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

Martin LaMonica Former Staff writer, CNET News
Martin LaMonica is a senior writer covering green tech and cutting-edge technologies. He joined CNET in 2002 to cover enterprise IT and Web development and was previously executive editor of IT publication InfoWorld.
Martin LaMonica
4 min read
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 Stirling engine idea to generate electricity. 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.

But Infinia is staying clear of the wholesale power supply business because it's harder to compete with fossil fuel power on price, said Clyde.

Electricity generated from fossil fuels, such as coal or natural gas, is by far the most common form of power generation in the U.S. and is generally cheaper per kilowatt, according to solar industry executives.

"We wish Stirling Energy Systems all the success in the world because they're using a Stirling engine," Clyde said. "But if you can go after markets where (financial) incentives apply, you're not really competing against utility scale" pricing.

Besides planning to make a far smaller product, Infinia's generator will have a different design from those built by Stirling Energy Systems.

Infinia builds what is called "free-piston machines." This relies on changing air pressure to move motor components without having parts rub against each other. That design eliminates the need for lubrication and substantially cuts down on maintenance, Clyde said.

Combined heat and power
Infinia has been operating for over 20 years as a supplier of motors to government agencies for space and military applications.

Three years ago, the company reorganized itself to pursue potentially higher growth in the clean energy market, said Clyde. The company was chosen to present at the Cleantech Venture Forum in September and is seeking to raise funds to commercialize the solar Stirling product.

But solar electricity is only one application of the company's Stirling engines, said Clyde.

"With a Stirling engine, the thing that's great about it is that it only requires a heat source. It doesn't care what the heat source is," he said.

In the case of its solar Stirling product, the heat source is the sun. But the company is investigating a range of other applications and smaller models, which could be used to create electricity from biogas, such as methane, or used as on-board generators on tanks or trucks.

Already, Infinia has licensed its design for a combined electricity and home heating unit to manufacturers in Japan, the Netherlands and Germany.

Sized to fit under a kitchen counter, the units will use natural gas to fuel a Stirling engine that makes electricity. The process also creates hot water, which is used in water-based heating systems.

Infinia has individual homes in mind for its Stirling solar-electric products as well.

"I live on about two acres," said Clyde. "I can't wait to be the first on my block with one of these."