I Don't Understand...

On the journey to Burnley we pass Coal Clough Windfarm, one of the oldest onshore wind farms in England (1992)
The original 24 turbines have been replaced (2015) with eight enormous ones (110m - 360ft)  (For reference Blackpool Tower is 158m - 518ft).
Despite it being a good breezy (and wet) day - none of the turbines were turning, therefore no electricity was being generated.
I don't understand.....