Molten salt storage has been proven in other countries in recent years, as described by our own Peter Fairley in a story on the Andasol 1 plant in Spain. Like the Spanish facility, BrightSource will use a combination of sodium nitrate and potassium nitrate in its system. Basically, the salts are heated during the day when the sun is shining using a heat exchanger, and the process is reversed at night when power is needed but no sun is available.
BrightSource's solar technology involves the solar tower concept, in which a huge array of thousands of mirrors -- known as heliostats, because they track the sun across the sky -- concentrates the sun's rays on to a centralized tower. Inside the tower, steam is generated from the heat, and the steam is used to run a turbine just as in a standard power plant. The molten salt storage will allow the turbines to turn after dark. Though possible to keep them turning all night, the company says a two- to six-hour window is optimal. BrightSource is currently building the Ivanpah Solar plant in the Mojave Desert, a 392-megawatt project that has generated controversy for its use of public lands and the potential environmental harm involved.
(Image via BrightSource Energy)
Dave Levitan is the science writer for FactCheck.org, where he investigates the false and misleading claims about science that U.S. politicians occasionally make.