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PV and solar thermal adds to global warming

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Posted by George on December 19, 2008, 2:57 am
A bloke I know pointed out that solar cells are now up to 40 percent
efficient. Couple of things came to mind so I looked up SolarSystems
and see they are using them. So I calculated a few bits for said
bloke. Here 'tis.

A SolarSystem project http://www.solarsystems.com.au/projects.html  

Here is more detail, upon which I have calculated some efficiency


So let's see how that works out.

270,000 Mw-hrs per year claimed output.
45,000 homes
6 Mw-hrs per year per home
16.44 kw-hrs per home per day (thatís a bit low compared to Western
Australia where the climate is much hotter but otherwise about right

As an aside, what about the other 90 percent of energy that is used by
non-domestic users?
$20 million cost

$.14 per kw-hr equivalent to 3,000,000,000 kw-hrs, i.e., 3,000,000
But the system delivers only 270,000 Mw-hrs per year. Ergo, system
will have to be in operation for 11.1 yeas before it pays for its
capital cost.

What is the running cost?

Insolation efficiency.

154 Mw per 800 hectares.
8e2 * 1e2 * 1e2 = 8e6 sq metres.

Insolation is nominally 1 Kw per sq metre at normal incidence.
System should deliver 8e3 Mw at peak efficiency. Ergo, ground cover
efficiency is only  154/8000 = 1.9 percent!!!!

With efficiency this low my calcs suggest we will have to cover 75
million sq kilometres with such collectors by 2050 to satisfy world
energy needs. I can't see it happening
Finally, am I Robbie  Crusoe or has anyone else wondered what happens
to the 90 percent (or more) solar energy that is absorbed but not
converted to electricity? As far as I can see  it will be dissipated
into the environment as waste heat. It seems to me that it will add to
global warming. Of course some will eventually be radiated into space,
a least that part that doesn't get trapped by the CO2 but overall it
seems to be to be counterproductive.

This is extraordinarily depressing.

** Posted from http://www.teranews.com  **

Posted by Russ in San Diego on December 19, 2008, 6:29 am

I think your question boils down to whether the albedo of a solar
panel is lower than that of the surface it's replacing.

Lower albedo generally means increased heat conversion. Even though
some 10% of light hitting a panel is converted to electricity instead
of heat, eventually nearly all of that electricity WILL end up as

I suspect there isn't really much difference.  Most of the time,
you're covering roof space with solar panels.  I doubt that there's a
big difference in effective albedo between a typical roof tile and a
solar panel.  You should be more concerned about home and asphalt road
construction, if you care to feel depressed about such things.  PV's
net effect, by decreasing GHG emission in the long term, is likely a
net positive.

Posted by George on December 19, 2008, 6:52 am

Yeah, I figured that. But I figure there aren't enough roof top panels
to make a real difference. Most bulk collectors will be put in deserts
where albedo is very high. So if absorptivity (in the desert) is more
like 10-20 percent, and all of a sudden it is increased to 95 percent
we get more energy.

** Posted from http://www.teranews.com  **

Posted by Eeyore on December 19, 2008, 2:43 pm

George wrote:

Only mega expensive space ones. More like 15% for what you can buy at
slightly more same prices.


Posted by Mauried on December 20, 2008, 9:26 pm
 On Fri, 19 Dec 2008 10:04:54 -0600, david.williams@bayman.org (David
Williams) wrote:

Mirrors are also a hell of a lot cheaper than Solar Panels.

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