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You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow. We're talking about alternative energies this hour, and up next a startling new study about the potential of wind power. I mentioned this before the break.

We know that wind - the wind doesn't blow all the time. It doesn't blow everywhere. You can't really predict it on a great extent to where it's going to be blowing, but despite this, researchers have estimated in a new study that using current technology, the wind could provide - listen to these numbers - 40 times the amount of electricity that the world uses.

And American wind alone, just here in the States, could provide 16 times the amount of electricity that Americans use. That prediction is a lot higher than we've heard before, but is it really feasible, and what would it take to scale up the wind? And do we have a power grid that could take all this energy, electricity that we generate and distribute it?

That's what we're going to be talking about next. My guests are - Michael McElroy is a professor of environmental sciences at Harvard. He's the co-author of a paper in the Proceedings of the National Academy of Sciences. He'll explain how he arrived at this estimate. Welcome to SCIENCE FRIDAY, Prof. McELROY.

Dr. MICHAEL McELROY (Harvard University): Good afternoon, thank you.

FLATOW: You're welcome. Revis James is the director of the Energy Technology Assessment Center at the Electric Power Research Institute. That is EPRI in Washington. He joins us by phone. Welcome to the program.

Mr. REVIS JAMES (Electric Power Research Institute): Thank you very much.

FLATOW: Let me begin with you, Michael. It's like - those are amazing numbers I quoted. Are they accurate? Is there that much wind energy around?

Prof. McELROY: Yes, I think there is. Let me just say a few words about how we arrived at these numbers or the nature of the study. What we were able to do was to use a database which provides information on how the wind blows everywhere in the world every few hours for an entire year, and also is a function of altitude. This database was developed essentially to support studies of air pollution, studies of atmospheric chemistry.

So what we did was to take a realistic turbine, in fact we took the GE 2.5-megawatt turbine, and we said if you distributed those around the world, subject to some constraints, how much could you really produce in the way of electricity over the course of a typical year?

And you know, as you mentioned, you know, the number was astonishingly large, but of course, there are some caveats here. One caveat is one of economics, and what we were doing was simply looking initially at what is the realistic physical limitation on how much electricity you could generate with wind? And it's much larger than we need all over the world, and in particular the United States is very rich in wind.

FLATOW: And you didn't use offshore sources either. You did not include those, right?

Prof. McELROY: No, we also did estimate the amount of offshore power that's available, and in this study - I mean, the study was motivated in part to examine the question of what options do we have to reduce our reliance on fossil-fuel-based energy if we're going to take seriously and deal with the climate challenge, climate-change challenge.

And so, yes, we did also look at offshore, which is indeed very significant as well, and in our study of offshore, we again made some constraints. We said, look, we looked at how much wind energy is available within 50 nautical miles of the nearest shoreline and in water depths of less than 100 - less than 200 meters with the view that that's potentially what is economically developable at the moment, and we also assumed somewhat larger turbines in offshore environments, 3.6 megawatt turbines.

FLATOW: Did you take into account that the wind doesn't blow all the time, these turbines wouldn't be turning all the time?

Prof. McELROY: Well, that of course is a very significant issue. In our study, we're essentially calculating how much electricity would be generated every few hours for a typical year.

So when the wind is not blowing at a particular place, we're not generating any electricity. So this is an integrated number for the amount that would be produced over the entire country or over a particular state or over a particular region of the world.

FLATOW: Is that a yes or a no? I couldn't figure that out.

Prof. McELROY: The answer is yes, it allows for the variability of wind over the course of a year.

FLATOW: Revis James, what's your reaction to this? It seems - is this a practical solution? Is his calculations or assumptions correct?

Mr. JAMES: Well, I think the paper is very solid, and you know, I think the potential is very large. We've known for some time that there's a great deal of wind and solar resource that's available.

The way that we like to frame questions about technology choices and options is more about what's cost effective and optimum. I think from a technical standpoint we are capable of building quite a few windmills and developing the transmission infrastructures that would be needed to connect those windmills to our power system. The question is: what is the most economic combination of technologies that will deliver electricity to the electricity system while meeting the various environmental constraints that we would like to meet?

FLATOW: Why would this not be economical?

Mr. JAMES: Well, there are a few reasons. I wouldn't say that you can say that it either is or is not economical. It's simply a matter of its cost in comparison to other choices.

Some of the reasons why there are costs associated with wind are that on - if you look at wind turbine and how much power it's capable of producing, and you measure the investment you must make per kilowatt of energy that you can produce, it's somewhat expensive. It's around 80 percent of what the same investment would be for a coal plant, for example, about two times what the investment would be for a natural gas plant.

So the capital investment for the amount of energy you get is significant, certainly not insurmountable, but it's significant.

FLATOW: But once the machine is up and operating, it's making wind much cheaper, electricity much more cheaply, right?

Mr. JAMES: That's true. You don't have a fuel cost, which is absolutely right. That's one of the advantages. The other aspect of the situation is that you would need to connect areas where we have a lot of wind resources, that have wind blowing at the proper conditions we can generate a large fraction of the time to the places where we're using electricity, and many of those areas are in fairly low-populated parts of the United States. So the existing transmission system is relatively sparse in some of those areas.

FLATOW: So we need - in other words, that's another way of saying we need to change the grid.

Mr. JAMES: I would say we would need to bolster the grid substantially.

FLATOW: Michael, what do you say to that?

Prof. McELROY: I think that Mr. James makes some very good points. Let me just talk a little bit about the economics. The numbers that we were quoting earlier assumed - referred to the amount of wind energy that was available to operate turbines at an efficiency of more than 20 percent. Now, that's a relatively low efficiency, and that's why there's such a large number.

Suppose we were to push to turbines that operated essentially at 37.5 percent of the time. That's closer to the best state of the art at the moment. Then the cost goes down. It goes down significantly because essentially the turbine is generating electricity for more than a third of the total rate of capacity of the turbine. And you know, there are places in the United States at the moment where wind turbines recently installed are operating at efficiencies slightly larger than 40 percent in terms of their so-called capacity factor.

So yes, the costs are significant, but again, as you mentioned and as Mr. James mentioned, this is a capital investment for which you have a 30-year return on the capital investment since the fuel is effectively free, and I think there are other opportunities to do things with it.

Yes, to comment on the grid build-out, that's a very, very important point. The studies that have been done so far by the Department of Energy, the 20 - so-called 2030 study, for example, tried to make an estimate of a much - of what the additional costs would be to connect the optimal places in the United States to the nearest grid, and the cost is about 20 percent of the capital cost of the turbine, so significant but not - it's not a game-changer, in my opinion.

FLATOW: 1-800-989-8255 is our number. Let's go - take a question or two from the phones. Steve in Ann Arbor. Hi, Steve.

STEVE (Caller): Hi. Yeah, I wondered, how much energy can you extract from the wind before you start to change the weather adversely itself?

FLATOW: Good question. Michael?

Prof. McELROY: That's actually a very good question. Roughly one percent of the total solar energy that's absorbed by the earth is converted to kinetic energy or wind and dissipated currently at the surface.

So we're talking about a relatively small fraction of that total. But if you were to push this to the limit, you know, the limit of many, many times more than current electricity, then one would have to be concerned about changing the structure of the circulation of the atmosphere, making the wind blow somewhere else.

Now, the studies that have been done suggest that to some extent this offsets the warming effect of additional levels of CO2, particularly at high latitudes. The circulation change that's predicted to occur under the extreme development of wind power brings less heat into the Arctic region, which offsets the warming that you get from greenhouse gases.

FLATOW: 1-800-989-8255 is our number. You can also tweet us. Our Twitter is @scifri, @-S-C-I-F-R-I. We'll take your questions that way.

When I talk to people in the wind-power industry, they say, you know, we could build these turbines as fast as we could, but we can't get the parts for them. You know, there's a shortage of parts. They're in such great demand. Revis, is that true?

Mr. JAMES: Well, let me just comment on that, Ira. First of all, generally, the power industry around the world has experienced an escalation in costs of several materials until - just until recently with the global recession experience early part of this year.

Part of the reason for that is there's several common materials that are used in different technologies, steel and concrete and so on, and the global development going on outside the U.S. so that's part of the reason.

Part of the reason is that the wind industry has grown so fast, I think its growth rate has somewhat outpaced the supply infrastructure's ability to provide the materials. That's another factor. If I could, I would like to make one...

FLATOW: Sure.

Mr. JAMES: …brief comment about cost.

FLATOW: Mm-hmm.

Mr. JAMES: The cost of these power plants, whether it's a wind turbine or it's a gas plant, any type of plant, it can be thought of in two ways. One is the investment you make to build it. But the other is the amount of cost over the lifetime of the plant for how much energy you can actually generate.

And when you look at the cost of a wind - or the production cost of a wind turbine, what it cost to produce a megawatt hour of electricity, for example. That's about $90 a megawatt hour if you don't have any kind of subsidies or tax credits. It's about $70 a megawatt hour if you do get those credits. That's what the credits are now, about $20.

Let's just - for purpose of comparison, a coal plant today, without CO2 capture and storage, which may, of course change, is around in the high 50s till the 60s per megawatt hour. Over the lifetime of a nuclear plant, those costs are in the mid 70s. So they're - when you consider the capacity factor, how often a plant can run and how much energy the fuel packs into a certain amount of mass, a lot of these technologies are a lot more comparable than they appear at face value. And so…

FLATOW: But you - but that's apples and oranges now because you haven't tacked on the other costs?

Mr. JAMES: Oh, well - no. When you look at these - when you look at these production costs per megawatt hour, you're looking at the cost…

FLATOW: But you haven't - but when you talked about coal, you haven't talked about the technology to take out the carbon dioxide and sequester it or any of that stuff.

Mr. JAMES: For example - okay, for example, if you do a calculation of what the cost of a coal plant might be, if it did CO2 capture and storage - right now, today, with the technology that exists, which is not very efficient, it certainly would be very expensive on the order - over a $100 per megawatt hour. That'd be about $10 megawatt hour higher than wind. But…

FLATOW: Right. So that's - then, it's not comparable?

Mr. JAMES: However. The technologies that are developing to improve that capture process are engineering problems. They're not basic science problems.

FLATOW: Well, can you say the same thing about wind power that the cost will come down as technologies get better to build these wind turbines?

Mr. JAMES: You certainly could. And what I would say to that is that if you look at the energy economic analysis have been done by EPRI and others, where you project what the benefits of researching these different technologies would be and you apply a CO2 constraint and you look at what is the most economic combination of technologies, what you see is that wind certainly does grow substantially, but you also see continued presence of quite a few of the other technologies.

FLATOW: Mm-hmm.

Mr. JAMES: So…

FLATOW: Yeah.

Mr. JAMES: …that's very revealing. And many groups have reached these conclusions outside of EPRI.

FLATOW: We're talking about wind technology this hour on SCIENCE FRIDAY from NPR News.

You're also talking about an unproven technology versus a proven technology, when we're talking about carbon sequestration versus the cost to build the wind turbine…

Mr. JAMES: Well…

FLATOW: …right? We don't know if it's going to work or not.

Mr. JAMES: Well, CO2 storage, there is some experience.

FLATOW: Well, but we, on a larger scale, we don't know. But we know if you keep building wind turbines, they're going to work. And there's no…

Prof. McELROY: If…

FLATOW: Go ahead. I'm sorry. You can defend yourself, Michael.

(Soundbite of laughter)

Prof. McELROY: Okay. If I could just weigh in a little bit here.

FLATOW: Sure. Go ahead.

Prof. McELROY: I think that the - first of all, we have no idea what the cost of carbon capture and sequestration is going to be, particularly if you have to retrofit existing coal fire power plants. I mean, it may not even be possible in many cases, to do it. But, you know, the best estimate of cost suggests is something like $100 a ton of carbon saved.

But now let's get to the real problem. In order to make a dent on the climate problem, we're talking about billions of tons of carbon per year that has to be sequestered. Now, where is that going to go? I mean, my sense is that it's going to be not only an economic - very serious political problem.

I mean, already in Holland, people are objecting to a prototype plant to bury carbon deep below their houses. So I think there's a political issue here as well. And as you said, wind is ready.

FLATOW: Yeah. There's a cost of disposing of the carbon that…

Prof. McELROY: Yes.

FLATOW: …that's a political cost and a - just a cost of just transporting it. And even if you're going to bury it deep under the ocean, you have to move it someplace.

Mr. JAMES: (Unintelligible)…

Prof. McELROY: If we were going to…

FLATOW: Sure. Go ahead, Revis.

Mr. JAMES: Yeah. I'd like to say that those are all really valid points. And I would say that that's the reason why there's a tremendous amount of effort invested in, you know, exploring what CO2 storage of large scales means. The DOE has many, many regional partnerships looking at larger and larger scales towards projects and many groups, including EPRI, involved in those projects.

But another comment I would make is that you can postulate what some of these things cost and then look at how sensitive the economic mix of technology would be in the future.

And even if you make some fairly conservative assumptions about future costs…

FLATOW: Yeah.

Mr. JAMES: …you still find that a lot of technologies tend to the play in a diverse portfolio in the future, rather than one or two technologies dominating it. It requires…

FLATOW: I understand that. Yeah.

MR. JAMES: …extremely a conservative assumptions to produce a world in which all wind or, say, all of any technology is a preferred approach to producing electricity.

FLATOW: Now, let me go to the other - let me play devil's advocate on the other side now. What about the cost, Michael, of storing electricity from these wind turbines? We don't have a great way to store that electricity, do we?

Prof. McELROY: Well, that's also a fascinating issue. And I had the opportunity to listen to your previous guest and his intriguing ideas about using chicken feathers to store hydrogen.

We thought a little bit about this. If you have, you know, at times, if you had a major development of wind power, or solar power for that matter, there may be times when you actually have more electricity than you actually need to use. So the question is, how do you store it?

Now, you know, if you're plugging into hybrids and electric cars, you can charge your cars at night, and that will make a difference in smoothing out the day-night variability in load demand. But there will also be a longer term storage issues if we push this thing to the limit.

Now, one very intriguing idea, I think - and this actually in common with other sources of electricity as well - is that if you have excess electricity, you can make hydrogen relatively efficiently, from an energy point of view, by electrolysis of water.

So you can route a discharge your water, you can make a pure hydrogen and pure oxygen. And then there's a double whammy. Not only do you have a relatively inexpensive source of hydrogen, but you're also have a source of pure oxygen that you could use in a conventional so-called oxy-fuel coal fire power plant, which will allow you to capture the CO2 more efficiently, because CO2 under those circumstance will be dominant component of the emissions.

FLATOW: All right. We're going to take a break, come back and talk a little bit more about this. Our number: 1-800-989-8255. You can tweet us at scifri at s-c-i-f-r-i.

Talking with Michael McElroy, who's published his paper in the Proceedings of the National Academy of Sciences. He's a professor of environmental sciences at Harvard. Revis James, director of the Energy Technology Assessment Center at EPRI in Washington, talking about something that's on everybody's mind these days: What do we do about alternative energies and whether we could really scale up wind power and find ways to store it? Maybe we'll store it - as we were talking about - as hydrogen - move it around. Or maybe we'll find other way storing it - they talk about in solar, in salt or something like that.

So stay with us. We'll be right back.

I'm Ira Flatow. This is SCIENCE FRIDAY from NPR News.

You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow talking with Michael McElroy, professor of environmental sciences at Harvard. Rev James -Revis James is director of the Energy Technology Assessment at the EPRI in Washington.

We're talking about in the last couple of minutes left ago about the potential for wind power.

Revis, what do you think about wind storage storing electricity? Is there work going on in that?

Mr. JAMES: There is a lot of work going there. I think hydrogen is an idea that's been discussed a lot. But one of the major - speaking from an engineering perspective, one of the major technologies that's attractive is the technology that has had some demonstration before, and that's compressed-air energy storage - pumping air into the ground and caverns under pressure and then allowing that air to come back out and regenerate electricity when you need it. And so, there are projects to scale that up and demonstrate that. EPRI is involved in some of those projects.

I think there are other things you can also do to try and allow the electricity grid to absorb a larger percentage of electricity production from wind. Storage is one thing. Another thing that you can do is try to improve the ability to move energy around the grid.

The degree to which you can do that allows you to rely upon other existing resources to offset the variability of wind and anything that will improve our management of grid, such as ability to control the flow of electricity within the grid helps achieve that. So there's much research going on on those areas as well.

FLATOW: Michael, can you do a study about solar and come up with the same sort of conclusion?

Prof. McELROY: Yes. As a matter of fact, we are doing that. This database that we have also includes detailed information on the amount of sunlight that's available to surface anywhere over the world.

And so, yes, we're, at the moment, engaged in a study to look at exactly how a combination of solar and wind would accommodate a major fraction of the anticipated amount of electricity, not only in the U.S., but around the world.

FLATOW: And so, you…

Prof. McELROY: If I could make a…

FLATOW: Sure.

Prof. McELROY: …just another brief point. One of the things that I think is attractive about the idea of renewable energy is that much of the resource -let's take the United States - much of the resource is available in some of the low density, as Mr. James pointed out, population areas of the country, some of the poorer areas of the country. So this is also an opportunity to bring jobs to places where it's needed. So there's an economic development opportunity here that is not to be understated.

The cost of - you know, I was looking at some of our numbers here. If we only use the areas where wind potential is very high, 37 close to 40 percent capacity factors, you would need to replace all of the current electricity in the United States. I'm not suggesting you should do that. You need about 500,000, 2.5 megawatt turbines.

Okay. Let me turn that into a number. That would cost a capital cost - total capital cost of about $2 to $3 trillion. But, of course, you can spend it all at once? No. Would you go to the extreme of replacing the entire electricity with wind, you would want a combination that Mr. James has pointed out, a combination of resources to provide for security.

But I think that there are real opportunities for renewable energy.

FLATOW: Mm-hmm. Revis, you agree that this…

Mr. JAMES: Well, I do agree that there are a lot of opportunities there. And I agree that also wind is going to play a significant role in the future portfolio. A lot of our work certainly projects that based on a…

Prof. McELROY: Yes.

Mr. JAMES: …wide range of different projections of possible conditions.

But one thing I would say is that it's important to recognize that the ultimate economic impact of electricity is what happens after you produced it to reach for the overall economy. So the - while producing electricity, building infrastructure to create jobs so that we can produce electricity in different forms and more of it is valuable.

Ultimately, the most important aspect of electricity is to be as efficient as possible in producing electricity so that we can provide low power - low cost energy to the rest of the economy. That is really what's going to leverage the economy.

FLATOW: All right. We're going to have to leave it there and come back to it. We'll wait to see your work on solar and wind when you're done with it, we'll have you come back. Would you come visit us on that, Michael?

Prof. McELROY: Thank you very much. My pleasure. You're so very…

FLATOW: You're welcome.

Prof. McELROY: …very stimulating conversation.

Mr. JAMES: Thanks for having me.

FLATOW: You're both very welcome. Michael McElroy is a professor of environmental sciences at Harvard. Revis James, director of the Energy Technology Assessment Center at the Electric Power Research Institute in Washington.

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