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SOLAR
The Department of Energy’s Solar Energy Technology Program, managed by the Office of Energy Efficiency and Renewable Energy accelerates the development of solar technologies as energy sources for the nation and world. The solar program also educates the public about the value of solar as a secure, reliable, and clean energy choice.
Developing technologies that take advantage of the clean abundant energy of the sun is important to reducing greenhouse gasses and helps stimulate the economy. Examples of solar technologies being developed by the Department of Energy and Industry are Photovoltaic cells, concentrating solar power technologies and low temperature solar collectors.
Photovoltaic cells convert sunlight directly into electricity and are made of semiconductors such as crystalline silicon or various thin-film materials. Photovoltaic's can provide tiny amounts of power for watches, large amounts for the electric grid, and everything in between.
Concentrating solar power technologies use reflective materials to concentrate the sun's heat energy, which ultimately drives a generator to produce electricity. These technologies include dish/engine systems, parabolic troughs, and central power towers.
Low-temperature solar collectors also absorb the sun's heat energy, but the heat is used directly for hot water or space heating for residential, commercial, and industrial facilities.
You can also find statistical information relating to the use of solar thermal and solar photovoltaic energy through the Energy Information Administration.
Solar calculations
The solar thermal collector performance rating is an analytically-derived set of numbers representing the characteristic all-day energy output of the solar thermal collector under standard rating conditions measures in Btu per square foot per day (Btu/ft2 day). In 2007, the average solar thermal performance rating for low-temperature collectors (metallic and nonmetallic) was 1,248 Btu/ft2 day, medium-temperature (air) was 918 Btu/ft2 day, medium-temperature (thermosiphon) was 926 Btu/ft2 day, medium-temperature (flat-plate) was 979 Btu/ft2 day, medium-temperature (evacuated-tube) was 851 Btu/ft2 day, medium-temperature (concentrator) was 2,150 Btu/ft2 day, and high-temperature (parabolic dish/trough) was 1,000 Btu/ft2 day.
Charles Fritts was an American inventor credited with creating the first working solar cell in 1884.
Fritts coated the semiconductor material selenium with an extremely thin layer of gold. The resulting cells had a conversion efficiency of only about 1% owing to the properties of selenium, which in combination with the material's high cost prevented the use of such cells for energy supply. Selenium cells found other applications however, for example as light sensors for exposure timing in photo cameras, where they were common well into the 1960s.
Solar cells later became practical for power uses after Russell Ohl's 1940s development of silicon p/n junction cells that reached efficiencies above 5% by the 1950s/1960s.
Today's best silicon solar cells are over 20% efficient, with industrial average over 13%.[1]
Solar panels and complete solar panel systems today power a wide variety of applications. Solar panels in the form of solar cells are still being used in calculators. However, they are also being used to provide solar power to entire homes and commercial buildings, even Google's headquarters in California.
