From my experience, solar alone can be an inconsistent source of electricity for a fan that must be on 24 hours/day (as soon as the sun goes down or it gets too cloudy the system stops). But, it is possible if you connect a few batteries to the system to overcome this; during the day the solar panels recharge the batteries, and at night the fan continues to run off the batteries. Although, from my calculations, the ROI is simply not there, especially if you consider the routine maintenance and inspections required of these systems.

If anyone else has found radon mitigation fans that run off renewable energy, i would be very interested too. Thank you.