Remember that bizarre episode in Freakonomics 2, where Levitt and Dubner went to the Batcave-like lair of a genius billionaire who told them that “the problem with solar panels is that they’re black.” I’m not the only one who wondered at the time: of all the issues to bring up about solar power, why that one?
Well, I think I’ve found the answer in this article by John Lanchester:
In 2004, Nathan Myhrvold, who had, five years earlier, at the advanced age of forty, retired from his job as Microsoft’s chief technology officer, began to contribute to the culinary discussion board egullet.org . . . At the time he grew interested in sous vide, there was no book in English on the subject, and he resolved to write one. . . . broadened it further to include information about the basic physics of heating processes, then to include the physics and chemistry of traditional cooking techniques, and then to include the science and practical application of the highly inventive new techniques that are used in advanced contemporary restaurant food–the sort of cooking that Myhrvold calls “modernist.”
OK, fine. But what does this have to do with solar panels? Just wait:
Notwithstanding its title, “Modernist Cuisine” contains hundreds of pages of original, firsthand, surprising information about traditional cooking. Some of the physics is quite basic: it had never occurred to me that the reason many foods go from uncooked to burned at such speed is that light-colored foods reflect heat better than dark: “As browning reactions begin, the darkening surface rapidly soaks up more and more of the heat rays. The increase in temperature accelerates dramatically.”
Aha! Now, I’m just guessing here, but my conjecture is that after studying this albedo effect in the kitchen, Myhrvold was primed to see it everywhere. Of course, maybe it went the other way: he was thinking about solar panels first and then applied his ideas to the kitchen. But, given that the experts seem to think the albedo effect is a red herring (so to speak) regarding solar panels, I wouldn’t be surprised if Myhrvold just started talking about reflectivity because it was on his mind from the cooking project. My own research ideas often leak from one project to another, so I wouldn’t be surprised if this happens to others too.
Once again XKCD is on hand to provide a useful info-graphic.
I was wondering about that very section of that very article. Do black foods really absorb more heat? Wikipedia's albedo page doesn't mention it.
And papers like Mondojoyan et al.'s Preliminary Modelling of Heat and Mass transfer During Grilling and Roasting of Meat have nice graphs (page 5, figures 4 and 5) of the empirical non-linearity and never mention surface color.
Are there any physical chemists in the house?
Well, I've got the requisite degree in physical chemistry, but it's been a little while since I've been practicing. I would be skeptical of any albedo argument here, given that the absorption levels for both browned and raw meat are high in the infrared. I'd be much more likely to blame changing moisture levels, and would suggest that the browning is a result of (and a sign of) a lower amount of water. That would explain the rapid rise in temperature better than any albedo argument I know of.
Aha – the Maillard reaction! Browning occurs at temps higher than boiling, which means that the water must be at least partially boiled away. At least according to wikipedia: http://en.wikipedia.org/wiki/Maillard_reaction
This Myhrvold guy may be very intelligent, but he doesn't seem to know very much about the stuff he talks about. Or maybe people only give publicity to the dumb stuff he says.
First, he's wrong about the albedo of solar sells being _a_ problem, much less _the_ problem. Yes, the albedo of the earth is very important, but no, installing enough PV to provide all of the electricity the world uses, or even several times that amount, won't make a difference. (Andrew, it's interesting that you say "experts seem to think" the albedo effect is negligible, rather than the stronger "the effect of the change in albedo is negligible).
Second, although it's _possible_ that Myhrvold is right about the albedo of food changing as it browns, I think it is very unlikely. There's little correlation between how much infrared light an object absorbs, and how much visible it absorbs. An object that is "dark" in the visible isn't necessarily dark in the infrared, nor is an object that is "light" in the visible necessarily light in the infrared. (Famously, snow absorbs IR quite well but is extremely reflective of visible light). If we cooked chicken by shining really intense visible light on it, then Myhrvold's argument would make sense, but for chicken cooking on a stovetop or in an oven, it doesn't. I think. I am not an expert on food, and it's possible that the IR absorptivity of some foods changes as they cook. But I doubt it.
I would look to moisture, rather than color, for the explanation of why some foods will seemingly cook slowly, then suddenly burn or scorch: I think most of the heat goes into vaporizing water — thus keeping the temperature at around 100C — until the water is gone, at which point the temperature climbs very rapidly. That's just a guess, though. I'm quite sure the answer is well known to people who study this sort of thing.
Given that I haven't thought seriously about albedo for about 25 years, I thought it would make more sense for me to say "experts seem to think" and link to physicist Raymond Pierrehumbert who explained it all in much more detail than I could.
To me, the saddest thing about the whole episode is not Myhrvold's physics errors (as we all know from Road Runner cartoons, even a genius can make the same mistake over and over and over again) or the journalists involved (it's natural to be intimidated by a billionaire with a Ph.D.) or Myhrvold's response to criticism (we can all be thin-skinned sometimes) but rather Levitt's response to his University of Chicago colleague. After Pierrehumbert explained the albedo story in an "open letter" to him, Levitt replied:
Pierrehumbert had not talked about "blasphemy" or anything like it. True, his "open letter" to Levitt was not exactly polite, but he was making a clear enough scientific point. It wouldn't have killed Levitt to have admitted he'd made a mistake.
Jeez, did I really write "solar sells"?
Andrew, I noticed that you had linked to Pierrehumbert's explanation. It's quite convincing, isn't it? I think so. And you certainly (still) have the physics chops to evaluate it. I don't think it's necessary, or even appropriate, to give a caveat about something like that. It's as if someone said "experts seem to think that if fewer people smoked, fewer people would get lung cancer."
I agree with you about Levitt's (and, for that matter, Myhrvold's) response. They said some very foolish things that they hadn't bothered to think about in advance, and rather than fess up, they acted like only a quasi-religious wacko would irritatedly point out their mistake. Nobody likes to be corrected, especially when it's done patronizingly, and I can understand some defensiveness. But when someone points out a major mistake, the first thing to do is admit to your mistake; then, if you want to complain about the tone the conversation, go for it.
Since Nathan has asked me to do projects/experiments in the past, I really want to reflect on them in this post. But, instead, I will just say that I look forward to the entertainment of reading his book. Thank you for the laugh though.
Yes it is true that the whitish sand of the Sahara has a high albedo (about 0.4) which reflects heat. That's why it's so damn hot there.
I would also be sceptical of this food albedo argument.
What matters is the albedo in the infrared, cooking at 450 F or approximately 500 Kelvin, would be a blackbody peak at about 5.8 microns. (Visible light is between 0.4 and 0.75 microns). When it turns black it is because the albedo has dropped for visible light. I don't know about food, but according to this paper
pure snow (with an albedo of nearly 1 in the visible) has an albedo of nearly 0 by the time you get to about 1.6 microns. So snow which white as can be in the visible is black in the infrared.
Clark Andersen sent the following comment which got eaten by the blog:
After reading the debate regarding temperature versus color, I recalled that many years ago I [Andersen] had empirically hypothesized (by laying-on of hands) that red cars were cooler than other colors, presumably due to red being nearer to infrared than other colors. I discussed this with my co-worker and we decided to go out into the parking lot and do a quick sampling to “definitively” resolve the issue. We used an infrared thermometer to measure the rooftop temperature and color of an assortment of cars and trucks in the parking lot. Temperature is in Fahrenheit, and the ambient temperature was about 71 in the shade. It appears that my hypothesis was incorrect, color does not seem to clearly affect the temperature, though albedo does. The following R code (which includes the data) makes a box-and-whisker plot which summarizes the results:
boxplot(white,silver,tan,green,red,gray,blue,burgundy,black,names=c("white","silver","tan","green","red","gray","blue","burgdy","black"),main="Vehicle temperature by color")
My thought when I read how PV solar panels radiate heat was that maybe that heat could be used to heat water by running water tubes over the panel to generate hot water.
Anyway now I read they are doing it here…
I like Clark Andersen's albedo data. I used it in an example of how to construct a funnel plot (similar to an analysis of means plot):