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The term solar power is used to describe a number of methods of harnessing Energy from the light of the Sun . It has been present in many traditional building methods for centuries, but has become of increasing interest in developed countries as the environmental costs and limited supply of other power sources such as Fossil Fuels are realized. It is already in widespread use where other power supplies are absent, such as in remote locations and in space. ENERGY FROM THE SUN The rate at which /m&2/day. {Link without Title} It should be noted that this is the Maximum available power, and not the Power delivered by solar power technology. For example photovoltaic panels currently have an efficiency of ca. 15% and, hence, a solar panel delivers 19 to 56 W/m&2 or 0.45-1.35 kWh/m&2/day (annual day and night average). The dark disks in the image on the right are an example for the land areas that, if covered with solar panels, would produce slightly more energy in the form of electricity than the total primary energy supply in 2003. {Link without Title} That is, solar cells with an assumed 8% efficiency installed in these areas would deliver a bit more energy in the form of electricity than what is currently available from oil, gas, hydropower, nuclear power, etc. combined. It should also be noted that a recent concern is that of Global Dimming , an effect of pollution that is allowing less and less sunlight to reach the earths surface. It is intricately linked with pollution particles and Global Warming , and is mostly of concern for issues of Global Climate Change , but is also of concern to proponents of Solar Power due to the existing and potential future decreases in available Solar Energy. The order of magnitude is about 10% less solar energy available at sea level, mostly due to more intense cloud reflections back into outer space (i.e. the clouds are whiter, brighter) because of the higher light scatter caused by smaller particle size water droplets that making them up, or would simply not even form in the first place but instead leave a clear sky in the absence of particluate pollution serving as gas-liquid phase change initiation, (i.e. droplet forming) sites. After passing through the Earth's atmosphere, most of the sun's energy is in the form of Visible and Infrared radiations. Plants use solar energy to create chemical energy through Photosynthesis . Humans regularly use this energy burning wood or Fossil Fuel s, or when simply Eating the plants. CLASSIFICATION A wide range of power technologies exist which can make use of the solar energy reaching Earth. These can be classified in a number of different ways. Method of energy transformation Solar energy can be transformed for use elsewhere or utilised directly. Direct solar power involves only one transformation into a usable form. For example:
Indirect solar power involves more than one transformation to reach a usable form. Many other types of power generation are indirectly solar-powered. Some of these are so indirect that they are often excluded from discussion of solar power:
Complexity of mechanism Solar power can also be classified as passive or active:
Focus type Effective use of solar radiation often requires the radiation (light) to be focused to give a higher intensity beam. Consequently, another scheme for classifying solar power systems is:
ADVANTAGES AND DISADVANTAGES OF SOLAR POWER Advantages
Disadvantages Solar power at the Earth's surface, has an number of disadvantages which must be addressed as engineering problems to make it an effective source of energy supply:
TYPES OF TECHNOLOGIES Most solar energy used today is harnessed as heat or electricity. Solar design in architecture Solar Design is the use of Architectural features to replace the use of grid electricity and Fossil Fuels with the use of solar energy and decrease the energy needed in a home or building with insulation and efficient lighting and appliances. Architectural features used in solar design:
Solar heating systems Solar Heating systems are generally composed of solar thermal collectors, a fluid system to move the heat from the collector to its point of usage, and a reservoir to stock the heat for subsequent use. The systems may be used to heat domestic hot water or a swimming pool, or to provide heat for a heating circuit (usually radiators or floor heating coils). The heat can also be used for industrial applications or as an energy input for other uses such as cooling equipment. In many climates, a solar heating system can provide a very high percentage (50 to 75%) of domestic hot water energy. In many northern European countries, combined hot water and space heating systems are used to provide 15 to 25% of home heating energy. Residential solar thermal installations can be subdivided in two kind of systems: compact and pumped systems. Both typically include an auxiliary energy source (electric heating element or connection to a gas or fuel oil central heating system) that is activated when the water in the tank falls below a minimum temperature setting such as 50 ° C . Hence, hot water is always available. Compact systems Also known as a ''monobloc'' system, a compact system consists of a tank for the heated water, a solar collector, and connecting pipes all pre-mounted in a frame. Based on the Thermosiphon principle, the water flows upwards when heated in the panel. When this water enters the tank (positioned higher than the solar panel), it expels some cold water from inside so that the heat transfer takes place without the need for a pump. A typical system for a four-person home in a sunny region consists of a tank of 150 to 300 Liter s and three to four square meters of solar collector panels. ''Direct'' compact systems are not suitable for cold climates. At night the remaining water can freeze and damage the panels, and the storage tank is exposed to the outdoor temperatures that will cause excessive heat losses on cold days. Some compact systems have a ''primary circuit''. The primary circuit includes the collectors and the external part of the tank. Instead of water, a non-toxic antifreezing liquid is used. When this liquid is heated up, it flows to the external part of the tank and transfers the heat to the water placed inside. However, direct systems are slightly cheaper and more efficient. A compact system can save up to 4.5 Tonne s annually of gas emissions. In order to achieve the aims of the Kyoto Protocol , several countries are offering subsidies to the end user. Some systems can work for up to 25 years with minimum maintenance. These kinds of systems can be redeemed in six years, and achieve a positive balance of energy (energy used to build them minus energy they save) of 1.5 years. Most part of the year, when the electric heating element is not working, these systems do not use any external source for power (as water flows due to thermosyphon principle). Flat Solar Thermal Collector s are usually used, but compact systems using vacuum tube collectors are available on the market. These generally give a higher heat yield per square meter but also cost more than flat collector systems. Pumped systems Systems using a circulation pump are used whenever the hot water tank is positioned below the solar panels. Most systems in northern Europe are of this type. The storage tank is placed inside the building, and thus requires a controller that measures when the water is hotter in the panels than in the tank. The system also requires a pump for transferring the fluid between the parts. The electronic controllers used by these systems permit a wide range of functionality such as measurement of the energy produced; more sophisticated safety functions; thermostatic and time-clock control of auxiliary heat, hot water circulation loops, or others; display or transfer of error messages or alarms; remote display panels; and remote or local datalogging The most commonly used solar collector is the insulated glazed flat panel. Less expensive panels, like polypropylene panels (for swimming pools) or higher-performing ones like Vacuum Tube collectors, are sometimes used. Solar heating thermal collectors There are three main kinds of solar thermal collectors in common use. ''Formed Plastic Collectors (such as polypropylene, EPDM or PET plastics)'' consist of tubes or formed panels through which water is circulated and heated by the sun's radiation. Used for extending the swimming season in swimming pools. In some countries heating an open-air swimming pool with non-renewable energy sources is not allowed, and then these inexpensive systems offer a good solution. This panel is not suitable for year round uses like providing hot water for home use, primarily due to its lack of insulation which reduces its effectiveness greatly when the ambient air temperature is lower than the temperature of the fluid being heated. A ''flat collector'' consists of a thin absorber sheet (usually copper, to which a selective coating is applied) backed by a grid or coil of fluid tubing and placed in an insulated casing with a glass cover. Fluid is circulated through the tubing to remove the heat from the absorber and transport it to an insulated water tank, to a heat exchanger, or to some other device for using the heated fluid. Flat-plate collectors for solar water heating were popular in Florida and Southern California in the 1920s. There was a flicker of resurgence of interest in them in North America in the 1970s. However, the main improvements now are occurring in other countries which have enabled effective use of solar heating in both private houses and large scale installations. Technical innovation has improved performance, life expectancy and ease of use of these systems, with Germany/Austria the clear leaders. Installation of solar hot water heating has become the norm in countries such as Israel and Greece, where there is an abundance of solar radiation, and Japan and Austria where there is considerably less. ''Evacuated tube collectors'' are made of a series of modular tubes, mounted in parallel, whose number can be added to or reduced as hot water delivery needs change. This type of collector consists of rows of parallel transparent glass tubes, each of which contains an absorber tube (in place of the absorber plate to which metal tubes are attached in a flat-plate collector). The tubes are covered with a special light-modulating coating. In an evacuated tube collector, sunlight passing through an outer glass tube heats the absorber tube contained within it. Two types of tube collectors are distinguished by their heat transfer method: the simplest pumps a heat transfer fluid (water or antifreeze) through a U-shaped copper tube placed in each of the glass collector tubes. The second type uses a sealed heat pipe that contains a liquid that vaporizes as it is heated. The vapor rises to a heat-transfer bulb that is positioned outside the collector tube in a pipe through which a second heat transfer liquid (the water or antifreeze) is pumped. For both types, the heated liquid then circulates through a heat exchanger and gives off its heat to water that is stored in a storage tank (which itself may be kept warm partially by sunlight). Evacuated tube collectors heat to higher temperatures, with some models providing considerably more solar yield per square meter than flat panels. However, they are more expensive and fragile than flat panels. Solar thermal cooling There are some new applications of thermal hot water, such as air cooling, currently under development. The absorber machine works like a refrigerator — it uses hot water to compress a gas that, once expanded, will produce an Endothermic Reaction , which cools the air. The main problem currently is that the absorber machine works with liquid at 90 °C, a fairly high temperature to be reached with pumped solar panels with no auxiliary power supply. The same pumped solar thermal installation can be used for producing hot water for the whole year. It can also be used for cooling in the summer and partially heating the building in winter. Photovoltaic cells Solar Cell s, also referred to as photovoltaic cells, are devices or banks of devices that use the Photovoltaic Effect of Semiconductors to generate electricity directly from sunlight. Until recently, their use has been limited due to high manufacturing costs. One cost effective use has been in very low-power devices such as Calculator s with LCD s. Another use has been in remote applications such as roadside emergency telephones, remote sensing, Cathodic Protection of pipe lines, and limited "off grid" home power applications. A third use has been in powering orbiting Satellite s and other Spacecraft . However, the continual decline of manufacturing costs (dropping at 3 to 5% a year in recent years) is expanding the range of cost-effective uses. The average lowest retail cost of a large solar panel declined from $7.50 to $4 per watt between 1990 and 2005 . With many jurisdictions now giving tax and rebate incentives, solar electric power can now pay for itself in five to ten years in many places. "Grid-connected" systems - that is, systems with no battery that connect to the Utility Grid through a special inverter - now make up the largest part of the market. In 2004 the worldwide production of solar cells increased by 60%. 2005 is expected to see large growth again, but shortages of refined Silicon have been hampering production worldwide since late 2004. Solar thermal electric power plants The two main types of solar thermal power plants are Solar Chimneys and Concentrating Solar Power (CSP) plants. Concentrated Solar Power (CSP) Plants
Solar chimney A Solar Chimney is a relatively low tech solar thermal power plant where air passes under a very large agricultural glass house (between 2 and 30 km in diameter), is heated by the sun and channeled upwards towards a convection tower. It then rises naturally and is used to drive turbines, which generate electricity. Energy Tower An Energy Tower is an alternative proposal for the Solar Chimney . The "Energy Tower" is driven by spraying water at the top of the tower; evaporation of water causes a downdraft by cooling the air thereby increasing its density, driving windturbines at the bottom of the tower. It requires a hot arid climate and large quantities of water, but it does not require a large glass house Solar pond A Solar Pond is a relatively low-tech, low cost approach to harvesting solar energy. The principle is to fill a pond with 3 layers of water: #A top layer with a low salt content #An intermediate insulating layer with a salt gradient, which sets up a density gradient that prevents heat exchange by natural Convection in the water. #A bottom layer has with a High Salt content which reaches a temperature approaching 90 degrees Celsius. The heat trapped in the salty bottom layer can be used for different purposes, such as heating of buildings, industrial processes, or generating electricity. Solar chemical Solar Chemical refers to a number of possible processes that harness solar energy by absorbing sunlight in a Chemical Reaction in a way similar to Photosynthesis in plants but without using living organisms. No practical process has yet emerged. A promising approach is to use focused sunlight to provide the energy needed to split water into its constituent Hydrogen and Oxygen in the presence of a metallic catalyst such as Zinc . {Link without Title} {Link without Title} {Link without Title} It is also possible to use solar energy to drive industrial chemical processes without a requirement for fossil fuel. Phytochemical energy storage (Biofuels) ''See Biofuels and Biodiesel '' The oil in plant Seeds , in chemical terms, very closely resembles that of petroleum. Many, since the invention of the Diesel engine, have been using this form of captured solar energy as a fuel comparable to petrodiesel - for functional use in any diesel engine or generator and known as Biodiesel . A 1998 joint study by the U.S. Department of Energy (DOE) and the U.S. Department of Agriculture (USDA) traced many of the various costs involved in the production of biodiesel and found that overall, it yields 3.2 units of fuel product energy for every unit of fossil fuel energy consumed. {Link without Title} Other Biofuels include ethanol, wood for stoves, ovens and furnaces, and methane gas produced from biofuels through chemical processes. Solar cooking A Solar Box Cooker traps the Sun's power in an insulated box; these have been successfully used for cooking, Pasteurization and fruit canning. Solar cooking is helping many developing countries, both reducing the demands for local firewood and maintaining a cleaner environment for the cooks. The first known western solar oven is attributed to Horace De Saussure . Solar lighting The interior of a building can be lit during daylight hours using Fibre Optic Light Pipe s connected to a parabolic collector mounted on the roof. The manufacturer claims this gives a more natural interior light and can be used to reduce the energy demands of electric lighting. {Link without Title} ENERGY STORAGE See Also: Grid energy storage For a stand-alone system, some means must be employed to store the collected energy for use during hours of darkness or cloud cover. The following list includes both mature and immature techniques:
Storage always has an extra stage of energy conversion, with consequent energy losses, greatly increasing capital costs. One way around this is to export excess power to the power grid, drawing it back when needed. This appears to use the power grid as a battery but in fact is relying on conventional energy production through the grid during the night. DEPLOYMENT OF SOLAR POWER TO ENERGY GRIDS Deployment of solar power depends largely upon local conditions and requirements. But as all industrialised nations share a need for electricity, it is clear that solar power will increasingly be used to supply a cheap, reliable electricity supply. Several experimental photovoltaic (PV) power plants of 300 to 600 kW capacity are connected to electricity grids in Europe and the U.S. Other major research is investigating economic ways to store the energy which is collected from the sun's rays during the day. Africa Africa is home to the over 9 million km&2 Sahara desert, whose overall capacity — assuming 50 MW/km&2 day/night/cloud average with 15% efficient photovoltaic panels — is over 450 TW, or over 4 million terawatt-hours per year. The current global energy consumption by humans, including all oil, natural gas, coal, nuclear, and hydroelectric, is pegged at about 13 TW. Australia Australia has one solar power station, at White Cliffs , New South Wales . It has fourteen three-metre parabolic dishes which each focus on a cluster of 16 water-cooled photovoltaic cells and delivers up to 45kWe in total to the grid. Asia As of 2004, Japan had 1200 MWe installed. Japan currently consumes about half of worldwide production of solar modules, mostly for grid connected residential applications. In terms of overall installed PV capacity, per year (i.e. 600 GW), far more than its current total consumption. In 2005, the Israeli government announced an international contract for building a 100 MW solar power plant to supply the electricity needs of more than 200,000 Israelis living in southern Israel. The plan may eventually allow the creation of a gigantic 500 MW power plant, making Israel a leader in solar power production. {Link without Title} Europe The 10 megawatt Bavaria Solarpark in Germany is the world's largest solar electric system, covering 25 hectares (62 acres) with 57,600 photovoltaic panels. {Link without Title} A large solar PV plant is planned for the island of Crete . Research continues into ways to make the actual solar collecting cells less expensive and more efficient. at Odeillo , French Cerdagne ]] A large parabolic reflector in Austria . The Plataforma Solar de Almería (PSA) in Spain , part of the Center for Energy, Environment and Technological Research (CIEMAT), is the largest center for research, development, and testing of concentrating solar technologies in Europe. {Link without Title} In the United Kingdom , the tallest building in Manchester , the CIS Tower, was clad in photovoltaic panels at a cost of £ 5.5 million and started feeding electricity to the national grid on November 2005. {Link without Title} On April 27, 2006, GE Energy Financial Services, PowerLight Corporation and Catavento Lda announced that they will build the world’s largest solar photovoltaic power project. The 11-megawatt solar power plant, comprising 52,000 photovoltaic modules, will be built at a single site in Serpa , Portugal, 200 kilometers (124 miles) southeast of Lisbon in one of Europe’s sunniest areas. {Link without Title} North America in California supplements water heating with Solar Panel s on the roof.]] In some areas of the United States, solar electric systems are already competitive with utility systems. As of 2005, there is a list of technical conditions that factor into the economic feasibility of going solar: the amount of sunlight that the area receives; the purchase cost of the system; the ability of the system owner to sell power back to the electric grid; and most important, the competing power prices from the local utility. For example, a photovoltaic system installed in Boston, Massachusetts , produces 25% less electricity than it would in Albuquerque, New Mexico , but yields roughly the same savings on utility bills since electricity costs more in Boston. In addition to these considerations, many states and regions offer substantial incentives to improve the economics for potential consumers. Congress recently adopted the first federal tax breaks for residential solar since 1985 -- temporary credits available for systems installed in 2006 or 2007. Homeowners can claim one federal credit of up to $2,000 to cover 30% of a photovoltaic system's cost and another 30% credit of up to $2,000 for a solar thermal system. Fifteen states also offer tax breaks for solar, and two dozen states offer direct consumer rebates. {Link without Title} Solar One is a pilot solar-thermal project in the Mojave Desert near Barstow, California .It uses heliostats, and molten salts storage technology, to achieve longer periods of power generation. Solar Two , also near Barstow, has now built and elaborated on the success of Solar One. It was an R&D project in Barstow, California, financed by the US federal Department of Energy. Solar Two used liquid salts as a storage medium in order to continue to provide energy for much of the time when sunlight is not available. Its success has lead to the larger Solar Tres project in Spain. On August 11 , 2005 , Southern California Edison announced an agreement to purchase solar powered Stirling Engine s from Stirling Energy Systems over a twenty year period and in quantities (20,000 units) sufficient to generate 500 megawatts of electricity. These systems — to be installed on a 4,500 acre (18 km&2) solar farm — will use mirrors to direct and concentrate sunlight onto the engines which will drive generators. Less than a month later, Stirling Energy Systems announced another agreement with San Diego Gas & Electric to provide between 300 and 900 megawatts of electricity.[http://www.stirlingenergy.com/breaking_news.htm The world's largest solar power plant is located in the s (4 km&2) of solar reflectors. This plant produces 90% of the world's commercially produced solar power. On January 12 , 2006 , the California Public Utilities Commission approved the California Solar Incentive Program , a comprehensive $2.8 billion program that provides incentives toward solar development over 11 years. DEPLOYMENT OF SOLAR POWER IN TRANSPORT Development of a practical Solar Powered Car has been an engineering goal for twenty years. The centre of this development is the World Solar Challenge , a biannual solar powered car race over 3021 km through central Australia from Darwin to Adelaide . The race's stated objective is to promote research into solar-powered cars. Teams from universities and enterprises participate. In 1987 when it was founded the winners average speed was 67 Km/h . By the 2005 race this had increased to a record average speed of 103 km/h. WORLD SOLAR POWER PRODUCTION Total peak power of installed solar panels is around 5,300 MW as of the end of 2005. (IEA statistics appear to be underreported: they report 2,600 MW as of 2004, which with 1,700 installed in 2005 would be a cumulative total of 4,300 for 2005). Large PV power plants SEE ALSO REFERENCES EXTERNAL LINKS
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