The snow could be cleared off with a shovel, but then you have to either pay someone to do it in the case of industrial solar, or in the case of home solar, go up on your roof when it's covered with ice and snow, not the safest maneuver. Defrosters might be possible but that might use more power than the panels generate. You'd have to raise the temperature of the panels to above the freezing point of water, which might be a change of 20 or 30 degrees F on really cold days. Some years are worse than others- 2014 was really bad, I didn't see bare ground until late April.