Snow and ice will be shed on their own from the modules over time. Because the panels are dark in color, they usually warm up and clear themselves of ice faster than the rest of the roof.
When there is snow on top, then there is little if any light that gets through. Some people scrape them off after a snow, but many people just go dark in the winter and make up for it in the Summer.
Here is some helpful information on Net Metering.