Only when they turn. That depends on whether it's windy... and whether the sites were well-chosen.
I drive along eastern Massachusetts fairly often. On Mass. Rte 3, around Plymouth, there's a turbine just off the road. I've never -- I mean NEVER -- seen the blades move. Clearly, somebody got overexcited about green (or maybe THE green) and put this in with OPM (other people's money).
I’ve never — I mean NEVER — seen the blades move.”
Can’t speak for Mass and their setup, but here there is a strong tax benefit for writing off “maintenance” of your wind turbine. You make money by spinning the rotors until you have made a small profit, then take it offline for maintenance, which zeroes your corporate profits and shelters other income due to the tax writeoff on maintenance.
In other words, tax dollars go from someone else to your account, which stops if you spin the turbine all the time and make a real profit, which is heavily taxed.