Regarding AC wind turbines, if the turbine's voltage does not match that of the load, a transformer would be necessary, and the turbine power curve should be adjusted to show the useable power output (the power output from the transformer) versus wind speed.  It seems unlikely that someone would install a 50 Hz wind turbine to serve a 60 Hz load, but if that was the case an AC-DC-AC converter would be necessary, and again the power curve should be adjusted to account for the corresponding losses.  If the turbine produces variable frequency power, again an AC-DC or AC-DC-AC converter is necessary, and the power curve should reflect that.