@TTN: Putting SSR transponders on the masts will not help. The position of wind turbine masts are very well known. The problem is that the masts and blades represent very big reflectors for Primary Surveillance Radar (PSR) RF signals. Modern PSR work by detecting the "doppler" content of the reflected RF signal. Doppler is the effect that increases the frequency of the reflected signal as the object moves towards the radar and reduces the frequency as the object moves away from the radar. By detecting the doppler frequency the radar derives the direction and velocity of the object. So with no wind, wind turbine blades have zero doppler content and are therefore ignored by the radar. However turning blades can give the same level of signal as a 747!
The company I work for has successfully demonstrated, to ANSPs and scientific bodies, techniques in the radar equipment that mitigate the effects of wind turbines so it is not necessary to go to the expense of in fill radars so expect to see more wind farms in future!.