Steering Wind Turbines to Greater Efficiency

July 18, 2019

Tiny changes in the orientation of wind turbines pay big efficiency dividends.

Renews.biz:

Researchers at Stanford University, in California, have shown that angling turbines slightly away from the wind can boost energy produced overall.

Pointing turbines slightly away from oncoming wind – called ‘wake-steering’ – can reduce that interference and improve both the quantity and quality of power from wind farms, and probably lower operating costs, according to the new research.

The study tested its modelling on a wind farm in Alberta, Canada, in collaboration with operator TransAlta Renewables.

The overall power output of the farm increased by up to 47% in low wind speeds, depending on the angle of the turbines.

In average wind speeds the output saw a 7-13% boost.

The results of the study were published on 1 July in Proceedings of the National Academy of Sciences.

Stanford professor of civil, environmental and mechanical engineering John Dabiri said: “To meet global targets for renewable energy generation, we need to find ways to generate a lot more energy from existing wind farms.

“The traditional focus has been on the performance of individual turbines in a wind farm, but we need to instead start thinking about the farm as a whole, and not just as the sum of its parts.”

Turbine wakes can reduce the efficiency of downwind generators by more than 40%.

Previously, researchers have used computer simulations to show that misaligning turbines from prevailing winds could raise production of downstream turbines.

However, showing this on a real wind farm has been hindered by challenges in finding a facility operator willing to halt normal operations for an experiment and in calculating best angles for the turbine.

Initially the Stanford team developed a faster way to calculate the optimal misalignment angles for turbines, before testing their calculations on the wind farm in Alberta.

“Through wake steering, the front turbine produced less power as we expected,” said mechanical engineering PhD student Michael Howland, lead author on the study.

“But we found that because of decreased wake effects, the downstream turbines generated significantly more power,” he added.

In slow winds, wake-steering reduced the amount of time that speeds dropped below the minimum that leads to power cut-out, the researchers found.

Notably, the biggest gains were at night, when wind energy is typically most valuable as a complement to solar power.

In the study, wake steering reduced the very short-term variability of power production by up to 72%.

The researchers also suggested that reducing variability can help wind farm owners lower their operating costs as turbulence in wakes can strain turbine blades and raise repair costs.

Dabiri said: “The first question that a lot of operators ask us is how this will affect the long-term structural health of their turbines.

“We’re working on pinpointing the exact effects, but so far we have seen that you can actually decrease mechanical fatigue through wake steering.”

While designing wind farms is typically a data and computationally intensive task Stanford University established simplified mathematical representations that reduced the computational load by at least two orders of magnitude.

This faster computation could help wind farm operators use wake steering widely.

“If we can get to the point where we can deploy this strategy on a large-scale for long periods of time, we can potentially optimize aerodynamics, power production and even land-use for wind farms everywhere,” said Dabiri.

12 Responses to “Steering Wind Turbines to Greater Efficiency”

  1. dumboldguy Says:

    Any good news is welcome, but I wonder why it took them so long to figure this out. Wind turbines have been around long enough that we should have nailed this down long ago. Did no one think to do at least do some wind tunnel tests with models?

  2. mboli Says:

    Scanning the article, I get the idea that one reason this hasn’t been tried before is the computational load.

    The problem is solved by hill climbing. It assumes some angles for each of the turbines, simulates an output, tweaks the settings, simulates again, repeating this exercise by tweaking the settings in the directions that seem to be pushing output in the desired direction. They mention that sometimes a genetic algorithm is used. The wind direction isn’t a single number for the whole field. And all this has to respond in real time.

    The authors make a big point of they have made some simplifications and approximations in order to achieve real-time control.

    The idea is cute. The point is that when you see a field, it usually looks like parallel rows of turbines. You have a row of towers next to each other facing the oncoming wind, then another row far behind the first one, and so on. The idea is that the array was built with respect to the most common wind direction: the turbines next to each other don’t interfere with each other in the first row. The big space behind he first row is because of the wake, then you get the second row.

    But what happens when the wind is blowing cross-wise? It blows along each row instead of against each row. All those side-by-side turbines swivel to face the wind, now they are behind each other in close formation. Wake city. If you swivel the angle a little bit, the wake doesn’t blow straight back into the next turbine, it goes off at an angle and partially misses.

    Anyway I’m a geek. I see an article like this and I want to read it.

    • rhymeswithgoalie Says:

      The problem is solved by hill climbing.

      (1) Is there an issue of local maxima?
      (2) If so, would it matter?

  3. jfon Says:

    ‘Turbine 4 is a Vestas V80 2.0-MW machine while the rest are Vestas V80 1.8 MW.’ So the nameplate capacity of this wind farm is 11 Megawatts – 11 thousand kilowatts.
    ‘For low wind speeds of u∞=5−6 m⋅s−1 and 325° ± 5° inflow, the total power of the six turbines increased from a temporal average of 390 kW to 570 kW, representing a 47% increase.’
    Or in other words, from about 3.5% of nameplate output to 5%. Unsurprisingly, they note ‘the resulting gains in annual energy production were insignificant at this farm’.
    Roughly speaking, the power of the wind goes with the cube of the windspeed, so if the turbine is designed for maximum power at 24 knots – a pretty stiff wind – then at twelve knots it will only be making an eighth of that. Twelve knots would still be classed as a good breeze by most people, but it won’t be making much power. If you’re just flying kites, sailing yachts, or drying your washing, that’s fine, but if you’re trying to power a grid, or even harder, charge up batteries to power a grid, the capacity factor is well below what would be acceptable in any fossil fueled plant. Since fossil fueled plants are what we’re trying to replace, wind is not going to achieve the deep carbon cuts that we need.
    It’s interesting that most of John Dabiri’s scientific papers have been on vertical axis wind turbines, which have proved in practice to be much more unreliable and unproductive than the standard Danish three-blade horizontal axis machines. (They vibrate themselves to bits, over time – metal fatigue from self-induced turbulence.)

    • redskylite Says:

      All depends where you live on this planet, wind is doing fine in such places as Scotland .

      https://www.ecowatch.com/scottish-wind-power-efficiency-2639219635.html

      and nuclear may help in some locations (without persistent winds) now they are investing sufficient money in it to sort out the overheating problems ..

      https://www.bloomberg.com/news/articles/2019-07-10/edf-is-preparing-its-nuclear-reactors-for-climate-change

      • J4Zonian Says:

        Yeah, places like Scotland, England, Wales, China, US, Germany, India, Spain…
        And offshore especially: Denmark, Netherlands, Belgium, Sweden, Vietnam, Finland, Japan, S. Korea, Ireland…

        Soon the US east coast, (30 MW built, 30,000 planned for the next 5 years or so) US west coast… and other areas. Because of dropping prices, even the US Southeast resistance to wind power is crumbling, despite the Kochs.

        I can think of no place on Earth that doesn’t have large amounts of either wind, sun or hydro, with smaller amounts of the other 2 plus geothermal, tidal, and other clean safe renewable sources. Most places have fairly large amounts of at least 2 of the 3, except the places that have extraordinary amounts of sun. If there are places that can’t supply all their needs locally, they can combine their local resources with energy from elsewhere.

        Most of Eurasia can and must be hooked up to a grid that encompasses North Sea, Central Asian and East Asian wind, Middle Eastern and North African solar, and geothermal in the western arc of the Ring of Fire, to supplement their local resources. The US (the Saudi Arabia of varied RE resources) can be linked to Canadian and Central American hydro and wind, and Central American and Caribbean solar and wind, and they can be hooked up to the varied resources of South America. Australia has solar and onshore and offshore wind; Africa has some of everything, if they’re allowed to use it for themselves rather than having it stolen.

        Since to avoid rapidly and exponentially rising risk of destroying civilization and wiping out millions of species we have to eliminate at least 90% of fossil fuels in the next 7 years, some of the solutions that people are counting on can’t possibly play any significant part–nukes, carbon prices of the sort Republicans will allow, ccs, population policies… RE can, but only if countries get serious and declare climate catastrophe an emergency and then act like it. If you live in the US, see if your representative and senators are co-sponsors of the Climate
        Emergency Declaration, and then write, call, and especially, visit to thank them or demand they support it.
        https://climateemergency.us/

        When wind turbines and solar PV are combined with dispatchable hydro, 24/7 solar (CSP) geothermal, batteries, pumped storage, and other storage, and demand response techniques in a distributed generation smart grid, they can supply all the energy every area of the world needs.

    • J4Zonian Says:

      The capacity of the new, and first, floating wind farm was 65% for its first 3 months in operation. Will probably be less over the course of a year, but the new Haliade-X 12 MW turbine (being built for tests onshore in Rotterdam https://fotopaulmartens.netcam.nl/futureland.php
      https://www.genewsroom.com/press-releases/ges-haliade-x-12-mw-prototype-be-installed-rotterdam
      is designed for 63%, and larger turbines coming soon (15 MW, 50MW SUMR wind turbine? eg.) will be even higher.

      Gas and coal in the US have 55-56% capacity factor.

      They’re still dropping because there are longer and longer times they simply can’t compete with wind and solar PV, as more renewables are built and the power, efficiency and capacity factor all keep increasing. Batteries will soon make solar PV and wind essentially dispatchable, joining 24/7 solar thermal (CSP), clothesline paradox solar heating and cooling, hydro, micro-hydro, and geothermal, as dispatchable clean safe renewable energy. Distributed generation, and demand response strategies added to the mix make it more than enough to provide 100% of the energy the world needs.

      So did I wonder if jfon didn’t know this, is lying about it to try to stymie acceptance of clean safe renewable energy, or is just so mentally ill he simply doesn’t know the difference? Once and for all I’d like to know if he is working or did work for the nuke industry or is just a fanatical fanboy, or if his mother tripped and broke her hip on a solar panel or something. If the first (ignorance), why is he spewing false statements on an important topic he knows so little (and such ideologically cherry-picked bits) about? If the second (lies) or third (nutsiness), he should get himself to a psychotherapist to figure out why he would do such a reprehensible, pathological thing.

      In any case, his pusillanimous pustulous self should please stop posting right wing fossil- and fissile-fueled nonsense. If all he has to support nukes is lies (and nuke supporters everywhere have proven that’s all they have, over and over and over and over and over for years) every point he posts makes the weakness of his argument, and his moral and intellectual bankruptcy more clear.

    • rhymeswithgoalie Says:

      Engineering-wise, it looks like the wind gradient from bottom of sweep to top is much more of an issue.

      In any case, wind farms tend to be sited where there the wind is faster (at tower heights), like open West Texas.

  4. dumboldguy Says:

    JFC! Jeffy must be off his meds again and is overreving—-could this be the time he throws a rod and his head explodes a la Mars Attacks and frees us from looking at his gish gallops of “pusillanimous pustulous” rantings? One can hope.

    “…his pusillanimous pustulous self should please stop posting right wing fossil- and fissile-fueled nonsense. If all he has to support nukes is lies (and nuke supporters everywhere have proven that’s all they have, over and over and over and over and over for years) every point he posts makes the weakness of his argument, and his moral and intellectual bankruptcy more clear”

    Anti-nukers have repeated over and over and over and over and over and over and over and over and over and over and over and over and over for years the same irrelevant crap about nuclear power. It remains the safest, cleanest source of large quantities of carbon-free energy—-that’s scientific FACT. Just because it’s too expensive and too “scary” for the ignorant and emotional doesn’t change that.

    (And Jeffy, don’t ever attend a convention of Crockers, if one is ever held—-you can likely add jfon to the list of those who would like to slap you silly and reset your brain. Also, your attempt at alliteration with the two P words is a major fail—-neither word quite fits the circumstances. Go take your meds and breathe deeply)

    • jfon Says:

      Just stumbled on this thread by accident. Thanks for the support, but I wouldn’t dream of slapping J4Z upside the head – free exchange of ideas and all that. Courtesy should, of course, be practised online just as off. It’s the lubricant for a functional democracy.


Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: