An Unusual Comparison with Nuclear

Ken Zweibel
January 03, 2011 | 14 Comments

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 (Source)

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.

See the online discussion in the comments at The Solar Review

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14 Comments

Thomas M
January 7, 2011

When you think about it, solar is actually a nuclear power. Only thing is, the reactor is a safe 93 million miles away......

ANONYMOUS
January 6, 2011

This is a ridiculous comparison. I don't pay my electricity bills with Cd, Te, or U ore, and the costs, availability, and environmental toxicity of these materials aren't proportional to their mass. A useful and usual unit of comparison would be price per unit of energy. There might be some unusual comparisons that are not useless, but this isn't one of them.
Steven

Therese Shellabarger
January 5, 2011

PV is not yet the right solar technology. What is good solar technology is passive solar and solar heat for things like hot water and stirling engines. So we'll have our hot showers and a motor to pump the water wherever we need it. We could also use solar heat to desalinate sea water, basically for free. I was thinking it might be possible to use sea platforms with a pipe to shore and stirling engines to literally pump the water as fast as it can be vaporized. At night, it would be quiet, but could also serve as a 24 hour marine sanctuary, similar to what oil platforms are like today, only less toxic.

Donald Wagner
January 5, 2011

rolf, your information is about one year out of date.

http://www.nytimes.com/2010/11/24/opinion/24iht-edmiller.html
"Germany added the equivalent of nearly 1 percent of its electricity supply with solar energy between January and August. The first 1 percent took 10 years to achieve; the next 1 percent just 8 months."

rolf westgard
January 5, 2011

Yucca Mountain is funded by one tenth cent charged for every kwh produced by a nuclear plant. That fund has collected over $20 billion which shows how much power those reactors generate. $10 billion has been spent on Yucca which should be opened. The rest is being siphoned off to fund big losers like wind and solar.
Germany is doing the same - extending the life of its nuclear plants and taxing them to fund all those solar panel decorated roof tops which provide less than 1% of its electric power.

ANONYMOUS
January 5, 2011

What you need to understand is the "levelized" cost of producing the power which for renewables usually omits the cost of energy storage during solar eclipse. Suggest you review projection of Power Plant Levelized Baseload Costs:
http://books.nap.edu/openbook.php?record_id=12710&page=58#p20019b279960058001

david watts
January 5, 2011

Rolf- you had me rotfl !!!
any nuclear proponent should never brandish the stick " taxpayer funded boondoggle".
i think it was David Carradine on Kung Fu who said " if you point a finger, three point back at you".
one huge reason nuclear has the lead on solar is hundreds of million dollar lobbyists,belly and snout to the trough.Another reason is, funnily enough....taxpayer funded boondoggles. Yucca mountain anyone?
i am not supporting this article,I am just trying to not have my morning coffee shoot out my nose as i read your comments.Have you auditioned for comedy central?

rolf westgard
January 5, 2011

As previous comments note, this article is complete nonsense. There is a reason solar is about one tenth of 1% of US electric power and nuclear is 200 times as much at 20%. You can get any result you want when you compare apples to oranges. At this point, solar is a taxpayer funded boondoggle.

Russ Finley
January 4, 2011

Who cares? PV won't be enough. We also need nuclear. One has advantages over the other.

Lawrence Carroll
January 4, 2011

Douglas-Meyer said, " "If renewable energy technology becomes cost competitive without subsidies, it will be the only power generation technology that is without subsidies".

Bravo! Bravo! :)

Douglas Meyer
January 4, 2011

Unfortunately these comparisons are a bit short on some BIG details, such as the energy required to enrich the U-235 isotope from 0.711% assay up to 5% or so for a commercial reactor (unless you have a Candu, which runs on natural assay material).

The comment on subsidies for RN power is classic, but the running joke is: "If renewable energy technology becomes cost competitive without subsidies, it will be the only power generation technology that is without subsidies".

Glenn Doty
January 4, 2011

Of course... for every 12 grams of CdTe used to make a solar panel, there's another 10-15 kg of glass, copper, aluminum, plastic, and other materials. So you are using literally 1000 times as much stuff as you claim in order to produce that energy.

To compare that with nuclear energy: the nuclear plant itself is on the order of ~100,000 tons of steel and concrete. A 1 GW plant will use something like ~7000 tons of uranium over the course of its lifetime, which means that it only uses a total of ~14 times as much material as you are claiming. Hence the total balance of stuff-to-energy is ~312 mg of stuff/kWh for nuclear energy, and ~2600 mg of stuff/kWh for PV.

That is reflected by the fact that energy from PV is considerably more expensive than nuclear energy - which itself is too expensive to be market viable.

Nick Cook
January 4, 2011

It all depends on how you do the comparison

The actual mass of material used per KWh in a nuclear reactor is given by e=mc2, done this way 1KWh uses 40pico-gm or 40billionths of a milligram!

Another consideration is that if the Uranium is used in a fast breeder reactor it produces more nuclear fuel than it consumes, if I recall correctly as plutonium(not as uranium or that be perpetual motion), so the potential energy form uranium nuclear fuel is potentially much higher than it appears first.

In reality what really matters is can a technology supply electricity at a reasonable price to the end consumer, based on the current levels of FITs for PV I would say this is currently not the case for most current PV.

By the way I'm not a fan of nuclear, so the scientists and engineers need to come up with alternative RE electricity technologies that are economically with existing tradition technologies without the need for massive subsidies. Personally I think there are some promising technologies out there that will do this.

William Fitch
January 3, 2011

Hi:

An interesting table of numbers...
A very intense result, one that allot of parties would not want to see on the front of the NYT...LOL..

It is allot like the difference between a fuel and a catalyst.
In a general sense, PV allows something to happen but does not chemically partake in the reaction, though does suffer degradation over time, minor in comparison... What is even more astounding is that these numbers are huge in difference even at the relatively poor total output percentage for PV, I.E.~10%. Just think of those numbers when they can net 30%...

.....Bill

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Ken Zweibel

Ken Zweibel has almost 30 years experience in solar photovoltaics. He was at the National Renewable Energy Laboratory (Golden, CO) much of that time and the program leader for the Thin Film PV Partnership Program until 2006. The Thin Film...