:confused:

What is the conversion factor for an area of 25,000' square foot converted to Horsepower with a wind speed of 20 MPH?

There is another factor that is important here : the conversion efficiency (which is never 100%).
The size and aerodynamic shape of the windmill blades is extremely important in this efficiency.
The produced power is a squared function of the surface area of the blades, and a linear function of the blade shape.

There is a lot of more and very interesting information on this Wikipedia website (http://en.wikipedia.org/wiki/Wind_turbine)