http://en.wikipedia.org/wiki/GE_Wind_Energy The rotor swept area is 4657 m^2, and wind speed is 11.5 m/s. Produced power 1.5MW. I assumed that the air density is 1.2kg/m^3, and computed, that the theoretical upper limit for produced power would be 4.25MW. This was obtained by computing the kinetic energy in an air mass of cylinder shape. So the turbine extracts 35% of the kinetic energy of the air flow? Is that a reasonable percentage? Looks quite large to me. How could the three blades with relatively small surface area extract this much?