PROTOTYPE
Alternative Solar

Solar cells promise clean and unlimited energy, but they’re notoriously inefficient at converting the sun’s rays into electricity. Phoenix’s Stirling Energy Systems and Sandia National Laboratories have teamed up to field-test an alternative solar technology that promises twice the efficiency of conventional silicon solar cells. (Efficiency is defined in this case as electricity produced per watts of sunlight falling on a given area.) The researchers have built a prototype power plant using six solar-powered engines. Each engine consists of a large dish, 11.6 meters in diameter, made up of 82 mirrors. The mirrors focus the sun’s rays onto a receiver containing a bundle of small hydrogen-filled metal tubes. The gas expands when it’s heated by the solar rays and cools as it passes through heat exchangers. This expansion and contraction drives pistons, which in turn drive a generator. Though individual solar-dish engines have already been tested as a way to provide on-the-spot power for remote locations, this is the first time anybody has used them to build a power plant. Stirling Energy Systems’ aim is to build plants with thousands of engines and sell the power – enough for tens of thousands of homes – to utility companies. The company is in discussions with utility companies in Arizona, California, Nevada, and New Mexico and hopes to have its first commercial plant running by 2007.

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