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 354MW SEGS, are concentrating solar thermal plants, but recently multi-megawatt photovoltaic plants have been built. Completed in 2008, the 46MW Moura photovoltaic power station in Portugal and the 40MW Waldpolenz Solar Park in Germany are characteristic of the trend toward larger photovoltaic power stations. Much larger ones are proposed, such as the 550MW Topaz Solar Farm, and the 600MW Rancho Cielo Solar Farm. Covering 4% of the world’s desert area with photovoltaics could supply all of the worlds electricity. The Gobi Desert alone could supply almost all of the world’s total energy demand.

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 and hydropower.


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. 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. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954. These early solar cells cost 286USD per watt and reached efficiencies of 4.5 – 6 per cent.

Solar power has great potential, but in 2008 supplied less than 0.002% of the world’s total energy supply. 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.

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 and a half after its chemical battery was exhausted. The successful operation of solar cells on this mission was duplicated in many other Soviet and American satellites such as Telstar, and they remain vital to the telecommunications infrastructure today.

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 telecommunications stations, off-shore oil rigs, navigational buoys and railroad crossings. These off-grid applications accounted for over half of worldwide installed capacity until 2004.

The 1973 oil crisis stimulated a rapid rise in the production of PV during the 1970s and early 1980s. Economies of scale which resulted from increasing production along with improvements in system performance brought the price of PV down from 100USD per watt in 1971 to 7USD per watt in 1985. Steadily falling oil prices during the early 1980s led to a reduction in funding for photovoltaic research and development 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 to 1996.

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

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 100MW in 200 to approximately 4,150MW at the end of 2007. 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. The power output of domestic photovoltaic devices is usually described in kilowatt-peak (kWp) units, as most are from 1 to 10 kW.

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. Photovoltaic production growth has averaged 40% per year since 2000 and installed capacity reached 10.6GW at the end of 2007, and 14.73GW in 2008. 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. Nellis Air Force base is receiving photoelectric power for about 2.2 cents per kWh and grid power for 9 cents per kWh.

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, introduced in 2006, and updated in 2009 with the passage of the Green Energy Act, allows residential home-owners in Ontario, with solar panel installations to sell the energy they produce back to the grid at 42 cents per kWh, while drawing power from the grid at an average rate of 56 cents per kWh. 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 cents per kWh for small roof-top systems, those less than 10 kW.

Photovoltaics are 85 times as efficient as growing corn for ethanol. On a 1 hectare block of land, enough ethanol can be produced to drive a car 48,000 kilometres a year or 4,020,000 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.

Source: Wikipedia.