Project

Solar Two experimental solar power plant in the Mojave Desert, California, USA. National Renewable Energy Laboratory

Solar One
Solar One was a pilot solar-thermal project built in the Mojave Desert just east of Barstow, CA, USA. It was the first test of a large-scale thermal solar power tower plant. Solar One was designed by the Department of Energy (DOE), Southern California Edison, LA Dept of Water and Power, and California Energy Commission. It was located in Daggett, CA, about 10 miles (16 km) east of Barstow. Solar One's method of collecting energy was based on concentrating the sun's energy onto a common focal point to produce heat to run a steam turbine generator. It had hundreds of large mirror assemblies, or heliostats, that track the sun, reflecting the solar energy onto a tower where a black receiver absorbed the heat. High-temperature heat transfer fluid was used to carry the energy to a boiler on the ground where the steam was used to spin a series of turbines, much like a traditional power plant. In the late 1970s, a competition was held by DoE to obtain the best heliostat design for the project. Several promising designs were selected and prototypes were built and shipped to the area for testing. Trade-offs involved simplicity of construction to minimize costs for high-volume manufacturing versus the need for a reliable, bi-directional tracking system that could maintain focus on the tower. Rigidity of the structure was a major concern in terms of wind load resistance and durability, but shading of the mirrors by support structures was to be avoided. The project produced 10 MW of electricity using 1,818 mirrors, each 40 m² (430 ft²) with a total area of 72,650 m² (782,000 ft²). Solar One was completed in 1981 and was operational from 1982 to 1986. Later redesigned and renamed Solar Two, it can be seen from Interstate 40 where it covers a 51 hectare (126 acre) site, not including the administration building or railyard facilities shared with a neighboring plant. Solar One/Two and other nearby solar projects are plainly visible via satellite imaging software at 34°52′18″N 116°50′03″W / 34.87167°N 116.83417°W / 34.87167; -116.83417. During times of high winds, blowing dust is sometimes illuminated by the reflected sunbeams to create an unusual atmospheric phenomenon in the vicinity of the power tower. These beams of light were depicted in several scenes, and a painting, in the 1987 movie Bagdad Cafe, which was filmed nearby. Nevada Solar One shares a similar name to Solar One, however it is quite different. It uses a solar thermal parabolic trough system and generates 64 MW.

Solar Two
In 1995 Solar One was converted into Solar Two, by adding a second ring of 108 larger 95 m² (1,000 ft²) heliostats around the existing Solar One, totaling 1926 heliostats with a total area of 82,750 m² (891,000 ft²). This gave Solar Two the ability to produce 10 megawatts. Solar Two used molten salt, a combination of 60% sodium nitrate and 40% potassium nitrate, as an energy storage medium instead of oil or water as with Solar One. This helped in energy storage during brief interruptions in sunlight due to clouds. The molten salt also allowed the energy to be stored in large tanks for future use such as night time. Solar Two was decommissioned in 1999, and was converted by the University of California, Davis, into an Air Cherenkov Telescope in 2001, measuring gamma rays hitting the atmosphere. Its name is now C.A.C.T.U.S..[1] "We're proud of Solar Two's success as it marks a significant milestone in the development of large-scale solar energy projects," said then U.S. Energy Secretary Bill Richardson. "This technology has been successfully demonstrated and is ready for commercialization. From 1994 to 1999, the Solar Two project demonstrated the ability of solar molten salt technology to provide long-term, cost effective thermal energy storage for electricity generation.", Boeing.

Solar Tres
Due to the success of Solar Two, a commercial power plant, called Solar Tres Power Tower, is being built in Spain by Torresol Energy using Solar One and Solar Two's technology for commercial electrical production of 15 MW.[2] Solar Tres will be three times larger than Solar Two with 2,493 heliostats, each with a reflective surface of 96 m². The total reflective area will be 240,000 m² (2.6 million ft²). They will be made of a highly reflective glass with metal back to cut costs by about 45%. A larger molten nitrate salt storage tank will be used giving the plant the ability to store 600 MWh, allowing the plant to run 24x7 during the summer.

Land use concerns
Solar thermal power plants are big and use a lot of land, but when looking at electricity output versus total size, they use less land than hydroelectric dams (including the size of the lake behind the dam) or coal plants (including the amount of land required for mining and excavation of the coal).[3]

 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.

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).

Resources

Solar One and Two Solar Power Plant (California, USA)