Strange device.
The 3.9A at 57V to start with.
Then peaks out at 250W at 500RPM.
At 150W output, the coils are dissipating 335W of heat. Not very efficient, 31%?
Seems like anything that slow, with a limited amount of power, would not be the best choice when trying to match the balance of a windmill.
I can't think of anything it would be very suited to.
Maybe the large version of the HF garden mill blades?
G-