I attended the Windpower Expo in Chicago last May. There were several vendors there that had samples of their blades on the exhibit floor. Everything I saw was made of fiberglass and fiberglass is invisible to RF. Radomes that protect radar antennas and microwave antennas are made of fiberglass for this very reason. What are these blades made of that are supposedly causing the interference? Carbon reflects RF, maybe the blades are carbon?
Most of the blades have CF or aluminum ribbing for lateral strength.
True, but the eddy currents (turbulence) when the blades are turning ARE visible to Doppler...that's how Doppler is able to detect winds. Doppler doesn't require a metallic target. It picks up minute particles and droplets that are moving in the winds. When there is little or no wind...no problem, but the stronger the wind, the more interference is created and shows up quite well on a WSR88-D.
Been there...watched it happen. But didn't get the t-shirt.
The blades are mostly fiberglass. Judging from the weather radar vs the Twin Groves Wind Farm in east central Illinois, it seems that most of the interference occurs when the blades are damp.