I live within sight of the largest wind energy field in North America. I’ve noticed that when the winds reach gale force (35+ mph) the turbines stop turning.
(pause)
some Net surfing later, I’ve found that a typical turbine starts to make power at 6 to 9 mph wind speed and hits full rated power at 30mph. From here to 55mph, rated power is maintained by adjusting blade pitch. Past 55 mph, the turbine is stopped and locked down to weather the strain.
These turbines are tall beasts. I’m deducing that wind speed at their altitude is higher than down at the ground. I’ve seen’em go when there are no more than 5mph in the yard.