There are three wind classes defined by the International Electrotechnical Commission (IEC).  IEC I defines high winds from 10 m/s.  IEC II defines medium winds from 8.5 m/s.  IEC III defines low winds from 7.5 m/s.  Vestas’ newest turbine, the V112-3.0MW, has a cut-in speed, or the minimum wind speed necessary for the blades to spin, of 3 m/s.  More information on wind class can be found at