Solar Two Experimental Solar Facility SIte, California

The site of Solar Two is currently an empty lot, since the plant was removed in 2009. For more than 20 years this experimental solar facility was the largest of its type in the country (and only one of two similar structures in the USA), and the first of four major solar power plants built in the region - for years the largest concentration of solar energy production in the world. Solar Two was built by the Department of Energy in 1981 as Solar One. It was a central receiver-type system, with a 200-foot collector tower onto which nearly 2,000 reflectors focused the sun's energy, producing up to 10 megawatts of power. Each of the reflectors was positioned automatically with a heliostat to track the moving sun. The heat transfer medium, which was heated in the "solar power tower," was circulated to the steam and electric generating facilities. It was a mixture of sodium nitrate and potassium nitrate with a high heat retention capacity, maintaining its temperature long enough to be stored in tanks after being heated, and could be used as much as several hours later to generate steam and subsequently, electricity. The DOE and Southern California Edison, which owns the ground, closed the power facility in the late 1990's. It was used as a gamma ray observatory by the University of California, for a few years, then demolished in November, 2009.