"IMM" wrote in message ...
"NickW" wrote in message
om...

Solar thermal however, I think should be exploited first as it seems
to yield the big numbers for something as simple as heating air.

Air heaters are very efficient. have one on the back wall of a conservatory
with the heat rising into the house, or loft and ducted down.

What is very efficient and economical, is a sun tracker focusing the sun via
lenses onto a heat exchanger and producing very hot water.

I like that approach too, tho its not problem free. I would go flat
plates /air first.

These can also
produce steam and run a small steam or Stirling engine/generator.

They can but its very impractical and very inefficient.

Even in
cloudy weather very hot useful water can be produced.

Partly cloudy yes, but qith full cloud youve got no way to concentrate
the diffuse sunlight.

Steam or Stirling
engines can be very small for high large torque.

Steam is the true master of inefficiency and bulk.

There is research in the
USA on sun trackers/heat generators for CHP applications, or cogen as the
Yanks say, and it appears more cost effective and efficient than most other
methods: PV cells, flat plate collectors, etc.

I'd be interested to see your refs then, as figures I've always seen
or calculated would suggest its a real no-no.

There are also additional problems with any steam setup due to legal
issues with the high pressure boiler. Plus PV and hot air are far more
reliable.

Regards, NT