Snow, ice and cold: what winter really does to your panels

Snow is the first worry of every new customer. It is a fair one, but field experience puts it in perspective. A module tilted at 35 degrees or more almost always clears itself: smooth glass, the residual heat of the cells and a low sun are enough to make the layer slide off within a few hours of a storm.

What surprises people more is that cold improves performance. A photovoltaic panel loses about 0.34% of its power per degree above 25 °C. At -15 °C that coefficient works in your favour: the voltage rises and the module produces beyond its rated power. A clear February day at -20 °C can therefore beat an overcast day in July.

The real winter constraint is not snow, it is day length. In Quebec City the sun rises at 7:30 a.m. and sets at 4:10 p.m. in late December, and its low angle lengthens the path the light travels through the atmosphere. That is why December production comes to about 40% of June production on an identical installation.

Two design decisions genuinely help. Tilting the array more steeply than the annual optimum (50 to 60 degrees rather than 35) favours the low winter sun and speeds up snow shedding. And a raised ground mount, where the site allows one, makes manual clearing possible on the rare occasions it becomes necessary.

Never climb onto a snow-covered roof to clear panels. The production you gain is never worth the risk, and a roof rake used from the ground is enough in the vast majority of cases.