Re: What would you do to save the environment?

On Sep 28, 7:27 pm, nos...@xxxxxxxxxx (Paul Ciszek) wrote:

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.

Which is absolutely trivial in terms of the energy blanace of the
Earth. Period. In other words, it's really not something to worry
about. My point way that the only thing you really need to concern
yourself with is the local effect of, say, 10% of the microwave beam
over the rectenna being lost as heat. At those energy densities, that
could be a factor... but still not even worth a sneeze in a global
sense.

SPS's are not perfect either... a lot of sunlight gets absorbed by
the cells and converted into heat instead of electricity.

Certainly. But thermal reradiation from the array is even more
negligable, from the standoint of the energy balance at the Earth's
surface, then energy loss at the rectenna. Put an Earth-sized SPS in
geosync: it can collect 1.3e+17 W, around 8000x the current
consumption. If *all* of that was reradiated as heat uniformly (in
other words, a "0%" efficiency). 35,800 km away (at the distance of
the Earth), that would be a radiated power of 8 w/m^2, or an increase
in the effective global insolation of 2 W/m^2, averaged over the
surface - just over 0.1%. If we can build a structure that big, I
think dealing with that sort of "environmental impact". It's just not
significant (at this scale).

Here's the difference: They are not on Earth, and the waste heat
is not going directly into the air or water.

No - a good portion of the waste heat instead leaves the system
altogether, unlike for earthly options. So here, an SPS again has a
lower impact.

Since they are orbiting Earth, Earth probably takes up a
big part of their "sky".

Not really. At geosync, the Earth takes up a very tiny fraction of the
sky. and yes, for a number of reasons you want it at geosync.

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.

Certainly - and you can do much, much better at microwave frequencies
than 50%. The problem is if you beam down even a third of the worlds
energy requirements into one rectenna: that's 1.5e+13 / 3 = 5e+12 W.
If the beam is 10 km in diameter, that's a power density of around 1.6e
+4 W/m^2. Best not loose more than about 5% of that, for a number of
reasons. Now, if you can support a larger rectenna... the limits can
be relaxed.

--
Brian Davis

.

Relevant Pages

  • Re: European Union cuts back Biofuel use
    ... energy will resume its normal percentage of a household budget. ... wasted heat going out the cooling system and exhaust to improve mileage. ... average household uses in electricity. ... Increase the size of the system, perhaps by 2, and one can fuel his electric ...
    (rec.outdoors.rv-travel)
  • Re: Dyson Sphere detection and future technology criteria
    ... 'heat' (energy) as infra-red on the other side of the Dyson Sphere, ... You can't get away from the need to re-radiate all the star's energy as ... All the energy that the earth receives from the ...
    (talk.origins)
  • Re: Dyson Sphere detection and future technology criteria
    ... 'heat' (energy) as infra-red on the other side of the Dyson Sphere, ... You can't get away from the need to re-radiate all the star's energy as ... All the energy that the earth receives from the ...
    (talk.origins)
  • Re: Dyson Sphere detection and future technology criteria
    ... 'heat' (energy) as infra-red on the other side of the Dyson Sphere, ... You can't get away from the need to re-radiate all the star's energy as ... All the energy that the earth receives from the ...
    (talk.origins)
  • Re: Nuclear energy and the EU
    ... in the morning in rural areas. ... I read an interesting article about geothermal energy. ... heat inside our globe to last for as long as the human race can possibly ... cool earth enough and we'd lose our magnetic field. ...
    (soc.culture.baltics)