And were getting another snow storm. If this is an example of how winters will be from now on, figuring out a system for keeping the panels clear is looking like a necessary investment in time and some experiments.
The problems with this seemingly simple task, is the wide range of variables involved.
I once heard that the Eskimo language has over 100 words for the different kinds of snow, and I am beginning to see why.
So far I have observed several things
1. if the temperature of the panels gets to slightly over 32, the panels will clear them self.
2. if the sun can hit the black panel surface, the melting will proceed nicely if the ambient temperatures allow the panel to raise above the 32 degrees, but if it is colder than 20F,even full sun on the panel will not be able to get the panel warm enough.
3. if snow remains on the panel, for a couple of sunny days, the water melting off the panels will saturate the snow bridging the 1" horizontal gap, and can freeze (like an Icicle) and then the ice forms a dam that holds the snow which needs to fully melt before the melting snow above can slide off
4. wet snow that freezes on the panel with the temps staying low will stick strongly to the panel surface, lite fluffy snow will easily blow off the panels.
The moisture content of the snow, the ambient temperatures as well as full sun or not are all strong variables that will effect the panels clearing.
Possible approaches and considerations:
A mechanical snow sweeper would have to run during the storm to prevent the buildup of snow.
Expecting a sweeper to move 5-12 inches of snow that has frozen to the panel surface would likely stress any reasonable mechanism.
Warming the panels and covering the gaps to allow the snow to slide off on its own may be the best approach. The issue then is how to get the heat to the panels and how to get the heat without it requiring more energy that is lost due to the lost electricity from the PV.
Playing with the real panels on the roof is way too dangerous, so I built a simple test fixture with my two spare panels so I can experiment safely while we are still in the deep of winter.
Changes to the jet stream due to climate change will likely make this type of winter more common, so it is something that needs to be looked at. Ice dams and roof over stressing due to the heavy snow load are also of concern.