What do you mean? Weighted with the characteristic curve of a "typical" (or test) turbine? Or <v³> averaging? Mean with Raleigh distribution of wind speeds? With Weibull distribution?

In ManfromMiddletown's link, they apparently use the mean with the Weibull distribution.

How different just the wind power densities for the same mean wind speed can be, can be seen on the example of three measuring sites in this NREL table (they used Raleigh distribution), and the first graph on page 18 of ManfromMiddletown's source is also indicative. The turbine power curve, and different turbine power curves are complications on this. Here is a graph from Answers.com, showing 2002 data from the Lee Ranch wind farm in Colorado (power is turbine power and thus includes the turbine power characteristics, the curves are the Raleigh models):

_{*Lunatic*, n.
One whose delusions are out of fashion.}