History of Solar Two
Solar Two is located east of Daggett, California. On historic Route 66, it is in the Mojave desert, a high desert surrounded by mountains. Originally, it was a prototype for the solar farm model of power plants. It consists of a field of 1,926 moving mirrors, called heliostats. Each heliostat is 42 m2, and can be pointed in any direction using a central computer control. When the plant was operational, the heliostats focused sunlight onto a central tower, heating water (or molten salt) to create steam and generate power with a turbine.
An artist's rendition of the solar farm concept.
The first incarnation, Solar One, was built in 1982 by the U.S. Department of Energy, Southern California Edison, the Los Angeles Department of Water & Power, and the California Energy Commission. It ran through 1988, and in 1995 was retrofitted to become Solar Two. A ring of larger heliostats, each 95 m2, was added to the perimeter of the field, and the plant was converted to heat molten nitrate salt (60 percent NaN03 and 40 percent KN03) from 500F to 1050F. This offered several advantages, most notably that the plant could still generate power during the night and in periods of cloud cover. Its run ended in 1999 generating 10 MW of power, enough to power 10,000 homes, and successfully showing that its technology could be scaled up to the cost-efficient magnitude of 100 MW. Christopher Powers, a spokesman for the Department of Energy, doesn't think that the solar farm technology will be pursued in the U.S. where other energy sources are cheaper, but it could have real world applications today where electricity is expensive and there is tons of sunlight, in places like the Middle East. [3]
University of California research teams began converting Solar Two into an Air Cherenkov Telescope in 2001 [5,6]. When cosmic charged particles or gamma rays hit the atmosphere they produce a cascade of secondary charged particles. This shower of particles emits visible photons called Cherenkov light for a very short duration of 10 billionths of a second (more about this process here) that spread out over a circle ~200m in diameter on the Earth's surface. Solar Two, with its vast surface area and individually controlled heliostats, is particularly well suited to observations of this type. Researchers brought 165 of the heliostats back into working order and installed secondary optics in the white portion of the tower. The secondary optics consist of a 6 meter spherical mirror that images the field onto an array of 80 photomultiplier tubes (PMTs).
For more on the history of gamma-ray astrophysics, visit: Wikipediea
References:
[1] Boeing
[2] Sandia Labs
[3] CNN
[4] House of Representatives
[5]SpaceRef.com
[6]BBC News
Solar Two and the surrounding area, courtesy of Google Maps