5 ms·

> Wind turbines with variable pitch blades do exist but add cost and mechanical complexity. I was about to suggest the idea of using gears like from a vehicle'

• richardhod 8y ago
  Yes, I'm curious about this, and a FAQ on the technical limitations which lead to the situation that GP mentions. I'd have thought that you could have a mechanical / electrical brake on the blades to keep velocities reasonable, or gears as uyou mention, or maybe it's other mechanical stresses.
  • Gibbon1 8y ago
    I think there is optimization pressure between the size of the generator and the median amount of power produced. Wind speed probably has some sort of log distribution. AKA wind speed hours/year 0-10 4000 10-15 2700 15-20 1100 25-30 600 35-40 300 40-50 50 50-55 15 At some point the cost analysis says the extra power generated isn't worth the cost of the oversize generator needed to extract it so just feather the turbine.
  • bigiain 8y ago
    The thing that's not obvious to most people is that the power contained in moving air is proportional to the cube of the airspeed. If you're local "average wind speed" is 5m/s (~12mph, a "Gentle Breeze" and #3 on the Beaufort scale), and you size your wind turbine to generate useful power (say, 1000W, for example) at that speed, you have two consequences due to that speed-cubed term. 1) When there's only light wind - say half your design average speed, you're only gonna get 1/8th of your 1000W target, so only 125W which isn't very useful if you've got a 1000W requirement. 2) The _bigger_ problem is when the wind blows faster than average. If you get twice average speeds, your turbine is going to generate 8kW which you'll need to safely deal with. But twice isn't your problem - in the real world it's not uncommon for 3 or 4 times average windspeed (what we'd normally just call "a windy day" and 7 or 8 on the Beaufort scale), at which stage you're going to need to safely dump 64kW of power - if your turbine hasn't been braked/parks appropriately (or torn itself to pieces.) If you're still spinning in hurricane conditions, you've got another doubling of windspeed, and another eightfold increase in power, so now your "1000W generator" is unleashing half a megawatt into your wiring and control electronics (or the plasma in the smoke where your wiring used to be...) Beaufort scale with speeds and descriptions: https://en.wikipedia.org/wiki/Beaufort_scale#Modern_scale https://en.wikipedia.org/wiki/Beaufort_scale#Modern_scale Some real world windspeed measurements showing upper end outliers of 8 times average speed: http://www.wind-power-program.com/wind_statistics.htm http://www.wind-power-program.com/wind_statistics.htm
    • hvidgaard 8y ago
      That assumes that the turbine have the same efficiency over all wind speeds. Realistically, it will not - but your point stands none the less.
• roland35 8y ago
  Yeah there are certainly options out there but at some point the blades will be simply spinning too fast to be safe and it will need to be actively braked. The other problem is adding the mechanical complexity all up in the nacelle of the wind turbine, where it is hard to service and maintain.
• eximius 8y ago
  Just a random shot in the dark but I imagine that you need variable pitch blades (in addition to or instead of gears) because gears would only regulate the speed of the turbine, but not the force exerted by the wind on the blade. Put it into a high gear in a high wind, it may not rotate fast and fly off due to angular momentum, but it might just snap off.
  • gomox 8y ago
    Generally speaking a stopped turbine's blades are mostly stalled and under much lower stress than when rotating (albeit in different direction). The angle of attack of the blades is designed for moving blades. The surprising result of this is that the brake force needed to keep the turbine stopped is much smaller than the one needed to stop it, despite the relatively low mass of the blades.