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. The average 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

The installation uses parabolic trough solar thermal technology along 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.


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.

SEGS plant history and operational data
Plant Year
Location Net turbine
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 / 35.0316; -117.348 (SEGS VIII and IX), 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 / 35.0142; -117.559 (SEGS III–VII)) 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 / 34.8631°N 116.827°W / 34.8631; -116.827 (SEGS I and II).

Accidents and incidents

In February 1999, a 900,000-US-gallon (3,400 m3) therminol storage 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.