I have a old treadmill motor I want to convert into a wind turbine. I understand how to calculate power (P=IV or P=(V^2)/R) but my problem is that I don't know how to calculate the wattage for my generator because I don't understand what to use as my load. I plan on connecting the generator to a grid tied inverter but I don't know the kind of load it will put on the generator so I can't decide which watt rating I want. When the turbine is moving at a good speed I get 40V out of the generator. When I use a 1k Ohm resistor as my load my wattage is way low. What would be a better resistor or method to calculate how much wattage my turbine can crank out?