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

Published on October 5th, 2009 | by Tina Casey

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Cool Energy's SolarHeart Brings Solar Power to Cold Climates



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.

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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

Tina Casey 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. You can also follow her on Twitter @TinaMCasey and Google+.



  • Steve Savage

    Thanks for the links. I’d like to try to find/build some of these because where I live (San Diego) it would be a far better way to get off the grid than using carbon-emission-intensive photovoltaic cells

  • Steve Savage

    Thanks for the links. I’d like to try to find/build some of these because where I live (San Diego) it would be a far better way to get off the grid than using carbon-emission-intensive photovoltaic cells

  • http://www.coolenergyinc.com Sam Weaver

    Regarding the capacity of the SolarFlow System, the engine is sized at 1.5kW peak power, and will operate about 30-40% of the hours of the year, depending on the number of collector panels, storage tank size, geographic location of the system, home heating load, etc. During its operating times, the engine will not always produce to its peak capacity, so a system is estimated to generate between 2500 and 5000 kWh per year, with the bulk of the production occurring in the warmer months, when the heat is not needed in the home. In the target markets, home electricity use averages 8000 – 10000 kWh per year.

  • http://www.coolenergyinc.com Sam Weaver

    Regarding the capacity of the SolarFlow System, the engine is sized at 1.5kW peak power, and will operate about 30-40% of the hours of the year, depending on the number of collector panels, storage tank size, geographic location of the system, home heating load, etc. During its operating times, the engine will not always produce to its peak capacity, so a system is estimated to generate between 2500 and 5000 kWh per year, with the bulk of the production occurring in the warmer months, when the heat is not needed in the home. In the target markets, home electricity use averages 8000 – 10000 kWh per year.

  • http://www.non-scalable.com Derek

    The Cool Energy system is supposed to provide about 1.5kw of energy, so unless they have up-ed the size of the engine, then providing 60% of home energy would have to come from buying multiple units. Or they are expecting people of the future to make do with only 2.5kw, that in it’s self might be a noble endeavor. Additional reporting at my site.

  • http://www.non-scalable.com Derek

    The Cool Energy system is supposed to provide about 1.5kw of energy, so unless they have up-ed the size of the engine, then providing 60% of home energy would have to come from buying multiple units. Or they are expecting people of the future to make do with only 2.5kw, that in it’s self might be a noble endeavor. Additional reporting at my site.

  • http://solartraining.blogspot.com solar training

    the flat plate tubes may be cheaper but they are nowhere near as effective as evacuated tubes

  • http://solartraining.blogspot.com solar training

    the flat plate tubes may be cheaper but they are nowhere near as effective as evacuated tubes

  • russ

    For residential use – the following applies.

    The solar panels by themselves will provide that much hot water – no need for this equipment for that service. I do that now with flat plate collectors in an active system which are much cheaper than the evacutated tube type.

    The SolarHeart unit may do better at generating electricity in the summer months. Is it cost effective?

    Sounds interesting but they provide practically no information on their web site that I could find. Only a few statements.

  • russ

    For residential use – the following applies.

    The solar panels by themselves will provide that much hot water – no need for this equipment for that service. I do that now with flat plate collectors in an active system which are much cheaper than the evacutated tube type.

    The SolarHeart unit may do better at generating electricity in the summer months. Is it cost effective?

    Sounds interesting but they provide practically no information on their web site that I could find. Only a few statements.

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