solar energy and how it works and what is its future 411

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 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.

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]
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 the daylight hours by tracking along a single axis. Parabolic trough systems provide the best land-use factor of any solar technology.^[3] The SEGS plants in California and Acciona's Nevada Solar One near Boulder City, Nevada are representatives of this technology.^[4][5] 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.^[6][7]
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.^[8] The 50 kW Big Dish in Canberra, Australia is an example of this technology.^[4]
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.^[4] 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.^[9] In 1931 a German engineer, Dr Bruno Lange, developed a photo cell using silver selenide in place of copper oxide.^[10] Although the prototype selenium cells converted less than 1% of incident light into electricity, both Ernst Werner von Siemens and James Clerk Maxwell recognized the importance of this discovery.^[11] Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954.^[12] These early solar cells cost 286 USD/watt and reached efficiencies of 4.5–6%.^[13]

Photovoltaic power systems

Main article: Photovoltaic system

Simplified schematics of a grid-connected residential PV power system^[14]

Solar cells produce direct current (DC) power, which fluctuates with the intensity of the irradiated light. This usually requires conversion to certain desired voltages or alternating current (AC), which requires the use of the inverters.^[14] Multiple solar cells are connected inside the modules. Modules are wired together to form arrays, then tied to inverter, which produces power with the desired voltage, and frequency/phase (when its AC).^[14]
Many residential systems are connected to the grid wherever available, especially in the developed countries with large markets.^[15] In these grid-connected PV systems, use of energy storages are optional. In certain applications such as satellites, lighthouses, or in developing countries, batteries or additional power generators are often added as back-ups, which forms stand-alone power systems.

Development and deployment

Main article: Deployment of solar power to energy grids

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.^[16] 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.^[17] 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.^[18][19] 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).^[20]
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.^[21] Photovoltaic production growth has averaged 40% per year since 2000 and installed capacity reached 39.8 GW at the end of 2010,^[22] 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).^[23]
There are also many large plants under construction. The Desert Sunlight Project 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.^[24] The Topaz Solar Farm is a 550 MW photovoltaic power plant, being built in San Luis Obispo County, California.^[25] 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.^[26] 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.^[27]

Main article: List of photovoltaic power stations

World's largest photovoltaic power stations (50 MW or larger)^[23]

PV power station	Country	DC peak power (MWp)	Notes
Golmud Solar Park[23][28][29][30]	China	200	Completed 2011
Sarnia Photovoltaic Power Plant[31]	Canada	97[23]	Constructed 2009–2010[32]
Montalto di Castro Photovoltaic Power Station[23]	Italy	84.2	Constructed 2009–2010
Finsterwalde Solar Park[33][34]	Germany	80.7	Phase I completed 2009, phase II and III 2010
Ohotnikovo Solar Park	Ukraine	80	Completed 2011
Solarpark Senftenberg[23][35]	Germany	78	Phase II and III completed 2011, another 70 MW phase planned
Lieberose Photovoltaic Park [36][37]	Germany	71.8
Rovigo Photovoltaic Power Plant[38][39]	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

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.

Main article: List of solar thermal power stations

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 [40][41][42]
150	Andasol solar power station	Spain	Granada	completed 2011, with 7.5h thermal energy storage[43][44]
100	Extresol Solar Power Station	Spain	Torre de Miguel Sesmero (Badajoz)	Completed December 2010[45][46][47]
75	Martin Next Generation Solar Energy Center	USA	Florida	steam input into a combined cycle [48]
64	Nevada Solar One	USA	Boulder City, Nevada

Economics

Projection of levelized cost of PV energy in Europe.^[49]

Bloomberg New Energy Finance, in March 2011, put the 2010 cost of solar panels at $1.80 per watt, but estimated that the price would decline to $1.50 per watt by the end of 2011.^[50] Nevertheless, there are exceptions-- Nellis Air Force Base is receiving photoelectric power for about 2.2 ¢/kWh and grid power for 9 ¢/kWh.^[51][52] Also, since PV systems use no fuel and modules typically last 25 to 40 years, the International Conference on Solar Photovoltaic Investments, organized by EPIA, has estimated that PV systems will pay back their investors in 8 to 12 years.^[53] As a result, since 2006 it has been economical for investors to install photovoltaics for free in return for a long term power purchase agreement. Fifty percent of commercial systems were installed in this manner in 2007 and it is expected that 90% will by 2009.^[54]
As of 2011, the cost of PV has fallen well below that of nuclear power and is set to fall further. The average retail price of solar cells as monitored by the Solarbuzz group fell from $3.50/watt to $2.43/watt over the course of 2011, and a decline to prices below $2.00/watt seems inevitable:^[55]