The Solar Electricity Generating Systems (SEGS) are a set of nine solar thermal power plants of combined 354-megawatts (MW, 474,700 hp) located at three separate facilities in California's Mojave Desert, United States of America. The plants use parabolic trough reflectors with an adjustable pitch to focus sunlight on clear tubes containing a synthetic oil running along the reflectors' focal lines. SEGS I–II (44 MW) are located at Daggett, SEGS III–VII (150 MW) are installed at Kramer Junction, and SEGS VIII–IX (160 MW) are placed at Harper Lake.
The installation uses a 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 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.
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