I have 3 10 panel arrays, two are at a high enough pitch so that once the temp gets even a little above freezing the snow slides off pretty easily (which presents some other issues). The other is at a lower angle and so the snow stays a lot longer - I don't think it would take that much heat to do the job; but I'll admit I haven't done the math yet.
I'm working with a roofing company and considering playing with the same heat tape they use to prevent ice dams on roofs. I was just about to pull the trigger on a test installation and we got 6" of snow that has lasted the better part of a month. As soon as the snow melts, we'll probably give one array a try and will post here when I have something to report.
On a related note - we live in Eastern Washington, which is great for solar; but, in the summer (110 Deg F ambient air temp), I've seen the panel software (APSystems) report 70 degree C panel temps. Just for the heck of it, I went out and sprayed down the panels with a garden hose and got the temp to drop to 25-35 C and saw a 10-15% increase in power production which dropped off as the panels reheated. I'm wondering if a pipe with some misting nozzles might be a worthwhile investment, which I could do at the same time as a wildfire protection system.