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> As noted in the article, wind can be highly variable in most areas. Optimizing a wind turbine for the average low speed (like here in the US Midwest) means that at super high speed winds can damage your turbine and it may need to be shut off. If you optimize for the high speeds you can get a ton of energy at those speeds but your turbine will mostly be still. Regions with a nice steady wind profile work better for power generation.

This problem is solved centuries ago. Just cover only part of the blade with cloth.

> 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's transmission (i.e. first gear is easy to turn, will shift to larger when certain condition achieved), but it sounds like these ideas have been hashed out already.

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.

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.

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

Some real world windspeed measurements showing upper end outliers of 8 times average speed: http://www.wind-power-program.com/wind_statistics.htm

That assumes that the turbine have the same efficiency over all wind speeds. Realistically, it will not - but your point stands none the less.

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.

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.

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.

I would have guessed that any large wind turbine would have to have variable pitch blades. You need to be able to feather the blades in case of high wind/overspeed, maintenance, or other need to stop/slow the rotational speed.