Hello physics forum, I am currently trying to figure out how to pick a generator for a horizontal axis mini wind turbine based on specs. I plan on buying a DC motor to use as a generator with blades directly attached to motor shaft. My goal is for the motor to be most efficient at 25mph wind speed, but also be able to generate power at lower wind speeds. Diameter of blades: 6" Wind speed from 0 to 25mph My calculations so far: Max power = 9 watts @25mph wind speed w/ perfectly efficient blade using equation: P=0.5*0.593*ρ*A*v^3 where P is power (W), 0.593 is Betz limit, ρ is air density (kg/m^3), A is swept area of blades (m^2), and v is wind speed (m/s). Is there any way to approach buying a generator mathematically? Some specs sheets on motors I see have voltage/torque/rpm/current@max efficiency, and stall torque/current. Thanks!