Probing the limits of wind power generation

wind farm
The Shepherds Flat Wind Farm is an 845 MW wind farm in the U.S. state of Oregon. Credit: Steve Wilson / Wikipedia.
(Phys.org)—Wind turbine farms now account for an estimated 3.3 percent of electricity generation in the United States, and 2.9 percent of electricity generated globally. The wind turbine industry is growing along all vectors, with increasingly sprawling farms of ever-larger and more densely sited turbines producing growing amounts of power. But the laws of physics are stubborn—wind turbines remove kinetic energy from the atmospheric flow. So engineers and scientists have sought realistic estimates of the limits to large-scale wind generation. Such estimates could provide guidelines for the maximum size and density to which a wind turbine farm can increase before reaching a point of diminishing returns.

An international group of researchers recently collaborated on a comparison of two different methods of estimating the limits of for , which has been reported in the Proceedings of the National Academy of Sciences. They approximated the dynamics by which remove kinetic energy from the atmosphere using the vertical kinetic energy (VKE) flux method and compared the results to those from the Weather Research and Forecasting (WRF) regional atmospheric model. Their findings are complex, and while the two techniques produce results that diverge in many ways, together, they illuminate atmospheric variables that are not obviously revealed by the two methods in isolation.

To evaluate the limits to generation, they used reference climatology of Central Kansas for the time period of May 15 to September 30, 2001. The simulation uses a horizontal farm grid spacing of 12 km with 31 vertical levels. Wind turbine characteristics were modeled on the technical specifications of existing models.

The WRF simulations include a realistic parameterization of wind turbines, and the results demonstrated that a greater installed capacity within a wind farm region increases the total rate of electricity generation. When the installed capacity of the wind farm is increased, the marginal return of electricity generation occurs during periods with higher wind speeds. The authors note that their results do not account for the effects of reduced wind speeds within wind farms, and that the numbers from WRF simulations are likely to be too high.

The VKE flux method captures the magnitude of wind power generation along with temporal variations, but does not account for atmospheric effects. While the daily mean estimates for produced by the two methods are closely correlated, WRF is much better at capturing accurate estimates at night—VKE underestimates nighttime generation magnitudes by almost 45 percent. "We attribute this underestimation of wind power generation by VKE at night to its use of the preturbine downward kinetic flux of the control. The atmospheric flow in [Central Kansas] typically decouples from the stable surface conditions at night in the summer, which leads to the formation of the low-level jet near the surface," the authors write.

Nevertheless, VKE captures the temporal dynamics and the reduction in wind speed quite well, and the authors consider the two methods to be energetically consistent with one another. The study concludes that comparatively simple methods can be applied to estimates of large-scale . The authors write, "Although many current wind farms are still comparatively small and can therefore sustain greater rates, an energetically consistent approach becomes relevant when the installed capacity of the wind farm approaches the flux into the wind farm region."


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As wind-turbine farms expand, research shows they could offer diminishing returns

More information: "Two methods for estimating limits to large-scale wind power generation." PNAS 2015 ; published ahead of print August 24, 2015, DOI: 10.1073/pnas.1408251112

Abstract
Wind turbines remove kinetic energy from the atmospheric flow, which reduces wind speeds and limits generation rates of large wind farms. These interactions can be approximated using a vertical kinetic energy (VKE) flux method, which predicts that the maximum power generation potential is 26% of the instantaneous downward transport of kinetic energy using the preturbine climatology. We compare the energy flux method to the Weather Research and Forecasting (WRF) regional atmospheric model equipped with a wind turbine parameterization over a 105 km2 region in the central United States. The WRF simulations yield a maximum generation of 1.1 We⋅m−2, whereas the VKE method predicts the time series while underestimating the maximum generation rate by about 50%. Because VKE derives the generation limit from the preturbine climatology, potential changes in the vertical kinetic energy flux from the free atmosphere are not considered. Such changes are important at night when WRF estimates are about twice the VKE value because wind turbines interact with the decoupled nocturnal low-level jet in this region. Daytime estimates agree better to 20% because the wind turbines induce comparatively small changes to the downward kinetic energy flux. This combination of downward transport limits and wind speed reductions explains why large-scale wind power generation in windy regions is limited to about 1 We⋅m−2, with VKE capturing this combination in a comparatively simple way.

© 2015 Phys.org

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Sep 02, 2015
You fools! Don't you realize that by sucking all the energy out of the atmosphere the winds will stop blowing and we will all suffocate?

Sep 02, 2015
Yeah, . . what happens when they use up all the wind and the air??

Willie Ward has already made that assertion, I think.


Sep 02, 2015
The fact is, I warned long ago about windmill farms removing the energy of moving air to do what it does. I received a torrent of "1's" from the Hate Mafia here and one individual went so far as to deny the law of the conservation of energy, saying that the wind retained the same amount of energy, even after it was converted to electricity! It's already being admitted that air on the lee side of windmill farms is abnormally warm, which I warned of. What of the banks who paid for these projects without thinking what they would do? Or, maybe, this perverting of the atmosphere is what they were really after. I also warned that the reflective surfaces of solar farms would prevent clouds from forming and where are the clouds that could end the drought in California?

Sep 02, 2015
" I also warned that the reflective surfaces of solar farms would prevent clouds from forming and where are the clouds that could end the drought in California?"
----------------------------------

OMG! How did we screw up so badly??

Really, . . "windmills" burning away clouds? Where were you when we needed smart people?

"Or, maybe, this perverting of the atmosphere is what they were really after."

Yeah, that's it! We Commies are even under your bed!

Sep 02, 2015
julian, there are negatives to anything we do, and the intelligent things to balance the differences and design for optimum practicality.

We will continue use wind until it is no longer the best fit, as we are expanding other sources such as geothermal, which will be growing soon in the West.

Sep 02, 2015
Weather report:

The loony gkam is currently flooding at a gale force of 1 post every 5 minutes, clearly in violation of both site and natural laws.

You really think what you have to say is that important?

Of course you do.

But its not.

fay
Sep 02, 2015
yes, there is a conservation of energy. Which means the energy is taken from winds but doesnt disappear, it is turned into electricity and then into heat, which again increases the energy of the winds.

Sep 02, 2015
which again increases the energy of the winds

No.

This is an interesting article. Wind power seems to be brought into question here as a viable long term and mega-source of electricity.

We will continue use wind until it is no longer the best fi


From the first sentence of the article:

Wind turbine farms now account for an estimated 3.3 percent of electricity generation in the United States, and 2.9 percent of electricity generated globally.

It never was a best fit, not even a fit, really, unless you're talking about the taxpayer reaction to the amount of subsidy dollars that go into this, and what the return on investment is(n't).


Sep 02, 2015
Consider: Previous pristine forest/jungle cover would have reduced windspeed too. But no-one objects to re-forestation/jungle patches for sustainable ecological biodiversity/health reasons. Windpower installations are for sustainable ecological/health AND economic reasons. There is always a trade-off. The trick is to go for the most return in health/ecology/economy terms. And if individual local Windpower installations are beyond the nominal concentration/size, then merely limit further localized expansion of said installation and deploy/expand elsewhere where no such localized limitation is necessary until that too grows beyond nominal. Reasonable folk include all factors, not just those they wish to base deniers/lobbyist propaganda on.

PS @Willie Ward: Read: http://www.abc.ne.../6745318

On top of all the other dangers/costs of Nuclear Power Proliferation, there is Nuclear Weapons Proliferation/Accidents.

Sep 02, 2015
You fools! Don't you realize that by sucking all the energy out of the atmosphere the winds will stop blowing and we will all suffocate?


I can handle that. But I don't know what we'll do when solar farms use up all the sun

Sep 02, 2015
This is an interesting article. Wind power seems to be brought into question here as a viable long term and mega-source of electricity.
From the first sentence of the article:

Wind turbine farms now account for an estimated 3.3 percent of electricity generation in the United States, and 2.9 percent of electricity generated globally.

It never was a best fit, not even a fit, really, unless you're talking about the taxpayer reaction to the amount of subsidy dollars that go into this, and what the return on investment is(n't).



Thank you, denglish, for once again brilliantly summarising what this article is *not* about. You should start a new career in satire.

Sep 02, 2015
As one who has worked in the energy industry for a couple of decades, wind is so unreliable its dangerous. You have to back it up with gas or coal online at minimum loads where the units are the least efficient and most polluting. In 2012 California had 2300 mw of wind available and on the hottest day of the year they got about 20 mw out of it. That is not cost effective nor saving anything. Use it to electrolyze water to make hydrogen and store it its all wind is really good for on a large scare. On cold windy days it will burn down power lines and you still have to keep the fossil units on line. Wind is maxed out already. Democrats are too easily deluded with fairy tails.

Sep 03, 2015

This is an interesting article. Wind power seems to be brought into question here as a viable long term and mega-source of electricity.

Where do you get that? All they say is that if you put up too many you get diminishing returns. There is no indication in the article that wind power cannot be expanded to many times what it is now (if adequately distributed).

Since the invention of these newfangled "power lines" it is not necessary to site all of these wind farms in central Kansas.

You have to back it up with gas or coal online at minimum loads where the units are the least efficient and most polluting.

Wind forecasts are good enough so that you don't have to run them at all most of the time. Even at minimum (and less efficient) levels the backup powerplants produce FAR less exhaust that when running optimally at full tilt.

Sep 03, 2015
All they say is that if you put up too many you get diminishing returns.

That's exactly where I get:
Wind power seems to be brought into question here as a viable long term and mega-source of electricity.


Thank you, denglish, for once again brilliantly summarising what this article is *not* about.

You quoted three things:
1. My reaction to the article describing diminishing returns on farming wind power.
2. The description of the dearth of power wind is actually providing.
3. The description of the very poor return-on-investment of subsidies according to the US government (as we discovered in an earlier thread)

Which one exactly do you take exception to?


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