Graeme,
Stirlings can be economical to construct, provided that you do not require
high power density. The German engine requires some fairly intensive
machining and in low volumes and high German labour cost does not make for a
cheap engine. Give this to the Chinese and it would cost $500 !
If you stick to about 1 watt shaft power per cc of power piston swept volume
- then the engine can be fairly simple, if not a little bulky - but for low
maintenance stationary applications this should be fine.
I have a friend in Pescadero CA, who is self-building some big Stirlings,
here is his URL for details/pictures.
http://www.symanski.net/stirlings/index.html
Jim is a welder by trade and no job is ever to big. He has a 30'long saw
mill rig, and a bulldozer with logging grabs to handle large trunks. He
invested in this when a flash flood in the creek dumped a load of prime
quality timber on his land.
For more Stirling links, see www.geocities.com/wastewatts/index.html
Ken.
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