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Re: Solar power



A great interest of The American Policy Inst., Inc, i.e., me, is to
determine if windmills and photovoltaic solar cells are net consumers or
producers of high-grade energy (Gibbs free energy, say). We use Emergy
Theory as modified by me, but the research is difficult and costly. No
one has done it!!! When someone tells you that solar energy now "costs"
x cents per kilowatt hour, you *know* they don't know which end is up.
We need to know the kWhrs/kWhr. I know you all get the point. Regards /
Tom
*****************************************************************************
On Wed, 17 Dec 1997 15:03:45 -0600 "Roger A. Pruitt" <phrp@fhsu.edu>
writes:
LUDWIK KOWALSKI wrote:

A message on wind energy (from another list) is posted below. Does
anybody
have a clear idea why progress in that area of technology, and in
attempts
of using other forms of solar energy, is so slow. Such sources of
power
are highly desirable in view of global warming.
Ludwik
Kowalski

**************************************************************************
Subj: RE: wind energy

Thanks, Jean, for sharing your piece on wind energy; a good and
useful
bridge from physics to a practical issue we all can benefit from.
Let
me add some statistics. But first one question. Should the area of
the
windmill be calculated from the area of all blades or as the area of
the entire circle?

Here are some numbers from a newspaper article:

1) Today close to 100,000 Danes own shares in the hundreds of small
cooperatives that opertate 4,700 windmills. And they are making
profits.

2) 20,000 people are employed by the wind industry in Europe.

3) In wind power, Europe has already overaten the United States,
which
led the drive to wind in 1980's. Europe's capacity of 4100 MW now
amounts
to two and a half times that of the United States, with Germany
alone
surpassing the capacity of American wind farms.

*******************************************************************
Jean wrote:
Your student is right : wind is air in motion, and you can tap
the
kinetic energy of the air with a windmill.

If you consider one square meter of vertical area normal to the
wind,
the amount of mass traversing it is:

area * speed * density of air ( = 1.3 Kg/cubic meter)

To obtain the corresponding energy, m v^2 /2 you obtain:

Energy = density * area * (speed)^3 /2

Where "area" is the area of the windmill. You have to use an
efficiency
factor, because downstream from the windmill the wind will still
have
some velocity left.

All this assumes the air acts as an incompressible fluid,
which
is not a bad approximation here. Otherwise, one needs the full
Bernouli equation.

For v = 10m/sec, the energy density is

1.3 * 1000/2 = 650 watt/m^2

comparable to the solar constant at sea level ( = 1 KW/m^2), but
of
course the transformation into usable form is different in both
cases.

Jean OOSTENS
******************************************************************

Perhaps of some interest is the fact that farms out here on the windy
high plains used to have numerous windmills pumping water for
livestock
and homes. These have largely been superceded by electrified water
pumps
which are easier to control and maintain. A local radio announcer
lived
across the street from me and had a modern wind generator installed in
his back yard. He sold surplus energy back to the utility company.
Many
neighbors squawked resulting in the city passing an ordinance
prohibiting further installations. I suppose they were afraid it would
attract lightning and/or fall on them in a wind storm. After having
numerous problems which meant that it often was not working, he had it
taken down.

Solar and wind energy are not benign. Does anyone have figures for
human
lives lost in the manufacture of photovoltaic devices and smelting of
steel and copper for wind machines?

Roger

================================
| Dr. Roger A. Pruitt |
| Department of Physics |
| Fort Hays State University |
| Hays, KS 67601 |
| Ph. (785) 628-5357 |
================================