Solar Energy Generating Systems

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Solar Energy Generating Systems (SEGS) is the largest solar energy generating facility in the world. It consists of nine solar power plants in California's Mojave Desert, where insolation is among the best available in the United States. SEGS III–VII (150 MW) are located at Kramer Junction, SEGS VIII–IX (160 MW) at Harper Lake, and SEGS I–II (44 MW) at Daggett respectively. NextEra Energy Resources operates and partially owns the plants located at Kramer Junction and Harper Lake.

Plants' scale and operations

The plants have a 354 MW installed capacity, making it the largest installation of solar plants of any kind in the world.Theaverage gross solar output for all nine plants at SEGS is around 75 MWe — a capacity factor of 21%. In addition, the turbines can be utilized at night by burning natural gas.

NextEra claims that the solar plants power 232,500 homes and displace 3,800 tons of pollution per year that would have been produced if the electricity had been provided by fossil fuels, such as oil.

The facilities have a total of 936,384 mirrors and cover more than 1,600 acres (6.5 km²). Lined up, the parabolic mirrors would extend over 229 miles (370 km).

Principle of operation

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The installation uses parabolic trough solar thermal technologyalong with natural gas to generate electricity. 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.

Mirrors

The parabolic mirrors are shaped like a half-pipe. 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 3000 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.

Heat transfer

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.

Individual locations

The SEGS power plants were built by Luz Industries, and commissioned between 1984 and 1991. Kramer Junction employs about 95 people and 45 people work at Harper Lake.

PLANT	YEAR BUILT	LOCATION	NET TURBINE CAPACITY	FIELD AREA	OIL TEMPERATURE	GROSS SOLAR PRODUCTION OF ELECTRICITY (MWH)
			(MW)	(M²)	(°C)	1996	AVERAGE 1998–2002
SEGS I	1984	Daggett	14	82,960	307	19,900	16,500
SEGS II	1985	Daggett	30	165,376	316	36,000	32,500
SEGS III	1986	Kramer Jct.	30	230,300	349	64,170	68,555
SEGS IV	1986	Kramer Jct.	30	230,300	349	61,970	68,278
SEGS V	1987	Kramer Jct.	30	233,120	349	71,439	72,879
SEGS VI	1988	Kramer Jct.	30	188,000	391	71,409	67,758
SEGS VII	1988	Kramer Jct.	30	194,280	391	70,138	65,048
SEGS VIII	1989	Harper Lake	80	464,340	391	139,174	137,990
SEGS IX	1990	Harper Lake	80	483,960		141,916	125,036

Harper Lake

SEGS VIII and SEGS IX, located at 35°01′54″N 117°20′53″W /35.0316°N 117.348°W, are the largest solar 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. SEGS VIII and IX have operated continuously and have been commercially successful since the very beginning.

Kramer Junction

This location (35°00′51″N 117°33′32″W / 35.0142°N 117.559°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.

Daggett

SEGS I and II are located at 34°51′47″N 116°49′37″W /34.8631°N 116.827°W.

Accidents and incidents

In February 1999, a 900,000-US-gallon (3,400 m³) therminolstorage tank exploded at the SEGS II (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 caustic soda. The immediate area of 0.5 square miles (1.3 km²) was evacuated.