A National Level Paper Presentation on
SOLAR – WIND HYBRID SYSTEM Submitted By
Atul M. Zope
Rameshwar V. Wagh
[email protected] [email protected]
Department of Mechanical Engineering Godavari College of Engineering, Jalgaon Year 2010 - 2011
SOLAR – WIND HYBRID SYSTEM Atul M. Zope1, Rameshwar Wagh2 1, 2,
GF’s Godavari College of Engineering, North Maharashtra University, Jalgaon, India
ABSTRACT Energy is vital for sustaining life on earth. Energy was, is and will remain the basic foundation which determines the stability of economic development any nation. It is needed to increase the quality of life at present the power shortage is a major hurdle in progress of the nation. Hence there is a need optimally and economically design and develop all the possible non-conventional energy resources to reduce the void between supply and demand of electrical power. The detailed study of electrical power systems is a key element of many curricula in Industrial Technology. The set-up consists of a photo-voltaic solar-cell array, a mast mounted wind generator, lead-acid storage batteries, etc. This hybrid solar-wind power generating system is extensively used to illustrate electrical concepts in hands-on laboratories and demonstrations in the Industrial Technology curriculum. These systems give better reliability, reduce pollution and are a good tool for the utility for demand side management. In coming years, man will have to increasingly depend on renewable energy sources. Because of the disadvantages involved in using solar or wind energy individually, a hybrid system which avoids the individual advantages will become more famous in coming years. Also the renewable energy equipments will become cheaper and efficient with modern technology.
INDEX Sr. No. 1 2 3 4 5 6 7 8 9
Title Introduction Design Approaches Working of Wind – Solar Hybrid System Methodology Establishment of A Solar Wind Hybrid Unit Existence of Solar Wind Hybrid System Overall View of The Plant Conclusion References
Page No. 1 2 2 3 4 5 7 8 8
I. INTRODUCTION Around 2 billion people world-wide do not have access to electricity services, of which the main share in rural areas in developing countries. The fact that rural electricity supply has been regarded as essential for economic development. It is nowadays a main focus in international development cooperation. A renewable energy resource is a favorable alternative for rural energy supply. In order to handle their fluctuating nature, however, hybrid systems can be applied. These systems use different energy generators in combination, by this maintaining a stable energy supply in times of shortages of one the energy resources. Main hope attributed to these systems is their good potential for economic development. Hybrid systems are another approach towards decentralized electrification, basically by combining the technologies presented above. They can be designed as stand-alone mini-grids or in smaller scale as household systems. One of the main problems of solar as well as wind energy is the fluctuation of energy supply, resulting in intermittent delivery of power and causing problems if supply continuity is required. This can be avoided by the use of hybrid systems which can be defined as “a combination of different, but complementary energy supply systems at the same place, i.e. .solar cells and wind power plants” A hybrid energy system consists of two or more energy systems, an energy storage system, power conditioning equipment and a controller. A hybrid energy system may or may not be connected to the grid. Examples of energy systems commonly used in hybrid configurations are small wind turbines, photovoltaic systems, micro hydro, diesel generator, fuel cells, micro turbines, and Stirling engines. Typically batteries are used for energy storage but other options are flywheels and hydrogen energy storage systems. Power conditioning equipment consists of one or more of the following: controlled rectifiers, inverters/grid-tie inverters, charge controllers, and DC-DC converters. The task for the hybrid energy system controller is to control the interaction of various system components and control power flow within the system to provide a stable and reliable source of energy. With the wide spread introduction net-metering, the use of small isolated or grid connected hybrid energy systems is expected to grow tremendously in the near future. A number of hybrid energy systems in use/ under going testing in various parts of the world. Design of a hybrid energy system is site specific and it depends upon the resources available and the load demand. Solar energy and wind energy are two renewable energy sources that can be effectively combined to produce electrical power by photovoltaics (PV) and wind turbines (WT) respectively. Hybrid PV/WT systems of several sizes have been developed and interesting results have been extracted from installations of these compound systems. Considering the application of PV and WT systems on buildings, the use of small size wind turbines is necessary. These WTs can be of horizontal or vertical axis, must be of low cut in wind speed and also aesthetically compatible with the building architecture. PV panels are more flexible than WTs regarding size and installation requirements and have been already applied successfully in several buildings. In this paper we present the concept of the hybrid PVT / WT systems, which combine photovoltaic, thermal and wind turbine subsystems, aiming to cover effectively electrical and thermal needs of buildings. The output from the solar part depends on the incoming solar radiation and is obtained during sunshine. On
the other hand the output of the wind turbine part depends on the wind speed at the location of the installation and is obtained any time of the day or night that the wind speed is over a lower limit. Therefore the PVT and WT subsystems can supplement each other, being primarily used to cover building electrical load and secondary to increase the temperature of the existing thermal storage tank of PVT system by their surplus electrical energy.
II.DESIGN APPROACHES Various models based on different approaches have been designed to get the optimum configuration. These can be classified as follows: Logistical Dynamic A)
Logistical Approach: Logistical models are used primarily for long term performance predictions, component sizing and for
providing input to economic analyses. Generally they can be divided in following three categories: Time series (or quasi –steady state) Probabilistic: Time series + probabilistic: As the name suggests models in this category are based on the use of a combined time series and statistical approach. B) Dynamic Approach : Dynamic models are used primarily for component design, assessment of system stability and determination of power quality. They are generally used for hybrid power systems with no storage capability, or systems with minimal storage such as flywheel. Depending on time step size and number of modeled components they can be divided into following three categories: Dynamic Mechanical: Dynamic Mechanical, steady state electrical model: Dynamic mechanical and electrical model: A combined approach of time series probabilistic + dynamic mechanical and electrical model gives the best performance of a wind solar hybrid system.
III.WORKING OF WIND-SOLAR HYBRID SYSTEM
Fig. No.1. Schematic of Wind- Solar Hybrid System During daytime, solar photovoltaic array converts sunlight into electricity and stores this DC power in battery bank. Wind generator starts generating power when wind speed exceeds the cut-in speed of the wind turbine. The wind turbine is of self regulated type with protection for over speed. The hybrid controller has inbuilt solar charge controller and wind charge regulator. It maximizes charging current and prevents excess discharge/overcharge of the batteries.
Inverter converts DC power into AC power to operate all standard electrical appliances. Inverter has inbuilt protection for short circuit and overload. During windy period, excess energy generated by wind battery charger is dissipated through a dump load.
Usually, a DC/AC inverter needs to be installed additionally. Hybrid systems are applied in areas where permanent and reliable availability of electricity supply is an important issue. Maintaining high availability with renewable energies alone usually requires big renewable energy generators, which can be avoided with hybrid systems. At favorable weather conditions, the renewable part of the system satisfies the energy demand, using the energy surplus to load the battery. The batteries act as “buffers”, maintaining a stable energy supply during short periods of time, i.e. in cases of low sunlight or low wind. Moreover, the battery serves to meet peak demands, which might not be satisfied by the renewable system alone. A charge controller regulates the state of load of the battery, controlling the battery not to be overloaded. The complementary resource produces the required energy at times of imminent deep discharge of the battery, at the same time loading the battery. In some regions the exploitation of both wind and solar resources can become favorable, i.e. at coastal or mountain areas with high degree of solar radiation. Of utmost importance is here that wind and solar energy supply complement each other so that energy provision is possible over the whole year. Main applications for rural electrification in developing countries include independent electric power supply for Villages, Farmhouses, Residential Buildings, Missions, Hotels, Radio Relay Transmitters, Irrigation systems, Desalination Systems.
IV. METHODOLOGY
In order to address the shortcomings of existing instructional techniques for electrical power systems, a hybrid wind-turbine and solar cell system has been implemented. The system was designed and implemented with the following goals: • To be completely different from traditional electricity labs and to be fresh and interesting. • To be intimately related to real-world industrial power issues such as power quality. • To show a complex, interrelated system that is closer to the “real world” than the usual simple systems covered in educational labs. • To motivate learning by introducing such elements as environmental and economic concerns of practical interest to the students.
V. ESTABLISHMENT OF A SOLAR WIND HYBRID UNIT The hybrid unit contains two complete generating plants, a PV solar-cell plant and a wind-turbine system. These sources are connected in parallel to a 12V DC line. The power is next connected to a DC to AC inverter and is then supplied from the inverter’s output to a single-phase 60 HZ, 120 VAC load. The overall project structure is presented in Figure 1. The wind turbine is installed at the top of a steel tower that has a height of 18.3 meters and a diameter of 8.9 cm. The wind turbine depicted is a 0.7 kW unit and the solar panels depicted number four in all with a capacity of 50 Watts each. The instrumentation panel depicted monitors the outputs of the generator using digital panel meters. A small wind turbine was chosen for its low maintenance and many safety features. One of the low maintenance features is the turbine’s brushless alternator and an internal governor. The turbine generates 0.4 kW when turning at its rated speed of 47 km/hr and it is capable of generating up to 0.7 kW at its peak wind speed of 72 km/hr. The actual system’s pictures are shown in Figure 2.
Fig. No.2. Actual Picture of Wind/PV Hybrid Power Station The turbine’s blades are made of a carbon fiber reinforced composite that will intentionally deform as the turbine reaches its rated output. This deformation effect changes the shape of the blade, causing it to go into a stall mode, thus limiting the rotation speed of the alternator and preventing damage in high winds. Another feature of the wind turbine is a sophisticated internal regulator that periodically checks the line voltage and corrects for low voltage conditions. The solar panels are 12 VDC units and were chosen for their ultra clear tempered glass that is manufactured for long term durability. Figure 3 shows the DC voltage measured across the 12 volt DC bus where the wind turbine and PV arrays outputs are connected. A slight ripple in power regulation can clearly be seen. This ripple is a function of the unpredictable nature of wind
and sunshine along with the dynamic effects of the electrical load. As mentioned earlier, one of the largest problems in systems containing power inverters is power quality. This problem becomes serious if the inverter used in the system does not have a good sinusoidal waveform output and causes problems such as harmonic contamination and poor voltage regulation. According to the IEEE (a professional society which codifies such issues) standards, a maximum of 3 to 4% total harmonic distortion (this is a quantitative measure of how bad the harmonic contamination is) may be allowed from inverter outputs. However, many inverter outputs have much more harmonic distortion than is allowed. The inverter used in this system has a power rating of a 1.5 KVA and was manufactured by Trace Technologies ®. The battery banks contain 4 deep-cycle lead-acid batteries connected in parallel. High power capacity heating resistors, energy efficient light bulbs, incandescent light bulbs, and two small AC motors constitute electrical loads that can be applied to the system. To monitor and store the voltage, current, power, and harmonic contamination data, two Fluke ® power quality analyzers (types 39 and 41) are used in the system. In addition, permanently mounted AC/DC digital panel meters form part of the system’s instrumentation.
Fig. No. 3. Established Wind/PV Hybrid Power Generation Unit
VI. EXISTENCE OF SOLAR WIND HYBRID SYSTEM A) Solar Energy: Advantages 1. The main advantage of solar energy is that this energy is free and available in plenty. 2. The equipments used for solar energy are simple in construction, also they require minimum maintenance. 3. It is pollution free. 4. The solar thermal power plants are feasible in deserts, dry sunny areas where other sources of energy is not available. 5. Solar p v systems are economical and feasible for remote, stand alone power plants Disadvantages 1. Solar energy is not in the concentrated form.
2. The capital investment for equipment is more than conventional ones. 3. Efficiency of the plant is less. 4. Low energy density, 0.1 to 1 kW / sq. m 5. Large area covered by solar collectors. 6. Direction of rays changes continuously, also varies during the day, season and with weather conditions. 7. Energy is not available at night and during cloudy periods.
B) Wind Energy: Advantages 1. Wind energy is readily available, nonpolluting power system so it has no adverse influence on environment. 2. Wind energy systems avoid fuel provision and transport. 3. On a small scale, up to a few KW system is less costly. On a large scale costs can be competitive with conventional electricity and lower costs could be achieved by mass production. 4. It has low operating cost and also can be useful in supplying electric power to remote areas where other energy sources are scarcely available. Disadvantages 1. Wind energy available is dilute and fluctuating in nature. 2. Unlike water energy, wind energy needs storage capacity because of its irregularity. 3. Wind energy systems are noisy in operation, a large unit can be heard many kms away. 4. Due to the involvement of the construction of high towers with gear box, generator, couplings, etc., the wind power system has a relatively high overall weight. 5. Large areas are needed, typically, propellers one to three meters in diameters. 6. Present systems are neither maintenance free nor practically reliable 7. Wind power plants can be located only in the vast open areas in locations of favorable wind.Such locations are generally away from load canters. 8. Presently, it is only in one to a few MW range, does not meet the energy needs of large cities and industries.
C) Existence of Solar Wind Hybrid Power Plants: As seen above, there are problems in utilizing the solar as well as wind energy efficiently. In order to overcome these problems, concept of ‘hybrid power plant’ is introduced. In this both solar and wind power plants are used so that their disadvantages are reduced to a considerable amount. As we know that sun is available in the day only, energy is not available during night from sun whereas wind energy is available throughout the day and its capacity increases in the nights. Here when sun is not available wind energy comes to play and vice-versa. Thus hybrid power plants are more useful than individual ones and therefore they are extensively used nowadays.
VII. OVERALL VIEW OF THE PLANT 10 KWp Wind-Solar Hybrid System at St. Martins Island( Bay of Bengal), Cox's Bazar
St. Martin’s Island - a remote coral offshore Island in the Bay of Bengal. This island is famous for marine and coastal bio-diversity and eco tourism. Ministry of Environment & Forest already taken up program for Conservation of Biodiversity, Marine Park Establishment & Eco-tourism Development in St. Martins Island. Sustainable Rural Energy under Local Government Engineering Department (LGED) with the finance from UNDP installed 10Kw Solar-Wind Hybrid System in St. Martins Island at Bay of Bengal, which is largest in Bangladesh. The hybrid system producing power combined with solar and wind resources to a centralized AC output system. The entire power supplying to Motel, Barrack, Central Plaza, Laboratory & Dormitory.
Centralized Wind-Solar Hybrid System
Solar Array of Centralized Wind-Solar Hybrid System at St. Martins Island of Bay of Bengal
IX.CONCLUSION Obviously, a complete hybrid power system of this nature may be expensive and too labor intensive for many Industrial Technology Departments. However, many of the same benefits could be gleaned from having some subset of the system, for example a PV panel, batteries, and an inverter, or even just a PV panel and a DC motor. The enhancements to instruction, especially in making electrical power measurements more physical, intuitive, and real-world are substantial and the costs and labor involved in some adaptation of the ideas in this paper to a smaller scale setup are reasonable. The use of solar and wind hybrid power generation is an especially vivid and relevant choice for students of Industrial Technology as these are power sources of technological, political, and economic importance in their state. The key elements of this test bed concept presented in this paper are two or more renewable power sources connected to a power grid with complex electrical interactions. In coming years, man will have to increasingly depend on renewable energy sources. Because of the disadvantages involved in using solar or wind energy individually, a hybrid system which avoids the individual advantages will become more famous in coming years. Also the renewable energy equipments will become cheaper and efficient with modern technology.
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