Wind turbines turning in no wind?

[Kuzey Cem]

So last week I was returning from a holiday (by car) and on the way I saw a field with about 20 wind turbines on it. They were slowly turning, as usual. At first it seemed normal but I suddenly realized, by the open window of the car, that there was no wind at all. So I wondered if there was an explanation for this? Maybe the wind turbines "store" some of the kinetic energy and use it for when there is no wind? Or maybe they have some sort of electrical source that keeps them going?
Thanks for your help.

 

[A.T.]

There is more wind at the height of the wind turbines than on the ground:
https://en.wikipedia.org/wiki/Wind_gradient