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From: pokey@well.UUCP (Jef Poskanzer)
Newsgroups: talk.politics.misc,sci.misc
Subject: Re: NOT greenhouse effect / solar power satellites
Message-ID: <5564@well.UUCP>
Date: 29 Mar 88 23:04:50 GMT
References: <22678@bbn.COM>
Distribution: na
Organization: Paratheo-Anametamystikhood Of Eris Esoteric, Ada Lovelace Cabal
Lines: 55

Steve Elias is, as Jerry Pournelle put it, "not merely uninformed but
aggressively misinformed."  This thermal pollution bullshit seems to recur
every few years.  Here's an excerpt from a message of mine way back in 1983:

    The Earth is currently receiving sunlight at the rate of 1.1e24 ergs/sec.
    That is ten million gigaWatts.  One million rectennas.  As far as I know,
    no-one is planning to build that many in the near future.  Let's look at
    a more reasonable number, say a thousand ten gigaWatt rectennas.  How
    much would this heat up the planet?  To raise the temperature of the
    world's oceans by one degree C takes 5.71e31 ergs.  If you consider the
    atmosphere alone, it takes about a thousand times less: 5.26e28 ergs.
    In one year, a thousand rectennas would receive 3.15e23 ergs (plus a
    bit because they are only 90% efficient).  Thus in the long run, the
    temperature of the oceans would rise by about 0.00000001 degrees per
    year; in the short run, the atmosphere would heat up by 0.00001 degrees
    per year.  Are you still worried?

Complete with spelling errors, no extra charge.  But that's only part of the
reason Steve is full of shit.  As John Carr and others mentioned, most of the
inefficiencies in SPSs are off-planet.  The conversion from microwaves to
electricity is extremely efficient.  (Yes, 90%.  Not 80%.  Not 50%.)  And the
physical structure of a rectenna is a coarse mesh -- it doesn't affect the
albedo (proportion of light reflected) of the land.

Now contrast that with ground-based solar, which Steve appears quite fond
of.  The collectors are only 15%-20% efficient, but they have albedos of
close to 0 -- they are black.  They absorb *all* the sunlight, turn 20%
into electricity, and emit the rest as heat.  Since large-scale ground-based
solar would be built in the desert, it's even worse: the land it would
cover up is extremely light, with an albedo of around 0.8, so the 80%
of the sunlight that would otherwise have been reflected back into space
is instead absorbed.

So the question is: for a given electrical capacity X, how much extra energy
gets absorbed by the Earth?  For SPS, the answer is simple: 1.1 X -- X itself
gets absorbed (eventually), and the 10% inefficiency in the collector gets
absorbed.  For ground-based solar, you absorb X, you absorb 4 X for the
collector inefficiencies, and you get to discount X because that's how much
was previously being absorbed by the desert before you covered it over.
The result, for those of you who are arithmetic-impaired, is 4 X.

So, if you insist on being utterly paranoid and worrying about the thermal
balance of the Earth, you should be out there campaigning hard for SPS,
since by your own criteria it's 3.6 times better!  DO YOU GET IT YET STEVE?
YOU'RE WRONG!  YOU'RE A MORON!  SHUT THE FUCK UP!


For the few reasonable people out there: the CO2-induced "greenhouse effect"
is very very different, and is indeed a serious problem.  But of course
SPS wins there too.
---
Jef

              Jef Poskanzer   jef@lbl-rtsg.arpa   ...well!pokey
               Most people on this network wouldn't recognize
                    subtlety if it hit them on the head.