to ensure functionality, reliability, optimality, and safety in their positions or when they interact and perform the power production operations. The tests were applied on each component alone to ensure it performs its task, and to measure the performance parameters in the laboratory environment. Other tests were applied on partially assembled systems, which include two or more simultaneously operating components to measure the parameters of systems included in the project equipment. Tests were done on both hardware and software components to assure that the system operation, measurement process, and calculations are done in a numerically and logically accepted manner. Components manufactured by the project group or under their direct supervision were designed and tested during various manufacturing stages to eliminate the chances of accumulating errors or software bugs occurrence. The automation components include: the lamp positioning system. This system includes a software facility used to operate and control. The lamp positioning system consists of the DC linear motor, the power supply, the controlling circuit, and the lamp mounted mechanism.


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6.3.2.1. DC linear motor A 36 Volts DC motor is used to move the lamp mechanism in a linear path. The motor was tested using a 36V power supply designed for this type of motors. The motor operated normally and smoothly in the 2 directions with no load applied to it.

Figure 6.14: 36V Motor power supply

6.3.2.2. Controlling circuit The motor movement in two opposite direction needed a circuit that can reverse polarity on the motor wiring as discussed in section 6.3.1, and this should be available through manual and software-automated means. An H bridge circuit was designed and manufactured by the project team. Tests were done on the experimental sample assembled by the group for evaluation purposes. A small 5V DC motor was used as the motor, and a 5V wire from a computer CPU power supply was used to power it through the H bridge circuit. The first sample didn’t work due to connection faults and it caused a short circuit in the power supply. Further samples were assembled and tested; the second test was not successful due to the fail of the relays used in the circuit. Relays are used to alter the polarity of the motor according to the signals or the switch position. Relays used did not conduct current on the normally open side, thus preventing the current from flowing to the motor. Other relays were bought and tested before making the third sample circuit, shown in Figure 6.13, which operated the motor successfully.


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Figure 6.15: The H bridge lamp position control experimental circuit

6.3.2.3. Controlling software The software used to control the circuit is LABVIEW. Several minor programs were developed to check the working procedures and the effectiveness of components and main program parts. For example, some minor programs were used to check the relay controlling system, and their results indicated that the current produced by the digital output channels of the card is not capable of energizing the relay coil.

6.3.3. Programming Programming 6.3.3.1. Introduction Programming the software tools used in the project is a main part of the project. Although not containing a lot of physical actions, but programming usually proves to be a mental challenge for every member of the team. Programming also needs a special type of team work, as every piece of software contains the personality of its programmer. The project experiments need software tools to control and monitor. These tools should contain friendly user interface easy for students that never used these tools before to cope with. It also should be designed to produce output in formats that are easy to understand when viewed, and also produce editable outputs that can be used later to write reports about the experiment.

6.3.3.2. Programming Language LABVIEW, the programming kit used, is a platform and development environment for a visual programming language from National Instruments. The graphical language is named "G". Originally released for the Apple Macintosh in 1986, LabVIEW (Laboratory Virtual Instrument Engineering Workbench) is commonly used for data acquisition, instrument control, and industrial automation on a Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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variety of platforms including Microsoft Windows, various flavors of UNIX, of UNIX, Linux, and Mac OS X. The latest version of LabVIEW is version LabVIEW 2009, released in August 2009. The programming language used in LabVIEW, also referred to as G, is a dataflow programming language. Execution is determined by the structure of a graphical block diagram (the LVsource code) on which the programmer connects different function-nodes by drawing wires. These wires propagate variables and any node can execute as soon as all its input data become available. Since this might be the case for multiple nodes simultaneously, G is inherently capable of parallel execution. Multiprocessing and multi-threading hardware is automatically exploited by the built-in scheduler, which multiplexes multiple OS threads over the nodes ready for execution. LabVIEW is a development system for industrial, experimental, and educational measurement and automation applications based on graphical programming, in contrast to textual programming - however, textual programming is supported in LabVIEW. LabVIEW has a large number of functions for numerical analysis and design and visualization of data. LabVIEW now has several toolkits and modules which brings the LabVIEW to the same level of functionality as Matlab and Simulink in analysis and design in the areas of control, signal processing, system identification, mathematics, and simulation, and more. In addition, LabVIEW has, of course, inbuilt support for the broad range of measurement and automation hardware produced by National Instruments. Communication with third party hardware is also possible thanks to the availability of a large number of drivers and the support for communication standards as OPC, Modbus, GPIB, etc. LabVIEW is a graphical programming language that uses icons instead of lines of text to create applications. In contrast to text-based programming languages, where instructions determine the order of program execution, LabVIEW uses dataflow programming, where the flow of data through the nodes on the block diagram determines the execution order of the VIs and functions.


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Figure 6.16: LabVIEW Block Diagrams

VIs, or virtual instruments, are LabVIEW programs that imitate physical instruments. In LabVIEW, the user builds a user interface by using a set of tools and objects. The user interface is known as the front panel. He then adds code using graphical representations of functions to control the front panel objects. This graphical source code is also known as G code or block diagram code. The block diagram contains this code. In some ways, the block diagram resembles a flowchart. Objects on the block diagram include terminals and nodes. The user builds block diagrams by connecting the objects with wires. The color and symbol of each terminal indicate the data type of the corresponding control or indicator. Constants are terminals on the block diagram that supply fixed data values to the block diagram. The front panel is the user interface of a VI. Generally, you design the front panel first and then design the block diagram to perform tasks on the inputs and outputs you create on the front panel. The user builds the front panel with controls and indicators, which are the interactive input and output terminals of the VI, respectively. Controls are knobs, push buttons, dials, and other input mechanisms. Indicators are graphs, LEDs, and other output displays. Controls simulate instrument input mechanisms and supply data to the block diagram of the VI. Indicators simulate instrument output mechanisms and display data the block diagram acquires or generates.


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6.3.3.3. Codes I. Control Code The Automatic control system designed to move the lamp closer and further from the solar panel needed a simple code. The code aims to produce signals by the DAQ card to either move the lamp up, down, or stop it. The relay board takes 2 signals from the program and executes accordingly. The front panel consists of 2 input Boolean Data type in the form of buttons. The connections are shown in the figure.

Figure 6.17: Lamp Controller

II. Measurements Code II.1. Introduction

The measurements code is much complicated than the control code. Its Block diagram contains Daq assistant task which produces matrices of measured data. These matrices are then divided into the data that is then collected, drawn and recorded into a spreadsheet. This is done for a number of times using a ‘for’ loop. The number of measurements and measurement time step are selected by the user before execution. II.2. Front Panel

The front panel shown in Figure 6.19 contains 2 inputs in which the user enters the number of measurements and the Delay time. The front panel shows, while executing the program, the measurements in the form of tables and figures. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Figure 6.18: Front Panel of Measurement recorder

II.3. Block Diagram

The Block Diagram is shown in Figure 6.20 and contains a ‘for’ loop to repeat the cycle for the number of measurements needed, and a flat sequence to reset values before starting. The measuring task takes the average of 100 measurements for every recorded reading. The data of the current, voltage, power, and temperature are arranged into a matrix that is finally printed into a spreadsheet. A user interface appears to ask the user for the path to save the spreadsheet. II.4. User Instructions

1- Select the number of measurements and the time delay between two points. 2- Press the run Button. 3- Adjust the lamp position using the Up and Down Buttons. 4- Press OK button to start recording measurements Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Figure 6.19: Measurement recorder Block Diagram

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Table 6.2: Block Diagram Main Components

Icon

Name

Objective

Daq Assistant

Contains the measurement orders, specifies the channels where volt, current, and temperature are measured to control the hardware.

For loop

Flat sequence

Executes its sub-diagram n times, where n is the value wired to the count ( N) terminal. The iteration ( i) terminal provides the current loop iteration count, which ranges from 0 to n-1. Consists of one or more sub-diagrams, or frames, that execute sequentially. Use the Flat Sequence structure to ensure that a sub-diagram executes before or after another sub-diagram.

Time Delay

Inserts a time delay into the calling VI

Arithmetic operators

Performs the arithmetic operations + , _ , / , …..

Array operations

X-Y Graph Constructor

Write to spreadsheet

These icons perform operations on Array Data. It add a new element to the array, converts it to matrix, builds a new array from elements, or transposes the matrix.

Formats data to be displayed on an XY graph.

Converts a 2D or 1D array of strings, signed integers, or double-precision numbers to a text string and writes the string to a new byte stream file or appends the string to an existing file. The data type you wire to the 2D data input or 1D data input determines the polymorphic instance to use.


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III. Characteristic curve drawer III.1 Introduction

The characteristic curves of the components; i.e. the solar cell, the fuel cell, etc…; are to be plotted using a code that allows the user to request the measuring process to start after he has adjusted the case he wants to test. The time between measurements is not critical. The user needs to specify the number of measured cases i.e. loads, connection methods, etc…; then the user starts the program. The user presses a button that enables him to start the measuring process. The graphs needed are plotted accordingly. Due to the difference in curves needed in each experiment, two sets of charts are available, and the user chooses between them before starting the experiment according to the component he is testing.

Figure 6.20: Characteristic Curve Drawer Front Panel

III.2. Front Panel

The front panel is shown in Figure 6.21. It contains a button used to read 1 measurement and draw it as a point on the corresponding graphs. The user selects the number of measurements points and also the Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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lamp control procedure is imbedded into the program to allow for lamp adjustment during working. A button is used to choose the corresponding graphs of the current case. The current two choices are fuel cell graphs or solar cell graphs. III.3. Block Diagram

The block diagram shown in Figures 6.22 and 6.23 shows the event case used to force the execution of the measuring process to wait until the READ button is pressed. A case structure is controlled by the case selection button, and is used to vary the inputs to the used graphs and disable the non-used ones. The measuring task takes the average of 1000 measurements every time the READ button is pressed. The ‘number of measurements’ input specifies how many times the ‘for’ loop is repeated. III.4. User Instructions

1- Press the run Button. 2- Adjust the lamp position using the Up and Down Buttons. 3- Select the Component you are testing using the Experiment selector 4- Press OK button to start recording measurement


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Table 6.3: Block Diagram Main Components

Icon

Name

Objective

Daq Assistant

Contains the measurement orders, specifies the channels where volt, current, and temperature are measured to control the hardware.

For loop

Flat sequence

Event Structure

Arithmetic operators

Array operations

X-Y Graph Constructor

Executes its subdiagram n times, where n is the value wired to the count ( N) terminal. The iteration ( i) terminal provides the current loop iteration count, which ranges from 0 to n-1. Consists of one or more subdiagrams, or frames, that execute sequentially. Use the Flat Sequence structure to ensure that a subdiagram executes before or after another subdiagram. Has one or more subdiagrams, or event cases, exactly one of which executes when the structure executes. The Event structure waits until an event happens, then executes the appropriate case to handle that event. Right-click the structure border to add new event cases and configure which events to handle. Wire a value to the Timeout terminal at the top left of the Event structure to specify the number of milliseconds the Event structure should wait for an event to occur. Performs the arithmetic operations + , _ , / , …..

These icons perform operations on Array Data. It add a new element to the array, converts it to matrix, builds a new array from elements, or transposes the matrix.

Formats data to be displayed on an XY graph.


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Write to spreadsheet

Converts a 2D or 1D array of strings, signed integers, or double-precision numbers to a text string and writes the string to a new byte stream file or appends the string to an existing file. The data type you wire to the 2D data input or 1D data input determines the polymorphic instance to use.


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Figure 6.21: Characteristic Drawer Block Diagram (part 1)


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Figure 6.22: Characteristic Drawer Block Diagram (part 2)


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6.4. References [1] Wikipedia. http://en.wikipedia.org/wiki/History_of_measurement. Wikipedia.org. [Online] [2] www.engr.usask.ca. https://www.engr.usask.ca/classes/EP/155/notes/Basic_Meters.pdf. [Online] [3] Cambridge, University Of. http://www.msm.cam.ac.uk/UTC/thermocouple/pages/ThermocouplesOperatingPrinciples.html. http://www.msm.cam.ac.uk/UTC/thermocouple/pages/ThermocouplesOperatingPrinciples.html. [Online] [4] Co., Tempsen Instruments. http://www.tempsensindia.com/catlog/HandBook/topic-3.pdf. [Online] [5] Wikipedia. http://en.wikipedia.org/wiki/Pyrheliometer. www.eikipedia.org. [Online] [6] Abbot, C. G. and Aldrich, L. B. The Pyrheliometric Scale. Astrophysical Journal. 03, 1911, Vol. 33.


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Bill of Materials and Cost

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160

Chapter 8

Fabrication and Assembly

Chapter 8

FABRICATION AND ASSEMBLY Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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8.1. Educational Stand Fabrication 8.1.1. Bench Fabrication 8.1.1.1. Design The project team intended to introduce the project idea in its shape as a first impression to the viewer. So, we started a brainstorming session to get a different design which confined in expressing the renewable energy system and our results were in Figure 8.1. Figure 8.1 (a) shows the bench in shape of tree. This design has the advantage of viewing the renewable and clean energies with analogy with what trees do in environment cleaning from CO 2. On the other hand, it was estimated to be very high and students would not be able to see the solar cell. Figure 8.1 (b) shows the second design which is a house model demonstrating the independent energy source “home refueling station“. The design was with movable solar roofs and full of internal stairs for components placement. This aimed at putting the components in different levels to have a good view for all components. It was large in size, complicated, costly and takes much time in fabrication.

(a) First design

(b) Second design Figure 8.1: Early bench designs

As we went further in thinking about the better design, we all agreed about the house bench in a simpler design. The simple expressing design of light weight shiny colored was made from Aluminum alloy ''Alumetal''. In a usual progress meeting, we generated the following ideas: 1) Solar panels to be placed on the sides of the house and changing the light source displacement.


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2) Placing the components on windows in the front of the house (in order to hide the case and undesired connections) 3) A compromise between the other designs was: solar panels on the internal side of fixed roofs with a matrix of lamps on the top of the house, only a half of the house front with windows for components placement and table with wheels for the whole bench as shown in Figure 8.2.

Figure 8.2: Third bench design

A great change in our plan has happened, see chapter 3, when we had to down size our system. The new system is characterized by small range and size of components (Solar panel-Fuel cell-Electrolyser).We tried to save our main design of the house although the changes which were imposed on us (sizes-filling material-sliders system), so we began to develop the design and make some modifications on it which were: (a) Placing all the components in the front of the bench in a geometric symmetry. (b) Adding sliders to support the movable plates of the components. (c) Resizing the bench/table to fit the new components and the average height of the students. (d) Decision to make a market survey to determine the plates (filling) material from: acrylic, fiber and wood. After that we drew the design using AutoCAD and Solidworks programs with plan views and isometric drawing as shown in Figure 8.3, Figure 8.4 and Figure 8.5. Also we made our market survey for getting the best materials and fabrication workshops and getting their prices. We selected ‘‘Acrylic’’ because of its pretty view, strength, preferred colors and durability (water and dust resistance) however its high cost over the other materials. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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Figure 8.3: AutoCAD bench isometric drawing


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Figure 8.4: Solidworks bench and table 3D drawing


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Figure 8.5: Solidworks bench and table 2D drawing


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8.1.1.2. Manufacturing The bench took 5 days to be finished with our design and materials as follows: 1. Saturday, 20-02-2010: We discussed the design with the worker, Mr. Gamal Rashad, the final details for the bench and the table and agreed to make and finish them by Sunday, 28-02-2010. 2.

Sunday, 21-02-2010: The worker bought the materials (Aluminum beams).

3. Monday, 22-02-2010: The materials were gone to the painting workshop to be colored with the required color. 4. Tuesday, 23-02-2010: The materials were delivered to the Aluminum workshop and the worker stared the fabrication. 5. Wednesday, 24-02-2010: At the morning, the bench was without the sliders and the worker gave us the Acrylic sheets dimensions to buy them. We faced some problem with the table as follows: a. The table was unstable, so we put small Aluminum triangles at each corner in the table and it appeared stable at that moment. b. The worker installed four wheels to the table. Some instability was noted, so we decided to put another two wheels in the midpoint of the two beams. 6. Thursday, 25-02-2010: The worker fixed the sliders in the bench and in the table and put the Acrylic sheets in its places. The surprise came when we put the bench on the table. Because of the Acrylic weight, the table started to vibrate again. After thinking for the alternatives which could be used to fix this problem, we decided to put triangular acrylic sheets at each corner in the table using the extra Acrylic sheet, as we bought two large acrylic sheets (200 x 130 cm), to not spend additional money in extra Aluminum beams and to save time wasted in buying and painting them. Finally, the table became stable again and ready to use as shown in Figure 8.6.


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Figure 8.6: Fabricated bench and table

Notes 



 

The bench was designed so that it is easy remove any part for further fabrication of components without the need to disassemble the lateral supports of the bench. We can just unseal the sliders screws and get out the plates. The angle of the roof is not a 90˚ one. This is due to easier fabrication and better shape of the house. This only affects the relative positioning of lamp to the solar panel which is solved as will be shown in the next section. We covered the rear of the bench to minimize dust. This was done under the consideration of permitting enough aeration for cooling the electronic components. When choosing the ’’Acrylic’’ material, we made estimation for the sheets required by calculating the bench areas and simulating them by paper cuttings.


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8.1.2. Solar Lamp Movement Fabrication 8.1.2.1. Idea It was not easy like expected. This was because the inclined roof for the bench which imposed a specific movement for the stand and consequently the lamp relative to the solar panel (PV) such that the perpendicular distance between them becomes the only parameter for the light density variation. The stand design began after the determination of the bench design but before its fabrication in order to make sure that the shape and mechanism attached to the bench will work and to determine the requirements needed in bench fabrication for its design. The position of the stand relative to the bench was discussed and there were many differences and objections on some ideas. We started to regenerate ideas and determine its degree of compatibility with the fabricated bench. The first two ideas were about positioning an inclined stand on the front of the bench to be seen or on its side, but they were refused as they will give a bad view. Besides, the first may conflict with the components while the second needs a complicated mechanism to drive the lamp. The third idea was a modification on the idea of the previous meeting that the stand will be inclined and hidden on the back of bench but the driving mechanism would be a wire-pulley system fixed on the side of the bench.

8.1.2.2. Motor After we finished the control circuit we started to install the lamp to the bench. We mounted the lamp on a straight bar which makes a right angle with the power screw of the motor (in order to simulate the variation in the sun’s light intensity by the changing the distance from the photovoltaic) Figure 8.7, then the whole system with the motor was placed at the back of the bench on an inclined aluminum bar to give the perpendicularity motion of the lamp for uniform light distribution. At the end of installation we used aluminum slots and two acrylic plates one was screwed with the power screw and the second was screwed to the bench to ensure the vertical motion without rotation or tilting due to lamp weight as shown in Figure 8.8.


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Figure 8.7: The photovoltaic placed on the inclined roof and the lamp is perpendicular on its face as the Sun

Figure 8.8: Lamp stand installation


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8.2. Educational Stand Assembly While we were designing the lamp stand, we managed to finish the boring and installing the components on the acrylic plates. We installed the Fuel cell, Electrolyser, switches (main switch-computer on/off lamp’s switches), loads (fan-heater-small lamp) and measuring devices’ panels as shown in Figure 8.9. After we finished the lamp stand installation, Figure 8.8, on the bench we fixed the solar panel on the roof as was shown in Figure 8.7. The following figures will show the whole bench assembled and some components installed.

Figure 8.9: The bench with the assembled components


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Figure 8.10: Back of the bench

Figure 8.11: Monitor and DAQ Card


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Figure 8.12: Different components assembled to the bench


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173

Operating Procedure of the Educational Stand

Chapter 9


Chapter 9 OPERATING PROCEDURE OF THE EDUCATIONAL STAND


174

Chapter 9


There is a variety of experiments the students can undertake to understand, compare and analyze every component in the system and/or the system as a whole. Nevertheless, 5 main experiments are minimally required for a complete understanding of the system. The procedures of each experiment are demonstrated in this chapter.

9.1. Experiment 1: Investigating the Solar Panel 9.1.1. Procedure

`

Figure 9.1: Solar Cell investigation

1. Set up the apparatus as shown in Figure 9.1. Set the variable resistance to ‘Open’. 2. Illuminate the solar module with the lamp by pressing on the lamp push button. 3. Adjust the position of the lamp to a certain distance e.g. 8cm. 4. Wait for approximately 5 minutes until the module has warmed up and the characteristic curve can be recorded at a relatively constant temperature. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

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5. Measure the respective values for voltage and current output at different resistances starting with the rotary switch in ‘open’ position (open) and then setting to decreasing resistances. The final measurement is taken in the ‘short circuit’ position. 6. By connecting the fan and the lamp two extra points can be located on the characteristic curves. This procedure can be repeated at different lamp positions.

9.1.2. Evaluation 1. Draw the IV diagram. 2. Interpret the characteristic curve. 3. Determine the maximum power point by drawing a graph of PV; power against voltage. 4. If this experiment is repeated at different lamp positions, a graph of maximum power can be plotted against the corresponding voltage as will be shown in chapter 10.


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Chapter 9


9.2. Experiment 2: Investigating the characteristic curve of the electrolyser 9.2.1. Procedure

Figure 9.2: Electrolyser investigation

1. Set up the apparatus as shown in Figure 9.2. Check the polarity!The positive terminal of the solar module unit must be connected to the positive terminal of the electrolyser, and the negative terminal of the solar module to the negative terminal of the electrolyser. Adjust the rotary switch of the load measurement box to ‘short circuit’. 2. Adjust the current from the solar module by varying the solar module by varying the light intensity by varying the lamp position. 3. Take a set of measurements of voltage and current during electrolysis and tabulate your results.


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9.2.2. Evaluation 1. Draw the VI and PI characteristic curves of the electrolyser. 2. Interpret your results.


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Chapter 9


9.3. Experiment 3: Investigating the characteristic curve of a fuel cell 9.3.1. Procedure

Figure 9.3: Single Fuel Cell investigation

The fuel cell must first be provided with a supply of hydrogen and oxygen from the electrolyser. 1. Set up the apparatus as shown in Figure 9.3. Check the polarity of the electrolyser. 2. Check that the gas tubes between the electrolyser and the fuel cell are correctly connected. Adjust the rotary switch on the load measurement box to ‘open’ circuit. 3. Record the characteristic curve of the fuel cell by varying the measurement resistance. Start position at ‘open’ then decrease the resistance step by step by turning the rotary switch to the right. Record the voltage and current for each resistance. Tabulate your results. Finally, measure the voltages and currents of the fan and lamp.


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Chapter 9


4. Further, connect the fuel cells in series as shown in Figure 9.4 and another in parallel as shown in Figure 9.5 and repeat step 3.

Figure 9.4: The fuel cells connected in series

Figure 9.5: The fuel cells connected in parallel

9.3.2. Evaluation

1. Draw the VI and PI characteristic curves of the single fuel cell, series fuel cells and parallel fuel cells. 2. Interpret your results and compare.


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9.4. Experiment 4: Solar Heater 9.4.1. Instructions

Figure 9.6: Solar heater experiment

1. Set apparatus as shown in Figure 9.6. 2. Adjust the lamp position either manually using push buttons or using buttons on the monitor screen. 3. Set the number of readings and time between each reading taken by the LABVIEW program on the monitor screen and press start. 4. Record values of voltage, current and temperature e.g. every 30 seconds.

9.4.2. Evaluation 1. Draw voltage, current and temperature curves against time. 2. Interpret your results.


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9.5. Experiment 5: Fuel Cell Heater 9.5.1. Procedure

Figure 9.7: Fuel cell heater experiment

1. Set apparatus as shown in Figure 9.7 by connecting the fuel cells in series. 2. Adjust the lamp position either manually using push buttons or using buttons on the monitor screen. 3. Set the number of readings and time between each reading taken by the LABVIEW program on the monitor screen and press start. 4. Record values of voltage, current and temperature e.g. every 30 seconds.

9.5.2. Evaluation 1. Draw voltage, current and temperature curves against time. 2. Interpret your results.


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9.6. Other Experiments The educational stand can be used for a set of experiments other than the basic 5 discussed above including: 1. The change of power output or photocurrent (in short circuit position) of the solar cell with lamp distance from the cell 2. The change of power output or photocurrent (in short circuit position) of the solar cell with the incident angle of the light.


Chapter 10

183

Results and Discussion

Chapter 10


Chapter 10

RESULTS AND DISCUSSION


185

Chapter 10


10.1. Introduction A monitoring system is used to monitor the characteristics of the components of the system. The software codes along with the measurement devices can test the components under different loading conditions. The educational use of the apparatus is greatly focused on this process. A student studying renewable energy should be familiar with the electrical characteristics of a fuel cell, an electrolyser, and a Photovoltaic cell and familiar with their behavior in a system. This chapter shows the results of experiments carried on the apparatus components.

10.2. Results and Discussion 10.2.1.

Electrolyser Characteristics Characteristics

The electrolyser is tested under different voltages, and the relations between voltage and power versus current is shown in Figures 10.1 and 10.2

Figure 10. 1: Electrolyser voltage-current curve


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Figure 10. 2: Electrolyser P-I characteristic curve

In Figure 10.1 the experimental results gives a standard VI characteristics for an electrolyser giving an open circuit voltage of 1.36 V and increasing voltage with increasing current. Figure 10.2 shows nearly linear Power-Current characteristics. The experimental results give an acceptable agreement with the theoretical predictions. The electrolyser used 0.31 W of electricity when a voltage of 0.49 V was applied on its terminals. The experimental data are limited due to the limit imposed by the photovoltaic cell used. 2 The cell was operated at intensity of about 2200 W/m .

10.2.2. Single Fuel Cell One of the two fuel cells is tested under different loads while working using all the available Hydrogen, by varying the resistance which is attached in series with the fuel cell. The relation between voltage and power versus current is demonstrated by a standard VI curve with an open circuit voltage of 0.93 V and power was raised to reach 0.63 W at 0.61 V. The theoretical curve gives higher predictions of an average of 0.18 V higher than theoretical voltages. In Figure 10.4, the theoretical power has a linear relation with


Chapter 10

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the current, but the experimental data gave some deviation from the linear relation. The cell gave power as high as 0.63 W at a voltage of 0.61 V.

Figure 10. 3: Single Fuel cell characteristic curve


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Figure 10. 4: Single Fuel Cell power - current characteristic curve

10.2.3. Fuel Cells in connection Fuel cell characteristics were investigated while it is working in a series or parallel arrangement. In both cases there were small differences from the single cell case. Nevertheless, these experiments allowed us to expand the curves range by dividing the load on the two cells.


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The results, shown in Figures 10.5 and 10.6, show the difference between the two cases. Parallel arrangement gave higher power and voltages and was closer to the theoretical results. Series arrangement ranges of voltages are narrower due to the fact that voltage is divided upon the two used cells, so the cell whose performance is being investigated gives lower voltages to supply the load than if performing alone, and the loads used in tests are identical. Open circuit voltage for parallel cells is 0.923 V and for series cells is 0.95 V. The theoretical open circuit voltage is 1.12 V which is higher by 0.18 V in average. Power characteristics were nearly linear in the range calculated. At higher currents the curve tends to deviate from the linear relation. Power reached 0.84W at 1.68 in case of series set of cells and 0.8W at 1.165A in case of parallel set of cells. Generally, theoretical are experimental results are close.

Figure 10. 5: V-I curve of a fuel cell in a set of cell


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Figure 10. 6: P-I curve of a fuel cell in a set of cells


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Chapter 10


10.2.4.

Heaters

10.2.4.1.

Heater Powered by Solar Cell 3

The heaters use the power of the photovoltaic cell to heat 10cm of water. The code measures voltage and current to compute power instantaneously and measures temperatures. Temperature data is used to compute the power gained by the mass of water in form of heat. Energy input of the system is calculated by adding the value of energy gain during the time delay to the sum of the preceding values.

The results are shown in Figures 10.7 and 10.8. The efficiency gives scattered characteristics at the start due to non-homogeneous temperature spread in the water. The efficiency then approaches about 25%.

3

Figure 10. 7: Temperature change of 10 cm of water heated by a Heater powered by PV cell


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Figure 10. 8: Efficiency change of 10 cm3 water heated by a Heater powered by PV cell

10.2.4.2.

Heater Powered by fuel Cell 3

The heaters use the power of the fuel cell to heat 10 cm of water. The code measures voltage and current to compute power instantaneously and measures temperatures. Temperature data is used to compute the power gained by the mass of water in form of heat. Energy input of the system is calculated by adding the value of energy gain during the time delay to the sum of the preceding values. The equations are mentioned in section 10.2.4.1. The results are shown in Figures 10.9 and 10.10. The efficiency gives non-sense characteristics at the start due to non-homogeneous of temperature spread in the water. The efficiency then approaches about 25%.


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3

Figure 10. 9: Temperature change of 10 cm of water heated by a Heater powered by fuel cell

3

Figure 10. 10: Efficiency change of 10 cm water heated by a Heater powered by PV cell


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10.2.5.

Solar Cell performance

10.2.5.1.

Characteristic curves

On 20 May 2010, in Cairo (longitude 30°, latitude 30°) experiments were carried out to determine the performance of the PV cell in sun light normal conditions. The measurements were obtained 3 times every hour. The Data is then averaged for every 2 hours. The detailed results are given in Appendix C. The averaged data are shown in the following graphs


Chapter 10

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Chapter 10

i.


From 6:00 to 8:00

Voltage (V)

1.94

1.73

1.56

1.28

1.02

0.60

0.44

0.31

0.20

0.11

0.07

Current (A)

0.00

0.02

0.04

0.07

0.10

0.13

0.13

0.13

0.13

0.13

0.13

Power (mW)

5.82

39.24

66.54

119.51

170.87

138.64

104.90

73.54

52.30

28.03

18.11


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Chapter 10

ii.


From 8:00 to 10:00

Voltage (V) Current (A) Power (mW)

2.29 0.00 6.53

2.28 0.03 59.88

2.27 0.05 117.73

2.25 0.12 259.63

2.21 0.22 492.38

2.08 0.44 908.40

1.90 0.55 1053.43

1.52 0.64 1013.22


Chapter 10

0.80 0.67 560.93

0.46 0.69 331.68

0.35 0.69 257.07

197


Chapter 10

iii.


From 10:00 to 12:00


2.29 0.00 5.22

2.28 0.03 59.29

2.28 0.05 117.04 1 17.04

2.26 0.11 243.34

2.24 0.22 501.06

2.17 0.45 985.38

2.13 0.61 1300.03

2.01 0.85 1710.71

1.29 1.08 1403.43

0.73 1.09 808.48


Chapter 10

0.56 1.10 624.86

198


Chapter 10

iv.


From 12:00 to 14:00

Voltage (V)

2.27

2.27

2.26

2.25

2.22

2.17

2.12

2.03

1.40

0.81

0.63

Current (A)

0.00

0.03

0.05

0.12

0.22

0.45

0.61

0.86

1.17

1.21

1.22

Power (mW)

4.87

57.03

115.69

258.90

495.68

978.82

1295.85

1734.55

1660.41

985.60

776.04


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Chapter 10

v.


From 14:00 to 16:00

Voltage (V)

2.26

2.25

2.25

2.23

2.20

2.13

2.06

1.87

1.08

0.62

0.48

Current (A)

0.00

0.03

0.05

0.12

0.22

0.44

0.59

0.79

0.90

0.92

0.93

Power (mW)

4.52

63.66

116.56

256.65

490.20

944.12

1224.65

1486.42

1000.56

586.00

458.73


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Chapter 10

vi.


From 16:00 to 18:00

Voltage (V)

2.19

2.18

2.17

2.14

2.08

1.78

1.47

1.05

0.55

0.30

0.23

Current (A)

0.00

0.03

0.05

0.11

0.21

0.37

0.42

0.44

0.46

0.46

0.46

Power (mW)

5.47

54.93

107.23

229.70

432.84

672.42

648.99

492.18

264.35

148.16

110.90


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Chapter 10

vii.


From 18:00 to 20:00

Voltage (V)

1.92

1.70

1.61

1.21

0.85

0.44

0.32

0.22

0.11

0.06

0.05

Current (A)

0.00

0.02

0.04

0.06

0.09

0.09

0.09

0.09

0.10

0.10

0.10

Power (mW)

5.15

37.04

62.47

104.06

113.11

65.70

48.61

32.97

16.82

9.26

7.09


Chapter 10

202


Chapter 10

viii.


The Average Data

Polynomial regression of 4th degree is used to get the average curves all over the day.


Chapter 10

203


Chapter 10

10.2.5.2.


Voltage at maximum power

The previous data were used to get the voltage at maximum power. The theoretical analysis gave lower predictions. The error might be in the specifications of the solar cell and its performance constants as well as environmental changes like global warming.

Figure 10. 11: Theoretical and Experimental Voltage corresponding to maximum power through the day


Chapter 10

204


Chapter 10


10.3. Further Interpretation This part possesses what we aim the students to understand after undertaking the experiment. Some of the interpretation should be realized solely by the student but some need to be explained by the teacher assistant supervising the student group.

10.3.1. Solar Cell Generally, if we wish to increase the output of the solar module at a given current, we must connect several solar cells in series: the overall voltage is then the sum of the individual voltages, while the current remains constant. If we wish to increase the current at a given voltage, we must connect the solar cells in parallel; in this case, the voltage remains constant, while the overall current is then the sum of the partial currents. In practical applications the load is the crucial factor that determines the number of solar cells and how they are connected to make up a solar module and in turn a solar generator. The power consumption of the load should always be as close to the MPP (maximum power point) as possible. In conclusion, 1. The characteristic curves differ from module to module. 2. For a fixed light intensity the characteristic curve for a solar module shows a constant current output for a range of voltages, i.e. as the load resistor is varied. 3. There is a MPP at which the module outputs its maximum power for a specific illumination.

10.3.2. Electrolyser The IV curve of the electrolyser shows that a current only starts to flow at a certain voltage, and it then rises continuously. The initial application of a small voltage does not cause an electrolysis current leading to the release of hydrogen at the cathode and oxygen at the anode; nothing appears to happen. The gases that may form at a small voltage are initially adsorbed on the surface of the electrodes; an electrochemical cell develops. This cell has a certain voltage known as the polarization voltage, which causes a current. This internal current acts in the opposite direction to the electrolysis current. More gas is adsorbed if the external voltage is increased. At a certain voltage, the gas pressure at the electrodes reaches the level of the external air pressure, and gas bubbles begin to rise at the electrodes. A further increase in the external voltage leads to continuous gas production and a steep rise in the electrolysis current strength. The minimum voltage at which the splitting of water begins is called the decomposition voltage. In our case this voltage is equal to the cell voltage of the H 2 //H2O//O2 electrochemical cell under standard Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

Chapter 10

205


Chapter 10


conditions. This value is 1.23V. Refer to equation 4.28.The difference between the theoretical decomposition voltage and the decomposition voltage that is determined experimentally is termed overpotential or overvoltage. The overpotential is a function of the electrode material, the texture of the electrode surfaces, the type and concentration of the electrolyte surfaces, the type and concentration of the electrolyte, the current density (current strength per unit area of electrode surface) and the temperature. In practical applications, the aim is to keep overpotential to a minimum. Thus, it is important to use very good, active electrode and electrolyte material. The student should notice: 1. The relationship between current and voltage in the electrolyser 2. The electrolysis needs a minimum voltage before it can start.

10.3.3. Fuel Cell The processes in the fuel cell are the reverse of those that take place in electrolysis. In the electrolysis of water, at least 1.23V must be applied before water begins to split, while in case of the fuel cell, a lower voltage than expected is generated for the same reasons. The characteristic curve is affected by the materials used for the electrodes and catalysts, the internal resistance, the temperature and the volume of the hydrogen and the oxygen being supplied. At a very small or zero current, the voltage across the fuel cell is approximately 0.9V. This voltage is called the off-load voltage (by analogy with a battery). It is very dependent on the volume and purity of the input gases. The more current is drawn from the fuel cell, the lower the voltage becomes. There is an exponential increase in the current as the voltage drops. The students should notice: 1. The voltage drops as the current taken from the fuel cell increases 2. The comparison between the characteristic curves of the electrolyser and the fuel cell Fuel Cells in Series and Parallel

When two fuel cells are connected in series, the operating voltage doubles if the current remains constant, as in the case of batteries. When two fuel cells are connected in parallel, the current doubles if the voltage remains constant. However, the voltage and current of the fuel cells are determined by the electric load. Solar Hydrogen Fuel Cell Electric Heater Educational Educational Stand - Cairo University | 2009-2010

Chapter 10

206


Chapter 10


The students should notice: 1. The connecting fuel cells in series results in a summation of the voltages at constant current 2. The connecting fuel cells in parallel results in a summation of the currents at constant voltage 3. That it is, ultimately the electric load which determines the fuel cells output


Appendix F

207

EWTR 910 TEMPERATURE PANEL DATA SHEET

Appendix F


APPENDICES


208

Appendix A

Thermophysical Properties of Matters

Appendix A

THERMOPHYSICAL PROPERTIES OF SELECTED MATTERS


209

Appendix A


The convention used to present numerical values of the t he properties is illustrated by this example:

Reference

Frank P. Incropera, David P. dewitt, Theodore L. Bergman, Adrienne S. Lavine ‘Fundamentals of Heat and Mass Transfer 6th Edition’, John Wiley & Sons, Hoboken NJ, 2007, ISBN / ASIN: 0470055545


210

Appendix A



211

Appendix A



212

Appendix A


Table A. 1: Therophysical Properties of Saturated Water


213

Appendix A



214

Appendix B

Free Convection Heat Transfer Correlations

Appendix B FREE CONVECTION HEAT TRANSFER CORRELATIONS


215

Appendix B



216

Appendix B



217

Appendix B



218

Appendix C

Solar Cell Actual Characteristic Curve Investigation

Appendix C SOLAR CELL ACTUAL CHARACTERISTIC CURVE INVESTIGATION


219

Appendix C


Abstract

This appendix demonstrates the results of the test undertaken on the solar cell to get its actual characteristic curve. The test was held on Thursday 20/05/2010. The solar panel was directed to south with thirty degree inclination angle ( ( = 30°) as show in Figure C.1. The results were recorded and processed using a LabView program (designed by the project team) and saved in an Excel sheet. The test was taken approximately every fifteen minutes from 05:43 AM to 7:59 PM (Cairo Local Time), fifty readings were recorded as following:

Figure C. 1: Solar panel facing south with thirty degree inclined angle

Results 05:43 AM

Voltage (V)

0.043

0.009

0.003

0.001

-0.001

-0.002

-0.002

-0.002

-0.003

-0.003

-0.003

Current (A)

0.002

0.002

0.003

0.003

0.003

0.003

0.002

0.002

0.003

0.003

0.003

Power (mW)

0.086

0.018

0.009

0.003

-0.003

-0.006

-0.004

-0.004

-0.009

-0.009 -0.009

-0.009

06:02 AM


1.145 0.003 3.435

0.433 0.007 3.101

0.247 0.115 0.059 0.027 0.019 0.012 0.004 0.002 0.001 0.009 0.009 0.008 0.008 0.009 0.009 0.009 0.009 0.009 2.223 1.035 0.472 0.216 0.171 0.108 0.036 0.018 0.009


220

Appendix C


06:21 AM


1.747 0.003 5.241

1.283 0.801 0.383 0.201 0.096 0.068 0.045 0.022 0.011 0.008 0.016 0.021 0.036 0.019 0.024 0.024 0.023 0.023 0.024 0.024 20.528 16.821 13.788 3.819 2.304 1.632 1.035 0.506 0.264 0.192

1.959 0.003 5.877

1.791 1.449 0.760 0.402 0.194 0.141 0.095 0.046 0.024 0.018 0.021 0.033 0.041 0.043 0.043 0.043 0.043 0.043 0.044 0.044 37.611 47.817 31.16 17.286 8.342 6.063 4.085 1.978 1.056 0.792

06:38 AM


06:57 AM


2.067 0.003 6.201

2.009 1.897 1.296 0.696 0.339 0.246 0.166 0.083 0.044 0.034 0.024 0.044 0.068 0.071 0.073 0.073 0.075 0.075 0.074 0.075 48.216 83.468 88.128 49.419 24.747 17.958 12.45 6.225 3.256 2.55

Voltage (V)

2.185

2.163

2.14

2.055

1.648

0.857

0.63

0.431

0.221

0.122

0.095

Current (A)

0.003

0.025

0.034

0.105

0.166

0.181

0.189

0.186

0.19

0.191

0.193

Power (mW)

6.555

54.075

72.76 72.76

215.775

273.568

155.117

119.07

80.166

41.99

23.302

18.335

Voltage (V)

2.223

Current (A)

0.003

2.209 0.025

2.192 0.059

2.142 0.112

2.021 0.202

1.212 0.255

0.887 0.255

Power (mW)

6.669

55.225

129.328

239.904 239.904

07:17 AM

07:33 AM

408.242 309.06

0.614 0.263

226.185 161.482

0.31 0.265

0.175 0.268

0.135 0.27

82.15

46.9

36.45

07:51 AM Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

221

Appendix C


Voltage (V)

2.247

2.237

2.223

2.184

2.101

1.499

1.121

0.774

0.738

0.377

0.212

Current (A)

0.003

0.025

0.051

0.113

0.211

0.314

0.324

0.33

0.316

0.322

0.323

Power (mW)

6.741

55.925

113.373

246.792

443.311

470.686

363.204

255.42

233.208

121.394

68.476

Voltage (V)

2.259

2.249

2.239

2.21

2 .152

1.859

1.393

0.961

0.481

0.267

0.204

Current (A)

0.003

0.026

0.052

0.114

0.216

0.388

0.403

0.409

0.407

0.407

0.407

Power (mW)

6.777

58.474

116.428

251.94

464.832

721.292

561.379

393.049

195.767

108.669

83.028

Voltage (V)

2.285

2.277

2.267

2.244

2.203

2.06

1.803

1.273

0.646

0.359

0.277

Current (A)

0.003

0.028

0.051

0.115

0.226

0.431

0.52

0.538

0.546

0.545

0.547

Power (mW)

6.855

63.756

115.617

258.06

497.878

887.86

937.56

684.874

352.716

195.665

151.519

08:09 AM

08:26 AM

08:43 AM Voltage (V)

2.285

2.28

2.271

2.25

2.21

2.086

1.897

1.385

0.715

0.396

0.306

Current (A)

0.003

0.026

0.052

0.116

0.229

0.435

0.547

0.588

0.604

0.602

0.603

Power (mW)

6.855

59.28

118.092

261

506.09

907.41

1037.659

814.38

431.86

238.392

184.518

Voltage (V)

2.296

2.289

2.281

2.261

2.224

2.125 2.125

2.01

1.624

0.839

0.474

0.366

Current (A)

0.003

0.026

0.052

0.116

0.221

0.443 0.443

0.58

0.687

0.708

0.715

0.713

Power (mW)

6.888

59.514

118.612

262.276

491.504

941.375

1165.8

1115.688

594.012

338.91

260.958

Voltage (V)

2.294

2.285

2.279

2.259

2.224

2.132

2.035

1.716

0.914

0.515

0.397

Current (A)

0.003

0.026

0.052

0.116

0.22 0.22

0.444

0.585

0.724

0.769

0.776

0.78

Power (mW)

6.882

59.41

118.508

262.044

489.28

946.608

1190.475

1242.384

702.866

399.64

309.66

09:00 AM

09:16 AM


222

Appendix C


09: 33 AM Voltage (V)

2.285

2.279

2.272

2.255

2.223

2.139

2.051

1.752

0.942

0.548

0.424

Current (A)

0.003

0.026

0.052

0.116

0.223

0.446 0.446

0.591

0.74

0.792

0.826

0.829

Power (mW)

6.855

59.254

118.144

261.58

495.729

953.994

1212.141

1296.48

746.064

452.648

351.496


2.295

2.288

2.283

2.265

2.238

2.165

2.101

1.913

1.037

0.626

0.485

Current (A)

0.002

0.026

0.052

0.115

0.224

0.462

0.604

0.808

0.871

0.939

0.945

Power (mW)

4.59

59.488

118.716

260.475

501.312

1000.23

1269.004

1545.704

903.227

587.814

458.325

Voltage (V)

2.3

2.295

2.29

2.275

2.247

2.18

2.122

1.974

1.172

0.667

0.513

Current (A)

0.002

0.026

0.052

0.115

0.224

0.453

0.611

0.833

0.984

1.002

1.002 1.002

Power (mW)

4.6

59.67

119.08

261.625

503.328

987.54

1296.542

1644.342

1153.248

668.334

514.026

Voltage (V)

2.288

2.285

2.282

2.264

2.238

2.173

2.116

1.979

1.162

0.675

0.52

Current (A)

0.002

0.027

0.052

0.116

0.224

0.453

0.61

0.836

0.976

1.011

1.011

Power (mW)

4.576

61.695

118.664

262.624

501.312

984.369

1290.76

1654.444

1134.112

682.425

525.72

Voltage (V)

2.28

2.278

2.272

2.256

2.228 2.228

2.165

2.111

1.988

1.171

0.655

0.494

Current (A)

0.002

0.026

0.051

0.116

0.224

0.45

0.607

0.84

0.983

0.983

0.96

Power (mW)

4.56

59.228

115.872

261.696

499.072

974.25

1281.377

1669.92

1151.093

643.865

474.24

10:07 AM

10:23 AM

10:40 AM


2.27

2.265

2.263

2.249

2.224

2.165

2.121

2.023

1.316

0.743

0.577

Current (A)

0.002

0.025

0.051

0.116

0.219

0.453

0.609

0.854

1.102

1.112

1.121

Power (mW)

4.54

56.625

115.413

260.884

487.056

980.745

1291.689

1727.642

1450.232

826.216

646.817


223

Appendix C



2.279

2.271

2.264

2.249

2.223

2.163

2.117

2.011

1.265

0.714

0.548

Current (A)

0.003

0.026

0.052

0.115

0.223

0.451

0.609

0.848

1.061

1.071

1.067

Power (mW)

6.837

59.046

117.728

258.635

495.729

975.513

1289.253

1705.328

1342.165

764.694

584.716

Voltage (V)

2.276

2.269

2.265

2.249

2.224

2.166

2.122

2.032

1.349

0.755

0.586

Current (A)

0.003

0.026

0.052

0.116

0.224

0.451

0.611

0.854

1.131

1.131

1.138

Power (mW)

6.828

58.994

117.78

260.884

498.176

976.866

1296.542

1735.328

1525.719

853.905

666.868

11:31 AM


2.305

2.3

2.295

2.284

2.263

2.209

2.17

2.091

1.571

0.903

0.704

Current (A)

0.002

0.026

0.05

0.06

0.231

0.461

0.624

0.879

1.316

1.351

1.366

Power (mW)

4.61

59.8

114.75

137.04

522.753

1018.349

1354.08

1837.989

2067.436

1219.953

961.664

12:04 PM Voltage (V)

2.279

2.276

2.266

2.252

2.224

2.164

2.115

2.01

1.327

0.772

0.59

Current (A)

0.002

0.025

0.052

0.115

0.224

0.452

0.608

0.849

1.111

1.154

1.143

Power (mW)

4.558

56.9

117.832

258.98

498.176

978.128

1285.92

1706.49

1474.297

890.888

674.37


2.281

2.278

2.272

2.26

2.238

2.183

2.142

2.064

1.53

0.872

0.69

Current (A)

0.002

0.026

0.051 0.051

0.116

0.224

0.437

0.617

0.872

1.281

1.304

1.337

Power (mW)

4.562

59.228

115.872

262.16

501.312

953.971

1321.614

1799.808

1959.93

1137.088

922.53


2.258

2.258

2.254

2.243

2.223

2.167

2.123

2.036

1.444

0.825

0.646

Current (A)

0.003

0.025

0.051

0.115

0.225

0.451

0.611

0.859

1.209

1.233

1.253

Power (mW)

6.774

56.45

114.954

257.954

500.175

977.317

1297.153

1748.924

1745.796

1017.225

809.438


224

Appendix C


12: 55 PM Voltage (V)

2.272

2.267

2.258

2.239

2.21

2.142

2.081

1.927

1.052

0.607

0.463

Current (A)

0.002

0.025

0.052

0.115

0.222

0.446

0.601

0.812

0. 883

0.91

0.899

Power (mW)

4.544

56.675

117.416

257.485

490.62

955.332

1250.681

1564.724

928.916

552.37

416.237

Voltage (V)

2.271

2.268

2.264

2.249

2.226

2.173

2.132

2.051

1.5

0.858

0.674

Current (A)

0.002

0.025

0.051

0.115

0.221

0.453

0.613

0.866

1.254

1.281

1.299

Power (mW)

4.542

56.7

115.464

258.635

491.946

984.369

1306.916

1776.166

1881

1099.098

875.526

01:12 PM


2.274

2.269

2.265

2.254

2.23

2.178

2.138

2.058

1.531

0.879

0.689

Current (A)

0.002

0.025

0.051

0.116

0.222

0.473

0.615

0.869

1.282

1.315

1.332

Power (mW)

4.548

56.725

115.515

261.464

495.06

1030.194

1314.87

1788.402

1962.742

1155.885

917.748

Voltage (V)

2.265

2.26

2.256

2.242

2.218

2.161

2.121

2.041

1.413

0.838

0.65

Current (A)

0.002

0.025

0.05

0.114

0.222

0.45

0.61

0.861

1.182

1.249

1.256

Power (mW)

4.53

56.5

112.8

255.588

492.45

972.45

1293.81

1757.301

1670.166

1046.662

816.4

01:46 PM

02:03 PM

Voltage (V)

2.295

2.286

2.284

2.27

2.245

2.191

2.147

2.06

1.416

0.818

0.634

Current (A)

0.002

0.025

0.051

0.12

0.224

0.456

0.618

0. 869

1. 184

1.224

1.22 4

Power (mW)

4.59

57.15

116.484

272.4

502.88

999.096

1326.846

1790.14

1676.544

1001.232

776.016


225

Appendix C



2.26

2.256

2.251

2.235

2.208

2.142

2.086

1.952

1.14

0.662

0.523

Current (A)

0.002

0.025

0.05

0.116

0.221

0.446 0.446

0.6

0.824

0.954

0.989

1.007

Power (mW)

4.52

56.4

112.55

259.26

487.968

955.332

1251.6

1608.448

1087.56

654.718

526.661

02:37 PM Voltage (V) Current (A) Power (mW)

2.26 0.002 4.52

2.258 0.025 56.45

2.253 0.051 114.903

2.239 0.114 255.246

2.211 0.22 486.42

2.143 0.446 955.778

2.09 0.601 1256.09

1.963 0.825 1619.475

1.152 0.965 1111.68

0.656 0.982 644.192

0.506 0.972 491.832


2.253

2.245

2.239

2.223

2.194

2.122

2.06

1.91

1.077

0.609

0.467

Current (A)

0.002

0.025

0.049

0.114

0.229

0.442

0.592

0.805

0.901

0.908

0.901

Power (mW)

4.506

56.125

109.711

253.422

502.426

937.924

1219.52

1537.55

970.377

552.972

420.767

Voltage (V)

2.255

2.253

2.244

2.226

2.198

2.123

2.06

1.882

1.017

0.575

0.445

Current (A)

0.002

0.025

0.051

0.114

0.228

0.442

0.593

0.793

0.852

0.861

0.859

Power (mW)

4.51

56.325

114.444

253.764

501.144

938.366

1221.58

1492.426

866.484

495.075

382.255

03:11 PM


2.237

2.228

2.222

2.203

2.167

2.071

1.964

1.534

0.787

0.472

0.366

Current (A)

0.002

0.048

0.05

0.113

0.215

0.431

0.565

0.648

0.66

0.709

0.708

Power (mW)

4.474

106.944

111.1

248.939

465.905

892.601

1109.66

994.032

519.42

334.648

259.128


2.256

2.249

2.242

2.224

2.193

2.113

2.033

1.798

0.96

0.553

0.426

Current (A)

0.002

0.025

0.061

0.114

0.221 0.221

0.44

0.584

0.758

0.804 0.804

0.758

0.832

Power (mW)

4.512

56.225

136.762

253.536

484.653

929.72

1187.272

1362.884

771.84

419.174

354.432


226

Appendix C



2.203

2.198

2.188

2.166

2.127

1.999

1.791

1.267

0.64

0.354

0.27

Current (A)

0.002

0.026

0.05

0.094

0.212

0.417

0.515

0.536

0.538

0.567

0.531

Power (mW)

4.406

57.148

109.4

203.604

450.925

833.583

922.365

679.112

344.32

200.718

143.37

Voltage (V)

2.234

2.224

2.216

2.193

2.152

2.039

1.901

1.439

0.744

0.409

0.309

Current (A)

0.002

0.025

0.051

0.112

0.216

0.424

0.547

0.607

0.624

0.613

0.602

Power (mW)

4.468

55.6

113.016

245.616

464.832

864.536

1039.847

873.473

464.256

250.717

186.018

Voltage (V)

2.187

2.179

2.173 2 .173

2.148

2 .097

1.88

1.54

1.11

0.583

0.329

0.254

Current (A)

0.002

0.024

0.049

0.111

0.209

0.392

0.442

0.47

0.49

0.496

0.495

Power (mW)

4.374

52.296

106.477

238.428

438.273

736.273

680.68

521.7

285.67

163.184

125.73

Voltage (V)

2.195

2.186

2.177

2.147

2.085

1.753

1.339

0.919

0.52

0.291

0.223

Current (A)

0.003

0.025

0.049

0.11

0.208

0.366

0.375

0.389

0.437

0.44

0.439

Power (mW)

6.585

54.65

106.673

236.17

433.68

641.598

502.125

357.491

227.24

128.04

97.897

Voltage (V)

2.157

2.143

2.09

1.989

1.417

1.056

0.724

0.364

0.202

0.155

Current (A)

0.003

0.025

0.048

0.107

0.199

0.297

0.305

0.308

0.31

0.309

0.308

Power (mW)

6.471

53.575

102.336

223.63

395.811

420.849

322.08

222.992

112.84

62.418

47.74

04:37 PM

04:55 PM

05:12 PM

05:28 PM 2.132


2.178

2.166

2.152

2.117

2.037

1.605

1.216

0.838

0.424

0.235

0.181

Current (A)

0.003

0.026

0.049

0.109

0.203

0.335

0.351

0.356

0.358

0.357

0.357

Power (mW)

6.534

56.316

105.448

230.753

413.511

537.675

426.816

298.328

151.792

83.895

64.617


227

Appendix C



2.129

2.112

2.092

2.028

1.827 1.827

1.021

0.749 0.749

0.514 0.514

0.261 0.261

0.145

0.111

Current (A)

0.002

0.024

0.048

0.105

0.183

0.214

0.22

0.219

0.223

0.223

0.224

Power (mW)

4.258

50.688

100.416

212.94

334.341

218.494

164.78

112.566

58.203

32.335

24.864

06:18 PM


2.081 0.003 6.243

2.056 2.024 1.905 1.366 0.679 0.491 0.331 0.165 0.09 0.068 0.024 0.045 0.098 0.139 0.144 0.143 0.142 0.143 0.142 0.141 49.344 91.08 186.69 189.874 97.776 70.213 47.002 23.595 12.78 9.588


2.052 0.003

2.021 0.023

1.979 0.046

1.791 0.092

1.103 0.111

0.543 0.115

0.394 0.116

0.267 0.115

0.134 0.116

0.073 0.117

0.057 0.116

Current (A) Power (mW)

6.156

46.483

91.034

164.772

122.433

62.445

45.704

30.705

15.544

8.541

6.612

06:52 PM


2.006 0.003 6.018

1.959 1.887 1.388 0.755 0.365 0.266 0.266 0.18 0.089 0.048 0.037 0.022 0.043 0.072 0.08 0.078 0.079 0.08 0.079 0.079 0.079 43.098 81.141 99.936 60.4 28.47 21.014 14.4 7.031 3.792 2.923

1.944 0.003 5.832

1.858 1.658 0.908 0.479 0.23 0.166 0.166 0.112 0.055 0.029 0.022 0.022 0.038 0.049 0.05 0.051 0.049 0.051 0.05 0.051 0.051 40.876 63.004 44.492 23.95 11.73 8.134 5.712 2.712 1.479 1.122

1.851 0.003 5.553

1.603 1.603 0.508 0.265 0.125 0.091 0.06 0.028 0.014 0.011 0.019 0.025 0.028 0.028 0.028 0.029 0.029 0.029 0.029 0.029 30.457 26.575 14.224 7.42 3.5 2.639 1.74 0.812 0.812 0.406 0.319

07:09 PM


07:26 PM



228

Appendix C


07:42 PM


1.435 0.002 2.87

0.552 0.008 4.416

0.298 0.009 2.682

0.135 0.009 1.215

0.068 0.031 0.022 0.013 0.004 0.002 0.001 0.009 0.009 0.009 0.009 0.009 0.009 0.009 0.612 0.279 0.198 0.104 0.036 0.018 0.009

Voltage (V)

0.245

0.053

0.026

0.011

0.002

0.001

-0.001

-0.002

-0.003

-0.003

-0.003

Current (A)

0.002

0.002

0.002

0.003

0.003

0.003

0.003

0.003

0.003

0.003

0.003

Power (mW)

0.49

0.106

0.052

0.033

0.006

0.003

-0.003

-0.006

-0.009

-0.009

-0.009


229

07:59 PM

Appendix D

NI USB-6008 DATA SHEET

Appendix D



230

Appendix D



231

Appendix D



232

Appendix D



233

Appendix D



234

Appendix D



235

Appendix D



236

Appendix D



237

Appendix D



238

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239

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240

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241

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242

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243

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246

Appendix D



247

Appendix D



248

Appendix D



249

Appendix D



250

Appendix D



251

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252

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253

Appendix D



254

Appendix D



255

Appendix D



256

Appendix D



257

Appendix D



258

Appendix D



259

Appendix D



260

Appendix D



261

Appendix D



262

Appendix E

PT100 TEMPERATURE SENSOR DATA SHEET

Appendix E



263

Appendix E



264

Appendix F


Appendix F

EWTR 910 TEMPERATURE PANEL DATA SHEET Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

265

Appendix F



266

Appendix F



267

Appendix F



268

Appendix F



269

Appendix G

Heater Experiments

Appendix G

HEATER EXPERIMENTS


270

Appendix G

Heater Experiments

I. Introduction These measurements measurements aim to know know if the electric heater behaviour behaviour works on on DC power supply and its ability to heat 100 gm of water.

II. Measurements components 1. Computer power supply. 2. Nickel-chrome wires 0.2 mm, 0.4mm and 0.95mm (heater). 3. Jar. 4. Multimeter. 5. Electric cables. 6. Bordun tube thermometer with accuracy 2°C and range 0°C - 100°C. 7. Carbon rods (Resistances). 8. Stopwatch.

Figure G.1: Measurements components


271

Appendix G

Heater Experiments

III. Measurements: According to H-30 Fuel Cell Voltage-Current Voltage-Current Curve, we tried to achieve the same voltages and currents.

1.

I= 1 A

V= 9.5 V P= 9.5 W

2.

I= 2 A

V= 9 V P= 18 W

3.

I= 3 A

V= 8.5 V P26 W

4.

I= 4 A

V=7.75V P= 31 W

5.

I= 5 A

V= 6 V P= 30 W

1. First Heater Measurement

Heater: V= 10.88 v R=13.4 Ω I= 0.81 A P= 8.81 W Diameter = 0.2 mm Length = 38 cm

Water: C = 4180 4180 J/kg.k (assumed as distilled water). Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

272

Appendix G

Heater Experiments

m= 100 gm. * Calculations: ∆T ideal = Power*time/(m*C) Power losses= m.C(∆Ti m.C( ∆Ti--∆Ta)/time ∆Ti: ideal ∆Ta: actual


273

Appendix G

Heater Experiments

Figure G. 2: First Measurement Tmperature Tmperature


274

Appendix G

Heater Experiments

Figure G. 3: First Measurement Power


275

Appendix G

Heater Experiments

2. Second Heater Measurement

Heater: V= 10.71 v R=9.8 Ω I= 1.09 A P= 11.674 W Diameter = 0.4 mm

Length = 113 cm Water: C = 4180 J/kg.k (assumed as distilled water). m= 100 gm. * Calculations: Calculations: ∆T ideal = Power*time/(m*C) Power*time/(m*C) Power losses= m.C(∆Ti m.C( ∆Ti--∆Ta)/time ∆Ti: ideal ∆Ta: actual

Figure G. 4: The second heater


276

Appendix G

Heater Experiments

Figure G. 5: Second Measurement Temperature


277

Appendix G

Heater Experiments

Figure G. 6: Second Measurement Power


278

Appendix G

Heater Experiments

3. Third Heater Measurement

Source: V= 10.27 v Heater: V= 9.52 v R=4.5 Ω I= 2.12A

P= 20.2W

Diameter = 0.4 mm Length = 49.3 cm Water: C = 4180 J/kg.k (assumed as distilled water). m= 100 gm. * Calculations: ∆T ideal = Power*time/(m*C) Power losses= m.C(∆Ti m.C(∆Ti--∆Ta)/time ∆Ti: ideal ∆Ta: actual


279

Appendix G

Heater Experiments

Figure G. 7: Third Measurement Temperature


280

Appendix G

Heater Experiments

Figure G. 8: Third Measurement Power


281

Appendix G

Heater Experiments

4. Fourth Heater Measurement

Source: V= 9.37 v 1.7 R1+R2(carbon rods): V= 1.53 v R=0.9 Ω I= 1.7 A Heater: V= 7.83 v R=2 Ω I= 3.915A P= 30.7 W Diameter = 0.95 mm Length = 58 cm 30.7 Water: C = 4180 J/kg.k (assumed as distilled water). m= 100 gm. *Notes: - Bubbles began at 180 sec. - Bubbles on the jar body at 400 sec. - fast bubbles at 800 sec. . - Boiling began at 980 sec. - High boiling began at 1200 sec. * Comment: There was an error in readings between 52°C -- 92°C * Calculations: ∆T ideal = Power*time/(m*C) Power*time/(m*C) Power losses= m.C(∆Ti m.C( ∆Ti--∆Ta)/time ∆Ti: ideal ∆Ta: actual

Figure G. 9: Fourth heater measurements measurements


282

Appendix G

Heater Experiments

Figure G. 10: Fourth Measurement Temperature Temperature


283

Appendix G

Heater Experiments

Figure G. 11: Fourth Measurement Power


284

Appendix G

Heater Experiments

5. Fifth Heater Measurement

Source: V= 8.94 v 5.25 33.1 Heater: V= 6.3v R=1.2 Ω I=5.25A P= 33.1W Diameter = 0.95 mm Length = 33 cm Water: C = 4180 J/kg.k (assumed as distilled water). m= 100 gm. *Notes: - Bubbles began at 100 sec. - Fast bubbles at 220 sec. . - Boiling began at 680 sec. - High boiling began at 1280 sec.

* Comment: There was an error in readings

between 61°C -- 93°C * Calculations: Calculations: ∆T ideal = Power*time/(m*C) Power*time/(m*C) Power losses= m.C(∆Ti m.C( ∆Ti--∆Ta)/time ∆Ti: ideal ∆Ta: actual

Figure G. 12: Fifth heater experiment


285

Appendix G

Heater Experiments

Figure G. 13: Fifth Measurement Temperature


286

Appendix G

Heater Experiments

Figure G. 14: Fifth Measurement Power


287

Appendix G

Heater Experiments

IV. Conclusion 1. Measurements Temperatures

Figure G. 15: Measurements Temperatures


288

Appendix G

Heater Experiments

2. Measurements location on H-30 Fuel Cell Voltage - Current curve

H-30 FC

Heaters

#

I (A)

V (v)

I (A)

V (v)

-

0

10.8

-

-

1

1

9.5

0.8

10.88

2

2

9

1.09

10.71

3

3

8.5

2.1

9.52

4

4

7.75

3.915

7.83

5

5

6

5.25

6.3

Figure G. 16: Measurements location on H-30 Fuel Cell Voltage - Current curve


289

Appendix G

Heater Experiments

A THEORETICAL STUDY TO ESTIMATE THE MAXIMUM SURFACE TEMPERATURE OF THE EXPERIMENT HEATER WIRES Problem Some nichrome heaters of dimensions shown were used to heat 100 grams of water in a jar. The wire is shaped into a helix. Estimate the maximum surface temperature reached for the following conditions. Heater

Length (cm)

Diameter (mm)

Power per unit area 2 (W/m )

Final water temp (T∞)

Isothermal Boiling?

1 2 3 4 5

38 114 49 58 33

0.2 0.4 0.4 0.95 0.95

36899 8221 32605 17735 33608

45 48 75 100 100

No. No. No. Yes Yes

Analysis For the First three heaters: Free convection relations were used to determine surface temperature by iterations. Relations from: Morgan V.T. (1975). The overall convective heat transfer from smooth circular cylinder. Advances in Heat Transfer (Academic) 11 (199-264)

Where:

And 2

h: heat transfer coefficient [W/m .K] D: pipe diameter [m] K: conductive heat transfer coefficient [W/m.K] -1

: expansion coefficient [K ] wire surface temperature [K] Solar Hydrogen Fuel Cell Electric Heater Educational Stand - Cairo University | 2009-2010

290

Appendix G

Heater Experiments

T∞: water temperature far enough from the wire [K] 3

water density [Kg/m ]

ρ:

water viscosity [Pa.s] Heaters 4 and 5 These two heaters caused the water to boil. Assuming local water saturation temperature near the wire, and nucleate boiling, we used the nucleate boiling relations to obtain a solution. No iteration was required. All properties is at saturation temperature. Nucleate pool boiling relations:

For critical heat flux:

Where

liquid viscosity [Pa.s] : latent heat of vaporization [J/Kg] 3

:

liquid water density [Kg/m ]

:

vapor water density [Kg/m ]

3

: surface tension [N/m] : liquid constant specific heat [J/Kg.K] : Prandtl Number


291

Appendix G

Heater Experiments

Results Heater 1 T∞[C]

4.50E+01

Q \\ (W/m2)

3.69E+04

Iteration

Tsur [C]

Tf [K]

g (m/s2)

b (1/K)

D (m)

n (N.s.m/Kg)

1 2 3 Iteration

60.0 53.5 54.3 Pr 3.42 3.57 3.57

325.5 322.2 322.7 K (W/mK) 0.65 0.64 0.64

9.81E+00 9.81E+00 9.81E+00 Ra 6.63 3.55 3.90

4.71E-04 4.45E-04 4.45E-04 c 1.02 1.02 1.02

2.00E-04 2.00E-04 2.00E-04 m 0.15 0.15 0.15

5.35E-07 5.46E-07 5.46E-07 h [W/m2.K] 4352.37 3955.11 4011.54

1 2 3

Tsur(new) 53.48 54.33 54.20

Heater 2 T∞[C]

4.50E+01

Q \\ (W/m2)

3.69E+04

Iteration

Tsur [C]

Tf [K]

g (m/s2)

b (1/K)

D (m)

n (N.s.m/Kg)

1 2 3 Iteration

60.0 47.8 48.7 Pr 3.33 3.77 3.77

327.0 320.9 321.3 K (W/mK) 0.64 0.64 0.64

9.81E+00 9.81E+00 9.81E+00 Ra 56.62 8.35 11.18

4.79E-04 4.37E-04 4.37E-04 c 1.02 1.02 1.02

4.00E-04 4.00E-04 4.00E-04 m 0.15 0.15 0.15

5.15E-07 5.83E-07 5.83E-07 h [W/m2.K] 2984.47 2234.37 2332.81

T∞[C]

4.50E+01

Q (W/m2)

3.69E+04

Iteration

Tsur [C]

Tf [K]

g (m/s2)

b (1/K)

D (m)

n (N.s.m/Kg)

1 2 3 Iteration 1 2 3

90.0 83.1 83.3 Pr 2.14 2.21 2.21

355.5 352.1 352.2 K (W/mK) 0.67 0.67 0.67

9.81E+00 9.81E+00 9.81E+00 Ra 315.98 270.21 271.63

6.52E-04 6.35E-04 6.35E-04 c 1.02 1.02 1.02

4.00E-04 4.00E-04 4.00E-04 m 0.15 0.15 0.15

3.53E-07 3.53E-07 3.53E-07 h [W/m2.K] 4010.63 3912.98 3916.01

1 2 3

Tsur(new) 50.75 51.68 51.52

Heater 3 \\


Tsur(new) 83.13 83.33 83.33

292

Appendix G

Heater Experiments

Heater 4 and 5 Properties of water at Tsat=373.15K μl h fg

2.79E-04 2.26E+06

N.s/m2 J/Kg

ρl ρv

957 0.596

Kg/m3 Kg/m3

σ cp l Pr Csf

5.89E-02 4.22E+03 1.76E+00 8.00E-03

N/m J/kg.k

Solving for surface temperature resulted in: Q chf

1105515

W/m2

Fourth Heater Fifth Heater

Q/A [W/m2] 17735 33608

Δt [C] 3 4

Tsurf max [C] 103 104

Conclusion Maximum attained Surface temperatures of the heaters were estimated as:

Heater No.

Analysis Type

Maximum surface Temperature [C]

1 2 3 4 5

Free convection Free convection Free convection Nucleate Boiling Nucleate Boiling

54 52 83 103 104


293

Appendix H

Matlab Code

Appendix H

MATLAB CODE

Solar Hydrogen Fuel Cell Electric Heater Educational Stand S tand - Cairo University | 2009-2010

294

Appendix H

Matlab Code

%% Solar Hydrogen Fuel Cell Modeling %%

%%The aim of this part is to calculate the radiation on the surface of the %%photovoltaic as well as the maximum power output of the photovoltaic %%throughout the duration of daylight at certain day n clc, clear n=90+30+31+30+31; m=1;

% The day

phi=30*pi/180;

% The latitude angle of cairo

delta1=23.45*sin(360*(284+n)/365*pi/180); delta=delta1*pi/180; % Solar declination angle in radians w_s1=(acos(-tan(phi)*tan(delta)))*180/pi; % Half sunshine hours in degrees w_s=w_s1*pi/180; beta=30*pi/180;

% PV tilt angle equals latitude angle

if 0
%%January %%February %%March %%April %%May %%June %%July %%August %%September %%October %%November %%December

if beta==phi-delta Cf=1; else Cf=1-1.17*(10^(-4))*((phi-delta)-beta)*180/phi; end H_o=(24*3600*1367/pi)*(1+0.033*cos(360*n/365*pi/180))*(cos(delta)*cos(phi)*sin(w_s)+w_s*sin(phi)*sin( delta))/1000000; K_T_avg=0.461+0.259*(sn); H=K_T_avg*H_o; H_d=(1.188-(2.272*K_T_avg)+(9.473*(K_T_avg^2))-(21.865*(K_T_avg^3))+(14.648*(K_T_avg^4)))*H; a=0.409+0.5016*sin((w_s1-60)*pi/180); b=0.6609-0.4767*sin((w_s1-60)*pi/180); R_d1=(1+cos(beta))/2; R_r1=0.3*((1-cos(beta))/2);

w=-w_s;


295

Appendix H

Matlab Code

while w
figure(1) plot(omega/15,I_gt,'b' plot(omega/15,I_gt, 'b', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon holdon holdon title('Variation title('Variation of total hourly radiation on tilted surface'); xlabel('\omega xlabel('\omega (hr)'); (hr)'); ylabel('Igt ylabel('Igt (W/m2)'); (W/m2)'); axis([-1.1*w_s*180/pi/15,1.1*w_s*180/pi/15,0,1000])

%This part is dedicated for PV Calculations for 4 cells solar panel %%The aim of this part is to determine the values of the shunt resistance %%and the series resistance num_PV=1; %% Information from DrFuelCell™ Professional datasheet Iscn = 1; Vocn = 2.3; Imp =0.9220; Vmp = 1.8439; Pmax_e = Vmp*Imp; Kv = -0.004; Ki = 3.18e-4; Ns = 4; length=0.2; width=0.13; NOCT=50+273.15;

%Nominal short-circuit current [A] %Nominal module open-circuit voltage [V] %Array current @ maximum power point [A] %Array voltage @ maximum power point [V] %Array maximum output peak power [W] %Voltage/temperature coefficient [V/K] %Current/temperature coefficient [A/K] %Nunber of series cells %Length of the photovoltaic module %Width of the photovoltaic module % Nominal operating cell temperature

%% Constants k = 1.3806503e-23; q = 1.60217646e-19; aa = 1.3; Eg=0.7;

%Boltzmann [J/K] %Electron charge [C] %Diode constant %Energy gap of Indium(III) nitride (InN)

%% Nominal values Gn = 1000; Tn = 25 + 273.15;

% Nominal irradiance [W/m^2] @ 25oC % Nominal operating temperature [K]

%% Adjusting algorithm % The model is adjusted at the nominal condition T = Tn; G = 1000; Vtn = k * Tn / q; Vt = k * T / q;

%Thermal junction voltage (nominal) %Thermal junction voltage (current temperature)


296

Appendix H

Matlab Code

Ion = Iscn/(exp(Vocn/(aa*Ns*Vtn))-1);

% Nominal diode saturation current

Io = Ion; % Reference values of Rs and Rp (Series & Shunt resistances) Rs_max = (Vocn - Vmp)/ Imp; Rp_min = Vmp/(Iscn-Imp) - Rs_max; % Initial guesses of Rp and Rs Rp = Rp_min; Rs = 0; tol = 0.001; % Power mismatch Tolerance P=[0]; error = Inf; %dummy value % Iterative process for Rs and Rp until Pmax,model = Pmax,experimental while (error>tol) % Temperature and irradiation effect on the current dT = T-Tn; Ipvn = (Rs+Rp)/Rp * Iscn; % Nominal light-generated current Ipv = (Ipvn + Ki*dT) *G/Gn; % Actual light-generated current Isc = (Iscn + Ki*dT) *G/Gn; % Actual short-circuit current % Increments Rs Rs = Rs + .001; % Parallel resistance Rp = Vmp*(Vmp+Imp*Rs)/(Vmp*Ipv-Vmp*Io*exp((Vmp+Imp*Rs)/(Vt*Ns*aa))+Vmp*Io-Pmax_e); % Solving the I-V equation for several (V,I) pairs clearV clearV clearI clearI V = 0:.1:Vocn; I = zeros(1,size(V,2));

% Voltage vector % Current vector

for j = 1 : size(V,2) %Calculates for all voltage values % Solves g = I - f(I,V) = 0 with Newton-Raphson g(j) = Ipv-Io*(exp((V(j)+I(j)*Rs)/(Vt*Ns*aa))-1)-(V(j)+I(j)*Rs)/Rp-I(j); while (abs(g(j)) > 0.001) g(j) = Ipv-Io*(exp((V(j)+I(j)*Rs)/(Vt*Ns*aa))-1)-(V(j)+I(j)*Rs)/Rp-I(j); glin(j) = -Io*Rs/(Vt*Ns*aa)*exp((V(j)+I(j)*Rs)/(Vt*Ns*aa))-Rs/Rp-1; I(j) = I(j) - g(j)/glin(j);

end end% end % for j = 1 : size(V,2)

% Calculates power using the I-V equation P = I.*V; Pmax_m = max(P); error = (Pmax_m-Pmax_e);

end% end % while (error>tol)


297

Appendix H

Matlab Code

%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%

disp(sprintf('PV disp(sprintf('PV Model info:\n')); info:\n')); disp(sprintf(' disp(sprintf(' Rp_min = %f',Rp_min)); %f',Rp_min)); disp(sprintf(' disp(sprintf(' Rp = %f' %f',Rp)); ,Rp)); disp(sprintf(' disp(sprintf(' Rs_max = %f',Rs_max)); %f',Rs_max)); disp(sprintf(' disp(sprintf(' Rs = %f' %f',Rs)); ,Rs)); disp(sprintf(' disp(sprintf(' a = %f' %f',a)); ,a)); disp(sprintf(' disp(sprintf(' T = %f' %f',T-273.15)); ,T-273.15)); disp(sprintf(' disp(sprintf(' G = %f' %f',G)); ,G)); disp(sprintf(' disp(sprintf(' Pmax,m = %f (model)' (model)',Pmax_m)); ,Pmax_m)); disp(sprintf(' disp(sprintf(' Pmax,e = %f (experimental)' (experimental)',Pmax_e)); ,Pmax_e)); disp(sprintf(' disp(sprintf(' tol = %f' %f',tol)); ,tol)); disp(sprintf('P_error disp(sprintf('P_error = %f',error)); %f',error)); disp(sprintf(' disp(sprintf(' Ipv = %f' %f',Ipv)); ,Ipv)); disp(sprintf(' disp(sprintf(' Isc = %f' %f',Isc)); ,Isc)); disp(sprintf(' disp(sprintf(' Ion = %f' %f',Ion)); ,Ion)); disp(sprintf('\n\n' disp(sprintf('\n\n')); )); %%%%%%%%%%%%%%%%%%%%%% T=Ta+((219+832*K_T_avg)*((NOCT-273.15)-20)/800)*Cf; Ipvn = (Rs+Rp)/Rp * Iscn;

% Nominal light-generated current

Ion=Iscn/(exp(Vocn/(aa*Vtn*Ns))-1); Io=Ion*((Tn/T)^3)*exp((q*Eg)/(aa*k)*abs((1/Tn)-(1/T))); m=1; w=-w_s; while w
% Actual light-generated current % Actual short-circuit current

% Voltage vector % Current vector

for j = 1 : size(V,2) %Calculates for all voltage values % Solves g = I - f(I,V) = 0 with Newnton-Raphson I(j)=1; g(j) = Ipv(m)-Io*(exp((V(j)+I(j)*Rs)/(Vt*Ns*aa))-1)-(V(j)+I(j)*Rs)/Rp-I(j); while (abs(g(j)) > 0.001) g(j) = Ipv(m)-Io*(exp((V(j)+I(j)*Rs)/(Vt*Ns*aa))-1)-(V(j)+I(j)*Rs)/Rp-I(j); glin(j) = -Io*Rs/(Vt*Ns*aa)*exp((V(j)+I(j)*Rs)/(Vt*Ns*aa))-Rs/Rp-1; I(j) = I(j) - g(j)/glin(j); end end% end % for j = 1 : size(V,2)

% Calculates power using the I-V equation P = I.*V; Pmax_m(m) = max(P); % PV efficiency in percentage efficiency(m)=Pmax_m(m)/(I_gt(m)*length*width)*100; zrd=Pmax_m(m); location=find(P==zrd); V_m(m)=V(location);


298

Appendix H if abs(w-0)<=0.001 for j=1:size(V,2) Vs_cr(j)=V(j); Is_cr(j)=I(j); Ps_cr(j)=Is_cr(j)*Vs_cr(j); end

Matlab Code % @ noon of the day

% PV characteristic Voltage % PV characteristic Current % PV characteristic Power

figure(2) plot(Vs_cr,Is_cr,'b' plot(Vs_cr,Is_cr, 'b', ,'LineWidth' 'LineWidth',2) ,2) xlim([0 Vocn+0.2]); ylim([0 1.1*max(I)]); gridon gridon title('Photovoltaic title('Photovoltaic I-V curve at max. intensity of specific day'); xlabel('PV xlabel('PV voltage, V [V]'); [V]'); ylabel('PV ylabel('PV current, I [A]'); [A]');

figure(3) plot(Vs_cr,Ps_cr,'b' plot(Vs_cr,Ps_cr, 'b', ,'LineWidth' 'LineWidth',2) ,2) xlim([0 Vocn+0.2]); ylim([0 Pmax_e+0.2]); gridon gridon title('Photovoltaic title('Photovoltaic P-V curve at max. intensity of specific day'); xlabel('PV xlabel('PV voltage, V [V]'); [V]'); ylabel('PV ylabel('PV power, P [W]'); [W]'); end m=m+1; w=w+0.001; end %% Outputs figure(4) plot(omega/15,V_m,'b' plot(omega/15,V_m, 'b', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon holdon holdon title('Variation title('Variation of optimum voltage through sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('Optimum ylabel('Optimum PV voltage, V_o_p_t [V]'); [V]'); axis([-w_s*180*1.1/pi/15,w_s*180*1.1/pi/15,0,max(V_m)*1.1]) figure(5) plot(omega/15,Pmax_m,'b' plot(omega/15,Pmax_m, 'b', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon holdon holdon title('Variation title('Variation of PV maximum power through sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('Maximum ylabel('Maximum PV power, P_m_a_x [W]'); [W]'); axis([-w_s*180*1.1/pi/15,w_s*180*1.1/pi/15,0,max(Pmax_m)*1.1]) figure(6) plot(omega/15,efficiency,'b' plot(omega/15,efficiency, 'b', , 'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of photovoltaic efficiency among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('PV ylabel('PV efficiency, \eta'); \eta'); axis([-w_s*180*1.1/pi/15,w_s*180*1.1/pi/15,0,15]) Pmax_max=max(Pmax_m); zrd1=Pmax_max; location=find(Pmax_m==zrd1); Vmax_max=V_m(location); disp(sprintf('For disp(sprintf('For the day = %f',n)); %f',n)); disp(sprintf('Max. disp(sprintf('Max. PV Power over the day [W] = %f',Pmax_max)); %f',Pmax_max)); disp(sprintf('The disp(sprintf('The corresponding voltage [V] = %f',Vmax_max)); %% %%Electrolyser Telec=Ta; % electrolyser temperature equals ambient temperature % reversible voltage (V) Urev=1.5184-1.5421*10^-3*Telec+9.523*10^-5*Telec*log(Telec)+9.84*10^-8*Telec^2;


299

Appendix H

Aelec=0.003; %%%%

Matlab Code

% electrolyser effective area (m^2)

electrolyzervoltage=1.8; forcounterofelectrolyzer=[1 for counterofelectrolyzer=[1 2 3 4]; m=1; w=-w_s;

% electrolyser voltage (1.4~1.8 V)

while w
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % first guess for the current of electrolyser Ielec(m)=Pmax_m(m)*num_PV/electrolyzervoltage; IA(m)=Ielec(m)/Aelec; % current density (A/m^2) del_m=0.1/1000; % thickness of membrane (assumed in range) (m) sig_m_ref=14; % reference membrane conductivity @80 C (0.14 S/cm) sig_m=sig_m_ref*exp((1/353)+(1/Telec)); res_ohm_m=del_m*(1/(Aelec*sig_m)); % membrane resistance (ohm) res_ohm_c=0; % neglect with respect to the membrane resistance res_ohm_an=0; % neglect with respect to the membrane resistance % activation overpotential of cathode (where jo,c=10^-3 A/cm^2) (V) eta_act_c(m)=(8.314*Telec/(96485))*asinh(IA(m)/(2*10)); % activation overpotential of anode (where jo,an=10^-7 A/cm^2)(V) eta_act_an(m)=(8.314*Telec/(96485))*asinh(IA(m)/(2*(10^-3))); % directly proporional with the current (approximate method) eta_diff(m)=0.1555*Ielec(m); U(m)=Urev+eta_diff(m)+eta_act_an(m)+eta_act_c(m)+(res_ohm_an+res_ohm_c+res_ohm_m)*Ielec(m); if (U(m)<1.4) U(m)=0; Ielec(m)=0; n_H2(m)=0; Q_H2(m)=0; else %Hydrogen molar flow rate from the electrolyser (mol/sec) n_H2(m)=0.99*Ielec(m)/(2*96485); Q_H2(m)=n_H2(m)*60*0.022414*1000000; %Hydrogen volume flow rate (ml/min) end P_w_sat=exp(13.669-(5096.23/Telec))*1.01325; % in bars t_elec=Telec-273; Y=42960+40.762*t_elec-(0.06682*(t_elec^2)); % absolute humidity phi_w=(1.5*P_w_sat)/(1.01325-P_w_sat); % relative humidity V_HHV=1.4756+(2.252*(10^-4))*t_elec+(1.52*(10^-8))*(t_elec^2); V_tn=V_HHV+(phi_w*Y/(2*96485)); O(m)=V_tn/U(m); if U(m)==0 O(m)=0; elseif U(m)>0 && O(m)>1 O(m)=1; end eta_elec(m)=O(m)*0.99*100; % electrolyser electric efficiency Heat_gen_elec(m)=U(m)*Ielec(m)*(1-O(m)); % Generated Heat (W) Heat_loss_elec(m)=(1/0.167)*(Telec-Ta); % Lost heat (W) Heat_cooling_elec(m)=Heat_gen_elec(m)-Heat_loss_elec(m);% Heat_cooling_elec(m)=Heat_gen_elec(m)-Heat_loss_elec(m); % cooling heat (W) if abs(w-0)<=0.001 l=1; for Ielec1=0:0.001:Ielec(m)

% @ noon of the day


300

Appendix H

Matlab Code

Ielec_cr(l)=Ielec1; % electrolyser characteristic current IA_cr(l)=Ielec_cr(l)/Aelec; eta_act_c_cr(l)=(8.314*Telec/(96485))*asinh(IA_cr(l)/(2*10)); eta_act_an_cr(l)=(8.314*Telec/(96485))*asinh(IA_cr(l)/(2*(10^-3))); eta_diff_cr(l)=0.1555*Ielec_cr(l); % electrolyser characteristic voltage U_cr(l)=Urev+eta_diff_cr(l)+eta_act_an_cr(l)+eta_act_c_cr(l)+(res_ohm_an+res_ohm_c+res_ohm_m)*Ielec_c r(l); l=l+1; end P_cr=Ielec_cr.*U_cr; % electrolyser characteristic power end m=m+1; w=w+0.001; end P_elec=Ielec.*U; electrolyzervoltage=abs(max(U))*1; end m; P_avg=sum(Pmax_m)/(m-1); P_tot=P_avg*num_PV*2*w_s*180/pi/15; Iaxis=max(Ielec); Qaxis=max(Q_H2); eta_elec_axis=max(eta_elec); P_elec_axis=max(P_elec); Heat_cooling_elec_avg=sum(Heat_cooling_elec)/(m-1); Heat_cooling_elec_tot=Heat_cooling_elec_avg*2*w_s*180/pi/15; Heat_gen_elec_avg=sum(Heat_gen_elec)/(m-1); Heat_gen_elec_tot=Heat_gen_elec_avg*2*w_s*180/pi/15; Heat_loss_elec_avg=sum(Heat_loss_elec)/(m-1); Heat_loss_elec_tot=Heat_loss_elec_avg*2*w_s*180/pi/15; Q_avg=sum(Q_H2)/(m-1); Q_tot=Q_avg*2*w_s*180/pi/15; %% Electrolyser outputs figure(7) plot(Ielec_cr,U_cr,'b' plot(Ielec_cr,U_cr, 'b', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('electrolyser title('electrolyser V-I curve at max. intensity of specific day'); xlabel('electrolyser xlabel('electrolyser currenct, Ielec. [A]'); ylabel('electrolyser ylabel('electrolyser voltage, V [volts]'); [volts]'); xlim([0.9*min(Ielec_cr) 1.1*max(Ielec_cr)]); ylim([0.9*min(U_cr) 1.1*max(U_cr)]);

figure(8) plot(Ielec_cr,P_cr,'b' plot(Ielec_cr,P_cr, 'b', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('electrolyser title('electrolyser P-I curve at max. intensity of specific day'); xlabel('electrolyser xlabel('electrolyser current, Ielec. [A]'); [A]'); ylabel('electrolyser ylabel('electrolyser power, Pelec. [W]'); [W]'); xlim([0.9*min(Ielec_cr) 1.1*max(Ielec_cr)]); ylim([0.9*min(P_cr) 1.1*max(P_cr)]);

figure(9) plot(omega/15,Ielec,'r' plot(omega/15,Ielec, 'r', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of electrolyser current among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('Electrolyzer ylabel('Electrolyzer current, I (A)'); (A)'); axis([-1.1*w_s*180/pi/15,1.1*w_s*180/pi/15,0,1.1*Iaxis]) figure(10) plot(omega/15,U,'b' plot(omega/15,U, 'b', ,'LineWidth' 'LineWidth',2) ,2)


301

Appendix H

Matlab Code

gridon gridon title('Variation title('Variation of electrolyzer voltage among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('Electrolyzer ylabel('Electrolyzer voltage, U (V)'); (V)'); ylim([0 1.1*max(U)]); figure(11) plot(omega/15,Q_H2,'r' plot(omega/15,Q_H2, 'r', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of hydrogen production rate among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('Hydrogen ylabel('Hydrogen volume flow rate, Q (ml/min)'); axis([-w_s*180*1.1/pi/15,1.1*w_s*180/pi/15,0,1.1*Qaxis]) figure(12) plot(omega/15,eta_elec,'g' plot(omega/15,eta_elec, 'g', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of electrolyser efficiency among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('electrolyser ylabel('electrolyser efficeinvy, \eta (%)'); axis([-w_s*180*1.1/pi/15,w_s*180*1.1/pi/15,0,1.1*eta_elec_axis]) figure(13) plot(omega/15,P_elec,'b' plot(omega/15,P_elec, 'b', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of electrolyser power among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('electrolyser ylabel('electrolyser Power, P (w)'); (w)'); axis([-w_s*180*1.1/pi/15,w_s*180*1.1/pi/15,0,1.1*P_elec_axis]) figure(14) plot(omega/15,Heat_gen_elec,'g' plot(omega/15,Heat_gen_elec, 'g', , 'LineWidth' 'LineWidth',2) ,2) gridon gridon holdon holdon title('Variation title('Variation of electrolyzer heat'); heat'); xlabel('\omega' xlabel('\omega'); ); ylabel('Heats ylabel('Heats Q (Gen. (green),Lost (red),Cool. (blue))(W)'); plot(omega/15,Heat_loss_elec,'r' plot(omega/15,Heat_loss_elec, 'r', ,'LineWidth' 'LineWidth',2) ,2) plot(omega/15,Heat_cooling_elec,'b' plot(omega/15,Heat_cooling_elec, 'b', ,'LineWidth' 'LineWidth',2) ,2) %% fuel cell P_fc=1; % Fuel cell pressure (atm) F=96487; % Faraday constant (mol/c) Tcell=Ta; % cell temperature equals ambient emperature Rgc=8.314; % universal gas constant in=3; % internal and fuel crossover equivalent current density (mA/cm2) io=0.1; % sum of cathode & anode exchange current densities (mA/cm2) r=2.54*(10^-4); % area specific resistance (ASR) (k?.cm2) m_fc=2.11*(10^-5); n_fc=8*10^(-3); HHV=141900; % Higher heating value of hydrogen (kj/kg) utilization=0.96; n_cell_fc=1; Emax=1.1; Afc=0.0016; % cell effective area (m2) A_fc=Rgc*Tcell/(2*0.5*F); P_H2=2/3*P_fc; P_O2=1/3*P_fc;

% hydrogen pressure (atm) % oxygen pressure (atm)

% reversibe voltage E_Nernst=1.229-(0.85*10^(-3))*(Tcell-298.15)+(4.3085*10^(-5))*Tcell*(log(P_H2)+0.5*log(P_O2)); m=1; w=-w_s; while w

302

Appendix H ifI_fc(m)>0 ifI_fc(m)>0 i(m)=I_fc(m)/Afc; Vact(m)=A_fc*log((i(m)+in)/io); Vohm(m)=(i(m)+in)*r; Vconc(m)=m_fc*exp(n_fc*i(m));

Matlab Code

% Activation voltage drop (V) % Ohmic voltage drop (V) % Concentration voltage drop (V)

Vcell(m)=E_Nernst-Vact(m)-Vohm(m)-Vconc(m); % produced cell voltage (V) Wcell(m)=I_fc(m)*Vcell(m); % heat released rate (W) Q_heat_fuelcell(m)=(Emax-Vcell(m))*I_fc(m)*n_cell_fc; % mass rate of produced water (kg/sec) m_H2O_fuelcell=I_fc(m)*n_cell_fc*(18.018/1000)/(2*F); % mass rate of consumed oxygen (kg/min) m_O2_fc(m)=m_H2_fc(m)/(2.0158*2)*32/1000/utilization*60; % volume rate of consumed oxygen (ml/min) Q_O2_fc(m)=m_O2_fc(m)*1000000/1.429; % cogeneration efficiency (%) eta_cell_cogen(m)=(Wcell(m)+Q_heat_fuelcell(m))*3600*100/(m_H2_fc(m)*HHV*1000); % electric power efficiency (%) eta_cell(m)=Wcell(m)*3600*100/(m_H2_fc(m)*HHV*1000); Powerdensity(m)=Wcell(m)/Aelec; % 2 cells with each half the hydrogen flow rate I_2(m)=I_fc(m)/2; i_2(m)=I_2(m)/Afc; Vact_2(m)=A_fc*log((i_2(m)+in)/io); Vohm_2(m)=(i_2(m)+in)*r; Vconc_2(m)=m_fc*exp(n_fc*i_2(m)); Vcell_2(m)=E_Nernst-Vact_2(m)-Vohm_2(m)-Vconc_2(m); % parallel % Power of one cell in parallel connection Wcell_1_p(m)=I_2(m)*Vcell_2(m); % series % power of one cell in series connection Wcell_1_s(m)=I_2(m)*Vcell_2(m); else i(m)=0; Vact(m)=A_fc*log((i(m)+in)/io); Vohm(m)=(i(m)+in)*r; Vconc(m)=m_fc*exp(n_fc*i(m)); Vcell(m)=0; Wcell(m)=I_fc(m)*Vcell(m); Q_heat_fuelcell(m)=(Emax-Vcell(m))*I_fc(m)*n_cell_fc; m_H2O_fuelcell=I_fc(m)*n_cell_fc*(18.018/1000)/(2*F); m_O2_fc(m)=m_H2_fc(m)/(2.0158*2)*32/1000/utilization*60; Q_O2_fc(m)=m_O2_fc(m)*1000000/1.429; eta_cell_cogen(m)=0; eta_cell(m)=0; I_2(m)=I_fc(m)/2; i_2(m)=I_2(m)/Aelec; Vact_2(m)=A_fc*log((i_2(m)+in)/io); Vohm_2(m)=(i_2(m)+in)*r; Vconc_2(m)=m_fc*exp(n_fc*i_2(m)); Vcell_2(m)=0; % parallel % Power of one cell in parallel connection Wcell_1_p(m)=I_2(m)*Vcell(m); % series % power of one cell in series connection Wcell_1_s(m)=I_fc(m)*Vcell_2(m);


303

Appendix H

Matlab Code

end if abs(w-0)<=0.001 s=1; for I1=0:0.001:I_fc(m) I_cr(s)=I1; i_cr(s)=I_cr(s)/Afc; Vact_cr(s)=A_fc*log((i_cr(s)+in)/io); Vohm_cr(s)=(i_cr(s)+in)*r; Vconc_cr(s)=m_fc*exp(n_fc*i_cr(s)); Vcell_cr(s)=E_Nernst-Vact_cr(s)-Vohm_cr(s)-Vconc_cr(s); Wcell_cr(s)=I_cr(s)*Vcell_cr(s); % 2 cells with each half the hydrogen flow rate I_2_cr(s)=I_cr(s)/2; i_2_cr(s)=I_2_cr(s)/Afc; Vact_2_cr(s)=A_fc*log((i_2_cr(s)+in)/io); Vohm_2_cr(s)=(i_2_cr(s)+in)*r; Vconc_2_cr(s)=m_fc*exp(n_fc*i_2_cr(s)); Vcell_2_cr(s)=E_Nernst-Vact_2_cr(s)-Vohm_2_cr(s)-Vconc_2_cr(s); % parallel % Power of one cell in parallel connection Wcell_1_p_cr(s)=I_2_cr(s)*Vcell_2_cr(s); % series % power of one cell in series connection Wcell_1_s_cr(s)=I_2_cr(s)*Vcell_2_cr(s); s=s+1; end end m=m+1; w=w+0.001; end I_fc_axis=max(I_fc); Vcell_axis=max(Vcell); Wcell_axis=max(Wcell); eta_cell_axis=max(eta_cell); eta_cell_cogen_axis=max(eta_cell_cogen); Wcell_1_p_axis=max(Wcell_1_p); Wcell_1_s_axis=max(Wcell_1_s);

%% Fuel cell Outputs figure(15) plot(omega/15,I_fc,'b' plot(omega/15,I_fc, 'b', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of Fuel cell current among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('current, ylabel('current, I (A)'); (A)'); axis([-w_s*180*1.1/pi/15,1.1*w_s*180/pi/15,0,1.1*I_fc_axis]) figure(16) plot(omega/15,Vcell,'r' plot(omega/15,Vcell, 'r', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of Fuel cell voltage among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('voltage, ylabel('voltage, Vcell (V)'); (V)'); axis([-1.1*w_s*180/pi/15,1.1*w_s*180/pi/15,0,1.1*Vcell_axis]) figure(17) plot(omega/15,Wcell,'k' plot(omega/15,Wcell, 'k', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of Fuel cell Power among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('Power, ylabel('Power, Wcell (W)'); (W)'); axis([-1.1*w_s*180/pi/15,1.1*w_s*180/pi/15,0,1.1*Wcell_axis]) figure(18) plot(omega/15,eta_cell,'y' plot(omega/15,eta_cell, 'y', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of Fuel cell Power efficiency among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('Power ylabel('Power efficiency, \etacell (%)'); axis([-1.1*w_s*180/pi/15,1.1*w_s*180/pi/15,min(eta_cell)-10,1.1*eta_cell_axis])


304

Appendix H

Matlab Code

figure(19) plot(omega/15,Wcell_1_p,'g' plot(omega/15,Wcell_1_p, 'g', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of one Fuel cell power in parallel connection among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('Power ylabel('Power , P (W)'); (W)'); axis([-1.1*w_s*180/pi/15,1.1*w_s*180/pi/15,0,1.1*Wcell_1_p_axis]) figure(20) plot(omega/15,Wcell_1_s,'g' plot(omega/15,Wcell_1_s, 'g', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('Variation title('Variation of one Fuel cell power in series connection among sunlight duration'); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('Power ylabel('Power , P (W)'); (W)'); axis([-1.1*w_s*180/pi/15,1.1*w_s*180/pi/15,0,1.1*Wcell_1_s_axis])

figure(21) plot(omega/15,2*Wcell_1_s,'r' plot(omega/15,2*Wcell_1_s, 'r', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon holdon holdon title('Variation title('Variation of two Fuel cells power in series & parallel connection among sunlight duration' ); xlabel('Solar xlabel('Solar hour, \omega (hr)'); (hr)'); ylabel('Power ylabel('Power , Wcell(series (red),parallel (green)) ( (W)'); plot(omega/15,2*Wcell_1_p,'g' plot(omega/15,2*Wcell_1_p, 'g', ,'LineWidth' 'LineWidth',2) ,2) axis([-1.1*w_s*180/pi/15,1.1*w_s*180/pi/15,0,1.1*max(2*Wcell_1_s)])

figure(22) plot(I_cr,Vcell_cr,'b' plot(I_cr,Vcell_cr, 'b', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('V-I title('V-I curve of one Fuel cell at noon of specific day'); xlabel('current xlabel('current I (A)'); (A)'); ylabel('Voltage ylabel('Voltage , Vcell (V)'); (V)'); ylim([0.9*min(Vcell_cr) 1.1*max(Vcell_cr)]);

figure(23) plot(I_cr,Wcell_cr,'b' plot(I_cr,Wcell_cr, 'b', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('P-I title('P-I curve of one Fuel cell at noon of specific day'); xlabel('current xlabel('current I (A)'); (A)'); ylabel('Power ylabel('Power , Wcell (W)'); (W)'); ylim([0 1.1*max(Wcell_cr)]); figure(24) plot(I_2_cr,Vcell_2_cr,'r' plot(I_2_cr,Vcell_2_cr, 'r', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('V-I title('V-I curve of one Fuel cell in parallel connection at noon of specific day'); xlabel('current xlabel('current I (A)'); (A)'); ylabel('Voltage ylabel('Voltage , Vcell (W)'); (W)'); ylim([0.9*min(Vcell_2_cr) 1.1*max(Vcell_2_cr)]); figure(25) plot(I_2_cr,Wcell_1_p_cr,'r' plot(I_2_cr,Wcell_1_p_cr, 'r', , 'LineWidth' 'LineWidth',2) ,2) gridon gridon title('P-I title('P-I curve of one Fuel cell in parallel connection at noon of specific day'); xlabel('current xlabel('current I (A)'); (A)'); ylabel('Power ylabel('Power , Wcell (W)'); (W)'); ylim([0 1.1*max(Wcell_1_p_cr)]); figure(26) plot(I_2_cr,Vcell_2_cr,'g' plot(I_2_cr,Vcell_2_cr, 'g', ,'LineWidth' 'LineWidth',2) ,2) gridon gridon title('V-I title('V-I curve of one Fuel cell in series connection at noon of specific day'); xlabel('current xlabel('current I (A)'); (A)'); ylabel('Voltage ylabel('Voltage , Vcell (V)'); (V)'); ylim([0.9*min(Vcell_2_cr) 1.1*max(Vcell_2_cr)]); figure(27) plot(I_2_cr,Wcell_1_s_cr,'g' plot(I_2_cr,Wcell_1_s_cr, 'g', , 'LineWidth' 'LineWidth',2) ,2) gridon gridon title('P-I title('P-I curve of one Fuel cell in series connection at noon of specific day');


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Solar Hydrogen Fuel Cell Water Heater (Educational Stand)

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