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Does anyone have information (or sites of available information)that
describe approximate cubic size of Stirling engines capable of
driving a 12-20 kW generator?

Jeffrey,

Don't confuse Stirling cycle engines with Otto cycle internal combustion engine. Internal combustion engines are "atmospheric" pressure engines because they intake and exhaust the working fluid (air) at 14.5 PSI. For this reason, the output is typically a function of the displacement. i.e. large displacement-large output.

This is not true for modern Stirling engines. The working fluid, often not air, is completely sealed inside the engine and at very high pressures. The output is more closely coupled with the internal pressure and not the displacement. Roughly speaking, doubling the internal pressure doubles the output regardless of the displacement.

The antique hot air engines that were produced in great numbers during the 1800's did work at normal atmospheric pressure. However, they did not produce significant power. A 500 cubic inch engine would only produce a few HP or less. The Stirling brothers, Robert and James, did make a 45 HP engine for a factory. It used several atmospheres of pressure but still had pistons several feet in diameter.


The links below show examples of some modern Stirling engines that produce 9 to 75 Kw of electric output.

http://www.stirlingenergy.com/

http://www.Stirling.dk/

Rick