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This article is about generation of electricity using solar energy. For other uses of solar energy, see Solar energy.
The PS10 concentrates sunlight from a field of heliostats on a central tower.
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Renewable energy

Solar power is by far the Earth's most available energy source, easily capable of providing many times the total current energy demand. The largest solar power plants, like the 354 MW SEGS, are concentrating solar thermal plants, but recently multi-megawatt photovoltaic plants have been built. Completed in 2008, the 46 MW Moura photovoltaic power station in Portugal and the 40 MW Waldpolenz Solar Park in Germany are characteristic of the trend toward larger photovoltaic power stations. Much larger ones are proposed, such as the 550 MW Topaz Solar Farm, and the 600 MW Rancho Cielo Solar Farm. Covering 4% of the world's desert area with photovoltaics could supply all of the world's electricity. The Gobi Desert alone could supply almost all of the world's total energy demand.[1]

Solar power is an intermittent energy source, meaning that solar power is not available at all times, and is normally supplemented by storage or another energy source, for example with wind power and hydropower.

Applications

Average insolation showing land area (small black dots) required to replace the world primary energy supply with solar electricity. 18 TW is 568 Exajoule (EJ) per year. Insolation for most people is from 150 to 300 W/m² or 3.5 to 7.0 kWh/m²/day.

Solar power is the conversion of sunlight into electricity. Sunlight can be converted directly into electricity using photovoltaics (PV), or indirectly with concentrating solar power (CSP), which normally focuses the sun's energy to boil water which is then used to provide power, and other technologies, such as the sterling engine dishes which use a sterling 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.

The only significant problem with solar power is installation cost, although cost has been decreasing due to the learning curve.[2] Developing countries in particular may not have the funds to build solar power plants, although small solar applications are now replacing other sources in the developing world.[3][4]

One fundamental difference between renewable energy and non-renewable energy is that non-renewable resources can be purchased as they are consumed, whereas with renewable resources, you pay up front for the next twenty years or so of energy.[5]

Concentrating solar power

Further information: Concentrated solar power and Solar thermal energy
File:Moody Sunburst.jpg
Solar troughs are the most widely deployed.

A legend claims that Archimedes used polished shields to concentrate sunlight on the invading Roman fleet and repel them from Syracuse.[6] Auguste Mouchout used a parabolic trough to produce steam for the first solar steam engine in 1866.[7]

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, 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.[8]

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.[9] The SEGS plants in California and Acciona's Nevada Solar One near Boulder City, Nevada are representatives of this technology.[10][11] The Suntrof-Mulk parabolic trough, developed by Melvin Prueitt, uses a technique inspired by Archimedes' principle to rotate the mirrors.[12]

Concentrating 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.[13][14]

A stirling solar dish, or dish engine system, consists of a stand-alone parabolic reflector that concentrates light onto a receiver positioned at the reflector's focal point. The reflector tracks the Sun along two axes. Parabolic dish systems give the highest efficiency among CSP technologies.[15] The 50 kW Big Dish in Canberra, Australia is an example of this technology.[10] The stirling solar dish combines a parabolic concentrating dish with a stirling heat 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.

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.[10] The Solar Two in Barstow, California and the Planta Solar 10 in Sanlucar la Mayor, Spain are representatives of this technology.[10][16]

Photovoltaics

Main article: Photovoltaics
11 MW Serpa solar power plant in Portugal

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.[17] 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.[18] Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954.[19] These early solar cells cost 286 USD/watt and reached efficiencies of 4.5–6%.[20]

Solar power has great potential, but in 2008 supplied less than 0.02% of the world's total energy supply[citation needed]. There are many competing technologies, including fourteen types of photovoltaic cells, such as thin film, monocrystalline silicon, polycrystalline silicon, and amorphous cells, as well as multiple types of concentrating solar power. It is too early to know which technology will become dominant.[21]

The earliest significant application of solar cells was as a back-up power source to the Vanguard I satellite in 1958, which allowed it to continue transmitting for over a year after its chemical battery was exhausted.[22] The successful operation of solar cells on this mission was duplicated in many other Soviet and American satellites, and by the late 1960s, PV had become the established source of power for them.[23] Photovoltaics went on to play an essential part in the success of early commercial satellites such as Telstar, and they remain vital to the telecommunications infrastructure today.[24]

The high cost of solar cells limited terrestrial uses throughout the 1960s. This changed in the early 1970s when prices reached levels that made PV generation competitive in remote areas without grid access. Early terrestrial uses included powering telecommunication stations, off-shore oil rigs, navigational buoys and railroad crossings.[25] These off-grid applications accounted for over half of worldwide installed capacity until 2004.[26]

Building-integrated photovoltaics cover the roofs of an increasing number of homes.

The 1973 oil crisis stimulated a rapid rise in the production of PV during the 1970s and early 1980s.[27] Economies of scale which resulted from increasing production along with improvements in system performance brought the price of PV down from 100 USD/watt in 1971 to 7 USD/watt in 1985.[28] Steadily falling oil prices during the early 1980s led to a reduction in funding for photovoltaic R&D and a discontinuation of the tax credits associated with the Energy Tax Act of 1978. These factors moderated growth to approximately 15% per year from 1984 through 1996.[29]

Since the mid-1990s, leadership in the PV sector has shifted from the US to Japan and Europe. Between 1992 and 1994 Japan increased R&D funding, established net metering guidelines, and introduced a subsidy program to encourage the installation of residential PV systems.[30] As a result, PV installations in the country climbed from 31.2 MW in 1994 to 318 MW in 1999,[31] and worldwide production growth increased to 30% in the late 1990s.[32]

Germany became the leading PV market worldwide since revising its Feed-in tariff system as part of the Renewable Energy Sources Act. Installed PV capacity has risen from 100 MW in 2000 to approximately 4,150 MW at the end of 2007.[33][34] After 2007, Spain became the largest PV market after adopting a similar feed-in tariff structure in 2004, installing almost half of the photovoltaics (45%) in the world, in 2008, while France, Italy, South Korea and the U.S. have seen rapid growth recently due to various incentive programs and local market conditions.[35] The power output of domestic photovoltaic devices is usually described in kilowatt-peak (kWp) units, as most are from 1 to 10 kW.[36]

Concentrating photovoltaics are another new method of electricity generation from the sun. Concentrating photovoltaics (CPV) systems employ sunlight concentrated onto photovoltaic surfaces for the purpose of electrical power production. Solar concentrators of all varieties may be used, and these are often mounted on a solar tracker in order to keep the focal point upon the cell as the Sun moves across the sky. Tracking is not required for concentrations of less than 2 to 5, but does increase flat panel photovoltaic output by up to 20% in winter, and up to 50% in summer.[37]

Experimental solar power

Main articles: Solar updraft tower, Thermogenerator, Concentrating photovoltaics, and Space-based solar power
Concentrating photovoltaics in Catalonia, Spain

A solar updraft tower (also known as a solar chimney or solar tower) consists of a large greenhouse that funnels into a central tower. As sunlight shines on the greenhouse, the air inside is heated, and expands. The expanding air flows toward the central tower, where a turbine converts the air flow into electricity. A 50 kW prototype was constructed in Ciudad Real, Spain and operated for eight years before decommissioning in 1989.[38]

Thermoelectric, or "thermovoltaic" devices convert a temperature difference between dissimilar materials into an electric current. First proposed as a method to store solar energy by solar pioneer Mouchout in the 1800s,[39] thermoelectrics reemerged in the Soviet Union during the 1930s. Under the direction of Soviet scientist Abram Ioffe a concentrating system was used to thermoelectrically generate power for a 1 hp engine.[40] Thermogenerators were later used in the US space program as an energy conversion technology for powering deep space missions such as Cassini, Galileo and Viking. Research in this area is focused on raising the efficiency of these devices from 7–8% to 15–20%.[41]

Finally, Space-based solar power is a theoretical design for the collection of solar power in space, for use on Earth. SBSP differs from the usual method of solar power collection in that the solar panels used to collect the energy would reside on a satellite in orbit, often referred to as a solar power satellite (SPS), rather than on Earth's surface. In space, collection of the Sun's energy is unaffected by the day/night cycle, weather, seasons, or the filtering effect of Earth's atmospheric gases. Average solar energy per unit area outside Earth's atmosphere is on the order of ten times that available on Earth's surface. However, there is no shortage of energy reaching the surface. The amount of solar energy reaching the surface of the planet each year is about twice the amount of energy that will be obtained forever from coal, oil, natural gas, and mined Uranium, combined, even using breeder reactors.[42]

Development, deployment and economics

Main article: Deployment of solar power to energy grids
Nellis Solar Power Plant, the largest photovoltaic power plant in North America

Beginning with the surge in coal use which accompanied the Industrial Revolution, energy consumption has steadily transitioned from wood and biomass to fossil fuels. 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.[43]

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.[44][45] 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).[46]

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.[47] Photovoltaic production growth has averaged 40% per year since 2000 and installed capacity reached 10.6 GW at the end of 2007,[26] and 14.73 GW in 2008.[48] Since 2006 it has been economical for investors to install photovoltaics for free in return for a long term power purchase agreement. 50% of commercial systems were installed in this manner in 2007 and it is expected that 90% will by 2009.[49] Nellis Air Force Base is receiving photoelectric power for about 2.2 ¢/kWh and grid power for 9 ¢/kWh.[50][51]

Commercial concentrating solar thermal power (CSP) plants were first developed in the 1980s. CSP plants such as SEGS project in the United States have a levelized energy cost (LEC) of 12–14 ¢/kWh.[52] The 11 MW PS10 power tower in Spain, completed in late 2005, is Europe's first commercial CSP system, and a total capacity of 300 MW is expected to be installed in the same area by 2013.[53]

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  Spain Seville Completed 2010
[54][55][56][57][58]
100 Andasol solar power station  Spain Granada
Completed 2009
[59][60]
64 Nevada Solar One  USA Boulder City, Nevada
50 Ibersol Ciudad Real  Spain Puertollano, Ciudad Real Completed May 2009 [61]
50 Alvarado I  Spain Badajoz Completed July 2009 [62][63][64]
50 Extresol 1  Spain Torre de Miguel Sesmero (Badajoz) Completed February 2010 [65][66][67]
50 La Florida  Spain Alvarado (Badajoz) completed July 2010 [65][68]

Solar installations in recent years have also largely begun to expand into residential areas, with governments offering incentive programs to make "green" energy a more economically viable option. In Canada the RESOP (Renewable Energy Standard Offer Program), introduced in 2006,[69] and updated in 2009 with the passage of the Green Energy Act, allows residential homeowners in Ontario with solar panel installations to sell the energy they produce back to the grid (i.e., the government) at 42¢/kWh, while drawing power from the grid at an average rate of 6¢/kWh.[70] The program is designed to help promote the government's green agenda and lower the strain often placed on the energy grid at peak hours. In March, 2009 the proposed FIT was increased to 80¢/kWh for small, roof-top systems (≤10 kW).[71]

Photovoltaics are 85 times as efficient as growing corn for ethanol. On a 300 feet (91 m) by 300 feet (1 hectare) plot of land enough ethanol can be produced to drive a car 30,000 miles (48,000 km)* per year or 2,500,000 miles (4,000,000 km)* by covering the same land with photo cells. The deserts of the South Western United States could produce sufficient electricity to fulfill all of the electrical needs of the United States, and could use electrolysis to produce Hydrogen from water to power aircraft.[72]

World's largest photovoltaic (PV) power plants[73]
Name of PV power plant Country DC
Peak
Power
(MW)		 Notes
Olmedilla Photovoltaic Park Spain 60 Completed September 2008
Strasskirchen Solar Park Germany 54
Lieberose Photovoltaic Park [74][75] Germany 53 2009
Puertollano Photovoltaic Park Spain 50 2008
Moura photovoltaic power station [76] Portugal 46 Completed December 2008
Kothen Solar Park Germany 45 2009
Finsterwalde Solar Park Germany 42 2009
Waldpolenz Solar Park[77][78] Germany 40 550,000 First Solar thin-film CdTe modules. Completed December 2008
Vepřek Solar Park[79][80] Czech Republic 35.1 186,960 modules,
completed September 2010
Planta Solar La Magascona & La Magasquila Spain 34.5

The annual International Conference on Solar Photovoltaic Investments, organized by EPIA notes that photovoltaics provides a secure, reliable return on investment, with modules typically lasting 25 to 40 years and with a payback on investment of between 8 to 12 years.[81]

Energy storage methods

Main articles: Grid energy storage and V2G
This energy park in Geesthacht, Germany, includes solar panels and pumped-storage hydroelectricity.
Seasonal variation of the output of the solar panels at AT&T Park in San Francisco

Solar energy is not available at night, making energy storage an important issue in order to provide the continuous availability of energy.[82] Both wind power and solar power are intermittent energy sources, meaning that all available output must be taken when it is available and either stored for when it can be used, or transported, over transmission lines, to where it can be used. Wind power and solar power tend to be somewhat complementary, as there tends to be more wind in the winter and more sun in the summer, but on days with no sun and no wind the difference needs to be made up in some manner.[83] The Institute for Solar Energy Supply Technology of the University of Kassel pilot-tested a combined power plant linking solar, wind, biogas and hydrostorage to provide load-following power around the clock, entirely from renewable sources.[84]

Solar energy can be stored at high temperatures using molten salts. Salts are an effective storage medium because they are low-cost, have a high specific heat capacity and can deliver heat at temperatures compatible with conventional power systems. The Solar Two used this method of energy storage, allowing it to store 1.44 TJ in its 68 m³ storage tank, enough to provide full output for close to 39 hours, with an efficiency of about 99%.[85]

Off-grid PV systems have traditionally used rechargeable batteries to store excess electricity. With grid-tied systems, excess electricity can be sent to the transmission grid. Net metering programs give these systems a credit for the electricity they deliver to the grid. This credit offsets electricity provided from the grid when the system cannot meet demand, effectively using the grid as a storage mechanism. Credits are normally rolled over month to month and any remaining surplus settled annually.[86]

Pumped-storage hydroelectricity stores energy in the form of water pumped when surplus electricity is available, from a lower elevation reservoir to a higher elevation one. The energy is recovered when demand is high by releasing the water: the pump becomes a turbine, and the motor a hydroelectric power generator.[87]

See also

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Notes

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  2. ^ Cost Of Installed Solar Photovoltaic Systems Drops Significantly Over The Last Decade retrieved 19 May 2009
  3. ^ Govt to bear 80% cost of generating solar power retrieved 19 May 2009
  4. ^ In India’s Sea of Darkness: An Unsustainable Island of Decentralized Energy Production retrieved 19 May 2009
  5. ^ Solar Power Hits Home retrieved 19 May 2009
  6. ^ Butti and Perlin (1981), p. 29
  7. ^ Gordon, Jeffrey, Solar energy, International Solar Energy Society, p.598 ISBN 9781902916231
  8. ^ Martin and Goswami (2005), p. 45
  9. ^ Concentrated Solar Thermal Power - Now Retrieved 19 August 2008
  10. ^ a b c d "Concentrating Solar Power in 2001 - An IEA/SolarPACES Summary of Present Status and Future Prospects" (PDF). International Energy Agency - SolarPACES. Retrieved 2008-07-02.
  11. ^ "UNLV Solar Site". University of Las Vegas. Retrieved 2008-07-02.
  12. ^ Suntrof-Mulk Parabolic Trough
  13. ^ Compact CLFR
  14. ^ Ausra compact CLFR introducing cost-saving solar rotation features
  15. ^ "An Assessment of Solar Energy Conversion Technologies and Research Opportunities" (PDF). Stanford University - Global Climate Change & Energy Project. Retrieved 2008-07-02.
  16. ^ David Shukman (2 May 2007). "Power station harnesses Sun's rays". BBC News. Retrieved 2008-07-02.
  17. ^ Perlin (1999), p. 147
  18. ^ Perlin (1999), p. 18–20
  19. ^ Perlin (1999), p. 29
  20. ^ Perlin (1999), p. 29–30, 38
  21. ^ Technologies
  22. ^ Perlin (1999), p. 45–46
  23. ^ Perlin (1999), p. 49–50
  24. ^ Perlin (1999), p. 49–50, 190
  25. ^ Perlin (1999), p. 57–85
  26. ^ a b "Renewables 2007 Global Status Report" (PDF). Worldwatch Institute. p. 11. Retrieved 2008-04-30.
  27. ^ "Photovoltaic Milestones". Energy Information Agency - Department of Energy. Retrieved 2008-05-20.
  28. ^ Perlin (1999), p. 50, 118
  29. ^ "World Photovoltaic Annual Production, 1971-2003". Earth Policy Institute. Retrieved 2008-05-29.
  30. ^ "Policies to Promote Non-hydro Renewable Energy in the United States and Selected Countries" (PDF). Energy Information Agency – Department of Energy. Retrieved 2008-05-29.
  31. ^ Foster, Robert. "Japan Pholtovoltaics Market Overview" (PDF). Department of Energy. Retrieved 2008-06-05.
  32. ^ Handleman, Clayton. "An Experience Curve Based Model for the Projection of PV Module Costs and Its Policy Implications" (PDF). Heliotronic. Retrieved 2008-05-29.
  33. ^ "Renewable energy sources in figures - national and international development" (PDF). Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (Germany). Retrieved 2008-05-29.
  34. ^ "Marketbuzz 2008: Annual World Solar Pholtovoltaic Industry Report". solarbuzz. Retrieved 2008-06-05.
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  36. ^ "Live Sites - links to over 800 monitored solar panels". Fat Spaniel. Retrieved 2009-05-18. The live feeds shown here cite figures in kilowatt-peak (kWp) units.
  37. ^ Tracking Systems Vital to Solar Success
  38. ^ Mills (2004), p. 19–31
  39. ^ Perlin and Butti (1981), p. 73
  40. ^ Halacy (1973), p. 76
  41. ^ Tritt (2008), p. 366–368
  42. ^ Exergy (available energy) Flow Charts 2.7 YJ solar energy each year for two billion years vs. 1.4 YJ non-renewable resources available once.
  43. ^ Butti and Perlin (1981), p. 63, 77, 101
  44. ^ Butti and Perlin (1981), p. 249
  45. ^ Yergin (1991), p. 634, 653-673
  46. ^ "Chronicle of Fraunhofer-Gesellschaft". Fraunhofer-Gesellschaft. Retrieved 2007-11-04.
  47. ^ Solar: photovoltaic: Lighting Up The World retrieved 19 May 2009
  48. ^ "Global Market Outlook Until 2013" (PDF). European Photovoltaic Industry Association. Retrieved 2009-05-22.
  49. ^ Solar Power Services: How PPAs are Changing the PV Value Chain February 11, 2008, retrieved 21 May 2009 [1]
  50. ^ Nellis Solar Power System
  51. ^ "An Argument for Feed-in Tariffs" (PDF). European Photovoltaic Industry Association. Retrieved 2008-06-09.
  52. ^ "DOE Concentrating Solar Power 2007 Funding Opportunity Project Prospectus" (PDF). Department of Energy. Retrieved 2008-06-12.
  53. ^ "PS10". SolarPACES (Solar Power and Chemical Energy Systems). Retrieved 2008-06-24.
  54. ^ Abengoa Rakes in $426M for 4 Solar Power Plants
  55. ^ "Abengoa Begins Operation of 50MW Concentrating Solar Power Plant". SustainableBusiness.com News. May 6, 2010. Retrieved 2010-05-07.
  56. ^ Abengoa Solar begins commercial operation of Solnova 1
  57. ^ Abengoa Solar begins commercial operation of Solnova 3
  58. ^ Abengoa Solar Reaches Total of 193 Megawatts Operating
  59. ^ Acciona y ACS inscriben sus termosolares en el registro de Industria
  60. ^ ACS aumenta un 22,6% las ganancias de su negocio de 'energía verde' en la primera mitad de año
  61. ^ José María Barreda and Ignacio Galán open IBERDROLA RENOVABLES’ first solar termal power plant
  62. ^ Acciona Status Solarpaces 2008 p.25
  63. ^ ACCIONA Energía develops 900-million-euro renewables projects in the region of Extremadura
  64. ^ ACCIONA opens its first CSP plant in Spain, in Extremadura
  65. ^ a b Lokalizacion de Centrales Termosolares de Espana
  66. ^ Solar Thermal Power Generation - A Spanish Success Story
  67. ^ ACS LAUNCHES THE OPERATION PHASE OF ITS THIRD DISPATCHABLE 50 MW THERMAL POWER PLANT IN SPAIN, EXTRESOL-1
  68. ^ Spain - A Solar Thermal Powerhouse
  69. ^ RESOP Program Update
  70. ^ Solar program in Ontario
  71. ^ Proposed Feed-In Tariff Prices for Renewable Energy Projects in Ontario
  72. ^ David Comarow, "Here Comes the Sun," Kyoto Planet Sustainable Enterprise Report, November 2008, Whitepaper.
  73. ^ PV Resources (2010). World's largest photovoltaic power plants
  74. ^ Germany Turns On World's Biggest Solar Power Project
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  76. ^ Amareleja Solar Central solar which cost 261 ME started today (29 Dec 08) at full capacity retrieved 21 May 2009
  77. ^ Large photovoltaic plant in Muldentalkreis
  78. ^ Germany's largest Solar parks connected to the grid (19 Dec 08)
  79. ^ FVE CZECH
  80. ^ FVE CZECH NOVUM s.r.o.
  81. ^ 3rd International Conference on Solar Photovoltaic Investments
  82. ^ Carr (1976), p. 85
  83. ^ Wind + sun join forces at Washington power plant Retrieved 31 January 2008
  84. ^ "The Combined Power Plant: the first stage in providing 100% power from renewable energy". SolarServer. 2008. Retrieved 2008-10-10. {{cite web}}: Unknown parameter |month= ignored (help)
  85. ^ "Advantages of Using Molten Salt". Sandia National Laboratory. Retrieved 2007-09-29.
  86. ^ "PV Systems and Net Metering". Department of Energy. Retrieved 2008-07-31.
  87. ^ "Pumped Hydro Storage". Electricity Storage Association. Retrieved 2008-07-31.

References

  • Butti, Ken (1981). A Golden Thread (2500 Years of Solar Architecture and Technology). Van Nostrand Reinhold. ISBN 0-442-24005-8. {{cite book}}: Unknown parameter |coauthor= ignored (|author= suggested) (help)
  • Carr, Donald E. (1976). Energy & the Earth Machine. W. W. Norton & Company. ISBN 0-393-06407-7.
  • Halacy, Daniel (1973). The Coming Age of Solar Energy. Harper and Row. ISBN 0-380-00233-7.
  • Martin, Christopher L. (2005). Solar Energy Pocket Reference. International Solar Energy Society. ISBN 0-9771282-0-2. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  • Mills, David (2004). "Advances in solar thermal electricity technology". Solar Energy. 76 (1–3): 19–31. doi:10.1016/S0038-092X(03)00102-6.
  • Perlin, John (1999). From Space to Earth (The Story of Solar Electricity). Harvard University Press. ISBN 0-674-01013-2.
  • Tritt, T.; Böttner, H.; Chen, L. (2008). "Thermoelectrics: Direct Solar Thermal Energy Conversion". MRS Bulletin. 33 (4): 355–372.
  • Yergin, Daniel (1991). The Prize: The Epic Quest for Oil, Money, and Power. Simon & Schuster. p. 885. ISBN 978-0-671-79932-8.
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