From: gary@ke4zv.uucp (Gary Coffman)
Subject: Re: Renewable energy from the sun
Reply-To: gary@ke4zv.UUCP (Gary Coffman)
Organization: Gannett Technologies Group
Date: Sat, 14 Nov 1992 18:10:07 GMT

In article <28116@castle.ed.ac.uk> cir@festival.ed.ac.uk (C Revie) writes:
>
[I wrote]
>>Emphatically yes, we have an energy surplus. The solar energy striking
>>the earth is about 7.8E18 kilowatt-hours per day. World energy consumption
>>is about 7E12 kilowatt-hours. So solar alone, if totally converted to
>
>
>>Then there are the non-solar sources of energy. We can tap the Moon's
>>gravitational energy via tide power plants. We can tap the radioactive
>>decay heat of the Earth via geothermal plants. We can tap nuclear power
>>directly through fission power plants. And hopefully we will soon be
>>able to tap fusion power directly in fusion power plants. The latter
>>three sources can rival the Sun in the amount and duration of available
>>energy they can supply. Note that all energy sources, including the
>>Sun, are nuclear energy sources, with the exception of gravitational
>>potential energy.
>
>
>The problem with tapping the sun's energy as we now do through burning
>fossil fuels, is that we are overloading the system. Not only is the
>earth receiving energy from the sun, but energy from the past, in the
>form of fossil fuels. Something that the biosphere is not designed to
>cope with over a long period of time. By living off solar energy as we
>get it, through wind power etc, or by using biofuels, we would not be
>altering the amount of energy in the system.

Our current energy consumption, from all sources, is 1/100,000th of
the energy received by Earth from the Sun. That's 0.001%, the change
in the Solar Constant during a 22 year solar cycle is more than an
order of magnitude greater than that. Our energy use is an *insignificant*
fraction of the natural *variation* in solar input to the Earth. We
are *not* overloading the Earth's energy balance due to the heat liberated
by burning fossil fuels.

>Admittedly these system are expensive, but this is due to the present
>miserly levels of investment that they receive, compared with fossil
>fuels. 

Your naive faith in the power of government directed R&D is touching,
but there is *no* assurance that *any* amount of R&D funding can break
fundamental Carnot limits on the low grade energy of diffuse sunlight.

>The other advantage of solar systems is that you don't get any
>problematic side effects, unlike fusion and fission. Yes burning
>biofuels gives off CO2, however this is CO2 which was verily recently in
>the air taken in by plants, it should not therfore alter the amount of
>CO2 going round the system. 

Nor does burning fossil, on a longer timescale. We can't say *what* timescale
is the proper one to measure this. The carbon cycle isn't understood to
within several orders of magnitude. There is considerable evidence that
some of the larger CO2 sinks are inorganic. Therefore it doesn't matter
much whether the CO2 is generated by burning wood or coal. In fact, the
deforestation from burning wood changes the albedo of the Earth a measurable
amount and may cause more harm than burning coal. Use of fission has
demonstrably less damaging effect on the environment than burning wood,
or coal, or oil. Fusion should be even cleaner.

>As the population grows, living within the capacity of the planets
>systems will become more important, a move to solar tecnologies is thus
>of prime importance.

That hasn't been proven. Indeed it is just an article of faith in some
quarters. It's certainly true that solar is a vast, but diffuse, energy
resource. Whether it's efficient or wise to forsake other energy systems
in favor of solar is still very much debatable. Our total energy use will
have to increase a hundredfold to even equal the *variation* in solar
energy striking the planet. We have a long way to go before our energy
use from other sources has a significant effect on the Earth's energy
balance.

Gary
Newsgroups: sci.energy,talk.environment