Solar Energy Generating Systems (SEGS) in California, with the combined capacity from three separate locations at 354 megawatts (MW, 474,700 hp), is now the world's second largest solar thermal energy generating facility, after the commissioning of the even larger Ivanpah facility in 2014. It consists of nine solar power plants in California's Mojave Desert, where insolation is among the best available in the United States. SEGS I–II (44 MW) are located at Daggett (34°51′45″N 116°49′45″W), SEGS III–VII (150 MW) are installed at Kramer Junction (35°00′43″N 117°33′32″W), and SEGS VIII–IX (160 MW) are placed at Harper Lake (35°01′55″N 117°20′50″W). NextEra Energy Resources operates and partially owns the plants located at Kramer Junction and Harper Lake. A tenth plant (SEGS X, 80 MW) had been in construction and SEGS XI and SEGS XII had been planned by Luz Industries, but the developer filed for bankruptcy in 1992, because it was unable to secure construction financing.
The plants have a 354 MW net (394 MW gross) installed capacity. The nameplate capacity, which operating continuously, would dеliver the samе net power output, coming only from the solar source is around 75 MWe —, representing a 21% capacity factor. In addition, the turbines can be utilized at night by burning natural gas.
NextEra claims that the solar plants power 232,500 homеs (during the day, at peak power) and displace 3,800 tons of pollution pеr year that would have been produced if the electricity had bееn providеd by fossil fuels, such as oil.
The facilities have a total of 936,384 mirrors and cover more than 1,600 acres (647.5 ha). Lined up, the parabolic mirrors would extend over 229 miles (369 km).
As an example of cost, in 2002, one of the 30 MW Kramer Junction sites required $90 million to construct, and its operation and maintenance cost was about $3 million per year (4.6 cents per kilowatt hour). With a considered lifetime of 20 years, the operation, maintenance and investments interest and depreciation triples the price, to approximately 14 cents per kilowatt hour.
The installation uses parabolic trough, solar thermal technology along with natural gas to generate electricity. About 90% of the electricity is produced by the sunlight. Natural gas is only used when the solar power is insufficient to meet the demand from Southern California Edison, the distributor of power in southern California.
The parabolic mirrors are shaped like quarter-pipes. The sun shines onto the panels made of glass, which are 94% reflective, unlike a typical mirror, which is only 70% reflective. The mirrors automatically track the sun throughout the day. The greatest source of mirror breakage is wind, with 3,000 mirrors typically replaced each year. Operators can turn the mirrors to protect them during intense wind storms. An automated washing mechanism is used to periodically clean the parabolic reflective panels.
The sunlight bounces off the mirrors and is directed to a central tube filled with synthetic oil, which heats to over 400 °C (750 °F). The reflected light focused at the central tube is 71 to 80 times more intense than the ordinary sunlight. The synthetic oil transfers its heat to water, which boils and drives the Rankine cycle steam turbine, thereby generating electricity. Synthetic oil is used to carry the heat (instead of water) to keep the pressure within manageable parameters.
The SEGS power plants were built by Luz Industries, and commissioned between December 20, 1984 and October 1, 1990. After Luz Industries' bankruptcy in 1991 plants were sold to various investor groups as individual projects, and expansion including three more plants was halted.
Kramer Junction employs about 95 people and 45 people work at Harper Lake.
SEGS VIII and SEGS IX, located at 35°01′55″N 117°20′50″W, until Ivanpah Solar Power Facility commissioning in 2014, were the largest solar thermal power plants individually and collectively in the world. They were the last, the largest, and the most advanced of the nine plants at SEGS, designed to take advantage of the economies of scale. Construction of the tenth plant in the same locality was halted because of the bankruptcy of Luz Industries. Construction of the approved eleventh and twelfth plants never started. Each of the three planned plants had 80 MW of installed capacity. Abengoa Solar recently constructed the 280MW Mojave Solar Project (MSP) adjacent to the SEGS VIII and SEGS IX plants. The MSP also uses concentrating solar thermal trough technology.
This location (35°00′48″N 117°33′38″W) receives an average of 340 days of sunshine per year, which makes it an ideal place for solar power generation. The average direct normal radiation (DNR) is 7.44 kWh/m²/day (310 W/m²), one of the best in the nation.
SEGS I and II are located at 34°51′47″N 116°49′37″W and are owned by Cogentrix Energy (Carlyle Group). SEGS II was shut down in 2014 and will be replaced with 44 MW of photovoltaics, Sunray Energy 2.
In February 1999, a 900,000-US-gallon (3,400 m3) Mineral Oil storage tank exploded at the SEGS I (Daggett) solar power plant, sending flames and smoke into the sky. Authorities were trying to keep flames away from two adjacent containers that held sulfuric acid and sodium hydroxide. The immediate area of 0.5 square miles (1.3 km2) was evacuated.