Re: What would you do to save the environment?


In article <1190999250.560390.284880@xxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Brian Davis <brdavis@xxxxxxxx> wrote:
On Sep 28, 10:27 am, nos...@xxxxxxxxxx (Paul Ciszek) wrote:

All heat-based power plants, including nuclear,
dump more energy as waste heat than they deliver as electricity.

Actually, they dump *all* their energy as waste heat; it's just a
question of where. Supplying the energy need by SPS isn't going to
increase the net heat released to the environment (compared to
generating the same energy by other methods), but it may significantly
impact local conditions if you're not careful.

Let me try to phrase it differently, then: For each megawatt of useful
electricity generated, which as you point out will eventually become
heat, a conventional (or nuclear) power plant must must also generate
several megawatts of waste heat that goes directly into the air or water.
For every megawatt of useful juice you get (maybe) three megawatts of pure
waste heat, for a total of four megawatts of heat warming up the planet.
Now, SPS's are not perfect either, and only convert some fraction of the
sunlight hitting them into useful electricity. Some gets reflected, but
designers try to minimize this. So, a lot of sunlight gets absorbed by
the cells and converted into heat instead of electricity. For thermo-
dynamic reasons I won't go into, it is best to just try to radiate this
away (usually from the back of the array) as quickly as possible rather
than try to convert it into electricity as well. Here's the difference:
They are not on Earth, and the waste heat is not going directly into the
air or water. Since they are orbiting Earth, Earth probably takes up a
big part of their "sky", so *some* of their radiated waste heat is
radiated towards Earth, but hopefully we can keep this fraction tiny.

So, now we deal with the issue of the transmission beam. It will not
be perfectly efficient either, nor will the antennas that are used to
capture it. So the question is, how much of the energy of the beam
will be wasted? If the answer is 50%, you're doing better, waste-heat-
wise, than an earthbound generator. There is also the benefit of not
generating any greenhouse gasses, but the same can be said for nukes.

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