Wind turbines can and do interfere with primary surveillance radars. That is why there is a Transponder Mandatory Zone around Thanet and the London Array - the TMZ allows ATC to use its SSR instead of primary radar. There is also a consultation running (check the CAA website) on a TMZ over a chunk of the Irish Sea near Liverpool to mitigate the effects of the turbines (290m blade height!) on Warton's PSR.
This is an issue that affects civ and mil airspace users.