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Electricity from heat (continued)

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Posted by harry on April 4, 2009, 6:24 pm
Re previous posting
Found this:-http://www.globalte.com/index.php?pageId=2&sId 

It exists!

Posted by Ken Maltby on April 4, 2009, 7:29 pm

  As do the numbers:



Posted by Eeyore on April 4, 2009, 7:44 pm

harry wrote:

Yes. 60W - 6kW of load. It's designed for off-grid situations. Very
(un)helpful. Now get a real life. Do you really think scientists aren't
already aware of this and its cost ?

If you want efficient power you need co-gen like this.

" In combined heat and power mode (CHP) they generate both electrical
power and thermal energy and so overall energy utilisation levels as
high as 95%. "


Posted by harry on April 5, 2009, 6:43 pm


Aha! Well CHP is something I know about having run industrial sized
The main problem is only rarely do the heating and electric
requirements meet what the CHP device is generating.  Ie, what do you
do in Summer with the heat when you want just electricity?   You "need
to have a need" for heat all year round. Unless you have very large
requirements and are using the device only to meet part of the load,
the economics just don't work out.  It's helpful if you can export
unwanted electricity. But this needs expensive synchronising
You need to be able to run the thing flat out all times to make it
So, no use for home power, only useful in an industrial situation.  We
used ours for a hospital laundry which needed heat and electricity all
the time.
At least the thermopile has no moving parts & hence presumably would
be more reliable  (and silent)...   Could it run off, say a wood fire?
Of course it too is a CHP device.
Cost?   Hmm Steam engines and turbines are also costly and inefficient.

Posted by andrew on April 5, 2009, 8:26 pm
 harry wrote:

I've had a 10kW(e) genset running as CHP, it paid because there was no grid
connection and the heat became essentially free and was vented in summer.

In my home town there is a 3 engine natural gas chp distributed heat and
electricity system, in summer the network carries chilled water from an
absorption cycle refrigerant running off exhaust heat.

I guess a lot has to do with the value of electricity, if you have none then
a few Watt hours to charge a battery for a laptop or led light is quite
valuable, if you have a grid connection and use 30kWhrs a day then you'd
only be prepared to pay the grid price, which is difficult to compete with
because utilities deal on such a large scale their costs are lower.

Today I went to a show where there were both antique and modern Stirling
engines doing work, these seemed to be working at a thermal conversion
efficcy of around 5%. I think a modern thermopile based on a peltier device
and running at a maximum 150C would compete with that.


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