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Wildly efficient Stirling engines

December 31st, 2006

I first became aware of the Stirling engine when reading about inventor Dean Kamen many years ago. He didn’t talk about the Stirling Engine in detail, but what I did find out was that it is an incredibly efficient non-combustion engine, that is powered by differences in temperature. (e.g. you can buy small a Stirling engine that is powered by the difference in the heat from your hand and the ambient temperature.

Sounds great right? In our home, maybe we could generate heat on the roof, and take cool from the ground and generate some free power, right? As is often the case, the first tip-off that there might be a problem with this logic is that nobody has done so already.

I did a little more research and it seems that unless you can get a heat differential of about 300 degrees Celsius, a Stirling engine practical for powering a typical home would itself need to be about the size of a typical home. Stirling engine size is proportional to the amount of power one needs, and inversely proportional to the heat differential between the cold and hot sides of the engine.

Another problem would seem to be the noise. The seemingly inappropriately named WhisperGen of New Zealand specializes in producing Stirling engine water-heater/power-generator combination units. According to their literature, these devices produce 63dBA of noise (and only a fraction of a house’s power requirements). While that’s quite quiet for a generator, it’s still the volume of a loud conversation, or air conditioner. That’s fine if one is encountering it from time to time, but to have it going in one’s home all the time would likely get a little grating.

It might very well be possible to overcome the heat differential limitation, but given the noise they generate it seems unlikely that Stirling Engines can be a part of any urban sustainable build.

Posted by Colin