Dishing out power with a solar engine

Infinia looks to an existing technology--the Stirling engine--to compete in solar-electric industry. Photos: Retro energy-harness

A company is trying to prove that a 19th-century design known as the Stirling engine has a place in the emerging market for clean energy.

Infinia, based in Kennewick, Wash., plans to release a dish--which will look like a large satellite TV receiver--that will use the sun's heat to generate electricity. The product is slated for final design later this year and commercial release in 2008.

The company's planned entrance to the fast-growing solar-electric market is somewhat unique. The great majority of solar companies are racing to squeeze as much electricity as possible out of photovoltaic cells built from silicon or other materials.

By contrast, Infinia's solar Stirling engine, which concentrates light from the parabolic dish, is a mechanical device, which the company claims can be more cost-effective than traditional solar panels.

"This design means that we can make more electricity for about half the relative space as photovoltaics," said Jim Clyde, Infinia's vice president of sales and marketing. "It won't be half the cost when we first get going, but it will be for significantly less capital cost."

Standard solar photovoltaic panels are generally 12 percent to 15 percent efficient at converting light to electricity, though some can go up to 22 percent. Infinia's planned 3-kilowatt Stirling engine will operate at 24 percent efficiency, Clyde said.

Solar generators

Stirling engines were invented in the 19th century as an alternative to steam engines. A Stirling motor has a closed cylinder that houses a gas, such as hydrogen, and a piston. Applied heat expands the gas to move the piston that, in turn, pumps other mechanisms, such as a crank, to create energy.

Infinia is one of a growing number of companies focusing on the clean energy sector. Several companies are seeking to commercialize existing technologies, such as a Stirling engine, in an effort to meet the demand for cleaner sources of energy.

The target customers for Infinia's first solar Stirling engine are larger organizations such as city governments, which are taking advantage of financial incentives--from such governments as the state of California--to use less-polluting forms of power generation.

Roughly 15 feet high, the dishes--which move to maximize light input during the day--are meant to compete against photovoltaic systems mounted on the ground, rather than panels on a homeowner's roof. Potentially, thousands of the generators can be placed together if enough land is available, according to the company.

Stirling sister
Infinia is not the only company trying to apply the . Perhaps better known in solar circles is Stirling Energy Systems, which is building power plants with arrays of giant dishes with more than 80 mirrors in the California desert to generate hundreds of megawatts of electricity. It has signed two power generation contracts with California utilities.

The initial solar Stirling engine design from Infinia calls for 3-kilowatt systems, which roughly suits the power needs of a residential home. Several connected ground-mounted systems could supply a larger customer, such as a city government.

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