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Electricity from heat (continued) - Page 2

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Posted by Eeyore on April 7, 2009, 2:12 am
 


harry wrote:


What do you think power stations do 24/7/365 ?

Graham


Posted by harry on April 7, 2009, 6:45 pm
 
wrote:

They are using cheap coal and residual fuel oil, not expensive diesel
fuel.  It's a cost thing. Also they are far more efficient than your
little genset at home.   Though only hitting 35%.
Some of the commie cities had district heating schemes. Only used in
the Winter period of course.
http://web.worldbank.org/external/projects/main?pagePKd283627&piPKs230&theSitePK@941&menuPK"8424&Projectid=P089078

Posted by Alistair Gunn on April 7, 2009, 6:53 pm
 harry twisted the electrons to say:

Also quite common in Austria, where they seem to be upgrading them from
straight district heating to CHP district heating.  Again, they only use
them during the winter.
--
These opinions might not even be mine ...
Let alone connected with my employer ...

Posted by Tim Jackson on April 7, 2009, 9:00 pm
 harry wrote:


Yes, they did.  I spent a couple of months in St Petersburg & Moscow.
It blew my mind to see people couldn't be bothered to turn off the hot
tap, just left it running over the dishes or whatever.

People turned their heating right up, didn't care about efficiency,
because communal meant what you used didn't reflect much in what you paid.


Tim Jackson

Posted by Tim Jackson on April 5, 2009, 8:51 pm
 harry wrote:

this.http://www.mandiesel.com/category_000082.html

Thermopiles are by their nature incredibly inefficient.  Handy when
you've got masses of temperature difference hanging around doing nothing
want a tiny amount of power, and don't have any other source handy.  You
might use one to run a radio receiver off a camp fire, just maybe, if
you could be bothered lugging the great thing around

The problem is that thermal conduction and electrical conduction in
metals are related, so anything that makes a good electrical conductor
between the hot and cold points also makes a good thermal conductor, so
for every watt of electricity produced you get some hundreds of watts of
conducted heat, Use worse conductors and you get proportionately more
electrical losses.

There's a picture of a 100W thermopile on this site, it's about a cubic
metre in size, and mostly metal.
www.dself.dsl.pipex.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm

But if you replace the metals with semiconductors you can get much
bigger voltages, and sometimes big differences between electrical and
thermal conductivity.  Regular electronic semiconductors are unsuited to
high temperatures, so practical thermoelectric generators tend to use
rather exotic materials.

You might want to start here.
http://en.wikipedia.org/wiki/Thermoelectricity


Tim Jackson

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