An Unusual Comparison with Nuclear
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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This is fantastic news. I would like to add that if you couple a passive solar design with active solar panels for a residential home or commercial office you could add to the efficiency of Solar energy with a similar lifetime of at least thirty years.
Interesting comparison. However, since you assume recycling for solar, why don’t you also include recycling for uranium? Using Storm-Smith’s rather pessimistic numbers assumes that we will continue using an inefficient once through fuel cycle that uses only 0.5% of the potential energy.
With full recycle, uranium can produce 8,000 kilowatt hours of electricity per gram or 8 kilowatt hours per milligram. Best of all, that energy release can be controlled by humans or automatic controls – it does not depend on the weather.
This is Awesome…
Naturally after reading this, any one can
vote for solar energy against the nuclear.
I vote for Solar – Always…
Sorry, gwsolar, but that “advantage” of solar is illusory because it’s temporary. You quote 0.5 mg/kWh for CdTe, and 24 mg/kWh for uranium. Problem is, that latter number is for today’s horribly inefficient thermal reactors. The coming generation of fast reactors will get about 140 times as much energy from a given amount of uranium. So for projections into the future, the amount of uranium needed per kWh will be closer to 0.17 mg U / kWh — some 3 times less than the your most optimistic CdTe prediction.
Dear Mr. Zweibel:
Would you be kind enough to point us to a CdTe PV module that has a 30-year warranty? And I wasn’t aware that nuclear plants burn (oxidize) uranium. Maybe you should write an article educating us about that, as well? When will you stop spreading misinformation?
I am sure I have made errors, but those don’t seem to be among them. I never say uranium is burned, just “used.” The traditional warranty of all PV (and CdTe included) is about 30 years (actually, 25) with a small annual loss that does not alter the arithmetic – I say “about 30″ in the text.
I am told that one milligram of nuclear reactor fuel can generate 315 kWh. Over its 25-year warranted life, 1 milligram of a CdTe panel (basically, glass) will generate less than 0.2 kWh (so even if it is recycled for free 40 times, over one thousand years, it will still generate just a puny 8 kWh) . Sorry. PV solar inefficiently converts the star energy as it reaches the panel, while fossil fuel and nuclear release star energy that has been stored over millions of years.
A correction: I gave too much credit to mass in my comment. Replace all references to milligram with gram!
Ken,
Your maths is wrong on Coal
30 years ~200k
60 years ~ 400k
90 years 1m
the nuke number is spot on.
Great figures though, really interesting way to view the subject
Thanks for recalculating those numbers. Actually, that’s what I meant by “5 millionths”, which is the same as one over 200,000; and for the others, too – they are just different ways of saying those numbers (but the same fraction). Note we agree on 90 years as “one millionth” or as you put it, a million.
It would be worth doing this as a cost per kWh of energy too. Pretty exciting and interesting. I’m also unclear on assumptions about solar variability (and accounting for latitude, cloud cover, and other regional differences).
Thanks for this different, very interesting perspective on energy sources. I have two comments on the comments. First, ECD-Fan criticized gwsolar for using the word “burn” in close proximity to the words “nuclear plant”. Apparently, the Fan did not notice that the first page of linked report on uranium usage describes “burner” nuclear reactors. Secondly, solar power is often criticized as being inefficient. I now realize that today’s nuclear power is “horribly inefficient” as well.