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# Re: Fuel Cells and "green" energy

Actually about 10,000 square miles to supply 20% of total energy (as
projected for the year 2100.) The 40,000 square miles is only if you use
the solar to make hydrogen and then burn the hydrogen in conventional power
plants to make electricity. This DOES solve the 'energy on demand' problem
with solar and wind but is much less efficient. To put the area in
perspective, 10,000 square miles is something like 1/2 the area of all the

For the same 20% of total needs supplied by wind you need 6.5 million 750 kW
wind generators that cover about 175,000 square miles. However, most of
this land can be used for farming or grazing.

There is yet another problem here. What is the lifetime of a photovoltaic
panel or a wind generator? One estimate I've seen for both is about 25
years. The problem then is that if you have a plan to put 100 wind
generators in place over the next 100 years (at 1 a year), you actually have
to install 250 generators over that 100 year period to have 100 working
units in the year 2100. This can increase the cost by up to a factor of
2.5. Therefore one has to be careful about comparing the cost per installed
watt of various energy sources. Hydro at about \$1/watt is still about the
best since a 100 year lifetime on a dam is quite feasible. Wind at the same
\$1/watt can cost more than twice that when the longevity factor is folded
in. Solar currently runs more than \$4/watt for just the photovoltaic panels
which should probably be doubled for the same reason (and the support
structures and voltage processing equipment needs to be folded into the
costs as well). The bottom line here is that the task of moving away from
the fossil fuels will require vast projects and huge expenditures. However,
the longer we wait to get started, the more difficult and more expensive it
will become.

Rick

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Richard W. Tarara
Associate Professor of Physics
Department of Chemistry & Physics
Saint Mary's College
Notre Dame, IN 46556
219-284-4664
rtarara@saintmarys.edu

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----- Original Message -----
From: "Shapiro, Mark" <mshapiro@EXCHANGE.FULLERTON.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, June 14, 2001 9:50 PM
Subject: Re: Fuel Cells and "green" energy

Jim,

There also is a considerable energy overhead in producing nonrenewable
energy. This includes the energy expended in exploration, extraction,
transportation, and refining (in the case of oil).

I believe Rick estimated something like 40,000 sq. mi. of photovoltaics in
order to make a major dent in US electric production. (I think this is a
high estimate, given the improving efficiency of solar voltaics.) This at
first glance seem like a lot of area to devote to solar panels; however,
in
reality this can be readily achieved by a combination of approaches
including the installation of solar panels on residential and commercial
rooftops in the high insolation areas, and the judicious use of land in
the
desert southwest.

When you are being force to pay \$1,500 per megawatt-hr by the Enrons of
the
world, solar and wind start to look pretty good.

Mark

http://www.IrascibleProfessor.com

-----Original Message-----
From: Jim Green
To: PHYS-L@lists.nau.edu
Sent: 6/14/2001 7:15 PM
Subject: Re: Fuel Cells and "green" energy

Anyway, to get
large amounts of solar and wind into the system as 'energy on demand'
sources may require up to 4x the generators and solar collection areas
as
would be needed if these were used directly. Such a system would then
require tens of thousands of square miles of photovoltaics and 10s of
millions of large (megawatt) wind generators.

We have not yet discussed the "amount of energy" (Ugh!) needed to
manufacture, repair, and replace the photovoltaics and wind generator
towers and turbines -- losses well beyond the thermal losses.

And would somebody be willing to venture a guess as to the number of
square
miles of turbines and photovoltaic fields which would be required to
make
any sort of meaningful difference in the whole issue.

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen