Xref: utzoo talk.politics.misc:8833 sci.misc:1277 Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!umd5!uvaarpa!mcnc!rti!xyzzy!throopw From: throopw@xyzzy.UUCP (Wayne A. Throop) Newsgroups: talk.politics.misc,sci.misc Subject: Re: efficiency / greenhouse effect / solar power satellites Message-ID: <758@xyzzy.UUCP> Date: 7 Apr 88 20:30:39 GMT References: <789@spdcc.COM> Followup-To: sci.misc Organization: Data General, RTP NC. Lines: 79 >, >>> eli@spdcc.COM (Steve Elias) >! throopw@xyzzy.UUCP (Wayne A. Throop) >!Looking in tables and such I think that the current energy use by humans >!on earth is something like 6x10^18 cal/yr. The current solar flux >!reaching earth is something like 1x10^24 cal/yr. That is, if human >!energy consumption was totally supported by SPS, and doubles every 10 >!years, and none of this consumption moves to space, we would see 1 >!percent of solar flux delivered to earth from our SPS system in about >!150 years. > as i mentioned in a previous article, the earth's albedo multiplies > down the incident solar flux by nearly 70%. But the fact that SPS is more efficent thermally puts the figure back up quite a lot. But I'm sure we can agree that we are talking at least a thousand times, and probably closer to ten thousand times, the current industrial activity. And again, this much industrial activity will totally destroy the biosphere long before thermal effects become important. > so 150 years is a bit of an overstatement, even with a ten year > doubling time for power needs. It very likely isn't much less than a century. (Also note that power needs are currently not doubling anywhere near as rapidly as 10 years, near as I can tell from the tables I've consulted.) > !And in thinking about this, it is well to remember that the sun is, > !itself, about 3% variable > could Wayne or anyone elaborate on this?? i'm under the impression > that the hiccups he refers to are sun-spots. they affect the solar > wind, but not the radiated EM energy from the sun, as far as i know. > does anyone have more information on this? I beleive that good old Sol can vary by 3 or so percent its power output over very long periods of time, and has done so in the past. There is some evidence that there is a feedback loop that keeps temperature (relatively) stable over the long term in spite of at least this much, and maybe more, solar variation, but there is some evidence that we are near the limit of breaking the loop if the sun heats up much more (or anything heats up an equivalent amount, for that matter). The feedback loop is: when things get too cold, the biosphere dies back, carbon dioxide accumulates, greenhouse effect, earth heats back up. When earth gets "too" hot, tropical and aquatic bioshpere expands, plankton & rain forrests convert excess carbon dioxide to oxygen, opens the shutters on the greenhouse, earth cools back off. Unfortunately, we are in a warming trend, plants have pumped about as much CO2 out as they can, and we are tending to add more despite what the biosphere can do. Potential bad news. (Above hypothesis from memory and severely condensed, from a NOVA episode entitled "The Gaia Effect", if memory serves.) But again, thermal pollution is a very small factor in this, not particulary significant in the face of the other effects, and further, SPS would be a smaller thermal polluter than almost any alternative. > but any negative feedback due to albedo changes would > not affect the solar power receiver stations themselves... they > would continue to soak up the same energy and release it as heat... True for albedo, but the CO2 effect is on the rate at which waste heat escapes to space by radiation. This would get rid of excess heat whatever the source. (If it works at all.) > i still hope to locate Frank Drake's notes on this subject. I would be very, very interested. I still don't beleive that thermal pollution is the most troublesome effect, and even if I did, I don't beleive that SPS is worse than, for example, ground-based solar power. So why Drake might single out SPS as environmentally dangerous is a mystery to me, one I'm currious to see a little more about. -- You know, when it's hot like this -- you know what I do? I keep my undies in the icebox. --- Marilyn Monroe in "The Seven Year Itch" -- Wayne Throop !mcnc!rti!xyzzy!throopw