So we could say in a 20mph (8.9 m/s) wind and a 6 ft dia ( 1.8 m) prop there is .....
Unfortunately we cant capture all of it and most blades range in the 20% to 40% range so we need to add this into our formula.....
Now there are some other losses we have to deal with... The generator or alternator we are using isn't 100% efficient so we need to add this into the formula. We can say that our blades are 40% efficient and our generator is 60% efficient so... Our overall efficiency would be ( .4 * .6 = .24 ) 24%. So now we add that into the total and we get...