Wind turbines operate under great turbulence, with consequences for grid stability

Wind turbines operate under great turbulence, with consequences for grid stability
Screenshot of a movie (see below) showing the power output vs. wind speed signals for a wind turbine. Credit: Patrick Milan, et al. ©2013 American Physical Society
(Phys.org) —While previous research has shown that wind turbulence causes the power output of wind turbines to be intermittent, a new study has found that wind turbulence may have an even greater impact on power output than previously thought. The researchers modeled the conversion of wind speed to power output using data from a rural wind farm. The results showed that the intermittent properties of wind persist on the scale of an entire wind farm, and that wind turbines do not only transfer wind intermittency to the grid, but also increase it. The findings highlight the importance of fully understanding the physics of wind turbulence in order to ensure future grid stability.

The researchers, Patrick Milan, Matthias Wachter, and Joachim Peinke, at the ForWind—Center for Wind Energy Research at the University of Oldenburg in Germany, have published their study "Turbulent Character of Wind Energy" in a recent issue of Physical Review Letters.

In their paper, the researchers address the challenges that large-scale wind energy production may bring to future . They explain that today's grids are powered mainly by a few large generators with controllable input (mostly gas, coal, hydraulic, and ). Power generation from these sources can be modified automatically in order to balance power generation and consumption, and thus ensure grid stability. But while today's power sources are largely controllable, is uncontrollable and highly intermittent.

For time scales larger than several minutes, the conversion of wind speed into can be modeled by a standard average power curve. But at smaller time scales, the researchers found that the conversion process diverges from this curve. Instead, short-scale conversion follows a more complex pattern involving multifractal scaling that is reminiscent of a 1962 theory of turbulence developed by mathematician Andrey Kolmogorov.

A movie of the trajectory of power output vs. wind speed signals for a wind turbine reveals very turbulent fluctuations. Credit: Patrick Milan, et al. ©2013 American Physical Society
"Looking at an operating wind turbine, one may get the impression that the turbine turns smoothly, but looking at the power output, which is the consequence of the forces and torques inside the machinery, we see that the fluctuations are very turbulent," Peinke told Phys.org. "Changes of MW (more than one thousand horsepower) in seconds become obvious. Thus one may compare a wind turbine with an airplane in the landing phase during a very windy situation. From outside, the airplane may look it's going quite smoothly, but inside there is another impression caused by turbulent dynamics. One should also note that a wind turbine has to operate permanently in this 'turbulent landing' condition."

The model also reveals that moderately intermittent wind power is converted to highly intermittent power output. In other words, do not only transfer wind intermittency to the grid, but they also amplify it. For instance, the researchers observed that changes in wind speed of about 11 m/s within 8 seconds may cause nearby wind turbines to change their by about 80%. The researchers attribute this amplification to the nonlinear conversion process and fast reaction time of the output to changes in wind speed.

"The features of small-scale turbulence are mapped by the wind turbines directly into the electric grid," Peinke said. "As turbulence and in particular the statistics of small-scale wind fluctuations are still considered to be an unresolved problem, this lack of knowledge may become important in the power grids, especially if such power grid are dominated by wind power. As these phenomena take place in the range of seconds, the dynamics of the power grid in these time scales have to be investigated in detail. One has clearly to state that the first step to solve a problem is to be aware of it and to understand it."

The data also shows that wind power intermittency does not only affect the output of individual turbines, as previous research has shown, but it also extends to entire , which has not been observed before. The researchers explain that wind farm intermittency is somewhat counterintuitive, since it might be expected that summing the output of wind turbines will average out their turbulent fluctuations. However, wind farm intermittency may be explained by long-range correlations observed in winds. While the wind farm the scientists observed covered an area of about 4 km2, wind correlations have previously been observed to extend to lengths of hundreds of kilometers. Based on these observations, the researchers expect that wind farm intermittency effects may persist up to these large scales.

Overall, the physicists conclude that their results stress the importance of accounting for the intermittent and multifractal nature of wind power when designing components for wind power, including energy storage technologies. They note that the situation is similar to the findings from many years ago of the intermittent and multifractal nature of the stock market. In both areas, frequent occurrences of fluctuations must be understood and accounted for in order to maintain stability and avoid widespread disruption.

In the future, the researchers plan to further investigate the consequence of wind turbulence on grid stability and develop methods to minimize the negative effects. New turbulence models may help lead to new concepts that reduce the power and load fluctuations on the grid.

"For all of these topics, a deep and comprehensive understanding of the complexity of turbulence is indispensable," Peinke said.


Explore further

Using fluctuating wind power

More information: Patrick Milan, et al. "Turbulent Character of Wind Energy." PRL 110, 138701 (2013). DOI: 10.1103/PhysRevLett.110.138701
Journal information: Physical Review Letters

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Apr 19, 2013
Turbulence leads to a condition in which the turbines are either accelerating or decelerating most of the time. In either state efficiency suffers and the generator is either driving the grid or being driven by it. If the other local generators within the same area of turbulence are also connected to the same grid, feedback will occur as turbines with higher output are electrically interacting with lower-output turbines. The feedback cycle times are unpredictable so perturbations get amplified.

Apr 19, 2013
wind farms need to be isolated from the grid by a storage system

Apr 19, 2013
wind farms need to be isolated from the grid by a storage system

Yup, that is the major problem with solar and wind power. There has to be backup ( natural gas ) generators idling/running all of the time to fill in the gaps. This lowers the commercial value of renewable energy by a substantial amount.

Apr 19, 2013
Sailors have known about this turbulence for aeons. When fast-moving air wants to turn your boat over at intervals, it is known as "puffs" or even "blasts". DOH! I say.

Apr 19, 2013
There are devices called diodes that allow the flow of electrons in only one direction. I'm sure they are in wide spread use in turbine fields. Therefore, one turbine cannot 'drive' another.
I know, this is an over simplification.
There are a multitude of proven electronic principles that allow for the elimination of this (over/under) speed condition.

Apr 19, 2013
Electric car batteries plugged into the grid make this problem academic

Apr 19, 2013
I thought that the interference of global breezes was the real danger from wind farms.

Apr 19, 2013
Electric car batteries plugged into the grid make this problem academic
It's still economical problem, as the amount of energy recuperated in this way during battery life-time is just few times higher, than the energy required for production of such batteries. Lithium-ion batteries have the ESOI value of 10, lead-acid batteries had an ESOI value of 2.
Report: Wind power kills jobs and increases electricity costs Ontario government's electricity plan is now 10 times more costly than installing pollution-control equipment on existing coal plants — an option which would have produced similar improvements in air quality.

Apr 19, 2013
For example the replacement of battery in Tesla roadster is about $30,000. Such a battery must be replaced after 500 to 700 cycles when its capacity falls bellow 70% - which is sufficient for three to six years of common operation. At the moment, when you enable the plugging of such battery into grid in both direction, its capacity could get drained to 70% just after single year - so you'll pay $30,000 every year instead of once per six years.

This is not an academic problem: the stabilization of grid with your car electricity is actually pretty expensive game.

Apr 19, 2013
Actually, the stabilization of the grid with lithium car batteries that have outlived the productive use in autos is very much a positive possibility. The value added from 'depleted' auto batteries is quite positive. Do some in depth reading before shouting you ignorance.

Apr 19, 2013
Electric car batteries plugged into the grid make this problem academic
It's still economical problem, as the amount of energy recuperated in this way during battery life-time
But batteries are best at small eddie currents like those generated by turbulence. The usage of each battery would be miniscule, and at least six magnitudes less then their full capacity

Apr 20, 2013
the stabilization of the grid with lithium car batteries that have outlived the productive use in autos is very much a positive possibility
Only theoretically. Such a batteries have low energy efficiency and a greater risk of explosion - so that their prolonged usage isn't recommended anyway. And where they should be recharged? Their placement inside of car has no meaning at the moment, if you buy a new battery. And the backup of grid from car batteries brings many other disadvantages. It for example means, when you come to your car, you can be never sure with readiness of your battery, because it could be just at the end of discharging cycle. Try to imagine, you need to visit remote hospital with your child - and your battery is drained, because it just helped to balance the grid.

Apr 20, 2013
Cars and planes have mechanics to dampen out turbulence. GE is pitching its "Brilliant" turbines with inter-turbine communication to manage downstream turbulence between peer turbines. Seems an imminently solvable problem

Apr 20, 2013
Electric car batteries plugged into the grid make this problem academic


Academic?? Solvable maybe, but it is still a hard problem to crack, especially on an industrial scale..

Apr 20, 2013
These battery storage systems have to be monitored on a regular basis by professionals or very tech savvy homeowners. Hydrogen gas from lead acid batteries is a problem. The installation would have to be done by professionals and a building permit would be required. Try this on your own and I could see the fire insurance being null and void if you had a house fire.

Apr 20, 2013
The ideal wind farm would use turbines connected directly to mechanical water pumps that filled a huge reservoir. Thus, power generation would be decoupled from wind speed.

Apr 20, 2013
the stabilization of the grid with lithium car batteries that have outlived the productive use in autos is very much a positive possibility
@ValeriaT Only theoretically. Such a batteries have low energy efficiency and a greater risk of explosion - so that their prolonged usage isn't recommended anyway.
Recommended by whom? Your cold-fusion crank crowd? Exploding bateries were caused by impurities, not the inherent design. FYI efficiency isn't the consideration here. Damping is
Electric car batteries plugged into the grid make this problem academic


Academic?? Solvable maybe, but it is still a hard problem to crack, especially on an industrial scale..
No harder than connecting your electric car to the mains

Apr 20, 2013
We were promised it would be a "safe, environmentally friendly source of limitless electricity". Rachel Maddow assures us, "We're never going to run out of wind". Minimal investment for maximal return. Now, among other things, turbulence affects output, and to a greater degree than the "scientists", who assured it they knew everything there was to know, thought! Add, too, the issue, mentioned in another PhysOrg article, that wind turbines, which I had already warned about and been mocked for, eliminate wind, causing turbines downwind of them not to operate as efficiently. What other complications that were known about but withheld form the public will crop up? It's the nuclear energy7 scenario all over again. They said it would be so cheap "It wouldn't pay even to meter it". Yet look what a disaster that turned out to be. Like overdevelopment and the Iraq Occupation, they get us into a catastrophe with lies, then demand more taxpayer money to dig out way out.

Apr 20, 2013
Your being mocked for the "depletion" of wind energy by wind farms is still justified. To equate wind energy generation with the disastrous results of nuclear reactors is grotesque and manipulative in your argument., then to play the taxpayer victim card is the icing on your disingenuous cake. Your objections to wind energy aren't based on science, but your political and economic agendas.

Apr 20, 2013
They said it would be so cheap "It wouldn't pay even to meter it".


This was said about fusion, not fission.

Apr 20, 2013
No harder than connecting your electric car to the mains


First you need an infrastructure to support such a feat, obviously.

Apr 20, 2013
No harder than connecting your electric car to the mains


First you need an infrastructure to support such a feat, obviously.
And it's there. It has been there for a century. It's called a plug

Apr 20, 2013
No harder than connecting your electric car to the mains


First you need an infrastructure to support such a feat, obviously.
And it's there. It has been there for a century. It's called a plug


First of all you need a smart meter so that the electric company can tell the battery pack/ car when there is excess power that needs to be stored. When the grid needs extra power the smart meter tells the battery to discharge. You then need an inverter that can change the DC battery voltage into 60 cycle AC that the grid can use.

Thus, it is just a little more complicated than just a "plug".

Apr 20, 2013
No harder than connecting your electric car to the mains


First you need an infrastructure to support such a feat, obviously.
And it's there. It has been there for a century. It's called a plug


First of all you need a smart meter so that the electric company can tell the battery pack/ car when there is excess power that needs to be stored. When the grid needs extra power the smart meter tells the battery to discharge. You then need an inverter that can change the DC battery voltage into 60 cycle AC that the grid can use.

Thus, it is just a little more complicated than just a "plug".
Only to the power company, which has incentive to install smart meters to reduce manual labor. Inverters are standard equipment in UPS systems. Hardly novel

Apr 20, 2013
So in your system how does the battery storage know when to store power and when to provide power?

Apr 21, 2013
So in your system how does the battery storage know when to store power and when to provide power?
I suspect voltage and phase would be a good way to read the current situation

Apr 21, 2013
I suspect that hundreds of these units all acting independently in the same neighborhood could lead to large voltage swings and instabilities almost like oscillation from a positive feedback loop. The amount of power supplied to a grid needs to be carefully controlled or it can do more harm than good.

Apr 21, 2013

Hype: "Your being mocked for the "depletion" of wind energy by wind farms is still justified. To equate wind energy generation with the disastrous results of nuclear reactors is grotesque."

Facts: Death toll of windmill accidents: about 400 p.a.
Death toll of nuclear accidents due to radiations on pure power plants in half century of nuclear age -- exactly 0 (zero). (Chernobyl was a military W-Pu producer, that made it unsafe.)
More luck next time.

Apr 21, 2013
I suspect that hundreds of these units all acting independently in the same neighborhood could lead to large voltage swings and instabilities almost like oscillation from a positive feedback loop. The amount of power supplied to a grid needs to be carefully controlled or it can do more harm than good.
They're acting in parallel, so no feedback loop therefore no chaotic swings

Apr 21, 2013


DJR you fail to take into account that ALL of the fossil plants have to be kept operational as a backup source when there is no wind. Wind energy sells for less because it is not constant and cannot be relied upon 100% of the time. If wind farms cause fossil plants to shut down due to cheap power then there has to be blackouts due to lack of supply. Wind and solar need a power storage device in order to reach their full potential.

Apr 21, 2013
I read the link and here is the main point of it.

"The Department of Energy's Pacific Northwest National Laboratory has developed a method of combining solar energy into the natural gas production process to produce cleaner energy output with the same fossil fuel input."

There is no real energy production there. Just cleaner.

Renewables will always be a bit player until we find out how to store the energy they produce in a cost effective manner.

Apr 21, 2013
It's so often the case that a point is no more valid than the "arguments" used to support it.
Note the objections to what I said.
Telekinetic saying I deserved to be mocked for saying turbines robbed flowing air of energy. Yet why, then, did PhysOrg write an article on that very phenomenon?
And Telekinetic can use loaded language as much as they want. Those without a point so often resort to overselling the vacuum, they're promoting. It is not "grotesque" to compare turbines with nuclear energy. They promised both would be limitless and cheap. Yet energy bills from nuclear plants never went down.
And dir finds it necessary to use the non argument tactic of lying, saying wind energy is bringing electric prices down. dir's gilding the subject with high flying verbiage about wind power being "vibrant" and "contributing so much to our progress as a species", doesn't change the facts.

Apr 21, 2013
Renewables will always be a bit player until we find out how to store the energy they produce in a cost effective manner.

It's called hydropumping. Even better, since clean water is being injected into reservoirs, silt buildup can be REDUCED. That can REJUVENATE old silt-laden reservoirs, making them again useful for hydroelectric AND new storage applications

Apr 21, 2013
I agree with water storage but it takes a lot of water to store 24 MWH of power. Something like 600 acre feet of water located 100 ft above the generator.

Apr 21, 2013
@praos-
"The accident destroyed the Chernobyl 4 reactor, killing 30 operators and firemen within three months and several further deaths later. One person was killed immediately and a second died in hospital soon after as a result of injuries received. Another person is reported to have died at the time from a coronary thrombosisc. Acute radiation syndrome (ARS) was originally diagnosed in 237 people on-site and involved with the clean-up and it was later confirmed in 134 cases. Of these, 28 people died as a result of ARS within a few weeks of the accident. Nineteen more subsequently died between 1987 and 2004 but their deaths cannot necessarily be attributed to radiation exposured. Nobody off-site suffered from acute radiation effects although a large proportion of childhood thyroid cancers diagnosed since the accident is likely to be due to intake of radioactive iodine fallout. Furthermore, large areas of Belarus, Ukraine, Russia and beyond were contaminated in varying degrees."


Apr 21, 2013
I also have talked to Russian immigrants who spoke of Chernobyl-related cancer deaths of relatives and acquaintances- information that is not made public because of a clampdown of truth in Russia.

@julianpenrod- Germany is in the process of shutting down all of its nuclear power plants because of the danger, and as industrialized as they are, they still know that it isn't worth the risk. After Fukushima, the Germans threw all that they had into renewables and will be nuclear-free in ten years.

Apr 21, 2013
"It is not "grotesque" to compare turbines with nuclear energy. They promised both would be limitless and cheap. Yet energy bills from nuclear plants never went down."-julianpenrod

It IS grotesque to compare the two, not because of the failed promise of cheap energy, but because of the failure of federal agencies to protect people from poorly designed cancer-causing nuclear facilities that are prone to human error in design and operation. A windmill will never cause mutations in DNA.


Apr 22, 2013
DJR I will admit when I am wrong. The article did not really explain the process just the result. I assumed that H2 had to be added to produce the syngas. I would be great to see a cost effective way to utilize sunlight and save fuel.

Apr 22, 2013
After Fukushima, the Germans threw all that they had into renewables and will be nuclear-free in ten years.

Small correction: After Fukushima we simply started shutting down nuclear reactors more rapidly than previously planned.

The end of nuclear had already been signed into law...well, until a few months BEFORE Fukushima when Merkel and her party reversed that law - which was close to political suicide for her party, but nevertheless mandated by her handlers in big business industries.
But after Fukushima upholding that decision would have been sure fire political suicide - and that would not have served her handlers at all. So she 'miraculously' re-reversed the decision.

The full scale investments into alternative energy had been started well before Fukushima (by the previously ruling socialdemocratic-green coalition)

Apr 22, 2013
Talk about pollution------the climate change issue is getting in the way of adopting a financially sound renewable energy policy. Corn ethanol is one major example. It's energy benefits are marginal at best and it is raising the cost of our food. Another article here wants to convert methanol to H2 in order to lower CO2 emissions. As long as dimwitted schemes like this exist I will continue to rant and rave. Sequestering CO2 is another bogus scheme. You are worried fracking, how about the effects of turning all those aquifers into seltzer water.

Apr 22, 2013
Talk about pollution------the climate change issue is getting in the way of adopting a financially sound renewable energy policy.
Apocalyptic events can do that

Apr 23, 2013
One cannot discuss renewable energy without discussing the politics that go along with it. Sorry to burst your bubble but ethanol was sold to the public as a green renewable alternative to gasoline whereas, hydroelectric does not qualify as such.
Not enough is known about the true effects of CO2 on the climate to make an economic decision worth 10s of trillions of dollars. The science community has prostituted their values to promote what, no doubt, some feel is a real concern. Oh my God, the polar bears are dying! Oh my God, polar ice that has never melted before is melting now. Oh, my God, this is the hottest summer ever! Oh my God.......... the list goes on and on. When these "Scientists" stop the hyperbole I might to start to trust them again.

Apr 23, 2013
Oh my God, polar ice that has never melted before is melting now. Oh, my God, this is the hottest summer ever! Oh my God..........

The 'oh my god' is your addition (and sometimes the media's). That's not the scientists. They simply report the numbers and the facts. If you don't like them that's your business - but facts remain facts.
If you want to trust them again only when they report facts you like then you have a serious misunderstanding about the nature of science.

Apr 23, 2013
So when a "Scientist" prepares a press release stating that the arctic ice extent is at an all time record low and digging deeper "all time" refers to 1979, that is just reporting the numbers.

Apr 23, 2013
DJR if you were to argue that we need renewables due to the fact that fossil fuels have a finite supply we would be in full agreement. But when some of the so called "solutions" wind up with a negative EROEI and a net loss to our economic viability I become argumentative. If something requires a government subsidy to be viable it is not ready for full scale economic integration yet.

Apr 23, 2013
"The subsidy argument is very specious - fossil fuels all have significant government support "

The fossil fuel industry is a net payer of income taxes whereas renewables are a net receiver of funding. Ethanol and electric vehicles are heavily subsidized and by and large have close to or a negative EROEI. I know that you think that Europe is about to revolutionize their economic system with renewables and that could be true if they do not go bankrupt first due to high energy costs and their costly social agenda.

Apr 23, 2013
And another thing- wars have never been waged over wind and sunlight.

Apr 24, 2013
I know that you think that Europe is about to revolutionize their economic system with renewables and that could be true if they do not go bankrupt first due to high energy costs and their costly social agenda.

You may notice that we've had this 'costly social agenda' for a long time - and we haven't gone bankrupt.

The fossil fuel industry is a net payer of income taxes whereas renewables are a net receiver of funding.

And if you go to history you will notice that in thir startup phase fossil fuels (and especially nuclear) were MUCH more heavily subsidized - and still are.
Why is it suddenly so unfair that alternative energy schemes get some subsidies in their startup phase? And only about 10% of that what oil and nuclear got at that?

If you want to cry 'foul' then at least don't by hypocritical about it.

Apr 24, 2013
""The data also shows that wind power intermittency does not only affect the output of individual turbines, as previous research has shown, but it also extends to entire wind farms, which has not been observed before""

Wonder why ?

Much of this article is crying wolf. Wind farms sites are selected for stable air flow.

The solution is expanded grid network so that weather fluctuations can be averaged and the power flow automatically dispatched by a system that is linked with the conventional generation so they operate together.
Add to this system networked weather stations that allow for 'prediction' of near term fluctuations and the problems become much more manageable.


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