Bird's-eye view of solar plant that works at night

Roger Highfield, editor, New Scientist magazine

(Image: Markel Redondo)

Sunshine can be turned into electricity at night in this thermosolar plant. Gemasolar, in Fuentes de Andaluc?a near Seville in Spain, is the first commercial-scale plant to use an innovative "battery" that stores energy as molten salts.

More than 2600 heliostats - flat mirrors - over 185 hectares reflect and concentrate sunlight onto the top of a tower. In the "power tower", potassium and sodium nitrate salts are heated to 565 ?C and then pass through a heat exchanger where they turn water into steam to drive turbines in the 19.9 megawatt plant.

When there's more heat than is needed to turn the turbines, some of the hot salt solution is stored in a tank. This battery allows electricity to be generated for up to 15 hours when there's no sunshine. "In summertime, we expect to run continuously most days," says Santiago Arias, technical director of Torresol Energy, which owns the plant.

In the winter, daily sunlight is inadequate for the plant to operate at full power throughout the night. Arias says Torresol can either run the plant until the battery is exhausted, or it can modulate the power of the turbine during darkness so it is at its maximum between 11 and 11.30 pm, when electricity demand - and price - peaks, "so we are able to reach the next day without stopping the turbine".

In this way Gemasolar should be able to generate electricity for 6500 hours a year, which the company claims is up to three times as long as other renewable energies.

Torresol is also building twin 50 MW parabolic plants in southern Spain. In these, oil in a pipe is heated by sunlight reflected from parabolic mirrors. They, too, will have molten salt batteries, able to generate power for 7.5 hours after the sun sets. The plants will begin commercial operation on 1 January 2012.

Source: http://feeds.newscientist.com/c/749/f/10897/s/19587489/l/0L0Snewscientist0N0Cblogs0Cshortsharpscience0C20A110C10A0Cbirds0Eeye0Eview0Eof0Esolar0Eplant0Bhtml0DDCMP0FOTC0Erss0Gnsref0Fonline0Enews/story01.htm

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