Snow Management for PV Arrays: Expectations vs. Reality

Between the years of 2010 and 2012, several of Alpine SnowGuards’ customers reached out to us hoping we could provide snow management solutions for solar PV arrays. This was an entirely new snow management problem that was evolving right along with the solar industry.

This new problem stemmed from a situation where solar PV arrays were being installed on composition (comp) shingle roof surfaces that typically don’t shed “much” snow or ice. In this case, the word “much” needs clarification, as snow on solar is a widely misunderstood situation.

In the Northeastern region of the U.S., snow tends to fall and melt over the course of a week or two. However, it’s pretty common for snowfall from multiple events to accumulate, and remain on, comp shingle roofs for weeks – even for the majority of a winter season. Eventually, these accumulations will reach density and viscosity levels that allow them to shed off the roof in the form of an avalanche. A similar phenomenon occurs on cedar shingle roofing.

Homeowners with comp shingle or cedar shingle roofs would most likely agree that they experience a sliding-snow-and-ice event at least once or twice a year. These events are less significant and less dramatic on a comp shingle roof than they would be had a solar array been installed over the comp shingle. Homeowners in areas with high snow volumes, like the Rocky Mountains, are likely to experience similar situations (often with greater frequency than the events in the Northeast and East coast regions).

As we first began to analyze this problem, we approached it from the perspective we were most familiar with: roof-mounted snow guards.

Based on our experience up until that point, we felt that the “best practice” for managing snow on solar was to install a roof-mounted device just below the array. This required a minimum landing zone of 24” below the butt of the array.

On a typical comp shingle or cedar shingle roof, one tier of roof mounted snow guards might be enough of a barrier to manage the snow mass. However, we were now faced with a situation where the roof area to be managed was no longer comp shingle or cedar, with their high friction surfaces and water absorption properties. What we faced were solar arrays (glass, no friction) that in most cases needed added snow management devices as supplements to the roof-mounted snow guards.

Back in 2012, Alpine launched a solar snow management system called Solar SnowMax-Standard (see below image). The system clamps directly to the panel frame in the vertical joint between the panels, and can be used on projects with Ground Snow Loads up to 50 psf (psf gsl).

This is where Alpine differs from most other snow guard manufacturers. We recognize that devices can be built to hold back an amount of weight, but that doesn’t necessarily translate to the amount of snow volume related to that weight. Physically, these brackets, when installed properly and in the right quantities, will resist snow loads up to 50 psf gsl. However, due to the need to prevent panel shading, these brackets and rails are limited to a maximum height of 2”. Our Solar SnowMax Shade Angle Analysis gives an overview of how we came to that conclusion.

The Solar SnowMax-Standard system (installed upslope between tiers) is 1” in height. Do some of you already foresee the problem??? The brackets and bars will structurally manage the given loads, but the depth of the mass resting against a 1” and/or 2” barrier has limitations. According to NOAA’s National Severe Storms Laboratory, thirteen inches of snow equals, on average, one inch of rain in the U.S., although this ratio can vary from two inches for sleet, to nearly fifty inches for very dry, powdery snow under certain conditions.

Alpine does not believe or maintain that the use of 1” and 2” high rails on PV arrays will always manage the snow mass in steep-slope, high snow load regions, to the expectation of the building owner.

Within the roofing industry, there are snow guards that are 2” tall. They seem to manage the release of snow and ice adequately. Alpine has sold such systems since the late 1990’s. Solar panels do not behave like typical roofing products, though. As soon as a solar panel begins to collect sunlight and activate, it begins to produce heat. As this happens, snow and ice on the array begins to melt faster than the same snow and ice accumulated on adjacent roof surfaces. Perfect, right? The snow mass is managed in a way that it doesn’t suddenly evacuate the array, but it clears more quickly than the comp shingle roof itself, allowing the panels to produce electricity. Sounds great, and it is, but snow and ice will still slide from these arrays in varying amounts and at varying speeds, depending on variables such as roof pitch, snow load, vertical length of array, snow density, etc., etc.

Now enter the expectations of the consumer….

The ideal system prevents a sudden release, is low-profile for aesthetic reasons and for the need to prevent shading, is cost-effective, easy to install and will retrofit existing arrays. Our system does all of this, however, just like the comp shingle roof we talked about earlier, there will be times when snow and ice still come off. For the building owner who believes that snow guards will cure all problems, this is a less than expected outcome.

When Alpine first introduced solar snow management solutions, we intended for the PV frame-mounted snow guards to supplement the traditional roof-mounted snow guards. Alpine’s stance is that all solar snow management systems start with the installation of a roof-mounted snow management system installed below the butt of the array (with a minimum 24” landing zone). Even with the roof-mounted system, snow and ice will still come over the rails under certain conditions.

It’s the responsibility of the solar installer to plan new installations, while allowing for a roof landing zone and a roof-mounted snow management system to be supplemented by array-mounted devices. For existing arrays that do not have a landing zone, the installer should either remove panels to allow for the landing zone, or understand that the array-mounted snow guards alone are limited in height, and are therefore, also limited in function. You can learn more in our Guidelines & Best Practices: Managing Snow on New Solar Installations.

I hope this helps shed some light on a very important, and relatively new topic: Managing snow on solar.

Until next time….

Brian Stearns

President & Founder, Alpine SnowGuards

We keep snow in its place

www.alpinesnowguards.com

info@alpinesnowguards.com

888.766.4273

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Alpine SnowGuards designs, engineers, and manufactures snow management systems from our facility in Morrisville, VT. We work closely with leading roofing contractors, engineering firms, developers, solar installers and roofing manufacturers to ensure we deliver quality products that do what we say they’ll do. Alpine SnowGuards can help a building qualify for LEED® credits.

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