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Solar power (also known as '''solar energy''') is a source of power that uses energy from the Sun . The term solar energy is used more specifically to describe the utilization of this energy through human endeavor. It is a Renewable Energy source that has been used in many traditional technologies for centuries. It is also in widespread use where other power supplies are absent, such as in remote locations and in Space . The primary forms of solar energy are heat and light. Secondary forms and effects include Photosynthesis , wind, the Gulf Stream , the Hydrologic Cycle , Fossil Fuel s and Electricity . Solar energy has a long history going back to prehistoric times. Primitive architects incorporated windows to provide light. The Greeks, Native Americans and Chinese warmed their buildings by orienting them toward the sun. Medieval European farmers used Thermal Mass and elaborate field orientation to increase crop yields. In 1865, the French engineer Auguste Mouchout successfully powered a steam engine with Sunlight . This is the first known example of a solar powered mechanical device. Over the next 50 years inventors such as John Ericsson , Charles Tellier, Henry E. Willsie, Aubrey Eneas and Frank Shuman developed solar powered mechanical devices which were used for irrigation, refrigeration and electrical generation. In 1954, researchers at Bell Laboratories developed a solar cell capable of converting light into electricity via the photovoltaic effect. This breakthrough marked a fundamental change in how power is generated. Since then solar cells have progressed from early cells priced at $1500 per watt to modern cells which cost less than $3 per watt. The utilization of solar energy spans from traditional technologies that provide food, heat and light to electricity which is uniquely modern. The diversity of form and long history of solar energy are manifest in a wide variety of applications. These include:
ENERGY FROM THE SUN ]], at the top of Earth 's atmosphere (top) and at the surface on a Horizontal square meter.]] On a global scale Solar Radiation reaches the Earth's upper Atmosphere at a rate of 174 PW. While traveling through the atmosphere, 6% of the incoming solar radiation ( Insolation ) is Reflected and 16% is Absorbed .1 Average atmospheric conditions ( Cloud s, Dust , Pollutant s) further reduce insolation by 20% through reflection and 3% through absorption. Earth Radiation Budget The absorption of solar energy in the atmosphere is not a loss of available energy. This energy produces our climate through its capture within derivative effects such as the hydrologic cycle, wind and ocean currents. Atmospheric conditions not only reduce the quantity of insolation reaching the Earth's surface but also affect the quality of insolation by Diffusing incoming light and altering its Spectrum . After passing through the Earth's atmosphere approximately half the insolation is in the Visible Electromagnetic Spectrum with the other half mostly in the Infrared and ultraviolet spectrum.http://www.grida.no/climate/ipcc_tar/wg1/041.htm#121 The flows and stores of solar energy are very large relative to human needs.
The first map shows the average global irradiance calculated from satellite data collected from 1991 to 1993. For example, in . At present, Photovoltaic panels typically convert about 15% of incident sunlight into electricity; therefore, a solar panel in the contiguous United States on average delivers 19 to 56 W/m&2 or 0.45 - 1.35 kWh/m&2/day.3 The dark disks in the second map on the right are an example of the land areas that, if covered with 8% efficient solar panels, would produce slightly more energy in the form of electricity than the total world primary energy supply in 2003. International Energy Agency - Homepage While average insolation and power offer insight into solar power's potential on a regional scale, locally relevant conditions are of primary importance to the potential of a specific site. TYPES OF TECHNOLOGIES Many types of technology have been developed to make use of solar radiation. Some classifications of solar technology are active, passive, direct and indirect.
Architecture See Also: Passive solar building design Solar architecture is designed to use the sun as much as possible for temperature control, lighting and ventilation while minimizing negative effects such as overheating and glare. The basic elements of solar architecture are building orientation, proportion, thermal mass and window placement.
Lighting See Also: Daylighting Light tube Daylighting is a passive solar method of using natural light to provide illumination. Daylighting directly offsets energy use in electric lighting systems and indirectly offsets energy use through a reduction in cooling load. IEA - Daylighting HVAC Interaction (pg 85) Although difficult to quantify, the use of natural light also offers physiological and psychological benefits compared to conventional lighting. Daylighting features include building orientation, package which accounts for factors such as Glare , heat gain, heat loss and time-of-use. Architectural trends increasingly recognize daylighting as a cornerstone of Sustainable Design . Hybrid solar lighting (HSL) is an active solar method of using natural light to provide illumination. Hybrid solar lighting systems collect sunlight using focusing mirrors that track the sun. The collected light is transmitted via Optical Fiber s into a building's interior to supplement conventional lighting. ORNL - Solar Technologies Program Daylight Saving Time (DST) utilizes solar energy by matching available sunlight to the time of the day in which it is most useful. Water Heating , Israel ]] See Also: Solar hot water Solar combisystem Solar pond Solar Hot Water systems use sunlight to heat water. Commercial solar water heaters began appearing in the United States in the 1890s. These systems saw increasing use until the 1920s but were thereafter gradually replaced by relatively cheap and more reliable conventional heating fuels. The economic advantage of conventional heating fuels has varied over time resulting in periodic interest in solar hot water; however, solar hot water technologies have yet to show the sustained momentum they lost in the 1920s. That being said, the recent price spikes and erratic availability of conventional fuels is renewing interest in solar heating technologies within the US. Butti and John Perlin - A Golden Thread (2500 Years of Solar Architecture and Technology) Part III, Solar Water Heating - John Perlin - Solar Hot Water Heating As of 2005, the total installed capacity of solar hot water systems is 88 GWth and growth is 14% per year. China is the world leader in the deployment of solar hot water systems with 80% of the market. Israel is the per capita leader in the use of solar hot water with 90% of homes using this technology. - Solar Hot Water in China - Solar Water Heating.In the United States heating swimming pools is the most successful application of solar hot water.[http://www.californiasolarcenter.org/history_solarthermal.html - John Perlin - Solar Hot Water Heating On a technical level, solar water heating is highly efficient (up to 87%) and is particularly appropriate for low temperature (75-150F) applications such as domestic hot water, heating swimming pools and space heating. The basic components of a solar water heating systems are solar thermal collectors, a storage tank and a circulation loop. NREL - Solar Hot Water The three basic classifications of solar water heaters are:
Solar water heaters are also classified by the type of circulation loop used to transmit and deliver heat. These can be direct or indirect.
A Solar Pond is a pool of salt water that collects and stores solar energy. A basic solar pond has three layers of water: # A top layer with a low salt content. # An intermediate insulating layer with a medium salt content. # A bottom layer with a High Salt content. The salt gradient produces a . Solar pond at University of Texas El Paso Heating, Cooling and Ventilation See Also: Solar heating Thermal mass Trombe wall Solar chimney
Photovoltaics See Also: Photovoltaics Solar Cell s, also referred to as photovoltaic cells, are devices or banks of devices that use the Photovoltaic Effect of Semiconductor s to generate electricity directly from sunlight. Until recently, their use has been limited because of 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 Spacecraft . To take advantage of the incoming electromagnetic radiation from the sun, solar panels can be attached to each house or building. The panels should be mounted perpendicular to the arc of the sun to maximize usefulness. The easiest way to use this electricity is by connecting the solar panels to a Grid Tie Inverter . However, these solar panels may also be used to charge batteries or other Energy Storage Device . Solar panels produce more power during summer months because they receive more Sunlight . Total Peak Power of installed PV is around 6,000 MW as of the end of 2006. Installed PV is projected to increase to over 9,000 MW in 2007. Installed PV power Solar Wave - Apr-07 Merrill Lynch This is only one part of solar-generated electric power. Declining manufacturing costs (dropping at 3 to 5% a year in recent years) are expanding the range of cost-effective uses. The average lowest retail cost of a large 2006 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 - those systems that use an Inverter to connect to the Utility Grid instead of relying on batteries - now make up the largest part of the market. In 2003, worldwide production of solar cells increased by 32%. World Sales of Solar Cells Jump 32 Percent Viviana Jiménez, 2004 Earth Policy Institute. Retrieved 2006. Retrieved 4 September 2006. Solar Power Plants s for power conversion.]] See Also: Solar thermal energy Parabolic trough Solar power tower Solar updraft tower Energy tower (downdraft) Solar power plants use a variety of methods to collect sunlight and convert this energy into electricity, distill water or provide heat for industrial processes. Concentrating solar thermal power plants are the most common form of solar power plant. Concentrating Solar Thermal (CST) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. CST technologies require Direct Insolation to perform properly. This requirement makes them inappropriate for significantly overcast locations. DOE - Solar Basics The three basic CST technologies are the solar trough, solar power tower and parabolic dish. Each technology is capable of producing high temperatures and correspondingly high Thermodynamic Efficiencies but they vary in the way they track the sun and focus light.
A Solar Updraft Tower (also known as a solar chimney, but this term is avoided by many proponents due to its association with fossil fuels) is a relatively low-tech solar thermal power plant where air passes under a very large agricultural glass house (between 2 and 8 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. An Energy Tower is an alternative proposal to the solar updraft tower. It 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 wind turbines at the bottom of the tower. It requires a hot arid climate and large quantities of water (seawater may be used) but does not require the large glass house of the solar updraft tower. Cooking See Also: Solar cooker A Solar Box Cooker traps the sun's energy in an insulated box; such boxes 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 breathing environment for the community. The first known western solar oven is attributed to Horace De Saussure in 1767, which impressed Sir John Herschel enough to build one for cooking meals on his astronomical expedition to the Cape of Good Hope in Africa in 1830.5 Today, there are many different designs in use around the world.6 Solar chemical Solar Chemical is any process that harnesses solar energy by absorbing sunlight and using it to drive an Endothermic or Photoelectrochemical Chemical Reaction . Prototypes, but no large-scale systems, have been constructed. One approach has been to use conventional solar thermal collectors to drive chemical dissociation reactions. Ammonia can be separated into nitrogen and hydrogen at high temperature and with the aid of a catalyst, stored indefinitely, then recombined later to release the heat stored. A prototype system was constructed at the Australian National UniversityK. Lovegrove, A. Luzzi, I. Soldiani and H. Kreetz "Developing Ammonia Based Thermochemical Energy Storage for Dish Power Plants." Solar Energy, 2003. http://engnet.anu.edu.au/DEresearch/solarthermal/pages/pubs/SolarEAmmonia4.pdf or http://dx.doi.org/10.1016/j.solener.2003.07.020. Another approach is to use focused sunlight to provide the energy needed to split water via to drive the photoelectrolysis of water. Current materials also require an electrical voltage bias for the hydrogen and oxygen gas to evolve from the surface, another disadvantage. Current research is focusing on the development of materials capable of the same water splitting reaction using lower energy visible light. Solar thermal energy also has the potential to be used directly to drive Chemical Processes that require significant amounts of process heat, including at high temperatures that can be otherwise quite hard to attainJ Murray. ''Investigation of Opportunities for High-Temperature Solar Energy in the Aluminum Industry'', National Renewable Energy Laboratory report NREL/SR-550-39819 (USA).. Solar Vehicles Nuna team]] See Also: Helios Prototype Electric boat Solar balloon Development of a practical Solar Powered Car has been an engineering goal for 20 years. The center of this development is the World Solar Challenge , a biannual solar powered car race over 3021 km (1877mi) 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 winner's average speed was 67 2006. Helios, named after the Greek sun god of the same name, was a prototype solar powered Unmanned Aircraft . AeroVironment, Inc. developed the vehicle under NASA's Environmental Research Aircraft And Sensor Technology (ERAST) program. On 13 August, 2001 , it set an unofficial World Record for sustained Altitude by a Wing ed Aircraft . It sustained flight at above 96,000 feet (29,250 m) for forty minutes, and at one time it flew as high as 96,863 feet (29,524 m). Later, in June 2003 , the prototype broke up and fell into the Pacific Ocean about ten Mile s (16 km) West of the Hawaiian Island Kauai . Helios is a forerunner of what some call artificial "atmospheric satellites". NASA claimed such atmospheric satellites might someday replace conventional Artificial Satellite s. The first practical solar boat was probably constructed in 1975 in England (see Electrical Review Vol 201 No 7 12 August 1977). By 1995 passenger boats began appearing and are now used extensively. Solar powered boats have advanced sufficiently to cross the Atlantic. The first crossing crossing of the Atlantic Ocean was achieved in the winter of 2006/2007 by the solar catamaran sun21.[http://www.transatlantic21.org With the present state of technology, many believe the time is right for the increased use of solar boats. A Solar Balloon is a black balloon that is filled with air. As sunlight shines on the balloon the air inside is heated. As the air is heated it expands reducing the density of the air inside the balloon relative the the air surrounding the balloon. As such, the balloon functions like a hot air balloon. Usage at the moment is restricted to the toy market, although it has been proposed that it be used in the investigation of planet Mars. Some solar balloons are large enough for human flight. Solar desalination See Also: desalination This technique uses solar energy to evaporate sea water. The Humid air is then condensed and Desalinated water is collected. ADVANTAGES
DISADVANTAGES
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, increasing the total 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. However, since the grid always has a positive outflow, the result is exactly the same. Electric power costs are highly dependent on the consumption per time of day, since plants must be built for peak power (not average power). Expensive gas-fired "peaking generators" must be used when base capacity is insufficient. Fortunately for solar, solar capacity parallels energy demand; since much of the electricity is for removing heat produced by too much solar energy (using conditioners). This is less true in the winter when the peak energy use is in the early evening when food is being prepared and lighting, heating, and entertainment equipment loads are higher. Winter heating loads can be time shifted by storing thermal energy in bulk materials such as rock, water, or thermal phase transition materials such as Glauber's Salt or Wax , provided solar illumination is sufficient. Wind Power complements solar power since it can produce energy when there is no sunlight but this advantage is highly dependant upon local and seasonal wind availability. DEPLOYMENT OF SOLAR POWER See Also: Deployment of solar power to energy grids "The Stone Age did not end for a lack of stones, and the oil age will end not for a lack of oil." — Sheik Yamani, Saudi oil minister, 1973 "We stopped using stone because bronze and iron were superior materials, and likewise we will stop using oil when other energy technologies provide superior benefits." — Bjørn Lomborg, The Skeptical Environmentalist (New York: Cambridge University Press, 2001), p. 120 Technology Roadmaps Deployment of solar power depends largely upon local conditions and requirements. All industrialised nations share a need for electricity and it is believed that solar power will increasingly be used as an option for electricity supply. The Very Large Scale Photovoltaic Power Generation (VLS-PV) proposal argues that "PV systems could generate many times the current primary global energy supply". Summary Energy from the Desert To compensate for night time energy demands they would need to be complemented with Pumped Storage . SOLAR POWER BY COUNTRY See the articles for individual countries listed at SEE ALSO
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