The New York Times reports on the emerging science of storing solar energy through the heating of salt, and the taxpayer loan to SolarReserve making this experiment possible:
If solar energy is eventually going to matter — that is, generate a significant portion of the nation’s electricity — the industry must overcome a major stumbling block, experts say: finding a way to store it for use when the sun isn’t shining...The Energy Department seems to agree: in September it gave SolarReserve a $737 million loan guarantee for its project in Nevada. The plant will generate 110 megawatts at peak and store enough heat to run for eight to 10 hours when the sun is not shining.
The public’s view on loan guarantees for solar projects has soured somewhat since the bankruptcy of Solyndra, a California company that received a $535 million loan guarantee to build a factory to make solar panels — only to see the market for the modules crash.
But the outlook has always been clearer for companies that make electricity, which, unlike solar modules, is generally presold by contract.
Technical details of the SolarReserve and BrightSource plants vary slightly, but both will use thousands of computer-operated poster-size mirrors aiming sunlight at a tower that absorbs it as heat.
SolarReserve absorbs the heat in molten salt, which can be used immediately to boil water, generating steam that turns a conventional turbine and generator. Hot salt can also be used to retain the heat for many hours for later use. BrightSource heats water that can be used immediately as steam or to heat salt for storage.
The plants rely on salt because it can store far more heat than water can. But once molten, it must be kept that way or it will freeze to a solid in part of the plant where it will be difficult to melt again. “You’ve made a commitment to those salt molecules,” said John Woolard, the chief executive of BrightSource.
The rest here.
