7 ms·

Three blades is the smallest number that reduces the vibrations due to the blades crossing the support structure. When a blade crosses the support its applied f

• mark-r 10y ago
  There's a question then, why are support towers solid? Maybe they should be made more like the Eiffel Tower?
  • elcapitan 10y ago
    Probably to be more durable, because of the closed surface - the Eiffel tower has very high maintenance costs as it has to be steadily re-painted. It would probably not be necessary that much for modern steels, but unlike wind turbines the Eiffel tower also does not stand close to the coast or directly in the sea, where highly corrosive winds blow.
    • Cerium 10y ago
      Additionally the enclosed space is useful. Inside the wind tower is a lot of equipment. There is the electronics for converting the power and monitoring the wind tower. There is a lift for ease of access to the nacelle. Current wind towers are 80m tall, next generation wind towers are more than 100m to access more reliable higher strength winds.
      • brandmeyer 10y ago
        I don't think this is a strong driver. GE 1.5 MW turbines only have a relatively small space near the base of the tower that is consumed by power electronics and control systems. Siemens has largely gone to a system where everything is in the nacelle. This way it makes it easier to completely test and connect the power electronics and control, since more of the work is done at the factory instead of in the field. Labor and equipment is much more expensive in the field than in the factory.
  • jacquesm 10y ago
    Because a lattice tower has much worse properties when it comes to interacting with the wind. The behavior of the air behind the rotor is as important as getting quality air to flow through the rotor. Some early windparks used lattice towers, and some of those survive to the present but they are now known to be worse performance wise than tubular towers.
    • logfromblammo 10y ago
      A Shukhov tower [0] has minimal wind loading, due to its hyperboloid sections. [0] https://en.wikipedia.org/wiki/Shukhov_Tower https://en.wikipedia.org/wiki/Shukhov_Tower
      • jacquesm 10y ago
        That profile is not very well suited to having a windmill on top of it. The problem is that the nacelle is tilted backwards only a few degrees so you need a very slender tower (or you'll have tower strikes in high winds).
        • logfromblammo 10y ago
          The cooling towers of a nuclear plant follow the same principle. The sides are formed from straight structural members angled in opposite directions (doubly ruled), and the gaps are filled with concrete. The profile of a hyperbolic wind tower may be altered such that the cross section at maximum height minus blade radius is at a minimum. The largely conical profile of the existing Shukhov towers were used for power transmission lines and a radio broadcast antenna. Check this out: http://www.pbs.org/wgbh/nova/next/tech/proposed-hyperboloid-energy-skyscraper-uses-simple-math-to-solve-a-big-problem/ http://www.pbs.org/wgbh/nova/next/tech/proposed-hyperboloid-...
          • jacquesm 10y ago
            Interesting! You'd think that the major wind power manufacturers would have looked at all possibilities. One major immediate concern is that these look quite ugly and fat compared to the relatively thin and slender supports that the latest generation of turbines uses. I'd love to see a side-by-side comparison of these towers and the various alternatives. http://cache1.asset-cache.net/gc/78480146-crowley-ridge-wind-power-alberta-canada-gettyimages.jpg?v=1&c=IWSAsset&k=2&d=wW%2BWqJ5Jns5%2FhtycaQeRKiwHOo%2B1W%2FQabqSCG%2F1%2FRWnbLBlDKuH8j9bn4OWw4zSv http://cache1.asset-cache.net/gc/78480146-crowley-ridge-wind... Is one example of lattice towers in production that I know of (but not like the ones you describe and I have never seen those being used for windmills).
  • scblock 10y ago
    Lattice towers were common in the past, and are still the best weight/material to strength choice. Other considerations have led to the tubular steel tower dominating, though a new generation of enclosed lattice towers is being developed. https://renewables.gepower.com/wind-energy/technology/space-frame-tower.html https://renewables.gepower.com/wind-energy/technology/space-...
  • cr1895 10y ago
    I know it's not really what you mean, but jacket foundations are fairly common in offshore wind. The emerged part is still always a solid tube. https://www.iscpc.org/images/gallery/Jacket_Foundations_EWE.jpg https://www.iscpc.org/images/gallery/Jacket_Foundations_EWE....
  • deleted 10y ago
    [deleted]
  • gumby 10y ago
    They kill a lot of birds too -- birds perch on the bars and then fly off only to be stuck by a blade they didn't see.
• jacquesm 10y ago
  This is spot on and the real reason. Thank for posting this, I was working on a much larger comment but yours is better because it says the same thing in fewer words. If tower thump were not an issue then a one bladed turbine would be the best possible turbine (cost efficiency wise). Further down he's even arguing for turbines with 12 blades, it's a ridiculous number and quite inefficient unless you want very high torque at low rpm such as for directly driving a mechanical waterpump.
  • Bartweiss 10y ago
    It's significant that high-solidity turbines with many blades are in use. As you say, they're quite common in small-scale settings like water pumping. An article purporting to 'discover' that design would probably be more shocking if it wasn't already in common use for sensible applications.
  • Loic 10y ago
    Jacques, you are too nice, you could have said you have also the practical experience of what is building a windmill[0]. A very nice read for people enjoying both using a computer and their hands building stuff. [0]: http://jacquesmattheij.com/how-to-build-a-windmill http://jacquesmattheij.com/how-to-build-a-windmill
    • mjs 10y ago
      Is there any particular reason why that piece never uses the phrase "wind turbine"? That's actually what it is, right?
      • shabble 10y ago
        At the risk of stereotyping; because he's Dutch? :)
      • jacquesm 10y ago
        Because lay-people call them windmills.
  • 10y ago
• tzs 10y ago
  For a two blade system, could that vibration problem be addressed by extending the support up beyond the nacelle, so that both blades cross slower wind spots at the same time?
  • brians 10y ago
    No. That changes whether the turbine is pitching up and down on top of the post, but doesn't change the fact that the turbine shaft is pulled out (or pushed into) the turbine with different force at the crossover point. That will create vibration even more in the long-post model you describe.
• chris_va 10y ago
  Random question, why not 1 blade and a counterweight?
  • brandmeyer 10y ago
    One-blade systems do have a counterweight. There are two parts to the vibration problem: One is that the flow field on the lee side of the tower is quite a bit different from the rest of the blade's sweep, so there is a once-per-turn torque pulse in that part of the path. The other is that the air flow field above the height of the nacelle is different from that below the nacelle. Since you are still in the planetary boundary layer, the airspeed varies with height.
• weinzierl 10y ago
  In the 1980s there was a hype of one and two blade designs. I always found the one blade designs most fascinating and vividly remember a video of the three one blade rotors of the Monopteros 50. Each blade was 56 m long. There was also GROWIAN, a two blade design with 100 m diameter on a 100 m tower. All of these projects were abandoned and the towers demolished. The three blade design has won for the reasons you stated. I searched hard for the Monopteros video but there isn't even a good picture which shows all three towers. By-catch: Wikipedia page about unconventional wind turbines [1] [1] https://en.wikipedia.org/wiki/Unconventional_wind_turbines https://en.wikipedia.org/wiki/Unconventional_wind_turbines
  • mikeash 10y ago
    Somewhat related, there are a few airplanes with one-bladed propellors, for example: http://www.alisport.com/eu/eng/silent2_targa1.htm http://www.alisport.com/eu/eng/silent2_targa1.htm In this example, it's used purely because of compactness when stowed.
• musesum 10y ago
  So, this is a redesign. I was told that old Windmills (used for milling) evolved to have an even number of removable blades. This allowed the mill to continue operating, while repairing a damaged blade -- simply remove the opposing blade, during repairs.
  • Bartweiss 10y ago
    This is generally true. Mill or pumping turbines generally have a lot of blades (for higher torque), which obviously increases the risk of blade failure. That can be offset by having designs which aren't decommissioned by blade loss. Of course, that's much less appealing for commercial installations, where access to the blades is expensive and difficult. edit: also, even blade counts on big, high-powered turbines tend to get into problems with resonance by being symmetrical.
• gcb0 10y ago
  by that single explanation, 12 blades would be even better...
• Bartweiss 10y ago
  The three blade approach also offers better outcomes for repair costs (and animal strikes). High-blade, high-solidity designs are more likely to break in extreme weather (even a stopped windmill takes a lot of strain at 70% solidity) and repair is usually necessary after failure of a single blade. Between that and your points, my impression is that many-blade designs aren't useful beyond small scale generation, which is exactly where they're still in use. There are an awful lot of three-blade advantages that went completely neglected in this piece.
• raverbashing 10y ago
  Looks like a support structure innovation is needed
• eonw 10y ago
  it was also explained to that in very cold weather, the three blade design helps prevent any single blade from gathering too much ice from the wind? so if the top one gets a lot of ice its weight will shift it around? i am no engineer, could be nonsense.