Stirling engines have been around since 1816, but achieved widespread commercial success between about 1880 and 1920. At that time they were commonly known as hot air engines and available in 4″, 6″ 8″ and 10″ bores, with power outputs generally less that 1hp. Manufacturers including Rider, Ericsson and Robinson were prevailent about a century ago. A hot air engine does not possess the regenerator, which characterises the true Stirling engine. During that time they were used primarily for domestic water pumping in large houses and ranches. By 1920, mains electricity was starting to appear in the cities and towns, and so Stirling pumps were generally replaced by electric motors. They were also used as small sources of mechanical power for dentists drills, laboratory machines, organ blowing, popcorn tumbling, fans and many other quaint, obscure Edwardian uses.

I have even seen a decorative “table fountain” in art Deco style which uses a small Heinrici engine to pump the fountain jet. Philips revised the Stirling engine in 1937, and began almost 50 years of R&D into making the Stirling a reliable prime mover for cars, buses trucks and ships. The vehicle engine reached its peak in the late 1960s through to the mid-1970s but generally came to an end in 1980 or so. Stirlings use a lot of intricately formed heat resisting steel in their heat-exchanger construction, and compared to gasoline or diesel engines, the manufacturing costs of the heat exchangers proved to be very high. There are really only 2 or 3 commercially available Stirlings, The 1000W generator set from Whispertech ($11,000) , the 11kW Solo161 engine from Solo Kleinmotoren of Stuttgart, and the 20kW STM 4-120 from Stirling Thermal Machines, (Ann Arbor, Michigan – I think).

Sunpower, of Athens Ohio, have experimental 1kW and 3kW free-piston machines designed to drive linear alternators. There also used to be a 5hp low tech engine the ST5 produced by Stirling Technology – but I think the rights to this have been sold to a Japanese company. It was a big (12″bore x 12″ stroke 660lbs) machine – but well suited to burning biomass. Cost about $5000 if I recall – website available.

Historical engines sometimes become available but these are large and heavy and made of cast iron – at 100 years + old, many of them are still going strong – obviously built to last.

In Munich, Germany, there is a group of young engineers working on amateur built engines – from a set of castings produced by Dieter Viebach. These will produce about 350W of electricity, and would be ideal for an off-grid holiday home, two engines could be combined on a common crankshaft to produce a 1hp design – ideal for a small boat. (Remember someone rowing can really only give about 1/10th horsepower). The Viebach design has an 80mm bore and a 75mm stroke. It can be built by borrowing automotive or compressor pistons and bores – eg 1600VW aircooled barrels. Europeans might beable to get scrap Citroen parts from 2CV and Ami cars. These have a really good crankshaft which can be easily adapted to a V twin design.

There appears to be no amateur built engines which exceed 1kW. I think this power level needs more development, and larger machine tools to fabricate.

If Stirlings are to succeed, we need a good robust reliable design, and get the Chinese to produce them for the rest of the World. That way the cost will be minimised. It is questionable though, whether, a good “universal” design has been found yet. There are so many ways of cutting a Stirling, that no one design appears to be a clear winner.

In my humble opinion, there is more power to be had from amateur constructed steam engines, than Stirling engines, and if they are driven from a temperature and pressure regulated monotube boiler, they can be made safe in operation. See the light blue links.

Expect at best only 10% thermal to mechanical efficiency for amateur built Stirling or Steam engines. For model Stirlings, you will be lucky to get 1%. However, there will be no shortage of heat available for domestic heating!