 Trough systems convert the heat from the sun into electricity. Because of their parabolic shape, trough collectors can focus the sun at 30-60 times its normal intensity on a receiver pipe located along the focal line of the trough. Synthetic oil circulates through the pipe and captures this heat, reaching temperatures of 390°C (735°F). The hot oil is pumped to a generating station and routed through a heat exchanger to produce steam. Finally, electricity is produced in a conventional steam turbine. The SEGS plants operate on natural gas on cloudy days or after dark, and natural gas provides 25 % of the total output.
