[extropy-chat] Greenhouse Power? (was A Grim Vision ...?)

[Lee Corbin]

Spike writes

> [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 
quite helpful!

> 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.
Thanks,

Lee