back to article Big new wind turbines too close together, says top boffin

A top American fluid-dynamics boffin says that new, larger wind turbines now going into service are going to have to be placed much further apart - which will have serious implications for the amount of energy produced by wind farms of the future. The latest wind farms now going into service use huge turbines with rotor …

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  1. C 2
    Boffin

    They can put them MUCH closer if ...

    They use a Solar Updraft Tower, like the one built in the 80's to prove it out...

    http://www.youtube.com/watch?v=XCGVTYtJEFk

    http://www.enviromission.com.au/EVM/content/technology_technologyover.html

    These have the advantage of being more reliable than pretty much anything else, also due to the heat retention of the ground under its collection canopy/greenhouse they run 24/365.

    A German civil engineer even has designs on the table with up to a 160 year lifespan.

    http://www.greentower.net/exec.php

    .. and Namibia may be building eight of those.

    1. crowley
      FAIL

      Eh?

      60Kw for 4.4 hectares of land? I wonder why it never took off in the intervening years...

  2. MaoSaysRTFM
    FAIL

    Best Not bother then...

    and keep burning the fossil fuels until they run out, and then we can turn off the leccy and give the finger to future generations.

  3. This post has been deleted by its author

    1. The Indomitable Gall

      Slowing the winds, slowing the tides

      Well, as we've already built massive amounts of buildings on land and many causeways and walls at sea, and as we've razed mountains and while raising other land, not to mention the dozens of aircraft stealing disrupting the high-altitude air currents, we're already interrupting the winds and waters more than a few turbines can.

      1. Anonymous Coward
        Anonymous Coward

        Good point.

        For some reason the actively taking energy out of the wind as opposed to merely diverting it feels different to me. And perhaps we should pay a bit more attention to just what our cities and such do to the weather --we already know that big cities have their own climate of sorts-- and razing of entire mountains I've never felt comfy about. Paint me a treehugger then. *sigh* Oh well, there's worse afflictions.

        OTOH, some plans are quite a bit more ambitious than "a few turbines". The fact that we've already made quite the impact is IMO no reason to disregard our responsibilities here. We still ought to take care we understand what we're doing.

        So how much impact will wind turbines have? How much impact do vapour trails and even the heat from high altitude jet aircraft have? Even if a single aircraft would be immeasurably small, what about the entire fleet? Given what other silly stuff boffins busy themselves with, they might as well look into this. We still might run into that pesky chaotic butterfly.

        1. TkH11

          @AC, vapour trails

          "How much impact do vapour trails and even the heat from high altitude jet aircraft have? Even if a single aircraft would be immeasurably small, what about the entire fleet? Given what other silly stuff boffins busy themselves with, they might as well look into this. We still might run into that pesky chaotic butterfly."

          It's been shown - very recently in fact - that the vapour trail of aircraft - one in fact - in a holding pattern does lead to the formation of a cloud. Clouds absorb radiation from the sun.

          There's validity in the butteryfly effect, chaos theory, indeed, weather forecasters - particurlarly the European Centre for Medium Range Weather Forecasts (ECMWF) in Reading employ mathematical models where they nudge the input stimulas to the mathematical model and re-run the simulation, and they do this for many repeated simulation runs and then compare the outputs, and you can get quite a wide range of output results, this then leads to a weather forecast being prepared of lower confidence.

          But they won't have the processing power available to them to take the model down to a very fine, high resolution so certainly they couldn't simulate the effect of a single cloud produced from the vapour trail of an airliner or a butterfly flapping its wings, but the principle is known about and valid.

          The difficulty is proving that a storm on one side of the planet was caused by the installation of some wind turbines on the other side of the planet.

          1. Jean-Luc Silver badge

            actually...

            I recall reading a climate analysis on North America in the immediate aftermath of Sept 11, when there were no commercial flights allowed for 3-4 days.

            And, yes, there seems to have been a measurable difference (few tenths of a deg C, but I don't remember which way).

        2. lawndart

          Whir-whir-whir

          What sort of local effects is the Horns Rev offshore wind farm producing?

          http://www.solaripedia.com/images/large/711.jpg

          All that cloud could be useful, or not.

          1. Anonymous Coward
            Anonymous Coward

            Local effects?

            I honestly haven't the faintest idea what it does, but it's a nice point and a nice picture.

    2. Jean-Luc Silver badge
      Joke

      Dude...

      "we don't know what building windfarms does to the climate..."

      Can you pass me some of that stuff you've been smoking? Must be powerful sh*t indeed.

    3. TkH11

      @AC

      You state:

      "Of course wind energy is indirectly solar energy and we don't know just what meddling with the climate does."

      but then you go on to say how you would cover the planet in PV cells! How do PV's work? They absorb sunlight, not indirectly but directly!

      So your argument the possible effect on the climate of wind farms is also entirely valid for PV cells!

      Then you go on to say that you'd rather PV cells are placed in space, presumably because they then could have no effect on the earth's climate.

      Seems to me that we're suffering from global warming, so where's that heat energy coming from? The sun, obviously. So, seems to me that a better idea would be to place those PV cells on the earth where they can absorb that radiation and convert to electricity instead of heating the earth and causing us problems.

      Now, I agree, we don't know the effect of it all, if we were to implement these alternative strategies in such a large way over the entire planet, perhaps the climate could be affected, no-one in their 40's can not have failed to notice that our weather is getting worse, the more frequent floods, hotter summers, colder winters are definitely occurring.

      Could we really make it worse by using lots of PV's, perhaps it might improve things. At the end of the day, we just don't know, but we can see how our climate is worsening if we don't do anything.

      1. Anonymous Coward
        Anonymous Coward

        TKH11, cover the planet? Read again.

        I said I wanted them in orbit, /solar orbit/, like the earth. Maybe I should've added "but that's certainly not on earth, kthx". Not in serious quantities anyway. That's purely from a "where do we get as much as possible energy from without interfering with our climate" standpoint. Conveniently forgetting that just beaming in energy in large enough quantities, nevermind using that energy, is going to cause interference itself. Whoops, another hole in my argument.

        Still and all, we need to get up the well to keep on expanding. If not for the space, then for the resources, for the energy, and for something to explore. So we might as well work on that space elevator and how to power it from space. And then figure out how to make use of so much energy without the planet overheating.

        Trying to cool down the earth with PV I don't think will work: We haven't changed earth's distance to the sun, and so the problem isn't direct /insolation/ but changes in how much energy gets out again. A cooling problem of sorts. Unless solar spots really have that much influence on insolation variations. In fact, current PV efficiencies mean that most energy isn't converted, but stays around as heat, and also isn't useful for passing to plants to do their thing with, it's going to be heavily dependent on just where on earth you put them whether the side effects will be positive or negative.

        On that note, I would like to see how putting solar energy harvesting devices in the desert could be leveraged for side effects. IOW: Put them in the desert, create shade, have green stuff grow there, and so bootstrap a fertile soil. But that really is another note and not primarily about the energy, though it would indubitably be welcome.

        As to our climate worsening, I think our sample size is too small as of yet. Back when we had series of hot summers and cold winters and cool summers and warm winters alike. Now we have a series with lots of nasty weather. No idea what the next series will bring. I think we should cut down on the hype and keep our eyes open. Too bad that panicking is the only thing that might get something done in politics, should it be needed.

    4. Anonymous Coward
      FAIL

      That's exactly...

      How China and India will bring their people into the 21st Century. As for future generations they will benefit from future technology - unless we've perished because we relied on windpower.

      Back to your yurt, hippy - and have a bar of soap.

  4. NoneSuch
    Joke

    Here is an idea

    Post a series of them around the House of Commons. All that hot air can be harnessed to run half the City of London.

  5. Richard 31
    Paris Hilton

    Spacing

    There presumably is a linear relationship between the spacing of the turbines and the trade-off between amount of energy generated by the turbines and their spacing. It would presumably then be a simple enough matter to calculate the maximum generateable power from a given plot of land.

    What i wonder is: Are all these wind farms slowing the planet down? The energy for powering these turbines has to come from somewhere. :)

    1. John Diffenthal

      Where is Bumble when you need a good title?

      "The new spacing model developed by Meneveau and Johan Meyers, an assistant professor at Katholieke Universiteit Leuven in Belgium, suggests that placing the wind turbines 15 rotor diameters apart—more than twice as far apart as in the current layouts—results in more cost-efficient power generation." Yup, sounds linear to me.

    2. TkH11

      @Richard31 turbine spacing

      I'm not an expert on aerodynamics, but one thing I've learnt over the years from my engineering background and knowledge of mathematics, is that few things in nature have a a simple directly linear relationship with a fixed constant of proportionality. There are some things, agreed, but I'm fairly sure the interaction of eddy currents in fluids created by two neighbouring obstructions isn't one of them. If things in aerodymamics were that simple, we wouldn't be using supercomputers doing highly intenstive computational fluid dynamics calcutions.

      Think about it, when the two objects are close together, there's going to be a signficant amount of interplay between the eddy currents, but as those turbines are spread further apart, the interplay will drop dramatically and beyond a critical distance will almost be zero.

      Accordingly, I'd expect a negative exponential relationship, and definitely not a simple linear relationship.

    3. Tom 13
      Coat

      I'll see your House of Commons,

      and raise you a capital in DC, plus 50 state houses.

  6. Filippo

    one quarter of the turbines?

    Unless the drop in efficiency is greater than 75%, which I strongly doubt, it doesn't make sense to follow his advice and space them twice as much. Surely it shouldn't be too hard to figure out the right distance to optimize power-per-area.

    Also, if we keep building wind farms, there will be more or less valid theories on how it affects climate sooner or later. I bet that, at some point, the exhaust from burning fossil fuels was considered negligible as well.

    1. Daniel Evans

      But think of the monies!

      One reason power companies might be interested in the research is the cost vs profit ratio - let's assume that closely spaced turbines are 50% as efficient as further spaced ones. That means your large-spacing farm costs 1/4 as much to build, but will still give 1/2 the income (each turbine is worth 2-close spaced ones) - halving the time it takes for it to pay itself off. They would also have 1/4 the maintenance cost, potentially meaning cheap 'leccy.

      Of course, there's long-term profit to be considered, and the fact we're lacking in infinite amounts of space for wind farms in which to generate all the power we need.

  7. ratfox Silver badge
    Paris Hilton

    100 meters!?

    Holy $#*!

    Even PH thinks that is too big!

  8. Anonymous Coward
    Boffin

    Legacy issues and risk management

    The real problem is the software used to plan wind farms. Each turbine in a wind farm produces region a turbulent, slowly-moving air behind it: the wake. How this interacts with the surrounding air flow and wakes from other wind turbines is quite complex, and for accurate prediction really requires the use of computational fluid dynamics.

    But the current software predicts turbine wakes upon empirical rules of thumb (linear superposition of wakes), or drastically simplified physics (ie. reduced eddy viscosity wake models) which only works once you have adjusted its parameters precisely based upon observation turbine wakes in similar circumstances. So why take such a simplistic approach? Much of this software is designed to run on desktops, and indeed was originally written for low-powerd 386s many moons ago - so really, there was no other option.

    Nowadays though, we have GPUs which allow more complex physics, which in turn allow for better energy yield prediction. It's well known that the likes of WindFarmer overpredict performance by around 5-10%: that amounts to around £2-5 million per year per wind farm in lost revenue. More detailed models require more number-crunching, but computing resources are cheap: with even as little as £20k can hire you more than enough horsepower.

    All this suggests a greater committment of planning resources would give a greater return; but industry is as industry does - and they are, as always, frightfully conservative.

    1. Anonymous Coward
      Anonymous Coward

      Either way...

      When the wind doesn't blow, the blames don't turn.

      "All this suggests a greater committment of planning resources would give a greater return"

      See above. Good money thrown after bad.

  9. JaitcH
    Alert

    Would a simple solution be to ...

    remove every other turbine in existing farms - which improve efficiency - and simply build new mounting bases to re-install the removed turbines.

    Hopefully UK wind-farm designers read The Register so they have time to make sure they optimise their configurations.

  10. Dave 32
    Grenade

    Wind Farms

    Why don't they just put the wind farms on the Moon? ;-)

  11. Steve X

    Use vertical-axis blades

    Which IIRC fit better with offshore than onshore farms anyway.

  12. Matt_V

    Rotor size

    wouldn't another way forward be to use smaller rotor sizes? I'm sure they could work out what size would be best to use per a given area of land to wring the most electricity out of it?

    1. jonathanb Silver badge

      Re: Rotor size

      No. The output increases exponentially for larger blades, so you want the largest blades possible.

      1. John Angelico
        Boffin

        Until...

        ...you get to an aerodynmically determined maximum velocity at the tip of each blade.

        The longer the blade, the greater the tip speed for a given speed of rotation. There is some maximum tip speed where the necessary revolutions would not be sufficient to overcome the mechanical inefficiencies of the generator set, and there would be insufficient power generated - or heaven forfend NONE AT ALL.

      2. Charles Manning

        not exponentially

        The power is proportional to the area swept ie. proportional to the square of the blade length.

        Power is also proportional to the **cube** of the wind speed. ie. If you halve the wind speed then power is reduced by 87%.

        That's why slowing the wind down causes such a problem. That is also why you want to get up away from the ground where surface friction slows the air.

    2. David Pollard

      ... apparently much better

      See: "Order-of-magnitude enhancement of wind farm power density via counter-rotating vertical-axis wind turbine arrays."

      http://arxiv.org/abs/1010.3656

  13. Ben M

    A Rather Frank Admission?

    It's nice to see they're finally admitting the dream doesn't quite match the reality. Wind farms underperform. They're being oversold.

    It's better to acknowledge the reality and seek ways to improve performance... rather than try to fudge the data and hope no one notices the gaping holes.

    (Tree rings, anyone?)

    1. Ammaross Danan
      Coat

      Wind Farms

      Wind Farms have been under fire by many since their inception due to the unrealistic predicted gains. For instance (under the old model even!) it was predicted one would have to blanket the state of Texas in wind turbines to power the USA. Of course, that's assuming the wind is actually blowing....In northern Scotland, this might be likely, but in many places it will take a wide variety of methods to provide a base load and peak load. I, for one, would dump wave generators in ocean currents, wind farms in usually-windy spots, lease windfarm land for livestock grazing, and provide base load with nuclear power. Build a plant by my city, I don't care. I'd suggest more hydro-electric, but we have a dam in almost every conceivable spot as it is....at least without the environmentalists going militia on us...

  14. Anonymous Coward
    Go

    100 meters diameter +

    If these things have 50m plus "wing span" and are rotating even lets say 1Hz... So the tip of a blade runs 2 * pi *50m per second... we would have a tip of blade at neck-breaking 314m/s which is close to mach 1. Ergo, these suckers (or blowers?) must rotate really slower than that.

    Watching them work is quite deceiving of how fast they can go. Or you must cope with transonic instability somewhere along the blade, which basically prevents most airliners today of going any faster without damage, (either to turbines or to airframe).

    Suddenly it makes more sense having more, smaller diameter wind turbines... Just find the sweet spot, if any, between spacing and size, as others mentioned.

    Meanwhile, what I see for somewhere in the future is all these green sources producing hydrogen, which would then be collected and sold in cells....

    ... and maybe a nuclear reactor or two burning all the radioactive waste in the short-term of 150 years or so. Nuclear reactors are prone to working better at full load, so in the wee hours its energy is used in breaking water in hidrogen and oxygen... etc...

    I won't mention how bad hidrogen storage and production must evolve...

    1. Steven Jones

      Smaller turbines are not the answer

      Smaller turbines are less efficient, they spin fast, make more noise, require more masts and, as they span less of the vertical height ot the moving air mass, are simply not going to have access to so much wind energy (and, before anybody suggests it, it is not practicable to vertically stack multipl wind turbines on the same mast for all sorts of reasons).

      However, it's hardly surprising the more energy that's taken out of the moving air stream, the more interactions there will be between nearby turbines and other windfarms.

    2. PJ 1

      1hz

      They tend to rotate at somewhere around 10-17 rpm. So less that 0.3 hz

      The problem with more smaller turbines is the increased cost of installing these and the increased maintenance costs.

    3. Stu_The_Jock
      Boffin

      1Hz ?

      I assume that you've never seen one of these BIG wind turbines in action. I've not been near the latest ones, but a number of years ago (quite a lot of them really) stood under the then biggest wind turbine in the UK on Orkney. Blades probably about 40-50m diameter, standing near it you heard the "Whummmmm" sound as a blade tip passed overhead every 4-5 seconds, so about 0.1Hz Generally the bigger they are, the slower the blades rotate.

    4. Daniel Evans

      The net says...

      The 'net claims these days you might get 20rpm out of these things, and anywhere from 5-20rpm is normal, giving speeds from 25-100m/s.

      Mind, wouldn't complain if my car did 100m/s in favourable winds...

  15. Cunningly Linguistic
    Joke

    Isn't this guy...

    ...just an American blowhard?

  16. ratfox Silver badge
    Joke

    Storing energy

    Why don't we store energy when we have too much of it by using the rotors to create wind we can harvest later?

    1. Anonymous Coward
      Anonymous Coward

      Short-Term Only

      Running them as fans wouldn't work for long - what's going to happen when all the wind has been used up? They're trying it already, have you ever noticed how windy it is when those things are turned on?

  17. jphn37

    complimentary turbulence?

    Just a thought, what would the effect on windflow if these huge turbines were interspersed with smaller ones? The turbulence from them might compliment one another and make it economic to place them closer together.

    Aerodynamics boffins, if you chose to accept this mission . . .

  18. Anonymous Coward
    Thumb Down

    Pointless study

    Wind farms aren't installed to harvest wind, they're installed to harvest subsidies, and those follow a very linear relationship with no interference from adjoining installations.

  19. Waderider
    Go

    Complicated.......

    I'd love to see the maths. All these nice round numbers like 'twice as far apart'. Bit much for me, reeks of pseudoscience, or at best journalism dumbing down research so much that it is indigestible for someone with half a brain.

    My mind boggles a bit when I think of the factors that would determine optimum rotor diameter spacing of turbine towers. Highly variable I'd say - humidy, air temperature (air density), instantaneous wind velocity, rotor speed/feathering, elevation changes between hub centres on adjacent turbines.

    I think the answer is wind turbines mounted in tracks so you can shift them about. At speed, in relation to real time conditions. Maybe.

  20. Tringle
    FAIL

    Blow Hard

    All wind turbines produce less than expected. This is because it is at base medieval technology, abandoned by earlier generations as soon as there were alternatives available.

    I have been watching the power output from the UK's wind farms on and off for a few months now: they have never, at any time I have been looking, produced more than 20% of capacity (that was once), usually hovering somewhere between 0% and 10%. Whatever the question is, wind power is not the answer. Unless it is how do we make our electricity 3 or more times more expensive than our neighbours (like Germany and Denmark have - yeah, I know they are neighbours too, but I mean their other neighbours ) whilst at the same time duplicating our power generation infrastructure because 20% of it can't be relied upon at all? Of all the possible alternative ways of generating electricity wind turbines are bottom feeders.

    As I write this the UK subsidy sucking turkeys are producing 900MW ( pretty much the highest figure I have seen) out of an installed capacity of just short of 6000MW, 2.0% of the demand. Coal, Gas and Nuclear are providing almost all of the rest.

  21. Anonymous Coward
    FAIL

    @ratfox

    "Why don't we store energy when we have too much of it by using the rotors to create wind we can harvest later?"

    Have I stumbled into Viz Comic by mistake?

    That really should be in the "Top Tips" section.

    1. Anonymous Coward
      FAIL

      Fail indeed..

      .. a complete failure to notice the joke icon.

      Unless of course you turn off images because it really was a shite joke so you wouldn't have twigged it was a joke from just the text.

  22. Anonymous Coward
    Flame

    "the power output from the UK's wind farms "

    A URL would be greatly appreciated.

    Thanking you.

    Flame simply because fossil fuels are nice and warm, aren't they.

    1. kwikbreaks

      Yes I thought that too..

      I did do a half-hearted search and found nowt. Watching the power meter would provide stiff competition for this box of cress I'm watching grow after the unfortunate accident when I painted the wall so I could watch that dry.

  23. Anonymous Coward
    FAIL

    Birdshredders!

    If a coal/gas plant killed as many birds and did as much damage to the landscape as windfarm, you can bet the Greens would be tripping all over their woollen socks to tear it down.

    Best use for a windfarm: raw materials, ready to be shipped to a recycling plant.

  24. Stewart Wood

    They should use VAWT helical (twisted) type (vertical axis wind turbines)

    The new generation VAWTS the helical (twisted) type

    Thrive in crowded conditions they even been proven to work in city's just as good as they work rural arias

    not only this but they Thrive on turbulent air so you can have them closer to the ground

  25. wiggers
    FAIL

    Power per unit area?

    The figures my group came up with 20+ years ago was 4 diameters spacing. I worked out that even at that spacing it would take roughly 60km sq of turbines to replace just one reactor of the nuclear power station I once worked on. I can't see that 7 or 15 diameter spacing would generate more power per sq km. The British Isles just wouldn't be big enough to fit all the required turbines! I noticed the model turbines being used in the wind tunnel experiment had a huge solidity ratio (fixed area/swept area) compared to a modern turbine. Not surprising he came up with some weird answers.

  26. skellious
    Black Helicopters

    Stack them up?

    Someone explain to me why you can't just have double-decker wind-farms. surely building a post is cheaper than buying double the land? (or will these have to be 750m tall posts?)

    Choppers because we could use them as wind turbines! (or more likely they would fly into my 3/4 KM turbines.

  27. Anonymous Coward
    Boffin

    Re: Power per unit area?

    Three things you've got to remember:

    1) Wind turbines over two decades ago were about half as efficient.

    2) Power is proportional to the square of the blade diameter.

    3) The higher the hub-height, the higher the winds - average wind speed increases logarithmically with height.

    4) Modern turbines much larger and placed much higher than turbines in previous years.

    This essentially means that the mean power/unit area of modern wind farms is much, much higher than in wind farms even a decade ago.

    1. Tringle

      It's a bit nippy out

      . . yet they are still worse than useless.

      URL for monitoring UK power generation is: http://www.bmreports.com/bsp/bsp_home.htm .

      Scroll down to 'generation by fuel type'. Hey guys, the wind is really blowing now - contribution is up to almost 23% of installed capacity.

      And I agree, watching cress grow is more exciting than waiting for any kind of 'green' energy to actually work.

    2. wiggers
      Happy

      Re: Power per unit area?

      I do know the formlae! The turbines I worked on came pretty close to the Betz limit and I'd be interested to see evidence for a doubling of efficiency over the period you mention. In any case the argument is about the spacing of similar turbines. Doesn't matter if they are old or new, large or small. The alledged increase in efficiency doesn't translate into an increase per unit area of land by spacing the turbines at more than 7 diameters. I'd question anything greater than 4 diameters being economical use of land.

  28. Anonymous Coward
    Boffin

    Re: Power per unit area?

    To give you an example, Kuriant 18 turbines had a peak power coefficient of (Cp) of roughly 0.20. Today, that can get up to 0.4 easily.

    Remember, power does not scale linearly with diameter - so in simplistic terms, a turbine twice the diameter could in theory produce quadruple the power.

    However, applying empirical laws to a problem that is essentially a highly non-linear interplay between mechanics and aerodynamics. Forget about the simplistic power equation: that is not how a real wind turbine behaves. Full-blown CFD is required to solve this problem, with LES turbulence modelling, detailed generator models, and explicit control mechanisms for blade pitch and turbine yaw correction. This is not what happens now in industry, despite the shortfalls of current wind farm planning tools being common knowledge within the renewables sector.

    1. wiggers
      Happy

      Re: Power per unit area?

      The Kuriant 18 was a tiny 18kW turbine of 30yrs ago, not surprising it had a low Cp. Turbines of 100kW plus have been pretty efficient for a while.

      Power output varies with the square of the diameter as you say, but the land area requred for each turbine also varies with the square. So the power density is pretty constant as you vary the diameter. The only advantages of larger turbines are economy of scale and reaching further out of the boundary layer. Typical wind farm power densities are in the region of 2W/m2*. (So you'd need 300km2 to replace a 600MW nuclear reactor, not 60 as I said previously, my bad.) If you double the spacing you get a quarter of this power per unit area so you would need to see each turbine becoming 4x as efficient to get any benefit.

      * http://www.inference.phy.cam.ac.uk/withouthotair/c4/page_32.shtml

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