If only after an unfortunate accident you first consider snow retention devices on a sloped roof with solar, it may be too late, says representatives of S-5!. A successful snow guard should be installed to the roofing structure with enough space to stop sliding snow—and that often changes solar design plans.
“We hope a solar contractor has anticipated the need for snow retention, because the most effective way is to use an engineered system that is directly attached to the roof itself and is designed specifically to resist those sliding forces which are calculated on a very job-specific basis,” said Rob Haddock, founder of S-5!, a snow retention system manufacturer.
If solar panels are installed near the edge of a roof, that leaves little room to secure a snow guard to the rooftop that can successfully hold back snow. And S-5! warns against installing retention devices directly to solar panels.
“The forces on a snow retention system can be enormous—much more than what you might first suppose,” Haddock said. “When we see people try to resist that force with some sort of device that attaches directly or indirectly to a module frame, it’s really scary. The module frame is not designed with the intent that something is going to pull on it in a lateral direction.”
The best plan of action for solar installers in snowy areas is to consider snow retention products when working on a project’s initial design. Not all roofs inherently need snow guards. If a solar array will be installed in an area where sudden avalanching snow isn’t a concern, then solar installers can proceed with any array design they want. But if snow shedding threatens life or property—maybe expensive landscaping or parked vehicles—then snow guards should be considered.
The best way to retain snow is to leave a significant amount of space between the solar array and the roof edge so snow can compact and densify on the roof area. The solar installer has to give up some roof space to account for this, but it’s the most effective way to retain snow. The shadows cast by a snow retention system also have to be considered. A snow guard has to stick up above the plane of solar modules, and its shadows can cast even higher. You don’t want solar panels affected by shading losses.
It’s also important to remember that a roof with no snow avalanche hazards before solar will almost always be a concern after its surface is covered with glass.
“There’s a lot of friction all over an asphalt shingle roof,” Haddock said. “The snow bank gets sort of interlocked with that structure and it provides a lot of frictional resistance. When you’re installing solar, you’re converting that roof into a slippery roof. You’re entering a new hazard, because snow had never slid off of it in the past, and now it’s potentially going to.”
Glass is obviously slippery, and when coupled with warm, dark solar cells that aid snow melt, a solar panel’s surface can be very slick.
“You now have a bank of snow that’s lubricated from melt water,” Haddock said. “All of that vector load gets transferred somewhere. If it’s not resisted, the snow bank will slide off the roof.”
S-5!’s pipe-like DualGard and X-Gard systems are just two of the company’s roof-specific snow retention products for metal roofs that help to hold back potentially damaging avalanches. Solar installers should review different snow retention systems before designing an array and installing that first solar panel. Any system chosen should be proven by independent testing and engineering calculation to resist vector forces that vary widely on a job-specific basis.