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Solar Energy

Published on October 5th, 2009 | by Tina Casey


Cool Energy's SolarHeart Brings Solar Power to Cold Climates

October 5th, 2009 by  

Homes in colder climates could generate their own electricity with SolarHeart, Cool Energy\'s low-temperature solar engine.

Building solar power plants in the desert is a no-brainer, but until now there hasn’t been a cost-efficient way to provide solar power directly to homes in colder, cloudier parts of the word.  Cool Energy, Inc. believes it can do just that.  Last month the Boulder, Colorado based company announced the release of SolarHeart, an engine designed for home use that can convert low-temperature solar energy into sustainable electricity, and also saving up to 75% on heating oil or propane.


The SolarHeart engine is based on the legendary Stirling engine design, which harkens back to the early 19th century.  Stirling engines run on changes in the pressure of hydrogen as it is alternately heated and cooled in a sealed chamber, which drives a piston.  Cool Energy plans to integrate the SolarHeart engine into a complete solar energy system built into individual homes and other buildings.  If SolarHeart lives up to its promise, we could all be just a heartbeat away from off-grid living.

Cool Energy, Inc.

Cool Energy has been making a name for itself by tweaking the nearly two century old Stirling platform into the engine of choice for solar energy design.  One clear advantage of the Stirling engine is its ability to run on practically any heat source including waste heat.  That makes it an ideal candidate for cogenerating electricity from the waste heat of factories, diesel generators, and other heat sources.  As part of Cool Energy’s SolarFlow system, the SolarHeart engine would be able to convert both solar and waste heat into electricity for use in homes and small commercial buildings.

The SolarHeart Difference

According to MIT Technology Review writer Kevin Bullis, Cool Energy’s proprietary SolarHeart engine works at only 200 degrees Celsius, far lower than the 500 degrees required to run a conventional Stirling.  Normally, a solar-powered Stirling engine would be unsuitable for most homes because it requires full sunlight and solar concentrators to get the high temperature.   Bullis also notes that Cool Energy was able to design a low-temperature engine by using plastics and certain ceramic materials that are poor conductors of heat.  These are used to separate the “hot side” and “cold side”, helping to keep the difference between the two sides higher than possible with the conventional metal design.

SolarFlow and Cold Weather Solar Power

In variable climates such as the northern U.S. and Canda, the SolarFlow system offers the best of both worlds.  In winter, the system’s solar collectors provide heat for the home.  In the summer, the SolarHeart engine converts excess heat into electricity, which could be used to run fans or air conditioners. That tightens up the payback period, making the system a more attractive investment for property owners.  Cool Energy anticipates that the complete SolarFlow system, which includes a thermal storage feature, will provide 80% of a home’s heat, all of its hot water, and 60% of its electricity.

More Stirling Engines in the Future

With their low maintenance requirements and ability to run on practically any fuel or heat source, Stirling engines make an ideal platform for alternative energy, and Cool Energy is not the only fan among solar innovators.  The high efficiency SunCatcher solar dishes use a Stirling-based power conversion unit to convert focused solar thermal energy into grid-quality electricity, Segway inventor Dean Kamen is working on an electric scooter that sports a two-piston Stirling under the seat, and Mitsubishi is looking into infrastructure support for its MiEV electric car, including a solar thermal dish hooked up to a Stirling engine.

Image: Mark F. Levisay on flickr.com.

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

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