In North America, over 75 percent of the roofs installed on residential construction projects are asphaltic composition shingles. If you live in an area that receives snow and ice, and your roofing material is composition shingle, you’ve probably never experienced a significant roof avalanche. The reason for this is the granules on the surface of the composition shingles function as friction. Snow and ice tend to cling to these granules while melted snow and ice in the form of running water work their way out from underneath the accumulated mass through gravitational pull. Many people describe this as “snow melting into the roof.”
If your roof surface is hard and smooth, as in the case of an installed solar array (i.e. glass), the melting run-off acts as an extremely effective lubricant between the panel surface and the accumulated snow mass above. As this happens, the panel surface becomes frictionless because there are no granules to allow run off as the mass is held in place.
The calculated snow load of a solar panel is approximately 800 lbs/panel (50 lbs/sq ft x 16 sq ft avg. panel). In the snowier areas of the country, that’s a wonderful thing, but it also comes with a caveat.
The incredibly heavy accumulated mass will eventually release and come barreling off like an avalanche, and when that happens, gutters are sometimes ripped off, shrubs are often flattened and destroyed and cars and other items in yards and driveways can be seriously damaged. These avalanches can damage expensive landscaping, parked vehicles, grills, gutters, plumbing vents and more — but even worse, they can harm people and animals in the surrounding areas.
As Vermonters, we’ve seen more than our fair share of injuries and property damage caused by snow sliding off roofs, and as a company with deep roots in the roofing industry, our interest in mitigating that experience is natural.
Managing (not to be confused with retaining) the snow accumulation on your solar array will slow the movement of the snow to prevent avalanches from occurring in the first place. Installing snow management solutions that were specifically designed for use on solar arrays will allow ice and snow to melt and shed off the array in a controlled manner, instead of releasing suddenly, and all at once, in the form of an avalanche. Because of the sheer weight of all that snow buildup, it’s imperative that the snow management system you choose is structurally sound and rugged in fabrication.
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For roofs with steeper pitches and areas that see heavier snow loads, multiple rows of snow management devices may be needed to properly manage the snow. If the area experiences snow loads greater than 50 psf, installers or roofing contractors may want to consider other options.
So, pay attention to those solar arrays in winter climates. Watch how snow and ice melts and falls from the array and be mindful of paths, sidewalks, driveways shrubs and, most importantly, people.
— Solar Builder magazine
[source: http://solarbuildermag.com/featured/do-you-need-a-solar-snow-management-system/]
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