SEGS I in California began operating in 1984 as the first commercial parabolic-trough solar-thermal plant.
SEGS means Solar Energy Generating Systems. The first unit was built at Daggett in the Mojave Desert, where long rows of curved mirrors focused sunlight onto receiver tubes containing heat-transfer fluid.
The heated fluid produced steam through a heat exchanger, and the steam drove a conventional turbine generator. Later SEGS units expanded the complex and demonstrated commercial operation at much greater scale.
SEGS I is distinct from Solar One, a central-receiver power-tower project, and from photovoltaic farms, which convert sunlight directly into electricity without a steam cycle.