Dishing Out Power With a Solar Engine
By Martin LaMonica
Wednesday 25 October 2006
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
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.
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.
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 US and
is generally cheaper per kilowatt, according to solar industry
"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
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
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."