This is the right question. Warehouse roofs are designed to counter snow load and wind uplift at "x" mph. Once those forces are exceeded, you can expect damage.
this might be a bit silly but... maybe not... could you siphon off a little bit of power from the panels to heat an array of heating wires just enough to melt snow on impact and then it'd drip off like rain?
Not at all. Afaik you won‘t even need wires for that. You can occasionally feed energy into the panels which produces a bit of heat there. It wouldn’t even have to melt (a lot) of snow - just enough that the bulk of it slides off.
That snow will then still be on the warehouse roof though.
But I wonder if some "maintenance bot" could eventually become established that's designed around the benefits of the regular grid structure. Perhaps "walking" from socket to socket like a gravity-well capable descendant of Canadarm? Wouldn't start as snowplows, but for maintenance tasks at lower frequency, large solar parks could even make very expensive units worthwhile, and from there the magic of mass market might bring prices down sufficiently far.
The parent comment is that the roof is designed for the structural load of the snow load and not much else. Solar panels need ballast, racking, thick teck cable, etc and can easily overload the structural design. I’ve just gone through this on a warehouse I own. Cheaper to build over the parking lot than add structural reinforcements for every column.