Cell-Less Solar Farms

This month, in the latest in a string of recent deals, Spanish solar-plant developer Abengoa Solar and Phoenix-based utility Arizona Public Service announced a 280-megawatt solar thermal project in Arizona. By contrast, the world's largest installations of photovoltaics generate only 20 megawatts of power.

Morse says that while the design of solar thermal power stations is rapidly diversifying, most will use essentially the same system for storing energy: tanks full of a molten salt that remains liquid at temperatures exceeding 565 °C. "It's basically two tanks with a lot of heat exchangers, pipes, and pumps," says Morse. For a sense of scale, consider that the 50-megawatt plants that Germany's Solar Millennium is building in Spain near Granada will employ 28,500 tons of molten salt in twin tanks standing 14 meters high and 38.5 meters in diameter.

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