Harvard research suggests real-world generating capacity of wind farms at large scales has been overestimated
Cambridge, Mass. – February 25, 2013 – “People have often thought there’s no upper bound for wind power—that it’s one of the most scalable power sources,” says Harvard applied physicist David Keith. After all, gusts and breezes don’t seem likely to “run out” on a global scale in the way oil wells might run dry.
Yet the latest research in mesoscale atmospheric modeling, published today in the journal Environmental Research Letters, suggests that the generating capacity of large-scale wind farms has been overestimated.
Each wind turbine creates behind it a “wind shadow” in which the air has been slowed down by drag on the turbine’s blades. The ideal wind farm strikes a balance, packing as many turbines onto the land as possible, while also spacing them enough to reduce the impact of these wind shadows. But as wind farms grow larger, they start to interact, and the regional-scale wind patterns matter more.
Keith’s research has shown that the generating capacity of very large wind power installations (larger than 100 square kilometers) may peak at between 0.5 and 1 watts per square meter. Previous estimates, which ignored the turbines’ slowing effect on the wind, had put that figure at between 2 and 7 watts per square meter.
In short, we may not have access to as much wind power as scientists thought.
An internationally renowned expert on climate science and technology policy, Keith holds appointments as Gordon McKay Professor of Applied Physics at the Harvard School of Engineering and Applied Sciences (SEAS) and as Professor of Public Policy at Harvard Kennedy School. Coauthor Amanda S. Adams was formerly a postdoctoral fellow with Keith and is now assistant professor of geography and Earth sciences at the University of North Carolina at Charlotte.
“One of the inherent challenges of wind energy is that as soon as you start to develop wind farms and harvest the resource, you change the resource, making it difficult to assess what’s really available,” says Adams.
But having a truly accurate estimate matters, of course, in the pursuit of carbon-neutral energy sources. Solar, wind, and hydro power, for example, could all play roles in fulfilling energy needs that are currently met by coal or oil.
“If wind power’s going to make a contribution to global energy requirements that’s serious, 10 or 20 percent or more, then it really has to contribute on the scale of terawatts in the next half-century or less,” says Keith.
If we were to cover the entire Earth with wind farms, he notes, “the system could potentially generate enormous amounts of power, well in excess of 100 terawatts, but at that point my guess, based on our climate modeling, is that the effect of that on global winds, and therefore on climate, would be severe—perhaps bigger than the impact of doubling CO2.”
“Our findings don’t mean that we shouldn’t pursue wind power—wind is much better for the environment than conventional coal—but these geophysical limits may be meaningful if we really want to scale wind power up to supply a third, let’s say, of our primary energy,” Keith adds.
And the climatic effect of turbine drag is not the only constraint; geography and economics matter too.
“It’s clear the theoretical upper limit to wind power is huge, if you don’t care about the impacts of covering the whole world with wind turbines,” says Keith. “What’s not clear—and this is a topic for future research—is what the practical limit to wind power would be if you consider all of the real-world constraints. You’d have to assume that wind turbines need to be located relatively close to where people actually live and where there’s a fairly constant wind supply, and that they have to deal with environmental constraints. You can’t just put them everywhere.”
“The real punch line,” he adds, “is that if you can’t get much more than half a watt out, and you accept that you can’t put them everywhere, then you may start to reach a limit that matters.”
In order to stabilize the Earth’s climate, Keith estimates, the world will need to identify sources for several tens of terawatts of carbon-free power within a human lifetime. In the meantime, policymakers must also decide how to allocate resources to develop new technologies to harness that energy.
In doing so, Keith says, “It’s worth asking about the scalability of each potential energy source—whether it can supply, say, 3 terawatts, which would be 10 percent of our global energy need, or whether it’s more like 0.3 terawatts and 1 percent.”
“Wind power is in a middle ground,” he says. “It is still one of the most scalable renewables, but our research suggests that we will need to pay attention to its limits and climatic impacts if we try to scale it beyond a few terawatts.”
The research was funded by the Natural Sciences and Engineering Research Council of Canada.
###
A video abstract by David Keith is available for viewing and download here.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
John M says:
February 25, 2013 at 4:50 pm
Recall, however, the comment I responded to was about GE making large profits from wind and escaping without paying income taxes. I did not say that GE did not benefit. GE probably did benefit by increased orders of equipment it manufactures. The original comment however, was not about benefit it was about taxes. The comment asserted without apparent basis that GE paid no income taxes because of wind tax credits, when there is no program that gives a tax break to the manufacturer for making wind associated equipment.
Another issue is the implication that somehow, if a business (or person) so arranges its affairs in order to get tax breaks, somehow it is the business that is evil. The business is just arranging to do the things that the Congress was encouraging it to do when Congress passed the tax law.
Chris4692
Actually, you responded by inventing the proposition that someone claimed GE directly got tax credits for installing windmills. I’m glad you admit that GE profits handsomely from tax credits, even if they don’t directly get the credit.
And GE does more that “arrange its affairs in order te get tax breaks”. They have one of the largest lobbying budgets of major corporations. Yep, just taking advantage of “things that the Congress was encouraging it to do.” Completely passive, and a victim of circumstances, I’m sure.
Chris4692
Take away federal tax dollars and both wind and solar would shrivel away to nothing. Only reason people (and power companies) buy into these forms of power is they get significant tax advantages (both federal and state).
As to GE tax rates, google is your friend. In terms of percentages, they seem to pay less than I do.
Current international nameplate wind power capacity is just short of 300 GW. If we say 30% of capacity is actually generated, lets be generous say 100 GW, possibly as low as 75 (being 25%).
As per article the suggestion that 3 TW might have to be generated “to avoid the dangerous consequences of CO2 caused climate change”, being 10% of current total power use, that would mean that we have to build 30 to 40 times as many wind suckers as currently installed.
I bet that GE loves that suggestion.
And as per Streetcred what would happen to the air temp in the shadow of these things? I guess that the cooling effect of wind will be reduced here, leading to real manmade warming.
Does the study predict how much more the air conditioners will run down wind of these wind turbines? Will it create a spiral of doom, with the AC use requiring more power requiring more wind turbines?
They talk, act as if there is no ready source of CO2 free energy. Why don’t they just build Nuclear – NO, None, Zero CO2? The fact that the environmentalists never consider Nuclear reinforces the fact that AGW is all a scam started by the ecological terrorists.
KevinM wrote, “if you put 100 identical windmills in a row with 1 inch clearance, do they each generate equal power? If not, then what stops one from doing it?”
If you put 100 identical windmills in a row, you’ve created a wind-farm which not only produces no power when there’s no wind, but which also produces almost no power when the wind blows from the wrong direction.
Two further thoughts/questions regarding the “Wind farms take energy out of the system” thing.
1) Don’t trees do the same thing? Wind blows. Runs into trees. Stops. The energy sort of goes into “pushing” the trees, thereby spinning the earth a bit faster or slower by some miniscule amount I guess. A wind farm would do the same sort of thing, but some of that “push” gets translated into energy. Is the “push” lost in that translation? If it’s not lost, then aren’t we, in a sense, creating energy out of nothing? That seems a bit illegal according to the physics law enforcers. :> Somehow I must be missing something along the way here, but at the moment I don’t see exactly what.
2) Has anyone ever computed a figure on the total amount of “wind energy” in the world? I.E., if I stayed up all night tonight and built enough wind farms to use it all up tomorrow, how much energy would I have produced? And what would be happening around the world the following day if I then immediately took all those wind farms down?
😕
MJM
Good question, and one I happen to think about. A partial answer can be found on page 21 of “The Nature of Violent Storms.” by Louis J Battan. A gust of wind has the equivalent of one Kwh. A dust devil 10 kwh. A tornado 10^4 kwh. A thunderstorm 10^6 kwh. A hurricane 10^10 kwh.
By the way, global output of electricity, by all known methods of generation; coal, gas, wind, et al is about 23 terrawatts
Peter C. says:
February 25, 2013 at 3:46 pm
“Any off world solutions ignore the fact we are at the bottom of a very deep gravity well that takes enormous amounts of energy(that we don’t have) to escape.”
Earth is in deep gravity well, but the Moon is not in such a deep gravity well.
Right now a bargain price for a around trip seat to the Moon would around 200 million
dollar. If the rocket fuel sold at fairly hideous amount on lunar surface [more than 10,000 times price rocket on Earth, then a bargain price for about 100 million per seat. If the cost of rocket on lunar surface was only 1000 times earth prices, then bargain seat cost could be about 50 million dollars.
To get lower price means one need to get lower cost to leave Earth- a sizable portion of the 50 million per seat would cost of leaving Earth.
And 50 million a seat is about cost to go to ISS- though the first paying astronaut buying a russian
launch pay around 20 million per seat [it’s gone up since then- but Space-X could and probably will at some point sell seat to ISS for about $20 per seat. Space-X is going thru MASA program to qualified to deliver crew to ISS.
Anyhow, if costs of lunar rocket fuel were only 100 times earth’s price, this would do not much in terms lower the cost to get to Moon, because even at high cost [1000 times earth price] it’s not a significant part of the entire cost.
But 50 million a seat to moon and back is cheap and such a low cost will encourage government and private parties to go to the Moon.
“The so called “space station”is so low in orbit it requires 20,000 lbs of fuel a year just to maintain orbit.”
This somewhere in ballpark. But facilities on the Moon don’t need to be re-boosted. So this means that even if it costs more to go to the Moon, the Moon facilities does not have this cost to maintain it. So if spent say 1 billion dollars for a “house” on the Moon. The house will be there
after the pyramids crumble- which may be nice, but in terms economics, one be certain it will be there in next 50 years- and with something like ISS, one does have such certainity- the bureaucrats have constantly discussing de-orbiting it within decade or so.
Or ISS not maintained for a year to two years, crashes into earth being if anytime junk and liablity.
A “house” on the moon could ignored for 5 years [not that this makes economic sense] and it’s still there, and one could argue the house is giving you lunar real estate.
So the permanent nature of the Moon, would encourage money spent on it- it has resale value.
Since lower the price of lunar rocket fuel will not significantly lower a seat price to the Moon- thereby sell more rocket fuel due to more demand, in order to get lower lunar fuel, one needs something more sensitive to high or lower price. So that could mean if something is exported from the Moon. If cheaper rocket fuel, means more exports, meaning more rocket fuel sold.
Another aspect which lower rocket fuel prices is competition, the threat of more competition.
And of course one going to get innovation which lower costs [also driven by competition].
One market that could exported to Earth is lunar regolith. Currently it’s worth far more than gold- 50 times more. But this price could lowered significantly. If you have lunar rocket fuel on the Moon, one should able to make profit selling lunar samples for less than their weight in gold. Perhaps the price of silver.
There is a lot science which could be done on the Moon. Moon has solar wind record, and could read the rocks as geologist do with earth rocks- it surface rock + 4 billion years old.
The Moon is excellent platform for telescopes- optical and radio.
As for the lowest cost of leaving the moon, one could use mass drivers. Or mag Lev trains to gain enough velocity to leave the Moon. One also use cannons. One needs about 1/4 of velocity to leave the Moon as compared to Earth, and high velocity is possible because the Moon is vacuum. In other words on earth if want go fast you have to fly high [to get to less atmosphere].
So cost of energy if could use them mass drivers on Earth would about $1 per lb payload.
Or 32 million joules per kg. Or 8.88 Kilowatt hours per kg.
But the atmosphere Earth makes this quite difficult and one dealing very high speed.
On the Moon in comparison it’s 2 million joules per kg- 0.55 kilowatt hours per kg payload to orbit.
So, to begin solar panels in space for earth consumption, the cost of electrical energy on the Moon must close to Earth costs- so say not 10 times more. So that would be around $1 per kilowatt hour of electricity- retail. And with a mass drive this means one could ship from the Moon to Geostationary orbit or L-points for less than $5-10 per kg. Since doing huge volume, the cost of mass driver itself is insignificant cost per unit delivered.
And so you making solar panel on the Moon which could unit cost of as much as 5 times price on Earth for same solar panels. And you can these ship these solar panel much differently then is possible on Earth. The solar panel size could be 100 meters square or large area- you flying in vacuum and “the roads” you use would be the mass driver. You accelerate it by the mass driver, and then steer it [requiring little energy] to final location
“Also little details like space being completely deadly to life,etc.”
Life is environmental protection act obstacle- deadly heavy metal waste, or even very dangerous radiative waste- these could future resources someone might “mine”- in meantime they can easily stored for millions of years at low cost and in no conceivable way harming the environment.
What would be pollution on the Moon, would be making an atmosphere. It’s a perfect vacuum which many could want to be preserved. So probably don’t want million of tonnes of CO2 released into the lunar vacuum- nor oxygen gas. There lot’s oxygen waste to be concerned about, but CO2 would too useful to waste.
Of course, one want to put life other than humans on the Moon. And genetically modified animals and plants are also not be a concern in terms effecting non-existence native life.
And basically as long as it doesn’t consume the solar system [galaxy or universe] it safer
for every living thing to be doing that kind of stuff on the Moon.
And making law that one needs to do it on moon first, might one more useful laws ever
passed.
And so using nuclear weapons for excavation could be done. But more exciting
would be building nuclear Orions:
http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29
We had to wait until someone published a peer reviewed paper in 2013 to learn that there is something called “wind shadow?” Words escape me.
As it is so often at WUWT, the comment section provides more information than the article they reference.
@ur momisugly Mike Bromley “The whole idea of “stabilizing the climate” is repugnant.”
Hey, maybe they can do something about precession while they are at it. Oh, and orbital eccentricity! 🙂
arthur4563 says:
February 25, 2013 at 3:44 pm
Sorry, but “wind is better than coal” not only is no good reason for wind, but in fact, wind
power has far less economic value than electricity produced by any conventional means, including coal. Uncontrollable power simply has little value and obviously cannot replace controllable power,
yet requires controllable backup, which means paying twice for every kilowatt hour of wind you buy
once to the wind provider, and again to the conventional power operator for providing backup,
generating capacity., even during those times when it is not producing anything. The side effect costs of uncontrollable power generation is always given short shrift, if mentioned at all. No matter how much uncontrollable power generation capacity is added to a grid, not one single controllable, conventional power generator can be eliminated.
//////////////////////////////////////////////
This is the simple point (free of science) that was known or ought to have been known to politicians when they rolled out the windfarm project. This simple fact shows the madness of wind.
In the Uk, we had a clear demonstartion of the futility of windpower in the winter of 2010. We had a blocking high over the UK which lasted for the best part of 6 weeks. The energy being contributed by wind during this period was about between 1 to 3% of name plate capacity (I recall that it occassionally reached as high as 8%). The experience of that winter should have halted all further windfarm development.
In the UK peak demand for energy is winter, especially during periods when there is a blocking high (as this usually results in cold weather brought about by cold arctic fronts). However, during these periods wind is at its least efficient.
No one designs an energy system where peak demand coincides with least efficiency of the system. An energy system must be able to provide peak efficiency when called upon for paek demand.
The politicians are well and truly culpable since the drive for wind is an obvious and crass error which anyone possessed of reasonable commonsense, and without the need for any scientific understanding, would appreciate is incapable of meeting demand and does nothing to reduce CO2 emissions.
Doug Proctor says:
February 25, 2013 at 3:58 pm
///////////////////////////////
The life expectancy of off-shore wind will be far less due to the harsh environment. Indeed, it will quickly become apparent that maintenance costs will be sky high such that maintenance will be skipped. Anyone who has experience of maintenance of ships and off-shore instalations will know this to be the case. When carrying out maintenance, even the costs of standby support vessels will make maintenance not cost effective, such that very quickly a large percentage of off-shore turbines will not be repaired and will stand idle (slowly decaying). I expect that Health & Safety will quickly produce such onerous guidelines (due to working at height on wet windswept slippery surfaces) that windows of opportunities (may be force 3 or below) for maintenance to be carried out will be rare.
Warning! Educated opinion follows, not direct personal experience! Anyone with better understanding, please feel free to correct me if I have not gotten this right!
The wind shadow behind a wind generator is not from drag produced by the blades — at least not on a modern “wing” style design. The shadow is produced by having the wind redirected. The wind — which is blowing toward the face of the generator — is slung sideways by the blades. If you stand immediately behind a well designed generator, the wind is not quite absent, but very noticeably lessened because it has been diverted. This is just like how an airplane wing in flight redirects air with a downward component after it passes over the wings. The now sideways moving wind (which has also lost some of its energy) creates a ball of turbulent, slower moving air as it interacts with the prevailing wind.
Jason Calley says:
February 25, 2013 at 10:06 pm
Jason, you’re about halfway there. Since the whole purpose of the wind turbine is to convert the kinetic energy of the wind velocity into mechanical rotational energy and then into electrical energy, the air downwind of the turbine must have less kinetic energy, and therefore lower velocity, than the air upwind of the turbine.
It might seem at first thought that the perfect wind turbine could convert 100% of the kinetic energy of the wind hitting it into mechanical and then electrical energy. But this would mean that the air in the back of the turbine would have zero velocity, which would have major “flow continuity” problems – where would the air go? In reality, the “perfect” wind turbine cannot convert much more than half of the kinetic energy of the wind in the circular cylinder hitting it to useful energy. The fact that the air on the downwind side has a lower velocity means that it must “spread out” in a sort of cone-shaped fashion. This widening cone actually limits how close the turbines can be spaced in a line perpendicular to the wind. It may not be intuitive, but the interaction of these cones downstream of the turbines can actually impact how efficient the turbines are.
All of these limitations occur even with “perfect” conversion of wind energy to mechanical energy. Perfect conversion would create no turbulent eddies downstream, etc. As with airplane wings, we know that perfect never happens. The required spacing of planes at airports is mainly due to the need to let the turbulent eddies from one plane die out before the next plane can take off or land.
The fundamental wind shadow effect has been known for as long as these wind turbines have been built. I studied this stuff in the 1970s, when I first got an understanding of these issues. The question is how bad the wind shadow effect really is. If you assume the perfect conversion, you will dramatically underestimate the effect. The problem is that even at this small scale, no computer models can accurately simulate turbulence. All must parameterize (i.e. “fudge”) it. So there is still a lot to learn, and I am not surprised by a study now that says that previous estimates of this effect were significantly off.
You need class 5 wind speeds at 100 m. There are not many places where you get that. Each turbine requires about 80 acres. Closer and you risk catastrophic failure where the blades from one turbine fail, pieces spin away and strike the neighboring turbines’ blades which then also fail. To produce about 10% of California’s electrical power needs, we would need about 10,000 to 20,000 1.5 MW turbines in 1200 to 2500 square miles of surface area. But that much area doesn’t exist on land with the required sustained wind speed. They have to be built off shore. That plan would be DOA.
In contrast, we could build 24 San Onofre scale nuclear power plants (a modern design, able to tolerate seismic shock, no need for elaborate cooling, and very little waste – can be done), on 3 square miles of land to supply 100% of our electrical power needs. Over 90% capacity factor versus 25 to 30% for wind.
Offshore wind power is much more expensive because the turbines and cables have to be hardened to tolerate corrosive salt conditions. Operation and Maintenance costs will be astronomical. Now we can have that levelized cost debate. Nah, I’d rather sleep.
Hey for the sake of the wind farm industry, why don’t we cut down all of the trees and increase our wind availability? Uhm…. sorry for suggesting that trees are robbing wind mills of their ability to save the world…
Is not the first time this conclusion has been drawn.
http://pielkeclimatesci.wordpress.com/2011/05/03/a-new-perspective-on-climate-science-by-l-miller-f-gans-and-a-kleidon/
Each turbine will slow the surface airflow, reducing its Coriolis component and allowing the airflow to move towards the center of the low pressure system.
I have no computer models to deduce (fabricate) the results of this, but my guess is that this will make the low pressures systems smaller with more violent cores. Whether this increase in core-speeds will be significant, I do not know.
Hey Curt, thanks for the response! As you point out, some of these factors (especially turbulence) are not easy — or in some cases, even possible — to model or calculate. Sometimes you just have to actually measure the real thing. Save us from engineers and scientists who think that every system can be simply modeled! Thinking of such scientists, I am reminded of one of my pet peeves, something that I encounter when discussing CAGW with the warming enthusiasts. I cannot count how many times I have heard, “Well, extra CO2 holds in the heat and causes warming! It is just basic physics!” Any time I hear “It is just basic physics!” my first reaction is a little voice in my head saying, “This person has no idea what he is talking about…”
Thanks again for an educational response!
Anyone remember that Chinese guy that built the wind-powered car?
http://en.rocketnews24.com/2012/11/28/chinese-farmer-builds-wind-powered-car-could-maybe-definitely-not-work-then-again/
What’s up with that?
Piers, your question about the wind-powered car reminded me of the innovative idea of wind-powered ships:
http://www.slate.com/blogs/future_tense/2012/06/22/wind_powered_cargo_ships_b9_s_radical_clean_energy_innovation.html
and, as you’ll see in the caption to the picture on this page:
http://sf.streetsblog.org/2010/05/13/wind-powered-transportation-then/
it becomes even more practical when you make use of tiny men to apply “sail-furling” technology!
What will they think of next???
– MJM
@ur momisugly michaeljmcfadden
Tiny men being in such short supply (ahem…) you may wish to try a more modern approach: http://bits.blogs.nytimes.com/2008/09/26/a-giant-yacht-sails-to-san-francisco/
Jason Calley suggested a more modern approach to dealing with the short supply of tiny men. Unfortunately, Jason’s link, http://bits.blogs.nytimes.com/2008/09/26/a-giant-yacht-sails-to-san-francisco/ seems to be just the same old stuff as it says, “The issue of length is important to all these guys, and the way you know that’s the case is how often they tell you that length is not important,”
;>
MJM
P.S. 20 stories tall *IS* quite impressive though!
Time to bring up the (now legendary) picture of the Danish Horns Rev windfarm: http://www.ict-aeolus.eu/images/horns_rev.jpg
You don’t need expensive research to see that lots of turbines does NOT equal lots more electricity…
Chris4692 says:
“The production credits go to those who build and operate the wind turbines, not the manufacturer. IIRC there is also a construction subsidy that goes to the owner, not the manufacturers. So how is it that GE, a manufacturer, gets a tax benefit?”
Chris, as others have said, a subsidy (direct) to the builders and operators is a subsidy (indirect) to the whole industry and GE was/is THE player with the entrenched lobbying clout to make a significant impact on making those subsidies happen. The fact that it benefits indirectly gives it somewhat cleaner optics politically, but it still has its hand(s) in the cooky jar up to the elbows.
There is a picture here worth a thousand words.. 🙂
http://withouthotair.blogspot.co.uk/2010/01/wind-farm-wakes.html