Xref: utzoo talk.politics.misc:8757 sci.misc:1256
Path: utzoo!mnetor!uunet!tektronix!reed!percival!bucket!leonard
From: leonard@bucket.UUCP (Leonard Erickson)
Newsgroups: talk.politics.misc,sci.misc
Subject: Re: greenhouse effect / solar power satellites
Message-ID: <843@bucket.UUCP>
Date: 4 Apr 88 03:23:11 GMT
References: <22678@bbn.COM> <5564@well.UUCP> <761@spdcc.COM> <4195@bloom-beacon.MIT.EDU> <763@spdcc.COM>
Reply-To: leonard@bucket.UUCP (Leonard Erickson)
Distribution: na
Organization: Rick's Home Grown Unix; Portland, OR
Lines: 77

In article <763@spdcc.COM> eli@spdcc.COM (Steve Elias) writes:
<!Efficiency has everything to do with thermal pollution.  For a fixed power
<!consumption, efficiency determines the amount of heat generated relative to
<!useful power.  A system with a 50% efficient converter would produce twice 
<!as much heat as a 90% converter (including the rest of the system, and the 
<!consumer).
<
<      you are wrong, here.  both the 'useful power' and the 'waste heat'
<      end up in the environment as heat.  

No he is *correct*! Assume 100 MW of useful power is needed. 

At 50% efficiency, we get 100 MW of power & 100 MW of heat, after use of
the power we have a *total* of 200 MW of heat.

At 90% efficiency we get 100 MW of power & 11.1... MW of heat, after use
we have a total of 111.1... MW of heat. 

If we use an SPS we get 100 MW *period*!

<      again:  efficiency doesn't matter.  SPS is the only power source
<      which uses energy which would not otherwise enter the earth's
<      atmosphere.  it is worse than most other power sources in this
<      respect.  why do you insist that efficiency is a factor?  all 
<      useful energy will turn up as heat in the environment.

See the above for an explanation of why efficiency matters.

<!If you are arguing that SPS are worse than earth-based systems capable of
<!generating the same power you are wrong.  If you are arguing against 
<!increasing our generating capacity you should say so.
<
<       i am arguing against increasing our generating capacity by 
<       collecting massive amounts of energy from exo-atmospheric sources.  
<!
<!My conclusions from these: the earth reacts to thermal pollution on a very
<!short timescale (days to weeks).  The timescale of the feedback by which 
<!an increase in temperature produces a runaway greenhouse effect is millions
<!of years.  On the other hand, the timescale for CO2 pollution to produce a
<!greenhouse effect is very short.  Adding heat will not raise the temperature
<!noticeably until the rate of addition approaches the solar flux on the earth.
<!Adding CO2 has already warmed the earth (the articles have numbers).  
<
<      yes!  my point is that hundreds of solar power satellites
<      WILL add energy on the order of the present solar flux!

Good grief. Try doing the math... To get an increase equivalent to the 
present *total* solar flux, you will need an area of SPS's *greater*
than the cross-sectional area of the earth!!! Assume an SPS is 50%
efficient (number picked solely to simplify the math). To get a 1%
increase in the Earth's heat budget, you'd need an energy input equal
to 1% of the total flux. At 50% efficiency, this means we'd need an
area equal to 2% of the Earth's. That is 4000**2*2*pi*.02 miles.
Or approximately 2 *million* square miles of collector. 
And that is a power generating capacity of around four and a half
MILLION  GIGAWATTS!!!!! That sounds like a lot more than a couple of
hundred SPS units. 

Also you are forgetting that every watt we send down means that all
the waste heat associated with generating a watt of power on the ground 
is dropped. Remember up above where I showed that generating a watt
of *power* means adding *more* than a watt of heat? So if an SPS
replaces a 100 MW 50% eff. plant on the ground, we have 100 MW *less*
heat! (11.1... MW less for the 90% efficienct plant).

Add in the lack of CO2 if it was a fossil fuel burning plant and you have
an even better gain. Note that fossil fuels are stored energy form the solar
flux millions of years ago.




-- 
Leonard Erickson		...!tektronix!reed!percival!bucket!leonard
CIS: [70465,203]
"I used to be a hacker. Now I'm a 'microcomputer specialist'.
You know... I'd rather be a hacker."