Cheaper Solar Thermal Power

A simpler design could reduce the cost of solar power generated by concentrating sunlight on Stirling engines.

Stirling Energy Systems (SES), based in Phoenix, has decreased the complexity and cost of its technology for converting the heat in sunlight into electricity, allowing for high-volume production. It will begin building very large solar-power plants using its equipment as soon as next year.

Sun catchers: This is the latest design of a system for focusing sunlight on a Stirling engine to generate electricity. Credit: Sandia National Laboratories/Randy Montoya

The company is currently building a 1.5-megawatt, 60-unit demonstration plant that will use the company's latest design. Stirling expects to finish that project by the end of the year. It also has contracts with two California utilities to supply a total of 800 megawatts of solar power in Southern California. The first of the plants that will supply this power could be built starting the middle of next year, pending government permits and loan guarantees from the U.S. Department of Energy (DOE).

The projects are part of a resurgence in what's known as solar thermal power. Various solar thermal technologies were developed starting in the 1970s, but a breakdown in government funding and incentives caused them to stall before they reached a scale of production large enough to drive down costs and allow them to compete with conventional sources of electricity. "It was a classic problem with solar. The market support to bring solar to high volume wasn't there," says Ian Simington, the chairman of SES and chief executive of the solar division of NTR, a company based in Dublin, Ireland, that bought a controlling share of SES last year.

Recent state mandates and incentives for renewable energy have led to a new push to commercialize the technology. There are over six gigawatts of concentrated solar power under contract in the southwestern United States right now, says Thomas Mancini, program manager for concentrated-solar-power technology at Sandia National Laboratory in Albuquerque, NM. That's equivalent to about six nuclear-power plants. BrightSource Energy has contracts to provide 2.6 gigawatts of solar power with concentrated solar power (a previous version of this story cited only one of two 1.3 gigawatt contracts), and Solar Millenium has announced a project that would generate nearly one gigawatt of power.

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Stirling Energy Systems technology uses 12-meter-wide mirrors in the shape of a parabolic dish to concentrate sunlight onto a Stirling engine. The difference in temperature between the hot and cool sides of the engine is used to drive pistons and generate 25,000 watts of electricity. The first phase of the company's large-scale projects will use 12,000 of these dishes to generate 300 megawatts of power. Simington expects electricity from the systems to cost between 12 and 15 cents per kilowatt hour, higher than the cheapest sources of electricity--such as coal-fired power plants--but competitive in many markets, especially in the afternoon, when prices are highest.

Earlier this month the company unveiled its production design. Compared to several prototypes that have been tested for several years at Sandia National Laboratory, the new design cuts about two metric tons from the weight of each dish and reduces the number of mirrors in each from 80 to 40. The simplified design can be built in large quantities using equipment in existing factories for automobiles.