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(2165 previous messages)
- 06:36pm May 11, 2002 EST (#2166
John Perlin has written From Space to Earth: The Story of
Solar Electricity (Aatic Publications 1999) , setting out the
enormous amount of work that's been done to harnass solar energy
since the first photocell in 1883. He summarizes much of that
information in Solar Power: The Slow Revolution in
Invention and Technology , Summer 2002.
The overwhelming problem with photoelectricity (something Exxon
and other oil companies know a lot about) is cost . Because
costs remain very high, after more than a century of work,
photocells provide less than a hundredth of a percent of the world's
Gisterme points out in questions in MD2137-2138 gisterme
5/10/02 3:44am that a hydrogen based solar energy system would
have major difficulties even if the photocells were free.
Gisterme raises other questions, too. I have some workups on
those questions, but the issue Perlin emphasizes needs treating
" Is it possible to make a
breakthrough reduction - a several order of magnitude
reduction - in the cost of photocells that can actually be
I still think so, but inventors are often wrong. Here was my
reasoning, from MD1131 rshow55
"People can now print photovoltaic layers on
flexible plastic sheets. For very large areas, in large scale
production, the marginal cost per unit area would approach 0 --
and metal conductive layers with small conductive losses for tens
of meters are also workable.
" The key technical problem is floating thin
assemblies of sheet plastic (perhaps 30 microns thick in all,
including top sheet, bottom sheet, and bubble floatation) with
very extensive areas -- and having the assemblies stand up to
wind, rain, wave, and whale problems, on the equatorial seas.
Now, to say that's "the key problem" is too simple, and I'm
embarassed to have used those words without qualification. It
doesn't adress any of the other problems gisterme points out.
But let's look at the logic, just that far, in isolation first.
The "photocell assembly" I'm positing, if it could be developed,
would use 1 cubic meter of material for 33,000 square meters of
photocell area. On glassy or very calm seas, with equatorial levels
of sunlight (if you could find such seas) - there might be a lot of
electrical energy generated on that basis. The calm sea would
provide a near-ideal supporting structure for the assembly. That's
much less material than any terrestrial photocell assembly
would involve. And a structure that would lend itself to very large
Proof of principle at the "simple" level of such a
photocell-sheet (assuming a calm enough sea) would involve
demonstration of a few tens (at most a few hundreds) of square
kilometers. A large area, but not the hundreds of thousands of
square kilometers that would be required (along with much else) to
take over the current world's energy needs.
Could a calm enough sea be found? I believe so. Before the age of
steam, equatorial seas were much feared by sailors, because there
was so little wind -- there are really terrible stories of ships
caught for weeks becalmed. Seas at latitudes close to the center of
convection for the earth (latitudes that vary with season) are
comparitively calm, and although thunder storms are common - large
circular storms would be extraordinarily rare insurable risks.
From quick calculations, I also believe that the "thirty micron
thick photo-assembly" could withstand significant wave action -
conform to the wave with only small bending strains or shears -- but
I was calculating curvatures short of the kind of wave severity that
causes extensive whitecaps.
- 06:38pm May 11, 2002 EST (#2167
The plastic sheet assemblies have water between the layers, and
sloshing would provide considerable damping of wind waves - a
damping that would increase rapidly with wave severity. For very
large arrays, that damping might be convenient.
To get this far (proof of principle for a sheet of a few square
miles) would involve major hurdles. If you could make this
breakthrough in photocell cost -- reducing photocell cost
several orders of magnitude from what it is now - the other issues
gisterme raises in MD2137-2138 gisterme
5/10/02 3:44am would remain.
If this breakthrough in photocell cost were made - those
other issues, I believe, would be well worth adressing, and feasible
Having looked some at Perlin's material, I'm not going to
consider land-based photocells further - after a century of
development, they remain much too expensive.
- 06:54pm May 11, 2002 EST (#2168
Perlin, John (1989) A Forest Journal;the role of wood in
the developement of civilization W.W. Norton & Company, New
Golden Thread : Twentyfive Hundred Years of Solar Architecture
and Technology by Ken Butti, John Perlin (Hardcover - June 1980)
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