Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!linus!security!genrad!decvax!harpo!seismo!hao!hplabs!sri-unix!dietz%usc-cse%USC-ECL@SRI-NIC
From: dietz%usc-cse%USC-ECL%SRI-NIC@sri-unix.UUCP
Newsgroups: net.space
Subject: Re: Space Solar Power
Message-ID: <13285@sri-arpa.UUCP>
Date: Wed, 2-Nov-83 21:54:00 EST
Article-I.D.: sri-arpa.13285
Posted: Wed Nov  2 21:54:00 1983
Date-Received: Sun, 6-Nov-83 20:13:52 EST
Lines: 61

In reply to ZBEN's "cogent" argument against SPS:

   [ZBEN]
   The most cogent argument I have heard against the satellite solar power
   idea is the resultant increase in heat pollution.  Thats right.  Those
   big solar panels out there are tantamount to increasing the absorption
   of solar power by the earth.

I thought I addressed this issue in one of my messages.  Space solar
power actually has comparatively low thermal pollution, compared to
other energy sources.

The reason is quite simple:  the thermodynamically limited part of the
light-to-electricity conversion process is done in orbit.  The SPS
radiates its waste heat INTO SPACE, not into a cooling tower (or
whatever) on earth.  The power transmission process (microwaves & power
lines) dissipates into the biosphere as heat maybe 10-15% of the energy
delivered to the user.  In contrast, ground based thermal electrical
generators (fossil fuel, fission, fusion, thermal solar, geothermal)
waste at least three fifths of the produced energy as heat (150% of the
delivered electrical power).

Ground based solar is also a thermal polluter.  Deserts are fairly
reflective (~35% of the energy is reflected), so much of the sunlight
hitting them goes right back into space.  A power plant, be it a
power-tower or a solar cell array, will decrease this figure to about
5%.  The result is that ground based solar puts about 110% of the
delivered power into useless waste heat (over and above what the desert
would have absorbed).  Hardly a "second order" effect!

The only electricity sources I can think of that produce less thermal
pollution than SPS are wind and hydroelectric -- but I wouldn't be
suprised to find that if you extracted enough energy from the wind
temperature differences between locations on the Earth's surface would
increase.  In any case wind and hydro can't supply more than a small
fraction of the energy we'll need.

If you're still worried about thermal effects of SPS, you can make the
rectenna reflective (polished sheet aluminum, say).  The intensity of
the microwave beam is only 1/2 that of sunlight (at the center; at the
edges it's much less), so this looks feasible.  Beyond that, you can
move manufacturing into orbit (assuming delivering the goods to earth
doesn't dissipate too much energy in the atmosphere).  After that, you
can move consumption into orbit -- space colonies!

   [ZBEN]
   I think the solar satellites are yet another government give-away to the
   high-tech aerospace industries.  We have plenty of desert right here on
   earth, with the advantage of breathable air for the repairmen.

But ground based solar can't supply more than about 5% of the nation's
electricity needs.  Beyond that, you need to solve the problem of large
scale electrical energy storage -- a very hard problem.  And it isn't
completely obvious that ground based solar is cheaper than space based.
A large concentrator mirror could conceivably be easier to build, aim
and maintain in orbit.  It could certainly be far less massive than
ground based heliostat arrays.

		Paul Dietz (dietz@usc-ecla)