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http://thesolarreview.org/2010/12/20/an-unusual-comparison-with-nuclear/



An Unusual Comparison with Nuclear
December 20, 2010
by gwsolar

We don’t burn solar modules to make electricity. If we could recycle 100% of them forever, we would produce an infinite amount of electricity per gram of material. Even in practical use, we use less PV material per kWh than uranium per kWh when we make PV electricity in comparison to nuclear electricity. The amounts of active materials used in PV are tiny.

Just how tiny? For an up and coming thin film, CdTe, we use about 12 gm of CdTe to make a square meter module. In a year in an average US location, we harvest about 11% x 1750 kWh/m2-yr, or 154 kWh/yr (after accounting for another 20% in losses, but not for an additional, but small annual loss). Thus in one year, we need 0.08 g/kWh. But wait! We don’t burn PV modules, and they don’t die after one year – warranties are about 30 years, so this is really one thirtieth of that, or 2.6 milligrams per kWh. Let’s make a table:

Amounts of CdTe Used with Different Recycling and Lifetime Assumptions
Assumptions about PV
CdTe milligrams/kWh
30 years operating life 2.6
60 years 1.3
90 years and 90% recycling (after 180 years) 0.5

In comparison, we burn:
Fuel Milligrams/kWh
Coal 500,000
Natural Gas 200,000
Uranium 24 (from http://www.stormsmith.nl/report20071013/partB.pdf
)

So the ratio of the use of CdTe to these fuels is as follows:
Assumptions about PV
CdTe/Coal Use per kWh CdTe/Uranium Use per kWh
30 years Five millionths A tenth
60 years Two and a half millionths One twentieth
90 years and 90% recycling (after 180 years) A millionth One fiftieth

So even without fancy assumptions about lifetime and recycling, today’s PV systems will use CdTe more conservatively than nuclear will use uranium by a factor of 10. But with reasonable recycling assumptions, made more realistic when one understands that CdTe manufacturers already recycle their modules, CdTe will use 20 and 50 times less material than nuclear per kWh of output. Compared to coal, of course, the numbers are out of this world. These differences in resource needs bear on the ultimate sustainability of the PV in comparison to other more resource-intense energy technologies.

Ken Zweibel
 

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