very low wind and wind turbines turning

Varies.

Those blades are big, heavy and flexable. They motor them round to prevent damage to the bearing(s) and to not have the blades take a set. If you see a turbne going slow watch a blade and how much it flexes as it goes past 12 o'clock.

Oh dear, these must be well and truly f**ked:

They haven't moved in years!

There is a wind farm here and a few years ago there was storm force wind, a nd then a power cut. The wind changed direction, still storm, and because t here was no power the turbines could not turn the blades to the desired ang le, the bearings were finished by the time the storm had passed. They turbi nes were only four months old.

and then a power cut. The wind changed direction, still storm, and because there was no power the turbines could not turn the blades to the desired a ngle, the bearings were finished by the time the storm had passed. They tur bines were only four months old.

There are three turbines up from my house, somewhere between 0.5 and 1 MW, there is no wind and they are turning at 17 rpm. There is also a 50kW turbi ne which is stopped. Since the load on the 50kW turbine is so much smaller, it does not need to turn. Would that be correct?

Well maybe some are broken in the brake department. Seriously though, I suspect each has a detector and uses that to decide. There has to be something that turns them and if the wind is that something I see no harm in them rotating even if off line. Brian

More like below 5mph Id say.

Because motors keep them turning to save the bearings from flat spots.

It could be the wind gradient: the wind speed drops off quite a bit as you get close to the ground. So depending on how high the blades are, the wind velocity could be higher than at ground level.

I reasonably frequently go past them and noticed they were finally working. Seems as though the radar issue has been resolved:

I'm sure I read somewhere that if they can't be turned by the wind (i.e.

(Before last year, I would have bothered to find some supporting evidence. So pleased that post-Brexit anything anyone asserts must be true. It's saved an awful lot of work ....)

there are calculators on the web for the wind gradient, and the effect is quite small, at low speeds anyway.