Re: Hullo Oz!

Oz wrote:


This one is really nutty but thermodynamically it should work.

The thing is that the sun is at some 3000C and that's a huge
differential that we ought to use. Now, realistic systems that can run
with a hotside of even 1000C are a tad thin on the ground (thermopile
stacks might be very efficient here), although this one probably can't
manage 1000C hotside.

http://www.globalte.com/index.php?pageId=2&sId=31

Yes they seem limited to about 400C with a conversion of a few % to
electricity. Caterpillar have some engines with them in the exhaust to
power the ancillaries. Phillips also make a small stove for the third world
that has one of these bismuth TEGs to power the combustion air fan.

In fact as I said in an earlier comment a steam based system still seems
trumps with a mixture of concentration and air insulation of the collector.
Nanotubes also hold some promise, as you realise the concentrators don't
add to the temperature, they just try to match the radiative losses by
appearing to increase the solid angle through which the sun's rays are
received. You can get the same temperature by pointing the collector
straight at the sun and reducing its radiative losses by limiting the
steradians it can emit over, the ultimate is a heliostatic, long tube
therough which light can only travel back to the sun.

Anyway, if we use a mirror to heat a working fluid (eg air) to say 300C
(which should not be hard) this can power a heat engine. Now we use this
heat engine to power a heatpump to cool the coldside (usefully) and we
will still have power left over to power a second heatpump doing the
conventional thing. This way we need no electricity!

See my earlier reply which crossed in the ether with yours, yes you should
be able to up the COP of a heat pump by using it in combined cycle to do
work, which can then be applied to run the heat engine.

AJH
.

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