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From: howard@metheus.UUCP
Newsgroups: net.followup
Subject: Re: Alternate Energy & Microwaves
Message-ID: <270@metheus.UUCP>
Date: Thu, 16-Aug-84 17:02:50 EDT
Article-I.D.: metheus.270
Posted: Thu Aug 16 17:02:50 1984
Date-Received: Thu, 30-Aug-84 01:49:29 EDT
References: <369@utastro.UUCP>
Organization: Metheus, Portland Oregon
Lines: 57


    >>They have another big advantage:  microwave-to-electricity conversion can
    >>be quite efficient (70-80%), whereas converting sunlight to electricity is
    >>dismally inefficient (15% is good for solar cells).  Of course, the power
    >>satellite itself probably uses solar cells, but it is out in space,
    >>where (a) the sun shines 24 hours/day, and (b) the waste heat does not
    >>go into Earth's biosphere.
    >>-- 
    >>				Henry Spencer @ U of Toronto Zoology

  >a) The sun shines 24 hours/day everywhere, not just out in space ...

I know Texas is in the Sun Belt, Ed, but REALLY!  There is something called
NIGHT!  Just ask Wendy if you don't believe me!

  >b) If the solar cells aren't there to convert the heat into electricity (i.e.
  >make some use of 15% of it) then it will *all* go into the earth's bioshphere
  >if it isn't reflected back into space.  The "saved" 15% will presumably get
  >converted into work somewhere, which degrades into heat, which enters the
  >earth's biosphere.  So where is the "waste?"

Henry was clearly referring to solar cells IN SPACE, ON THE SOLAR POWER
SATELLITE.  The efficiency advantage he refers to could be relative
to a scheme in which you used a huge space mirror to reflect sunlight
to a solar power station on earth.  Or, if the albedo of a solar cell is
significantly lower than that of sand, then more light will be absorbed
by the solar cell than by the desert it replaces, leading to real excess
heat in the biosphere.  All the solar cells I've seen look pretty much black.
If we assume that sand = albedo 0.6 and solar cells = albedo 0.1 then the
excess heat will be (.6 - .1) - .15, or 35% of the total energy of the
sunlight falling on them.  So the total biosphere heat for ground-based
solar would be 3.33 watts per watt of electricity, whereas for microwave
beaming it would be 1.33 watts of heat per watt of electricity.  That's where.
[P.S.  Anybody got REAL albedo numbers for this computation?]

  >c) If the Sunsat is put up it will be bright enough to rival the full
  >moon, just from reflected light alone (the moon reflects ~8%, is bigger
  >but is *much* farther away, and the inverse-square law does a bit of
  >good) ...  which means ground-based astronomy goes out of business,
  >since most of the interesting observations of quasars, distant
  >galaxies, black hole candidates and vibrating stellar corpses are
  >confined to "dark time," when the moon is nearly aligned with the sun
  >and the night sky is dark.

Ground-based astronomical OBSERVATION is slowly going out of business anyway,
because it can't compete with observations made from satellites, except in
lower cost.  But ground-based astronomy will do just fine; witness all the
analysis of Jovian moons by ground-based astronomers.

  >d) If all astronomers become shoe salesmen or zoologists then who will be
  >watching when the Klingons come?

A goodly share of the TV audience at the time, no doubt.

	Howard A. Landman

	"Searchlight casting for faults in the clouds of delusion"