October 25, 2006 4:00 AM PDT

Dishing out power with a solar engine

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.

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17 comments

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Advantages over photovoltaic cells
The US residential house uses 120 VAC electricity but solar cells produce direct current (DC) voltage. This means you have to have an inverter to transform the electricity to a usable form for the house. The sterling engine can produce electricity at 120 VAC directly and also at 60 HZ which means the output can be fed directly into the power grid.
Posted by Seaspray0 (9714 comments )
Reply Link Flag
Invertor still necessary
Because the Stirling engine output depends on weather conditions, its RPM won't be stable, thus output voltage and frequency not stable, too. Therefore, and invertor (like those used in uninterruptible power supply) is still necessary.
Posted by alegr (1590 comments )
Link Flag
Stirling A/C anybody?
Better use for the solar energy would be to drive an air conditioner. When one needs AC, sun shines the best, and the direct drive from an engine to the compressor can be used, without conversion to electricity.
Posted by alegr (1590 comments )
Reply Link Flag
Heat can run A/C directly.
Solar heat can generate cooling directly in an absorption cooler.

Remember? The propane operated refrigerator in your dad's camper.

Heat to heat is more efficient than driving a compressor.
Posted by disco-legend-zeke (448 comments )
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Stirling Engines
More good news on the energy systems.
I suspect mass uptake of solar energies will only become attractive to Mr & Mrs Suburbia when it's available at a Drive-Thru (their cars seem big enough to carry one}.
Cynicism aside, this is a very heartening article, great to see discussion on the potential of this technology.
Posted by m.o.t.u. (96 comments )
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Fuel cells are also 19th century technology
The fuel cell was first demonstrated before the 20th century, but was resurrected and pursued in earnest only when the US space program had a need for a "clean" power source with its characteristics. I don't care when a technology was invented. If it is an appropriate idea for today, let's use it.
Posted by James Anderson Merritt (251 comments )
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Re: Fuel cells are also 19th century technology
I'll agree with you on that one. If it works, it works - and
hopefully it'll lead to bigger and better idea in the future.

Charles R. Whealton
Charles Whealton @ pleasedontspam.com
Posted by chuck_whealton (521 comments )
Link Flag
How about the Whispergen?..
<a class="jive-link-external" href="http://www.whispergen.com/index.cfm" target="_newWindow">http://www.whispergen.com/index.cfm</a>

This device admittedly runs on natural gas fuel at the moment but I can't see why it might not be made to run from a solar concentrator. It is quite a neat New Zealand development of the Stirling cycle and is available now.
Posted by jasred (21 comments )
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Good to See
It's good to see the proliferation of this technology. With advances in Plug-in hybrids etc..., we're laying the groundwork for a much cleaner, intelligent future. With improvements in metal, the Stirling engine has become much more practicle.
Posted by MrHandle (71 comments )
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Such as Hydrogen??? <<--spin>>
Are you trying to put some negative spin on this story with that reference? Hydrogen would never be used in a Sterling engine. The seals required would be monstrously expensive, and the things hydrogen under pressure does to metal alone would preclude its use - too much maintenance. I can't believe a CNET reporter would be that inept.

Your negative spin won't work either, if anyone looks a little deeper. Those engines, even at that size, use barely enough gas to cause a small fire if there were an accident (and if it was flammable). They use it like an air conditioner, closed loop, and it is never burned. The efficiency of a Sterling engine is best when using a phase-change liquid, like a refrigerant. You'd have to keep hydrogen at some ungodly cold temperature, depending on pressure, to make it boil from liquid to gas in the Sterling loop - Yet another impracticality.

Could someone with a brain check these stories? Sheesh.
Posted by chrisw63 (26 comments )
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Sheesh
A short literature and web-site search would indeed reveal that many Stirling engines use hydrogen and it is slippery to contain and often times requires a make up process to maintain performance (like a periodic refill). Also, not all Stirling engines are created equal, Kinematic versions (Solo, Kockems, STM, Dean Camen) have life, reliability and maintenance issues. The Free Piston varieties have been proven for long life and the Hellium versions are normally hermetically sealed for their long life, the reason most commercial focused programs are using Free Piston Stirling engines (Infinia, Rinnai, Enatec, Bosch)
Posted by columbus801 (1 comment )
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Here is another
<a class="jive-link-external" href="http://www.acrosolarlasers.com/" target="_newWindow">http://www.acrosolarlasers.com/</a>
Posted by Michael Labay (9 comments )
Reply Link Flag
ahhhh sir can somebody tell how much the cost of stirling engine power by solar??? i need for my data gathering on my research.. and can somebody refer to a site where can look for it??
Posted by may23lui (1 comment )
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