A typical wind power generator produces approximately 30 percent of the theoretical maximum power it could produce on average, as reported by the European Wind Power Administration and Global Wind Energy Council. Losses of efficiency due to the mechanical action of the generator are already included in the theoretical maximum.
The power output of a wind power generator depends largely on the availability of sufficiently strong wind, but wind turbines shut down in a very strong wind to prevent mechanical damage. Minimum wind speeds of 10 to 11 miles per hour are required for power generation, while wind speeds of over 50 MPH initiate shutdown in most wind power generators. Sustained winds of approximately 30 MPH lead to optimal power generation. As wind speeds are rarely in this precise range on a constant basis, the effective efficiency of most wind power generators is approximately 30 percent of the system's theoretical maximum.
The theoretical maximum power of any wind power generator is limited to approximately 59 percent of the available wind energy by a phenomenon known as Betz's law. Betz's law arises due to the need for some amount of air to escape the generator to allow new airflow to enter the generator, making it impossible for any wind power generator to capture 100 percent of the energy in the wind that drives it.