SOLAR ENERGY EXPLOITATION HISTORY Solar energy is not a new idea but people have been using the sun to meet their everyday fuel needs for centuries. The solar power technology of the 7th century B.C. was the use of a magnifying glass to concentrate sunlight to make fire. By the 6th century A.D., public and residential sunrooms were a commonplace. The world's first solar collector was built in 1767; it was later used for solar cooking on shipping expeditions. The first solar (photovoltaic) cell in the United States that generated enough power to run electrical equipment was invented in 1954. By 1973, the University of Delaware built the world's first residences powered by photovoltaic technology. Today, solar power is one of the world's top alternative fuels being used in almost every facet of business and home life.
India is one of the few countries with long days and plenty of sunshine (abundant solar energy), especially in the Thar desert region. Solar thermal energy is being used in India for heating water for both industrial and domestic purposes. A 140 MW integrated solar power plant is to be set up in Jodhpur but the initial expense incurred is still very high. BENEFITS OF SOLAR ENERGY
renewable resource, meaning that it continuously renewed by nature no carbon emissions Solar energy plants are also a lso relatively cheap to construct Reduce country's dependence on fossil fuels/foreign oil will be reduced Can result in more jobs instead of sending money overseas to large oil countries such as Saudi Arabia. Not a solution in areas with little sunlight or heavy rainfall Solar power plants also need large spaces spa ces for equipment, which can be difficult to find in heavily populated or industrialized areas.
DOWNSI DOWNSI D ES
FUN FACTS
Solar is the Latin word for sun. The largest solar energy plant will be in Deming, New Mexico, and will cover 1,300 hectares and employ between 300 and 400 people. This power plant will be functional starting in 2011. T he second largest solar plant is less than 100 miles away in Gila Bend, Arizona, and covers 769 hectares. "
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ELEMENTS OF SOLAR POWER Solar radiation The first element of solar power is the source of energy itself: radiation released by the sun via sunlight. Even though all parts of the Earth receive sunlight, the quantity varies depending on the landscape, weather, season, time of day and location.
Solar radiation reaches the Earth's surface as diffuse or direct energy. When it is diffuse radiation, some of it has been reflected r eflected or absorbed by material such as water vapor, dust, forest fires, clouds, air molecules, pollutants and volcanoes. When the sun's radiation has not been dispersed prior to reaching the Earth's surface, then it is called direct dir ect beam solar radiation. Technologies Technologi es The second element is the technology used to transform solar radiation into usable power source, i.e. using solar energy to generate electricity. The three t echnologies echnologies as of 2011 are y y
Photovoltaic Solar-thermal technologies technologies
HOTOVOLTAIC P
The word photovoltaic is derived from the word photo -- which comes from the Greek word for light -- and volt which pertains to electricity. Scientists at the Bell Telephone company discovered photovoltaic technology in 1954, according to the National Renewable Energy Laboratory. They discovered that when silicon was exposed to light, it released an electrical charge. Shortly after, organizations began using photovoltaic cells and solar panels to power watches, solar panels and calculators. "
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MECHANISM A photovoltaic (PV) panel is a device that converts solar energy directly into electricity. It is composed of many individual photovoltaic cells (dozens or even hundreds); each contributes a small portion of the total power. Photovoltaic panels, in turn, can be wired together to create arbitrarily large solar power plants. Photovoltaic panels are made out of a semiconductor, such as silicon, and a coating that helps to absorb light. S emiconductor v/ s coating S emiconductors are not good at conducting electricity--that's what makes them semiconductors. S ilicon, for example, forms a crystalline structure. E ach molecule is bonded to the electrons of its neighbors, leaving no free floating electrons to move around and create a current. T he silicon used in PV panels is " doped " silicon-meaning that trace amounts of other molecules have been added to make it a semiconductor. T hese trace molecules bond with the silicon, but provide extra electrons which are not tightly bonded. W hen a sufficiently strong photon of sunlight hits the cell, it can knock an electron free. T he coatings on solar cells are specifically designed to ab sor b as much energy from the photons as they can. U sually around 15 to 20 percent of the sun's light can be transferred into electrical power when it hits the solar cell. T he rest is lost in heat and the uncertainty of the electron transference process. T he coating on the cell helps to ab sor b the light while a glass layer protects the cell, but the real work is done b y layers of the semiconductor.
Photovoltaic cells work on the atomic level. Light, naturally, is made of photons, which can act as both waves and particles and hold small amounts of energy. Remember: P hotons can either pass through objects or be reflected b y them. Reflected light is what we see, and what forms the colors that the human eye perceives. Ab sor bed light is what gives objects heat in the sunlight, and certain sub stances can ab sor b more heat than others--black objects, for example.
Two different kinds of semiconductors, a negatively charged and a positively charged version, are placed on top of one another, with a junction in the middle that acts as a barrier between the two parts. The sunlight strikes the solar cell, the top negative part of the semi-conductor, which causes its molecules to vibrate more and the electrons of its atoms to jump up energy levels and even leave their atoms to fill spaces in the opposite, positively-charged side of the cell. If a wire is place at contact points between the front and back of the cell, the electrons will flow through it to reach the other side, creating a flow of charge, or a current. This electric current can be used to charge batteries or power simple equipment.
satellites and spacecraft that could draw constant power fr om the sun, solar powered watches, clocks, traffic signs and water pumps ecologically friendly devices since they produce no noise or pollution B ENEFITS as a by-product No moving parts that need oil or chemical reactions that cause corrosion and so panels can last for decades without the need for repair. PV power plants provide an efficient investment as there is no cost to fuel them and limited maintenance. Note: Photovoltaic panels are mounted in areas where they receive maximum exposure to the sun such as on roofs, the tops of cars or others. U SES
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I MPACTS OF PV
Financial and economical effect: The more electricity a structure can draw from solar panels, the less it will take from the electrical grid; hence lowering the homes or business's power. Solar panels on cars can similarly lower or remove the vehicle owner's need to purchase gasoline, depending on how they are integrated into the vehicle's power train.
Effects on air pollution: As solar panels contribute electricity to an existing grid, the need for electricity generated from fossil fuel-burning plants diminishes. By reducing the use of coal-burning power plants, certain forms of air pollution such as the emission of greenhouse gas are also reduced. Air pollution from petroleum-based automobile emissions is also noteworthy, especially in large urban areas, and the application of solar technology in cars and other vehicles has the potential to reduce pollution in the air we breathe.
Conservation of natural resources: Fossil fuels find uses besides being burned for energy. One example of alternative petroleum use is in the production of polyester, a synthetic fabric that, along with cotton, makes up 80 percent of the clothing worn throughout the world. Petroleum is used in a number of other products, including clothing, plastics, building materials, solvents, lubricants, dyes, soda, synthetic rubber, synthesized vitamins and pharmaceuticals.
A ROUN D THE GLOBE : PV power plants are located across the world, the majority of which reside in Europe. There are two PV power plants, located in Spain, which have the capacity to produce 20 megawatts. Masdar, a government owned company in Abu Dhabi has plans for a 100 megawatt PV power plant as of January 2011. As investors see the viability of Photovoltaic power, new power plants are consistently coming up across the globe. A DVANCEMENT : Since 2007, PV power has been developed on a much larger scale. Rising fuel costs and reduced prices in technology have made PV power plants much more appealing to large investors. T he cost of PV power continues to decrease, making PV power more economically feasible than concentrated solar power. Advancements in technology have allowed PV power plants to use tracking systems that track and monitor the sun's movement for harnessing optimal amounts of energy. These systems generate more power than traditional fixed or mounted systems.
S OLAR-THERMAL TECHNOLOGIE S
S O LAR HEATING
Solar Water Heaters (SWH)-a way of harnessing the sun¶s free energy; designed to deliver hot water for most of the year; however, in winter there sometimes may not be sufficient solar heat gain to deliver sufficient hot water. In this case a gas or electric booster is normally used to heat the water. At its core, a solar water heater uses sunlight to heat water. The core of a solar water heater is a solar collector and a storage tank. A solar collector is basically a glazed, insulated box with a dark-colored interior and, usually, a bunch of tubes or passageways for water flow. (Glazing is a coat of material, typically glass that aids in heat retention.) The solar collector turns the sun's radiation into heat. A storage tank holds the water. Solar thermal collectors capture and retain heat from the sun and transfer this heat to liquid. Two types: non-concentrating and concentrating. Compare
Solar to Conventional Water Heater
SOLAR WATER HEATER: FREE energy from the Sun Annual operating cost: $50 Storage Capacity: 80-120 gal
STANDARD WATER HEATER: COSTLY gas or electric Annual operating cost: $500+ Storage Capacity: 40-50 gal
Life expectancy: 15-30 years
Life expectancy: 8-12 years
Lifetime operating cost: $1,000 Does NOT pollute environment
Lifetime operating cost: $10,000 Depletes fossil fuels
Increases equity in your home 25% return on your investment
No added value to your home No return on utility payments
Protection from future increases
At mercy of utilities/government
Hot water during blackouts!
No hot water during blackouts
There are two basic types of solar water heaters: passive or active. A passive heater uses nothing but forces of nature. An active heater uses electrical pumps and controls to move water around the system. Passive heaters: y
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or Integral collector-storage passive systems: It features one or more water tanks inside a solar collector (no tubes). The water warms up right inside the tank, and either gravity or natural convection (the tendency of hot water to rise) moves water from the tank to a home's pipes. Thermosyphon systems: Water flows through the tubes of a solar collector when warm water rises as cooler water sinks (natural convection). From the storage tank, the water travels into the home's water pipes. Batch
The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than integral collector-storage passive systems. Active systems typically fall into one of three cat egories: y
circulation systems: Water moves through the solar collectors and into a storage tank with the help of electrical pumps and controls. Direct
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Indirect circulation systems: Instead of heating water, the solar collectors heat a heat transfer fluid, such as antifreeze. The antifreeze then flows into the sealed piping of a heat exchanger, where it is surrounded by water. The water picks up the heat from the antifreeze (but never mixes with it), and is then pumped into a storage tank. Drainback : A drainback system is like the indirect system except that it uses distilled water as the heattransfer liquid, and it has a separate drainback tank for the distilled water. Pumping all of the heattransfer liquid out of the system and into an interior tank makes it ideal for colder climates, since the liquid isn't exposed to extremely cold weather. "
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Benefits: save money on electric bill SWH allows consumers to save money in the long run as the fuel source (the sun¶s energy) will always be free. corresponding reduction in pollution Conserving nonrenewable fuels for applications for which there are currently no easily available renewable energy sources. Solar water heaters work in every climate Today's SWH technologies can be operated efficiently and affordably in any climate. Systems are specifically designed for various climatic and geographical areas of the country. y
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Drawbacks: High installation cost and the payback period depends on where you live, how much hot water you use, and the cost of electricity. y
If having less sun that supposed to. Cloudy days combined with increased demand and are a problem for such systems. This is another reason why SWH always require a backup system such a gas or electric booster to heat the water. y
Some other concerns include: y
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Temperature: If you live in a very cold location, direct heater models (batch, thermosyphon and direct-active) might be unavailable to you due to the risk of freezing. Home orientation: To have an efficient setup, you need to have a mounting location with considerable sun exposure; city dwellings may not q ualify. Water quality: If your home's water is particularly hard or acidic, you may not be a candidate for an active system. Hard or acidic water can corrode water-circulation systems. Power requirements: Since active systems rely on electrically powered machinery, they won't work during a power outage. Building regulations: Some areas, like those prone to earthquakes, have strict weight limits for roofmounted equipment. A solar water heater might be too heavy
S YSTEM COST In sunny, warm locations, where freeze protection is not necessary, an ICS (batch type) solar water heater can be extremely cost effective. In higher latitudes, there are often additional design requirements for cold weather, which add to system complexity. This has the effect of increasing the initial cost (but not the life-cycle cost) of a solar water heating system, to a level much higher than a comparable hot water heater of the conventional type. C ONCENTRATING S OLAR-THERMAL TECHNOLOGY
In this technology, mirrors are used to concentrate sunlight onto devices that collect the energy to transform it into heat. That heat is then used to create steam, which in turn drives a turbine to produce electricity. It's similar to the way fossil fuel-burning power plants work except the steam is produced by the collected heat rather than from the combustion of fossil fuels. The main CSP technologies that are used today include thermal storage, linear concentrator, power tower and dish/engine systems.
The collectors used here are usually the non-concentrating ones: flat plate, batch collectors and evacuated tube batch (ETB) collector. y
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F lat plate collectors-are insulated, weatherproofed boxes that contain a dark absorber plate (that allows solar energy to pass through but reduces heat loss) under one or more glass or plastic (polymer) covers. They also feature a heat-transport fluid (air, antifreeze or water) to remove heat from the absorber. Unglazed flat-plate collectors²typically used for solar pool heating²have a dark absorber plate, made of metal or polymer, without a cover or enclosure. I ntegral collector-storage systems( ICS)or batch collectors- In a simple way one could consider an ICS solar water heater as a water tank that has been enclosed in a type of 'oven'(walls are thermally insulated)that retains heat from the sun as well as heat of the water in the tank. Using a box does not eliminate heat loss from the tank to the environment, but it largely reduces this loss. Evacuated T ube Batch ( ETB) collector - consists of parallel rows of evacuated glass tubes each tube containing a glass outer tube and metal absorber tube attached to a heat pipe.
The vacuum that surrounds the outside of the tube greatly reduces convection and conduction heat loss to the outside, therefore achieving greater efficiency than flat-plate collectors, especially in colder conditions. This advantage is largely lost in warmer climates, except in those cases where very hot water is desirable, for example commercial process water. The high temperatures that can occur may require special system design to avoid or mitigate overheating conditions. Life of the vacuum varies from collector to collector, anywhere from 5 years to 15 years. The calculation of long term cost and payback period for a household SWH system depends on a number of factors. Some of these are: y y y y y y y y y
Price of purchasing solar water heater (more complex systems are more expensive) Efficiency of SWH system purchased Installation cost State or government subsidy for installation of a solar water heater Price of electricity per kW.h Number of kW.h of electricity used per month by a household Annual tax rebates or subsidy for using renewable energy Annual maintenance cost of SWH system Savings in annual maintenenance of conventional (electric/gas/oil) water heating system
S olar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors.
Low-temperature collectors are flat plates generally used to heat swimming pools. Medium-temperature collectors are also usually flat plates but are used for heating water or air for residential and commercial use. (Solar heating) High-temperature collectors concentrate sunlight using mirrors or lenses and are generally used for electric power production (concentrating solar-thermal technology).
C O NCENTRATING S O LAR -THERMAL TECHNOLOGY In this technology, mirrors are used to concentrate sunlight onto devices that collect the energy to transform it into heat. That heat is then used to create steam, which in turn drives a turbine to produce electricity. The main CSP technologies that are used today include thermal storage, linear concentrator, power tower and dish/engine systems. Concentrating solar power plants generate electricity by using the energy from the Sun to heat a fluid, which produces steam used to drive a generator, which in turn creates electricity. Solar power towers are surrounded by a large array of thousands of parabolic mirrors that track the Sun's rays and reflect them to a heat receiver mounted on top of the tower. The central tower receiver then uses the high temperature generated to create steam for driving an electric generator facility at the base of the tower. Solar thermal troughs also generate electricity by creating steam. This system uses concave mirrors in a U-shape trough to focus the energy to a closed-system pipe at the focal point of the trough. The oil circulating through the pipe is heated and creates steam to drive a generator.
S O LAR HEATING
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reduce heat loss by placing the water tank in a thermally insulated box. This is achieved by encasing the water tank in a glass-topped box that allows heat from the sun to reach the water tank. However, the other walls of the box are thermally insulated, reducing convection as well as radiation to the environment. In addition, the box can also have a reflective surface on the inside. This reflects heat lost from the tank back towards the tank.
The heat from the hot end of the heat pipes is transferred to the transfer fluid (water) in a heat exchanger called a manifold . The manifold is wrapped in insulation and covered by a sheet metal or plastic case to protect it from the elements. "
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. In the non-concentrating type, the collector area (i.e. the area that intercepts the solar radiation) is the same as the absorber area (i.e., the area absorbing the radiation). In these types the whole solar panel absorbs the light. The concentrating ones are exclusively in solar power generating stations or for research purposes. Because of the world's changing climate and environmental problems, alternative to nonrenewable energy sources such as fossil fuels are being exploited. One of them in solar energy because it is non-polluting and so helps in lessening greenhouse gas emissions, is being studied. Solar energy can be used to heat buildings and generate electricity and light with minimal impact on the environment. Solar energy is an existing technology that will play a significant role in green energy revolution. Fossil fuels like coal contribute to the presence in the air of fine particulates that cause lung diseases such as asthma, emphysema or cancer. Coal plant emissions also contribute to greenhouse gas concentrations in the atmosphere.
