Solar Power

Solar power is the conversion of sunlight into electricity. Sunlight can be converted directly into electricity using photovoltaics (PV), or indirectly with concentrated solar power (CSP), which normally focuses the sun's energy to boil water which is then used to provide power. Other technologies also exist, such as Stirling engine dishes which use a Stirling cycle engine to power a generator. Photovoltaics were initially, and still are, used to power small and medium-sized applications, from the calculator powered by a single solar cell to off-grid homes powered by a photovoltaic array. They are an important and relatively inexpensive source of electrical energy where grid power is inconvenient, unreasonably expensive to connect, or simply unavailable.
Concentrating solar power
Further information: Solar thermal energy and Concentrated solar power
Concentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated heat is then used as a heat source for a conventional power plant. A wide range of concentrating technologies exists: the most developed are the parabolic trough [discuss], the concentrating linear fresnel reflector, the Stirling dish and the solar power tower. Various techniques are used to track the sun and focus light. In all of these systems a working fluid is heated by the concentrated sunlight, and is then used for power generation or energy storage.[2] Thermal storage efficiently allows up to 24 hour electricity generation.[3]

A diagram of a parabolic trough solar farm (top), and an end view of how a parabolic collector focuses sunlight onto its focal point.
A parabolic trough consists of a linear parabolic reflector that concentrates light onto a receiver positioned along the reflector's focal line. The receiver is a tube positioned right above the middle of the parabolic mirror and is filled with a working fluid. The reflector is made to follow the sun during daylight hours by tracking along a single axis. Parabolic trough systems provide the best land-use factor of any solar technology.[4] The SEGS plants in California and Acciona's Nevada Solar One near Boulder City, Nevada are representatives of this technology.[5][6] Compact Linear Fresnel Reflectors are CSP-plants which use many thin mirror strips instead of parabolic mirrors to concentrate sunlight onto two tubes with working fluid. This has the advantage that flat mirrors can be used which are much cheaper than parabolic mirrors, and that more reflectors can be placed in the same amount of space, allowing more of the available sunlight to be used. Concentrating linear fresnel reflectors can be used in either large or more compact plants.[7][8]
The Stirling solar dish combines a parabolic concentrating dish with a Stirling engine which normally drives an electric generator. The advantages of Stirling solar over photovoltaic cells are higher efficiency of converting sunlight into electricity and longer lifetime. Parabolic dish systems give the highest efficiency among CSP technologies.[9] The 50 kW Big Dish in Canberra, Australia is an example of this technology.[5]
A solar power tower uses an array of tracking reflectors (heliostats) to concentrate light on a central receiver atop a tower. Power towers are more cost effective, offer higher efficiency and better energy storage capability among CSP technologies.[5] The PS10 Solar Power Plant and PS20 solar power plant are examples of this technology.
Photovoltaics
Main article: Photovoltaics

The 71.8 MW Lieberose Photovoltaic Park in Germany.
A solar cell, or photovoltaic cell (PV), is a device that converts light into electric current using the photoelectric effect. The first solar cell was constructed by Charles Fritts in the 1880s.[10] The German industrialist Ernst Werner von Siemens was among those who recognized the importance of this discovery.[11] In 1931, the German engineer Bruno Lange developed a photo cell using silver selenide in place of copper oxide,[12] although the prototype selenium cells converted less than 1% of incident light into electricity. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954.[13] These early solar cells cost 286 USD/watt and reached efficiencies of 4.5–6%.[14]
Photovoltaic power systems
Main article: Photovoltaic system

Simplified schematics of a grid-connected residential PV power system[15]
Solar cells produce direct current (DC) power which fluctuates with the sunlight's intensity. For practical use this usually requires conversion to certain desired voltages or alternating current (AC), through the use of inverters.[15] Multiple solar cells are connected inside modules. Modules are wired together to form arrays, then tied to an inverter, which produces power at the desired voltage, and for AC, the desired frequency/phase.[15]
Many residential systems are connected to the grid wherever available, especially in developed countries with large markets.[16] In these grid-connected PV systems, use of energy storage is optional. In certain applications such as satellites, lighthouses, or in developing countries, batteries or additional power generators are often added as back-ups. Such stand-alone power systems permit operations at night and at other times of limited sunlight.
Development and deployment
Main article: Solar power by country

Nellis Solar Power Plant, 14 MW power plant installed 2007 in Nevada, USA
The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. However, development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal and petroleum.[17] In 1974 it was estimated that only six private homes in all of North America were entirely heated or cooled by functional solar power systems.[18] The 1973 oil embargo and 1979 energy crisis caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies.[19][20] Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan. Other efforts included the formation of research facilities in the US (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer Institute for Solar Energy Systems ISE).[21]
Between 1970 and 1983 photovoltaic installations grew rapidly, but falling oil prices in the early 1980s moderated the growth of PV from 1984 to 1996. Since 1997, PV development has accelerated due to supply issues with oil and natural gas, global warming concerns, and the improving economic position of PV relative to other energy technologies.[22] Photovoltaic production growth has averaged 40% per year since 2000 and installed capacity reached 39.8 GW at the end of 2010,[23] of them 17.4 GW in Germany. As of October 2011, the largest photovoltaic (PV) power plants in the world are the Sarnia Photovoltaic Power Plant (Canada, 97 MW), Montalto di Castro Photovoltaic Power Station (Italy, 84.2 MW) and Finsterwalde Solar Park (Germany, 80.7 MW).[24]
There are also many large plants under construction. The Desert Sunlight Solar Farm is a 550 MW solar power plant under construction in Riverside County, California, that will use thin-film solar photovoltaic modules made by First Solar.[25] The Topaz Solar Farm is a 550 MW photovoltaic power plant, being built in San Luis Obispo County, California.[26] The Blythe Solar Power Project is a 500 MW photovoltaic station under construction in Riverside County, California. The Agua Caliente Solar Project is a 290 megawatt photovoltaic solar generating facility being built in Yuma County, Arizona. The California Valley Solar Ranch (CVSR) is a 250 megawatt (MW) solar photovoltaic power plant, which is being built by SunPower in the Carrizo Plain, northeast of California Valley.[27] The 230 MW Antelope Valley Solar Ranch is a First Solar photovoltaic project which is under construction in the Antelope Valley area of the Western Mojave Desert, and due to be completed in 2013.[28] Electricity Generation from Solar[29] | Year | Energy (TWh) | % of Total | 2005 | 3.7 | 0.02% | 2006 | 5.0 | 0.03% | 2007 | 6.7 | 0.03% | 2008 | 11.2 | 0.06% | 2009 | 19.1 | 0.09% | 2010 | 30.4 | 0.14% | 2011 | 58.7 | 0.27% | 2012 | 93.0 | 0.41% |
Photovoltaic power stations
Main article: List of photovoltaic power stations World's largest photovoltaic power stations (50 MW or larger)[24] | PV power station | Country | DC peak power
(MWp) | Notes | Agua Caliente Solar Project[30] | USA | 7002250000000000000 250 AC | 397 MW when complete | Charanka Solar Park[31][32] | India | 221 | Completed 2012 | Golmud Solar Park[24][33][34][35] | China | 200 | Completed 2011 | Mesquite Solar project | USA | 7002150000000000000150 | up to 700 MW when complete | Neuhardenberg Solar Park[24][36] | Germany | 7002145000000000000145 | Completed September 2012. A group of 11 co-located plant by the same developer[37] but with different IPPs | Templin Solar Park[24][38] | Germany | 7002128470000099999128.48 | Completed September 2012 | Toul-Rosières Solar Park[39] | France | 7002115000000000000115 | Completed November 2012 | Perovo Solar Park[40] | Ukraine | 100 | Completed 2011 | Sarnia Photovoltaic Power Plant[41] | Canada | 97[24] | Constructed 2009–2010[42] | Montalto di Castro Photovoltaic Power Station[24] | Italy | 84.2 | Constructed 2009–2010 | Finsterwalde Solar Park[43][44] | Germany | 80.7 | Phase I completed 2009, phase II and III 2010 | Okhotnykovo Solar Park | Ukraine | 80 | Completed 2011 | Solarpark Senftenberg[24][45] | Germany | 78 | Phase II and III completed 2011, another 70 MW phase planned | Lieberose Photovoltaic Park [46][47] | Germany | 71.8 | | Rovigo Photovoltaic Power Plant[48][49] | Italy | 70 | Completed November 2010 | Olmedilla Photovoltaic Park | Spain | 60 | Completed September 2008 | Strasskirchen Solar Park | Germany | 54 | | Puertollano Photovoltaic Park | Spain | 50 | opened 2008 |
Concentrating solar thermal power
Main article: List of solar thermal power stations
Commercial concentrating solar thermal power (CSP) plants were first developed in the 1980s. The 354 MW SEGS CSP installation is the largest solar power plant in the world, located in the Mojave Desert of California. Other large CSP plants include the Solnova Solar Power Station (150 MW), the Andasol solar power station (150 MW), and Extresol Solar Power Station (100 MW), all in Spain. The 370 MW Ivanpah Solar Power Facility, located in California's Mojave Desert, is the world’s largest solar thermal power plant project currently under construction.
The principle advantage of CSP is the ability to efficiently add thermal storage, allowing the dispatching of electricity over up to a 24-hour period. Since peak electricity demand typically occurs at about 5 pm, many CSP power plants use 3 to 5 hours of thermal storage.[50] Largest operational solar thermal power stations | Capacity
(MW) | Name | Country | Location | Notes | 354 | Solar Energy Generating Systems | USA | Mojave Desert California | Collection of 9 units | 150 | Solnova Solar Power Station | Spain | Seville | Completed 2010
[51][52][53] | 150 | Andasol solar power station | Spain | Granada | completed 2011, with 7.5h thermal energy storage[54][55] | 150 | Extresol Solar Power Station | Spain | Torre de Miguel Sesmero | Extresol 1 completed February 2010
Extresol 2 completed December 2010
Extresol 3 completed August 2012, with 7.5h thermal energy storage[56][57][58] | 100 | Palma del Rio Solar Power Station | Spain | Palma del Río | Palma del Rio 2 completed December 2010[56]
Palma del Rio 1 completed July 2011[56] | 100 | Manchasol Power Station | Spain | Alcázar de San Juan | Manchasol-1 completed January 2011, with 7.5h heat storage[56]
Manchasol-2 completed April 2011, with 7.5h heat storage[56] | 100 | Valle Solar Power Station | Spain | San José del Valle | Completed December 2011, with 7.5h heat storage[56][59] | 100 | Helioenergy Solar Power Station | Spain | Écija | Helioenergy 1 completed September 2011[60][61]
Helioenergy 2 completed January 2012[56][60][61] | 100 | Aste Solar Power Station | Spain | Alcázar de San Juan | Aste 1A Completed January 2012, with 8h heat storage[56]
Aste 1B Completed January 2012, with 8h heat storage[56] | 100 | Solacor Solar Power Station | Spain | El Carpio | Solacor 1 completed February 2012[56]
Solacor 2 completed March 2012[56][62] | 100 | Solaben Solar Power Station[63] | Spain | Logrosán | Solaben 3 completed June 2012[56]
Solaben 2 completed October 2012[56] | 100 | Helios Solar Power Station | Spain | Puerto Lápice | Helios 1 completed May 2012[56]
Helios 2 completed August 2012[56] |