Worked on looking at the effects of windfarms on ATC operations in the UK for several years (but by no means an expert
).
At this present moment in time the only mitagation "proven" to work is infill radars with terrain shielding however the loss of low level coverage can be a major concern.
There are a couple of current sensor manufactuers who believe that they have deveoped/ improved their current radar technologies enough to differentiate between moving targets and turbine blades with good results(and have currently installed this at at least three locations,i can think of off hand).
There are also some new companies who are developing new infill technoligies which can be placed virtually anywhere without receiving windfarm interference. These systems have been demonstrated with good results however it is fairly new technology and requires some robust work to get it to full approval status
Windfarm issues not only cause unwanted clutter in traffic area they can also cause track suppression and track deviation (to name two other issues) as signals are suppressed in and around windfarms and ac returns are picked up from multipath results caused by turbine blades.
Not too sure if that helps, hopefully it should