Are Solar Panels Really Black? And What Does That Have to Do With the Climate Debate?

Nathan Myhrvold is a polymath’s polymath, the former chief technology officer at Microsoft who, by the time he was 23, had earned, primarily at UCLA and Princeton, a bachelor’s degree (mathematics), two master’s degrees (geophysics/space physics and mathematical economics), and a Ph.D. (mathematical physics). He is co-founder of Intellectual Ventures, a firm comprising many other scientists, including climate scientists, whose counterintuitive views on global warming and its possible solutions are explored in the final chapter of SuperFreakonomics. A climate-activist blogger didn’t like the chapter, accusing Levitt and Dubner of chicanery (a charge that Dubner rebuffed here) and accusing Myhrvold of not understanding the physics behind solar power. Oops. Below you can read Myhrvold’s views on the tenor of the global-warming debate in general and solar power in particular. Watch this space for further rebuttals of shouted claims of error and evil.

One of the saddest things for me about climate science is how political it has become. Science works by having an open dialog that ultimately converges on the truth, for the common benefit of everyone. Most scientific fields enjoy this free flow of ideas.

There are serious scientific and technological issues in studying our climate, how it responds to human-caused emission of greenhouse gases, and what the most effective solutions will be for global warming. But unfortunately, the policy implications are vast and there is a lot at stake in economic terms.

It seems inevitable that discussions of climate science would degenerate to being deeply politicized and polarized. Depending on which views are adopted, individuals, industries, and countries will gain or lose, which provides ample motive. Once people with a strong political or ideological bent latch onto an issue, it becomes hard to have a reasonable discussion; once you’re in a political mode, the focus in the discussion changes. Everything becomes an attempt to protect territory. Evidence and logic becomes secondary, used when advantageous and discarded when expedient. What should be a rational debate becomes a personal and venal brawl. Rational, scientific debate that could advance the common good gets usurped by personal attacks and counterattacks.

Political movements always have extremists — bitterly partisan true believers who attack anybody they feel threatens their movement. I’m sure you know the type, because his main talent is making himself heard. He doesn’t bother with making thoughtful arguments; instead, his technique is about shrill attacks in all directions, throwing a lot of issues up and hoping that one will stick or that the audience becomes confused by the chaos. These folks can be found at the fringe of every political movement, throughout all of history. Technology has amplified them in recent years. First with talk radio and then with cable TV, the extremists found larger and larger audiences.

The Internet provides the ultimate extremist platform. Every blogger can reach millions, and given the lack of scrutiny or review over content, there is little accountability. Indeed, the more over-the-top the discourse is the better — because it is entertaining. Ancient Romans watched gladiators in much the same way that we read angry bloggers.

That seems to be the case with Joe Romm, a blogger with strong views about global warming and what he calls “climate progress.” In a recent series of blog posts, Romm levels one baseless, bald charge after another. What provoked this? The best summary I’ve seen comes from a comment by DaveyNC to the Freakonomics blog which says:

No, no, no, no — you have committed apostasy; heresy! You are not allowed to speak of warming except in the most emotional, alarmist tones!

You are not allowed to follow an objective, skeptical line of reasoning in this matter. You are not allowed to consider whether or not it is cost-efficient or even possible to cease all carbon emissions; you simply must do it.

That pretty much sums it up, as far as I can tell. SuperFreakonomics dares to comment on climate issues in a manner that Romm sees as contrary to his agenda, so he sets out to smear the book and me as a figure in the book.

Romm’s method of attack is pretty simple. He takes as many statements as he can, interprets them — or misinterprets them in the worst possible way — and then subjects them to ridicule. As an example, he goes on and on about a comment that I made about how solar photovoltaic cells have a problem because they are black. Romm attacks me as if I think that this means that solar cells are bad. Yet that wasn’t the point in SuperFreakonomics at all. I am quoted in the book as follows:

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 percent gets turned into electricity, and the rest is reradiated as heat — which contributes to global warming.

Although a widespread conversion to solar power might seem appealing, the reality is tricky. The energy consumed by building the thousands of new solar plants necessary to replace coal-burning and other power plants would create a huge long-term “warming debt,” as Myhrvold calls it.

“Eventually, we’d have a great carbon-free energy infrastructure, but only after making emissions and global warming worse every year until we’re done building out the solar plants, which could take 30 to 50 years.”

Please note that the quote says that solar could provide a “great carbon-free infrastructure.” That hardly makes me anti-solar-energy, now does it? But to a partisan like Romm, it’s better to ignore that line — so he does. He quotes somebody’s calculation arguing that over very long periods of time, solar cells save emissions. Well, of course they do. It’s so much easier to attack if you take things out of context.

Since this is at least partly a technical point, I will go to the trouble of explaining it further.

The point I was making to Dubner and Levitt is the following: when you build a solar plant it costs you energy. Lots of energy. Pacca and Horvath, in a 2002 study, found that the greenhouse gas emissions necessary to build a solar plant are about 2.75 times larger than the emissions from a coal plant of the same net power output (1.1 * 10^10 kg [editor’s note: numbers corrected from an earlier version] of CO2 to build the solar plant versus 4 * 10^9 kg of CO2 per year for coal). The numbers vary depending on the specific technology, but there are dozens of “Life Cycle Assessment” papers on solar photovoltaic cells that document a similar effect. So building the solar plant hurts global warming, at least during the construction period. Once you turn it on and are able to throttle back a coal plant because you get electricity from the solar cells, you gradually earn back the deficit through CO2 emissions that are saved. You need to operate the solar plant for at least 2.75 years before you break even versus the coal plant — at least versus CO2 emissions. This is very much like the old adage “you need to spend money to make money.” You need to “spend” some carbon emissions in order to create a carbon-free infrastructure which will ultimately yield a carbon emission “profit.”

Solar cells pretty much have to be “black” in the energetic side of the solar spectrum because they absorb sunlight! Of course no material is a perfect absorber, so when I say “black,” what I mean is very high absorption of light — 90 percent or more. Solar cells often have a bluish tint to them because they reflect a tiny bit more blue light than other colors, but that is small enough that it doesn’t matter for our purposes here.

Unfortunately, solar cells are not very efficient. Efficiencies of 9 percent to 13 percent are typical for current widely deployed technology. In the future that will change, and some laboratory examples are better, but this is what people deploy now. So for every watt of electricity they generate, current solar cells throw about 10 watts into the climate as heat. Some of this heat would have occurred anyway when the light was absorbed by the ground, but the most effective solar cell installations are in deserts where the albedo is pretty high (.4 to .5) and there is little cloud cover, so the solar cells cause a bunch of heating that would not have otherwise occurred. A typical coal power plant gives off about 2 watts of thermal heat for each watt generated, so the direct thermal heating from solar plants is likely to be as large or larger than that from coal plants.

The blackness of the solar cells factors into this start-up period. It’s well known in climate circles that the Earth’s albedo (how much light the surface reflects from the surface) is very important. It’s one of the reasons climate scientists are worried about Arctic sea ice melting; you go from a white surface that reflects 90 percent of the light (albedo 0.9) to ocean which is almost black and reflects 10 percent or less (for an albedo of 0.1). Climate studies published in peer-reviewed journals have shown that making roofs white would potentially be a great help against global warming. Other studies have looked at the impact of forests and logging on albedo. It is well known that albedo matters; this isn’t my private theory — it is mainstream climate science.

If you mount the solar cells on a rooftop or other surface that is already black or very dark, then it won’t make much of a difference. But, that’s just because the dark surface is already contributing to global warming (two wrongs don’t make a right!), and in any event, most large-scale solar installations are aimed at deserts or other terrain that has pretty high albedo. Romm makes a point of showing a photo of a solar-cell array on a roof, saying this refutes me. It doesn’t; my comments were clearly about large-scale deployment.

Over time, the CO2 savings from operating the solar plant (versus coal) would accumulate and be much larger that the warming caused by the “blackness.” It does not make solar cells bad in absolute terms; that’s why I say they are part of a “great carbon-free infrastructure” solution. But it does count against them and needs to be factored into the start-up costs. The effect would be to increase the time you need to run the plant before it breaks even.

The next part of the point is that we need to build out lots of renewable energy if it is going to make a difference. If we finish one plant today, it takes it three years to break even. Three years may not be the exact number, but let’s use it for simplicity. Next year we finish two more plants, and the next year we finish four more plants. Regardless of whether the numbers are 1, 2, 4, or some other sequence, we need to build the increasing amounts if we’re going to get a lot of plants built. But notice this: the three-year break-even times start to overlap and pile up as we build more and more plants.

The net result is that we may not get much CO2 benefit from the solar plants until we are past the rapid-growth phase of building out new plants. If we go hell-bent for leather in building solar plants for the next 50 years or so, it is entirely possible that we won’t see much small benefit for 30 to 50 years. In the long run, we still get benefit from the solar plants — lots of benefit (hence the “great carbon-free infrastructure”) — but in the near term, we may get little or no benefit. I say “may” because the details matter, and it is beyond the scope of what I can do here to calculate and explain them all; but the basic effect is that the time to get real benefit is delayed. A large part of this is due to the energy it takes to make them, and some is due to their blackness.

This is one of the dilemmas we face as a society. If we rapidly invest to make a new renewable-energy infrastructure, the very fact that we are making that investment can delay the onset of the benefit. It’s really hard to cut emissions quickly unless you cut consumption quickly, which society doesn’t seem very keen to do. So when people say “Let’s build out solar massively between now and 2050 in order to cut emissions,” I say yes, we’ll get the emissions cut, but in the short-term there may be less benefit than you think.

I made all of these points to Dubner and Levitt — both in person and in e-mail comments I made on a draft of the chapter. They incorporated as much as they felt they could while telling their story. SuperFreakonomics is not a technical book on the science of global warming; it is a popular book that treats these details at a high level. And besides, the three little paragraphs on solar isn’t the main point of the chapter — it is a small side-show that illustrated a point: that I feel many people are too optimistic about plans to solve global warming.

At the time I reviewed the chapter, I felt that, taken together as a whole, it is true to the spirit and flavor of what I said and believe. SuperFreakonomics did not explain all the numbers and details behind the comment on solar cells, but it is not supposed to. Instead, it touched on the highlights, including the key point that I am a fan of renewable energy sources (i.e. a “great carbon-free infrastructure”). I just think we need to understand the limitations accurately, particularly the short-term implications that most people neglect.

I am not anti-solar or anti-renewable energy. I am a co-inventor on several solar energy inventions, and my company has done a number of others with other inventors. We also have inventions in other forms of carbon-free energy production, energy conservation, and transmission. But Romm interprets my remarks as an “amateur takedown of solar” which he had to attack.

It’s taken me an awful lot of words to respond to just one of Romm’s many ravings, and I can’t tackle them all here. Sometimes he takes things out of context, as he does above. Other times he just blasts with crude broadsides of “sheer illogic,” “patent nonsense,” and the like without any argument at all. The unfortunate asymmetry is that it is much easier for him to throw stuff on the wall to see if it sticks than it is to carefully write on the wall with explanations and arguments.

Strangely, he gives comparatively little attention to the main point of the chapter, which is geoengineering. His primary objection is that it might cause some as-yet-unknown harm or unintended consequence. And I agree, which is why SuperFreakonomics says this:

Nor is he arguing for an immediate deployment of Budyko’s Blanket — but, rather, that technologies like it be researched and tested so they are ready to use if the worst climate predictions were to come true.

The way you deal with things you don’t know about is to research them! That’s what we are advocating. Through that process we would get a much better understanding of what, if any, harms would come from the geoengineering solution.

But before we get too worried about the potential harms, let’s get a grip. Geoengineering is proposed only as a last resort to try to reduce or cope with the even greater harms of global warming! The global-warming community has treated us to one scary scenario after another. Some are predicted by the science, some are extrapolations beyond current science, and some are not much better than wild guesses, but they could happen. Should we fail at cutting enough and those things occur, geoengineering might offer a better option.

It is very tempting to dismiss Romm as just another angry blogger. The Internet is full of them, and they blog on all sorts of issues. The problem here is not just about his posts and the SuperFreakonomics book; there is a larger issue at work.

This kind of attack makes it very difficult for people to suggest new ideas. I have thick enough skin to laugh it off when Romm attacks me, but plenty of people don’t. The politicization of science has a terrible impact on the unfettered discourse of ideas that is so important to making progress. This has been a big impediment to geoengineering. Serious climate scientists who are privately interested in geoengineering are loathe to discuss it publicly because they worry that somebody like Romm will attack and ridicule them if they do. Indeed, part of the reason I chose to work on geoengineering and chose to go public about it is to try to get the topic to be more widely discussed.

The point of the chapter in SuperFreakonomics is that geoengineering might be good insurance in case we don’t get global warming under control. Nobody can tell you today exactly how much CO2 we can emit without causing grave environmental harm. Nobody can tell you at what point the world will find the political will, the money, and the technological innovation to solve the problem. In a situation like that, can the world afford to turn its back on what could be a promising approach should we fail with our other efforts?

That’s the question that SuperFreakonomics asks, and that is the question on which we should be focused.


The biggest problem is that journalists and politicians don't understand the scientific process. The dialog in science, as you said, is undertaken to converge on truth. The dialog in politics is, at least in the current US system, a means to express a more and more radical position in an effort to garner publicity and votes. Journalism in its current US embodiment is a he-said-she-said, "balanced" effort to avoid having anything to do with truth - it's easier to report the controversy. So neither journalists nor politicians understand dialog by people with differing positions in an effort to come to the truth, all the people with the loudest megaphones understand is conflict; therefore, scientific dialog is presented as if it were a position rather than an effort to discover truth.

Jeffrey McManus

> So for every watt of electricity they generate, current solar cells throw about 10 watts into the climate as heat

Maybe I'm thick, but this part doesn't make sense to me, and it seems like it's the lynchpin of your defense. Where do these 10 watts come from? Aren't they from solar energy that was here already? It can't be the case that solar panels generate more energy than they receive from the sun. (Unless you're saying that the solar panels manufacture energy, which isn't possible according to the physics I understand.)

Dr. Tonic

Awesome post! Very very good points made there.

It is really too bad how many people don't want to hear it though. They want to live in their own little green world - even if it isn't green; odd isn't it.


Excellent follow up - I agree with your take on geo-engineering completely. Keep fighting the good fight!


Personally, I am not convinced of the "truth" of AGW. Some days, it's tempting to simply pick a side and start throwing rocks. But it's rational, calm, methodical explanations like Mr. Myhrvold's that convince me that common sense may one day prevail, and that "deniers" and "believers" might actually find some common ground on this divisive issue.

[And I thought the abortion chapter in the first book was controversial!]


This isn't exactly related to the article, but it is inspired by it. Ever since Socrates (at least) each generation has been complaining about the moral failings of the next. Is it the same way with politics? We feel like the internet has radicalized politics, but has it really done so, or have people felt like this since the dawn of politics?

Dan M

"If we go hell-bent for leather in building solar plants for the next 50 years or so, it is entirely possible that we won't see much small benefit for 30 to 50 years."

Not quite. Over that timescale, surely many of the current fossil plants would need to be replaced or substantially rebuilt. Assuming the CO2 cost to build (not just run) a fossil plant is similar to the CO2 build-cost of a solar plant of equivalent output, you'd see an immediate net CO2 benefit by choosing to build the solar plant instead. Same is true for a new plant required by increased energy consumption.

Casey Barker

Jeffrey, those watts are gained from absorption of solar radiation that would otherwise be *reflected* into space by a lighter colored ground cover. When you see the earth's deserts from space, they appear light in color because they're very reflective, and all that light energy is dissipated into space. Solar panel farms would appear dark in color because their black surfaces absorb most of the light, and most of what they absorb just heats up the panels, which in turn heat the air around the panels, raising atmospheric temperatures slightly. It's a small effect, but in the quantities we're talking, it adds up. In this case, 10w of atmospheric heat per 1w of electricity generated. (Of course, even that 1w of electricity eventually turns into heat, too!)


Nathan - as a scientist (theoretical chemical physics) that lives in a hotbed of environmental shrillness (Boulder, CO) I feel your pain. Thanks for being so eloquent about how science works. I say it everyday (though not as good as you) an people never get it.

Jeffery - what Nathan is saying is that there are 11 watts of energy coming in from the sun, the solar cell turns that into 1 watt of electricity and 10 watts of heat (bad for global warming). If the solar cell weren't there and the 11 watts of energy from the sun hit the desert sand, 1/2 of that would be reflected back into outer space, so only about 5 watts would be turned to heat.

Solar cell: 11W sun -> 1W electricity + 10W heat
Desert sand: 11W sun -> 5W heat + 6W reflected to outer space


@ Nosybear

Absolutely agreed. I would love t osee people actually have a discussion (a real one) about the scientific principles involved, as well as the relative merits of various solutions.

Unfortunately politics precludes reason, logic and thoughtful disucssion. People are just too emotionaly involved.


I'm a little confused by your numbers. In your initial calculation, you calculate the cost of *building* a solar panel, and compare them to the cost of *running* a coal plant. In other words, in your accounting of CO2 costs, you omit the costs per watt of building a coal plant.

This omission would only be correct if one assumes that the solar panel is being built solely to replace the output of a previously existing coal plant. But that's not really true. Due to the increasing energy requirements of our world, the real question being asked is whether to build a coal plant *or* a solar panel to meet new energy demand. In that scenario, one must compare the cost per watt of building the coal plant vs the solar panel, then compare the cost per watt of running each device, to get a true measure of the total costs and "break-even" point of each strategy.

Most environmentalists (I suspect), aren't advocating shutting down all the fossil fuel plants and switching completely. After all, there's been a massive investment of capital (and CO2 emissions!) to build the plants. At most, what they advocate is that when these plants reach the end of their useful life and need to be replaced one way or another, that we should consider building green plants.

At any rate, without taking into account the carbon cost of building a new coal plant, you're break even analysis is inaccurate for the most common scenario we face today.



Why, thank you, Mr. Myrhvold! I may have to get out of my pajamas now before I post here.

It is a shame that the mere mention of another possibility besides anthropogenic causes for global warming results in the collapse of any further useful discussion. We're not even allowed to mention that there will be benefits to warming. I am certain that the people of Iceland and Greenland will enjoy being able to grow crops for a longer period of time each year.

One gloomy day, when I wasn't feeling well enough to leave the house, I forced myself to read the IPCC Summary. I was startled to learn that it does not represent scientific consensus. In fact, it represents political consensus on how the findings of the IPCC will be presented. A review is conducted of various studies in a given area and depending on that review, the IPCC will state that X "may" cause warming or it "does" cause warming or it "is possible" that it causes warming. In other words, if the various reviewed studies split 60-40 on a topic, then the IPCC will say that it "may" cause warming. And then everybody agrees that "may" is the right word and it gets printed that way. That hardly changes the underlying science. The science, to this layman's reading of the report, is most definitely not settled.



I think your post sort of proves a point that I have seen in several posts. Basically that the chapter while it might have had good intentions, was not written by people who completely understand the issues and can explain them in layman terms clearly and unequivocally (like you have done), and hence the overall feel of the chapter might not be the one L&D intended.


I don't have a problem with this point, and I haven't read the chapter, but I would like to see a Freakonomics response to the relatively persuasive points of Paul Krugman, to wit that the authors misrepresented authors' intentions in quoting their papers... can you guys post some kind response to those critiques?


I imagine that you omit the costs of building a coal plant because it's already built. The debt has been incurred and is no longer relevant since you're trying to claw back *future* emissions.

Now you can make the case that you can start replacing coal plants with solar plants, or compare the marginal differences in choosing solar over a coal plant for newer capacity. But the context is that swapping an extant infrastructure to a new technology creates the carbon debt, despite the fact that the new tech is carbon-free in its running. Then it's highly relevant to ask about the sunken costs of building a new solar plant for the sole purpose of eventually decommissioning a coal-burning plant that still has many years of life left.

Aaron Huertas

Mr. Myhrvold,

Your words on the blog are very different in tone and content from what readers will find in the book. Particularly, your view that "Geoengineering is proposed only as a last resort to try to reduce or cope with the even greater harms of global warming! " is not reflected in the book at all. Instead, the books presents geoengineering as an alternative to reducing carbon dioxide emissions. In fact, the book goes out of its way to justify the presence of excess CO2 in the atmosphere and to discount its role in disrupting our climate and that is where many of its scientific errors are made.

While I appreciate you clarifying your views here, you must admit that readers who read the book, but fail to read your blog post will walk away with the exact opposite impression you leave here.

Aaron Huertas
Union of Concerned Scientists

Dirk Angry

"Where do these 10 watts come from? "

They come from the sun. When you put on a black shirt in the sun it gets warmer than when you put a white one, right? that difference in energy is the energy that was not reflected, but turned into heat instead.

In this case, change a white t-shirt for the desert and a black one for a solar cell


Oops. Forgot to include one more question-

I appreciate your discussion of the effect of the different albedos for solar panels and the ground. It's something I hadn't seen before. While I would agree with you that solar panels, by not utilizing all the heat they absorb, and reflecting much less than the underlying land would have, ultimately radiate more heat than the underlying land would.

However, and please correct me if I'm wrong, I thought that the overwhelming source of the "greenhouse effect" is the composition of the atmosphere and its ability to absorb radiated heat and reflect it back to the earth. In other words, whether light gets absorbed (solar panels) or reflected (ground) makes a difference only in the ultimate wavelengths (infrared in the former, and visible light in the latter) that the energy is radiated back to the atmosphere. Ultimately, it all still gets radiated back.

While this does have an effect on whether the energy is absorbed by greenhouse gases and reflected back to us (due to the specific absorption profiles of the different gases: most of what they can absorb is infrared), by far the larger factor is whether that greenhouse gas is present in the first place. In other words, the fact that the solar panel emits less CO2 means that on balance, it causes less "greenhouse effect" *even though* it also radiates more infrared light.

I haven't read your full chapter (although I'll probably stop by the bookstore and check out the book now :-), so I'm not sure if you account for this, but I do believe that in terms of relative importance, the CO2 that isn't released into the air is far more important to the overall temperature than the lower albedo of solar panels.

Indeed, according to Wikipedia (search for greenhouse effect), if there were no greenhouse effects and we relied solely on the black body radiation of the earth's surface (which is what factors like albedo affect), the average surface temperature could be as low as -0.4F vs 57F that it is now.


A Siegel

So, this is the chapter's point:

"The point of the chapter in SuperFreakonomics is that geoengineering might be good insurance in case we don't get global warming under control."

If that is the case, why are there so many misrepresentations of scientists' beliefs?

Why the serial errors as so well documented by Lambert, Connelly, Pooley, and others?

That one sentence is one that Romm, Lambert, Connelly, Pooley, the UCS, and others would likely be able to agree with ... yet, they certainly aren't showing any indication of agreeing with the chapter.


Dr. Myhrvold,
Thanks for the explanation--you have inspired me to go look at more complete calculations. I suspect that when you measure thermal heat exhausted plus energy spent in mining of the coal versus the difference in albedo, solar comes out ahead, but it's certainly a calculation worth making if you care about global warming.

I would suggest, however, that you leave the first 5-10 paragraphs out of your post when you are forced to make this argument again in the future. No need to spend time urging us to keep the debate on the science--just keep the debate on the science and we will get the point.