Some numbers:
Based on the voltage drop when the load switches in the internal resistance of the turbine would come out about .83 ohms. If you use that value an additional load of 8 ohms would keep the voltage above 85 volts so no power loss from the inverter. It would appear the 1 KW rating is right at 100 volts at 10 amps using those numbers. You could then add another switch that turns on at say 97 volts turning on the other 8 ohm resistor. Assuming their are two 8 ohm resistors available. This would keep the total load the same as it is now. The turn off points could be around 87 and 90 volts. A poor mans pwm.
In any case the numbers may come in handy when trying to set the duty cycle on the board.
Power loss in the turbine at full power -- 83 watts
PS. Yes the FET on the board is only rated at 60 volts.