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

[spike]

> bounces at lists.extropy.org] On Behalf Of Lee Corbin
...
> 
> Keith writes
> 
> > Think about how hot it gets inside a parked car in the summer
> > and you will get an idea of how hard it would be to seal up a
> > greenhouse.  You could also look up the power bills for cooling
> > Biosphere II.
> 
> 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


Lee this may have already been answered by others.  I am way behind on my
email due to a business trip and vacation.

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, 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.  You would do better with even low efficiency solar cells.

Let me know when you have some time, I will bring over to your house my
thermodynamics book and show you the equations.

spike