but a good rain washes the dirt off them for you, and as for the snow, the color and position of the panels makes it so the snow comes off of them pretty quickly with some sunshine.

In fact, in CT, we were outside 2 days after a larger snowfall. Nice sunny, though still cold, day. I think we were building a snowman, and shoveling out the walk. We got surprised as all of a sudden, almost ALL the snow slid off of the panels and down into the garden near the walkway.

The sun, even with the blockage, can heat up that black glass like surface, then the snow melts from below. At a point, the pitch of the roof and the water layer below just acts as a slide.