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Solar Power Put to Good Use
Current Shunts writes "Teams from all over the U.S. and Canada will be competing this summer over a 2,500 mile course from Austin, Texas in the United States to Calgary Alberta Canada for the 2005 North American Solar Challenge. The purpose of this event is to promote renewable energy technologies, integrate science and engineering disciplines, and give competitors an opportunity to showcase their technical and creative abilities." At the same time, zestyalbino writes "Construction on the world's largest solar tower [RMIT] may begin next year in Mildura, Australia. In a nutshell, "An ever present large mass of air under an expansive transparent collector (seven kilometres in diameter) is heated by solar radiation (greenhouse effect) providing a continuous flow of hot air to drive electricity generating turbines located around the base of the one-kilometre tall central tower." There's also an article on Wired."
"The Solar Tower concept operates on a simple rule of physics - hot air rises" The Solar Tower project uses hot air generated in a big green house to spin a wind turbine. It looks like a cool idea if you ask me. Aneway, the point is, not every form of solar power uses photovoltaic cells. But you do have a point, the chemical cost for photovoltaics right now is very high.
We are the Borg...
My father invented and patented this idea; the US patent, granted in 1981, was originally filed in 1975. He never got a dime out of it, and the patents, in Canada, Australia, Israel, and the US, have all expired. I guess he was ahead of his time. More information here.
What chemical costs might those be? For solar cells, they're quite low -- nothing at all like integrated circuits, if that's what you had in mind. Last I looked, the only chemical waste that the larger plants in the US produced in large enough quantities to report to the EPA was a bit of sodium hydroxide. The plants are larger now than they were then, but the only other chemicals that are commonly used in significant quantities are glycol, sometimes hydrofluoric acid, phosphoric acid (or in some plants POCl3), silane, aluminum, silver, and silicone. Solvents are used only in very small quantities.
Chemical safety specialists generally regard silane as the most problematic chemical in a PV plant, and even then it is more of an occupational safety issue than a pollution or "chemical cost" issue.
Let's just ignore the chemical costs of making solar collectors
Which don't approach the cost of the power that they generate unless you factor in the time for return on profit compared to other forms of power.
Hu and White in 1983 published the results of a study on Solarex panels; energy payback was 6.4 years, with panels that had 12.4% efficiency. This was from 1977 cells. Nowadays, the numbers are generally 1-3 years. Amorphous pay back the fastest - some even under 1 year.
The rest of the time, they're just generating power. Dollar payback time is usually 4-10 years.
Don't take a knife to a gunfight, or even a knife to a knife fight. Take a gun to a knife fight.
"At temperatures up to 70 C beneath the greenhouse, nothing is going to grow there and soil moisture will be lost rapidly."
.au, at least). Salt is carried to the surface by the water table rising. Anything that causes a lowering of the water table prevents further salination, so accellerated surface evaporation is as good as revegitation. Again, this has all been taken into account.
The highest temperatures will be in the center of the array, and closest to the ceiling. The temerature at ground level and around the rim will be lower, thanks to the very convective effect that makes the whole proposition feasible, but by how much will depend on the ceiling height. Remember thermal gradients; it may not be possible to use the entire area, but a good portion of it will never come close to70 C. I have to point out that growing plants under it is actually part of the proposal, it isn't my idea. If you don't think it's possible, tell the people planning it, I'm sure they'll appreciate the advice.
"It may be possible to use this land to extract salts for industrial use"
Not really, it's common sodium chloride, and much more readily available in commercially attractive deposits elsewhere; desalination plants along the nearby Murray River, for example.
"From this I gather that, as a first approximation, energy expended to evaporate water will be lost"
Two points: (1) Mildura receives little rainfall (irrigation is vital), so surface water isn't as much of an issue as you might think, and (2) this has probably been included in the effciency calculations.
"I doubt that a large expanse of even more highly salinated land is going to contribute much to the local environment."
You don't understand the mechanism behind land salination (in
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