Is it OK to add a thermostat/humidistat to the solar powered fans?

Air Vent would not recommend adding a thermostat/humidistat to the solar fan.

Air Vent would not recommend adding a thermostat/humidistat to the solar fan because we don't know how a low voltage device (solar fan) will respond by adding some additional high voltage components (thermostat/humidistat) to the power circuit. It may rob some power available to the motor going through the extra components.