Why solar energy trumps coal power
The color of solar cells — and their short energy payback — are trivial factors when considering the huge climate benefit they provide in avoiding the release of CO2 from the combustion of fossil fuels.
That was a central point in my first post debunking the error-riddled book Superfreakonomics. By failing to retract the many glaring errors I pointed out in my original post weeks ago — and instead blowing an aerosol smokescreen with false claims that Caldeira did not say the book misrepresented his views (see here) — Levitt brought upon himself the detailed and devastating takedown by Geophysicist Raymond T. Pierrehumbert, which focused on the same exact paragraph in the book that I debunked:
“A lot of the things that people say would be good things probably aren’t,” Myrhvold says. As an example he points to solar power. “The problem with solar cells is that they’re black, because they are designed to absorb light from the sun. But only about 12% gets turned into electricity, and the rest is reradiated as heat — which contributed to global warming.”
In my post, I noted that there were three and a half major howlers in this one tiny paragraph and that California Energy Commissioner Art Rosenfeld called this “patent nonsense” when I read it to him. Within minutes of my posting, a former lead engineer at Princeton Plasma Physics Lab “emailed me to be sure I don’t miss the forest for the trees here in debunking this,” as I wrote at the time. He pointed out that climatologist Ken Caldeira, of all people, had an analysis showing it was trivial:
As Ken Caldeira so grippingly points out (and I tried to make graphically clear in my Stanford talk last year), each molecule of CO2 released thermal energy when it was formed — that’s why we formed it. In the case of electricity generation, about 1/3 of its thermal energy went out a wire as electric power, the rest was released promptly as waste heat. But each molecule of CO2, during its subsequent lifetime in the atmosphere, traps 100,000 times more heat than was released during its formation.
A hundred thousand is a big number. It means that running a handheld electric hairdryer on US grid electricity delivers a planet-warming punch comparable to [the heat given off by] two Boeing 747s operating at full takeoff power for the same time period. The warming is delivered over time, not promptly, but that don’t matter; the planetary heating is accrued, the accountants would say, the moment you hit the switch.
And so I immediately added that in the original debunking (see here), which Levitt and Dubner obviously read and chose to ignore.
The graphic above is a PowerPoint from the engineer meant to illustrate the factor of 100,000.
Several people asked me for the analysis that derived the factor of 100,000. Climatologist Ken Caldeira was kind enough to share it with me and give me authority to post it. It is a previously-unpublished joint analysis by Caldeira and NYU’s Martin Hoffert titled, “Warming from fossil fuels,” which is now posted here. The abstract reads:
Put another way, as Caldeira and Hoffert write in their final paragraph:
In other words, when we burn carbon and release CO2 to the atmosphere, only 0.001% of the total warming comes directly from the release of chemical energy during burning. The remaining 99.999% of the warming is associated with the trapping of outgoing longwave radiation by that CO2 in the atmosphere.
Thus the color of the solar cells or the heat they reradiate is utterly trivial. What matters is that they replace the burning of fossil fuels and prevent the fossil carbon from ever being released. As an aside, Pierrehumbert notes that coal plants also give off massive amounts of waste heat because they are so inefficient, so “That makes the waste heat of solar cells vs. coal basically a wash,” even ignoring this factor of 100,000.
Levitt and Dubner need to retract that entire paragraph, much as they have agreed to correct their claim that Caldeira believes “carbon dioxide is not the right villain” in future editions.
Because they failed to quickly own up to the egregious mistakes in that one paragraph, they left themselves open to Pierrehumbert writing his “An open letter to Steve Levitt,” accusing Levitt of “academic malpractice”:
So, the bottom line here is that the heat-trapping effect of CO2 is the 800-pound gorilla in climate change. In comparison, waste heat is a trivial contribution to global warming whether the waste heat comes from solar cells or from fossil fuels. Moreover, the incremental waste heat from switching from coal to solar is an even more trivial number, even if you allow for some improvement in the efficiency of coal-fired power plants and ignore any possible improvements in the efficiency of solar cells. So: trivial,trivial trivial. Simple, isn’t it?
… A more substantive (though in the end almost equally trivial) issue is the carbon emitted in the course of manufacturing solar cells, but that is not the matter at hand here. The point here is that really simple arithmetic, which you could not be bothered to do, would have been enough to tell you that the claim that the blackness of solar cells makes solar energy pointless is complete and utter nonsense. I don’t think you would have accepted such laziness and sloppiness in a term paper from one of your students, so why do you accept it from yourself? What does the failure to do such basic thinking with numbers say about the extent to which anything you write can be trusted? How do you think i
t reflects on the profession of economics when a member of that profession — somebody who that profession seems to esteem highly — publicly and noisily shows that he cannot be bothered to do simple arithmetic and elementary background reading? Not even for a subject of such paramount importance as global warming.
And it’s not as if the “black solar cell” gaffe was the only bit of academic malpractice in your book….
Levitt first tried to respond to my debunking of that paragraph by letting Myhrvold reply. But that backfired when Myhrvold repudiated the core argument of the chapter! Myhrvold’s “defense” was so lame that Berkeley economist Brad Delong posted on his blog an extensive debunking of it, written by Nicholas Weaver, which ends with perhaps the best one-sentence judgment on the book and its key source that I’ve seen so far:
… what is happening is I have to conclude that anything Myhrvold says has to be assumed to be false until proven otherwise, and by unquestioningly accepting his assumptions, anything Drubner and Levitt say may need to be taken the same way.
On October 30, Levitt replied directly to Pierrehumbert on RealClimate with another attempted aerosol smokescreen:
I enjoyed your intentional misreading of my chapter on global warming! I think it has really contributed to moving towards a solution to these important problems.
Myrhvold’s *main* point was about the energy required to produce the solar cells, not the radiated heat. He has expanded on it here:
http://freakonomics.blogs.nytimes.com/ 2009/ 10/ 20/ are-solar-panels-really-black-and-what-does-that-have-to-do-with-the-climate-debate/
His view is simply that solar panels are not a *short-run* solution to cooling the planet. I doubt you could disagree with that, given the arguments you make in your own blog post.
So he, and we, thought it made sense to explore some solutions that DO cool the earth in the short-run.
That doesn’t mean you don’t work on long run solutions as well.
I’m not sure why that is blasphemy.
As anyone can see, it is not an “intentional misreading.” Quite the reverse. Just go to the now-searchable Superfreakonomics on Amazon and put “reradiated” into the search engine. Pierrehumbert replied directly:
Steve, glad to see you’re reading this.
Something I have found rather bizarre about your responses to the criticisms of your climate chapter is the way you continually try to change history about what you actually wrote, which is plainly there for anybody to see. I found it so unbelievable that you included the “black solar cell” meme when I first heard it that I actually went over to Borders and stood there and intentionally read (not misread) the chapter to see if it was true. Anybody reading what you wrote would never, ever guess that the waste heat effect was so trivial unless they already knew the subject from some other source. And as for the “short term vs. long term” issue, here’s something to chew on: if you instantaneously built a solar array big enough to meet the entire world electricity demand, you would only have to wait something under a year before the avoided CO2 radiative forcing paid back the waste heat effect.
The payback time for recouping the carbon cost of manufacturing solar cells is somewhat longer, but still substantially less than the lifetime of the solar cells — and coming down as technology improves. So, there is really no sensible construction I can put on your statement.
Yes, lots of people couldn’t believe the book was as bad as I had asserted — especially since the publisher made me take down PDF of the chapter I had posted and also asked Amazon to end the searchability, so no one could see the contents until the book was actually out. But now everyone can see it was as error-riddled as I said, and that every single statement I made in the original post was accurate.
I’ll address the energy payback argument further in a later post.
NOTE: I have updated this post slightly for absolute clarity since some people might not read the first debunking post that I linked to above (click here), which lays out the timeline of how I came to include this factor of 100,000.