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Technology Stocks : Applied Materials No-Politics Thread (AMAT)
AMAT 235.13+2.2%Nov 10 3:59 PM EST
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To: Gottfried who wrote (22787)4/2/2008 6:05:12 AM
From: allatwwk  Read Replies (1) of 25522
 
the mirror based solar plants are thermal, no PV, no AMAT. While these plants use clever technology, they also use natural gas as a fuel. The plants, as best as I can tell, are sized to run using only solar power on hot days. The mirrors focus light onto tubes carrying an oil like substance that can achieve very high temperatures. This 'oil' is sent into heat exchangers, where it shares its heat with water, converting it to steam. The steam drives turbines and electricity is the result.

An alternate approach is to use a field of mirrors that focus their light onto a tower and heat the water directly. A good chunk of the PGE contract uses this approach.

But on cloudy days or merely warm days, the steam won't heat enough. At night, the oil (or water) won't heat (though a reservoir of hot fluid could be produced for nights). And turbines are expensive -- you would like to use them 24/7. So natural gas is often used to complement the solar heating. I don't know if the annual reduction in natural gas use is 20% or 80%, however.

Which is a long way of saying that solar thermal is clean, but it still produces greenhouse gases, though at a lower rate than a traditional natural gas plant would.
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