Calculating the energy production of a wind turbine

The bottom line with a wind turbine is how much energy it produces.  Do not confuse this with the maximum power output!  Rated power output is only achieved at rated windspeed, which will only occur from time to time.  The energy produced depends on the average power and not the peak power.  This in turn depends mostly on the turbine’s physical size (diameter) and the site average windspeed.  Most of the energy will be produced while the turbine it generating less than its rated maximum power.  In these everyday winds, the power depends on the size of the turbine, and not it’s power rating.
Here is a chart I did that estimates annual energy production for different sized turbines in different annual mean windspeeds.  It is a bit pessimistic (turbines do exceed these predictions in many cases) but it shows the basic trends.

 

Manufacturers will offer similar looking estimates of the energy production of their turbines in kWh per year assuming various different site average windspeeds.  These figures can also be calculated, using the data for the wind turbine’s power output versus windspeed (the Power curve) and the data for how many hours per year the wind will blow at different windspeeds