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.


renee

MR, you're entirely right, and the critics who do a magnificent job of refuting many of the technical problems in this chapter have said exactly the same thing. Among their critiques:

First, much of the time solar panels get put on roofs, which are many different colours and have widely varying absorption specra. With the ongoing desertification in the world, we're honestly calculating the loss from a few hectares of solar panels every hundred kilometers as being significant?

Second, that secondary heat can also be put to use, to heat water or glycol that can also be used to generate electricity as well - or simply be used to heat, particularly in the Northern hemisphere.

Third, solar panel efficiency is getting better all the time - it's around 18% these days (and Honda has one that's 28-30%, but it's pricey.)

Fourth, nobody's seriously suggesting doing solar power in isolation (almost wrote "insolation.") Urban heat islands are a problem, that's why emphasis is now on things like green roofs, park and wilderness areas, and alternative construction methods.

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DrS

Good post! Albedos, energy used during production, acknowledgement of the fact that people aren't going to drastically cut consumption... all things rarely mentioned when speaking of solutions.

I don't know about his whole "science" thing, but it seems like it could really help inform some of the political opinions around this climate issue.

Ian

Mr. Myhrvold,

You make a number of reasonable points about the tone of dialogue, especially on the internet (e.g., polarized debate, protecting territory, primary goal of being heard, etc.). Interestingly, on blogs devoted to global warming relata, each "side" thinks the data are with them, and it is only the other side that is politicized.

You also mention that the Superfreakonomics chapter "...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..."
I disagree here - on several of the topics, the lack of numbers can be misleading and can further polarize a discussion. For example, take your break-even time of 2.7 yrs for solar vs. coal plants. The time frame is crucial to deciding whether it's worth it to build solar. A qualitative statement, without specifics to the effect that solar has costs that we should consider vs. coal leaves us to wonder about the extent of the costs - with just the slightest motivation, some people will assume that the costs are huge, and others negligible. It's better to tether the issue when possible than to leave it to everyone's imagination.

Hunter,
You mention that you're not convinced about the "truth" of AGW, but you appreciate Mr. Myhrvold's "calm, methodical explanations." Take a look at the scientific literature for much, much, much more of the same, in even greater detail... You'll find the science is understated, and basics of the AGW picture clear.

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Don Monroe

Oops, that should have been 6.7W-4.6W. The answer, 2.1W, was correct.

Ed

Well, I have ordered the book, so I will read the chapter. I am not a scientist, and my knowledge of economics is limited to a BA.

I believe Gavin Schmidt of real climate dot org took a look at the geo-engineering concept. I don't know if anyone has responded to his statements.

I agree the geo-engineering concept should be researched. But I am wary of the politics of the situation too. For many years, calling for studies have been the favored tactics of delayers on many sides of political issues. Besides, there are other concerns besides pushing carbon into the atmosphere. I think we should make an investment in solar and wind technology now, and work through market based mechanisms to reduce our use of fossil fuels now, to replace our use of scarce resources and maintain a supply that will be available for generations to come. The fact that the manufacture and installation of solar cells and their subsequent use will add more carbon and heat than they take out of the atmosphere for many years to come is an argument to get started right away to my way of thinking. If we delay because we might find some other way out of man made global warming, we may find that all options slip out of our hands. And we may so delete our supply of oil at least that travel by car will only be available to the rich.

I understand that few if any actions are unambiguously good (for example, the role of the Clinton education tax credits in the current rise of tuition at colleges/universities), but I still see the end goal, a “great carbon-free energy infrastructure”, as worthwhile enough that we should strive to achieve it. If we do not build solar farms, we may contribute somewhat less to global warming in the next thirty years. But there after we also may have no means of reducing it.

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Zeke Hausfather

Dr. Myhrvold,

I fear you are somewhat overestimating the albedo and LCA impacts of solar PV. Lets examine a hypothetical 1 m^2 panel in California's Mohave Desert.

Lets assume a 12% efficiency panel (PV_eff = 0.12).

An insolation of 6.6 kWh / m^2 / day (insolation = 6.6, characteristic of the Mohave Desert per NREL).

A carbon intensity of grid electricity of 0.387 kg CO2 per kWh (grid_CO2 = 0.387, based on eGRID numbers for CAMX grid and CA's average transmission losses).

A 20-year-lifetime-weighted carbon intensity of electricity from PV panels from Ruether et al 2004 of 0.18 kg CO2 per kWh (pv_CO2 = 0.18, almost 50% of the emission of a grid kWh).

The albedo effects of our PV panel are a bit harder to model, but lets use the white roof numbers from Akbari 2008 who modeled a 100 kg per m^2 CO2_eq reduction from painting black roofs white (assuming for the moment that putting PV panels over sand is the equivalent of painting a white roof black). We should modify this estimate to take into account the fact that the insolation in Mohave (6.6 kWh / m^2 / day) is considerably higher than the national average (around 5 kWh / m^2 / day), so this becomes 100 * 6.6 / 5 = 132 kg CO2_eq per m^2 albedo forcing. Lets call this albedo_forcing.

Now, we get the lifecycle carbon savings from our 1 m^2 PV panel by the equation:

Lifetime_CO2 = PV_eff * insolation * 365.25 * panel_lifetime * (grid_CO2 - pv_CO2) - albedo_forcing

A quick check sees that the "albedo debt" from the panel is paid off in 27 months, and over the expected 20-year life of the panel it saves 1065.6 kg CO2 relative to the base case of using grid electricity.

Now, this is a fairly simple analysis, and the big uncertainty is the albedo number used (though the roof-derived numbers should give us a ballpark figure).

Zeke Hausfather
Yale Climate Media Forum
http://www.yaleclimatemediaforum.org/

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Curt Renshaw

One of the things that Nathan doesn't mention is the following: The sun delivers about 1kW of energy per square meter to the earth at high noon. There is nothing we humans can do to increase this number. No energy is delivered at night, and throughout the day, the energy varies roughly as the cosine of the angle, but we will ignore that. Solar panels are about 8-12% efficient. Let's assume that doubles to 20% somehow. In that case, a 1 square meter (3.3ft x 3.3 ft) solar panel (assuming the energy can somehow be stored for later use, not practical now) would generate 1kW*20%*12hrs (half a day) or 2.4 kWHrs per day. This is enough energy to power a 100 W light bulb all day! A typical 50 ft x 20 ft home could have the equivalent of about 90 of these panels (allowing room for stacks, etc). Of course, some energy would need to be diverted to moving the solar panels to track the sun, but ignore this for now. Thus, if one got really good at turning off all appliances when not in use, and limited laundry to only when even extreme environmentalists wouldn't want to stand next to you, dialed down the water temperature, and fired up the home theater only on special occasions to watch An Inconvenient Truth, while still using good old natural gas to heat the home in winter (forget air conditioning), then one could probably power such a modest home. Of course, there would not be much left over to charge your currently coal-powered Prius or other hybrid or electric car (yes, electric cars are actually coal-powered cars, much like the Stanley Steamer of days gone by, since electricity comes predominantly from coal powered plants). But I have digressed quite beyond the scope of this article….

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pts

In your treatment of solar cell efficiency here you say that solar cells are only 9-13% efficient with low albedo; i.e. unconverted light turns into heat. This does not have to be the case.

Even today's solar cells are very efficient at converting light energy (percentage in high 90's) **of the wavelengths they can convert.** It turns out that only ~9-13% of sunlight energy is in these convertible wavelengths and that's where your cited efficiency number comes from.

The "blackness" of solar cells can be mitigated if coatings are added to the cells to reflect all wavelengths that cannot be converted. This wouldn't change the overall efficiency of the cells (we can't change the composition of sunlight), but coatings could make their albedo perhaps as high as .8 or more. (.91=1-.09 to .87=1-.13)

Today these coatings would be prohibitive in cost, but mass production could change this.

Owen

We can get to it later but for now I'll ignore your albedo argument...

There are three options in building solar plants:

1. We are replacing the current power plant only to save carbon

2.There is more demand for energy so we need more overall power

3.The coal plant needs replaced because it is old (or something).

You assume the first to be true because you compare carbon costs of an operating plant to building a solar plant. Ok, let's take that assumption.

Why is it bad to spend two years and nine months of carbon straight away? Politicians are giving us until 2050 to solve the problem. That would be 40 years of carbon at the current rates. We are talking about hypothetically solving the problem in two years and nine months.

In fact, how is geoengineering a fail safe when this is a solution that takes, and I repeat, two years and nine months?

Ric

The science behind the claims related to CO2 accumulation in the atmosphere has been developing quite slowly over the past few decades with careful debate and progress in the science through specialized forums. Because the issue has found scientific legitimacy, it has finally broken through the glass ceiling of the scientific cathedral and reached us. The contentious political discussion is not related to the validity of it's claims, but because the theory of global warming has immense geopolitical implications that affect an infinite number of vested interests it has and will always generate inflammatory remarks for everybody actively involved. It is like the debate on health care in the USA. The technical aspects can be worked out but the political interests are not very malleable. One should not be surprised by this shrillness. At least people are not being sent to the gallows or burned alive. Yet.

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charles

Ian...that's exactly the point. It's a complex system. The numbers change daily based on a nearly infinite set of possible inputs. So, in actuality, it's more productive to think less specifically. This is why we need to be very wary of "experts" showing up with point solutions. This isn't an issue that can be addressed that way.

Christopher

To the Author and Jeffrey McManus:

Wouldn't the difference in heat thrown off by solar panels be something like the difference between the heat thrown off by the 'natural desert floor' (near .4 or .5) and the heat thrown off by the near-black solar panels of (near 0.1).

In other words, it wouldn't be 1 watt of solar electricity generation versus 10 watts of solar heat generation, because a good amount of that solar heat generation would have occurred, regardless due to the albedo of the desert floor.

So, instead, 1 watt of solar electricity may be generated vs perhapd a 30 to 40% increase in heat generation at that one location in a vast desert.

Yes, there would be an increase in heat created by the solar plant, but it would be nothing like 10 to 1 for solar heat vs solar electricity, once existing heat is taken into account.

I believe Jeffrey McManus is correct. The laws of thermodynamics cannot be avoided.

The amount of solar energy present remains the same. What changes is the amount reflected vs absorbed, causing some percentage increase in atmospheric heating over the comparatively small solar plant acreage vs vast area of the desert.

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jose

I am all for researching alternatives to carbon dioxide controls. But things should be put in a clearer way (than in the book).

The first thing that must be said (as I understand the discussion) is that, if you are looking at geoengineering as a possible solution, you believe that the problem is larger than what most people believe. Not only you are not a denialist, but you are an "alarmist", or, as Levitt put it (somewhat dismissively), a "hysterical". This is because, if you consider such an extreme solution, you think that a catastrophe could be happening in the near term; that is, before we can curtailed emissions enough to stabilize the system (this is clearly stated by Caldeira in his comments to Romm).

Second, and more specifically to your calculation about solar panel costs, you are assuming that the cost of constructing a plant (in terms of CO2 emissions) will be constant in those 50 years. However, in general, when you expand to a large scale, research into it becomes more profitable, and therefore some new technology is discovered that reduces the costs. For example, the cost of a steam engine (por unit of energy produced) was reduced drastically (perhaps to 1/100) in the 100 years after its appearence. My guess would be that the cost of solar plans would be reduced similarly (say, from 2.75 years to 0.0275 years before breaking even), once we decide to go "all-solar". In this case, of course, "all-solar" looks much better than in your account.

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Jason

As an example he points to solar power[1,2]. “The problem with solar cells is that they're black[3], because they are designed to absorb light from the sun. But only about 12 percent[4] gets turned into electricity, and the rest is reradiated as heat[5] — which contributes to global warming[6].

Although a widespread conversion to solar power might seem appealing, the reality is tricky[7]. The energy consumed by building the thousands of new solar plants necessary to replace coal-burning and other power plants would create a huge[8] long-term[9] “warming debt,” as Myhrvold calls it[10].

“Eventually, we'd have a great carbon-free energy infrastructure, but only after making emissions and global warming worse[11] every year until we're done building out the solar plants, which could take 30 to 50 years[12].”

[1] Argument does not apply to mirror based solar technology.
[2] Nor is it really a problem in the long run.
[3] Actually slightly blue.
[4] Dependent on technology.
[5] "The rest" does not include the entire 1367 W/m^2 reaching the Earth from the Sun
[6] But not over the entire lifetime.
[7] Inasmuch as going into debt to buy a car is "tricky"
[8] Not all factors contributing to this calculation have been incorporated. Simplifications have been made. No reference scale for huge has been made.
[9] Assuming all factors have been incorporated (see [8])
[10] A debt that would be paid off.
[11] Overall, the global warming situation gets better.
[12] Assuming there aren't people like me holding up the process by casting doubt on proven technologies and instead advocating making the atmosphere smell like rotten eggs.

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sean

It seems that you are comparing coal plant waste heat to solar panel waste heat to estimate the benefits yet ignore the heat from increased CO2 in the atmosphere which is an order of magnitude larger than the waste heat.

misterb

First of all, let's apply the maxim of unintended consequences to geoEngineering. If ever there was a scenario where unintended consequences could be fatal, this is it!

Secondly, we have to be careful when people confuse science and engineering. We are talking about engineering solutions to the threat of global warming - not science. The distinction is that science is about revolutions, engineering is about tradeoffs. And it's the tradeoffs that we would have to make to stabilize our climate that cause the uproar and the politics. As any professional engineer will tell you, marketing (in this case politics) and engineering are always in tension. The politicians always want it too soon, too perfect and too cheap, and all the engineers can do is work with what science gives us.

dubious

Excellent post. One point I would make is that the surface area required by the solar cells are utterly insignificant on a global scale. Scientific American had a story on a plan for complete solar power for the USA, with a plant that would take up some 200 square miles (iirc) and could be built in 50 years (with current tech).

Point is, that is such a minute area compared to the entire earth that it would have no effect on earth's albedo.

Will Cross

"Regardless of whether the numbers are 1, 2, 4, or some other sequence ... the three-year break-even times start to overlap and pile up as we build more and more plants."

So you're saying that even if we could replace all coal plants this year with solar plants, atmospheric carbon would be higher (for 3 years) than if we'd done nothing at all.

This is true, but deeply misleading. Our goal is to minimize peak atmospheric CO2 levels, which means summing net CO2 emissions every year and trying to minimize the maximum value.

To achieve that goal, whether we've got a 1-year, 2-year, or 10-year CO2 "debt" for solar power, the earlier we make the conversion, the lower peak atmospheric CO2 levels will be. Do the math.

Emphasizing peak emissions rather than peak CO2 levels is either foolish or downright disingenuous.

Paul Klemencic

Lets start by looking at thermal energy rejected by power plants and compare that with the energy balance on planet earth. Looking at various sources, we see the earth is getting hit with somewhere between 160,000 to 174,000 terawatts of solar energy. Power plants on our planet use about 16 terawatts, with 80-90% coming from fossil fuels such as coal, oil or gas, so this heat is added to the incoming energy from sunlight (not mentioned in your analysis).

The actual average thermal efficiency of power plants is closer to 35% compared to the 50% thermal efficiency you used in your calculations. Solar panels get between 10-20% thermal efficiency of the absorbed sunlight, but CSP (solar thermal) plants get 35-45% thermal efficiencies on the absorbed sunlight.

If we do the calculations, the amount of thermal heat added to the atmosphere from fossil fuel power plants is about 14.5 terawatts.

If all the fossil fuel plants were replaced with solar panels, then the panels would intercept roughly 120 terawatts, and reflect and re-radiate roughly 88% of that energy, with rest going to the electricity consumer. You focus on the difference in albedo in your analysis, which might be as high as as 40-50%, although most roofs or parking lots would have similar albedos compared to the panels so the difference is minor. But you forget and ignore the long wave radiation from the panels. Most of the LWR is going to make its way up and out of the atmosphere; although the LWR is going to be absorbed and reradiated several times. Eventually the net outflow will be most of the LWR from the solar panels (likely over 98%). If the electricity produced is consumed and adds to heating of the atmosphere, eventually much of it will escape outward as well.

CSP projects will have a substantially lower albedo, reflect more light, generate power with higher thermal efficiencies, and thus the the amount of sunlight intercepted will be less. It is funny how you decided "black" solar panels would be placed in your high albedo deserts, but ignored the much more likely mirrors of a solar concentrating thermal project. ( Hmmm, didn't fit your politics?) But the net effect of both solar power technologies in terms of adding thermal energy to the planetary system is about the same; very close to a net of zero.

But fossil fuel plants added the "mined" thermal energy directly additive to the incoming solar energy. So in terms of net thermal energy added to the planetary system, fossil fuel plants are much worse, contrary to the comments about the "trouble with solar panels is that they are black".

In spite of all of this, not very many people are concerned about the thermal energy release of these power sources.. the releases are almost insignificant compared to the planetary heat balance, as the number above show. Contrary to the statements in the SuperF chapter, the problem isn't the heat directly, its the increased concentration of greenhouse gases intercepting outgoing long wave radiation. One molecule of CO2 added to the atmosphere, and causing increased water vapor positive feedback, will end up trapping over 100,000 times the energy released when the carbon was burned to CO2.

So the statement "the problem with solar panels is that they are black". Total nonsense.

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ray bans on my face

This was absolutely a great post. It provided a lot of insight and relayed information that i was unaware of, and think that we all need to consider. Although I found the information to be very clear and explanatory, there are still a few people that are somehow able to misinterpret the information you have provided. Those people should read the piece over a couple times.