An Introduction to Solar Thermal Electric Power

All solar thermal systems capture the energy of the sun by absorbing light as heat. Solar thermal power systems focus sunlight, usually with mirrors, to heat a fluid to high temperatures and drive an engine. This approach stands in contrast to photovoltaic solar power systems, in which light interacts with special materials directly to separate charges and generate electricity. Photovoltaic power enjoys many advantages, such as unattended operation and small-scale feasibility, but remains significantly more expensive as a source of large-scale power than solar thermal technologies. The modern era of large scale solar power generation was born in California’s Mojave Desert in the 1980s, when Luz Industries built a total of 354 MW of Solar Electric Generating System, or SEGS, power plants. The SEGS plants use long parabolic mirrors with pipes at the focus point, where circulating oil is heated to 700 F (350 C). The oil is pumped through heat exchangers which boil water to make high-pressure steam, which drives turbine generators to make electric power. For many years the SEGS plants produced the majority of the world’s solar electric power. Subsequent research in solar power generation has reduced the cost of parabolic trough power systems, and has developed several optical systems other than the parabolic trough. Recently, Abengoa has placed in service the PS-10 power tower system, which employs a field of reflectors which move in two dimensions to focus light at the top of a tower, where a boiler is located which absorbs the light and generates steam. Such systems have been in development since the 1960’s. A large pressure tank, or “steam accumulator”, stores energy as pressurized hot water and allows the plant to continue generation in cloudy conditions for up to an hour.