On Tue, 27 Dec 2011 11:06:05 -0800, Daniel Prince
wrote:

I have read that Stirling Engines are very efficient, very quiet and
that they can use any fuel or heat source. The downsides to them
are that they are big and heavy and they do not like to vary their
operating speed. These downsides would be a problem in vehicles but
not in an electricity generator for a home.

I think a Stirling Engine would be very good for an emergency
generator for a home. I wonder if anyone has ever marketed one.

Yes, they have. Here's one:

http://www.whispergen.com/main/aboutus/

There's one made in California that produces, IIRC, up to 5 kW and is
fueled with wood pellets.

I
suspect that a Stirling Engine would last a very long time with
minimal maintenance.

Stirlings have two problems. One is lubrication, although the more
advanced companies in the business have largely overcome that one. The
other is the life of the hot-side heat transfer unit and the
"economizer," which is the transfer-gas heat-storage/regenerator.

They run at very high tempertures; they're typically made of
superalloys; they're expensive, and eventually lose efficiency.

It's not that the problems can't be overcome. It's just that they're
expensive.

They are fascinating machines and I still hold out hope that someone
will build one that blows away IC engines for off-grid and backup
generation.

--
Ed Huntress