[extropy-chat] Greenhouse Power? (was A Grim Vision ...?)
lcorbin at rawbw.com
Fri Apr 27 01:19:23 UTC 2007
> [Lee inquired]
>> Why doesn't this furnish a productive energy source? That is, the
>> temperature difference generated between such an enclosure and
>> the outside sounds as though it could be useful.
> Lee this may have already been answered by others. I am way behind on my
> email due to a business trip and vacation.
:-) You answer it even better than Robert did, whose reply was
> The reason greenhouse effect doesn't provide an energy source is that the
> efficiency of running a heat engine in a greenhouse would be very low. To
> estimate a maximum Carnot efficiency using greenhouse effect, take the
> difference in temperature inside a typical greenhouse minus the temperature
> outside, probably about 10 kelvin,
The temperature difference is ~10 degrees K
> and divide by the temperature outside, at
> least high 200s, probably about 300. A Carnot cycle using a greenhouse as a
> hot thermal energy reservoir (TER) and the outside as the cold TER could
> produce power at around 3% efficiency at best, which is still probably on
> the high end.
Ah, yes, it's coming back. I do now recall in thermodynamics this
calculation being carried out for steam engines, where the temperature
difference is ~50 or ~100 K if I recall correctly.
> Let me know when you have some time, I will bring over to your house my
> thermodynamics book and show you the equations.
:-) I may have more thermo books than you do! But you've saved me 15
or 20 minutes looking it all back up, and making sure I had the right equations.
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