SOLAR ARRAY ALTERNATIVES
(A Response to Questions About Construction)
As Found in the January/February 2015 issue of “Minnesota Community Living”
By: Walt Burris, BEI Exterior Maintenance Corp.
In the January/February 2015 issue of “Minnesota Community Living” there is an article on page 10 by Matt Drewes addressing many of the issues surrounding the installation and maintenance of pedestal-mounted solar arrays. Specifically, he raised a number of considerations regarding the impact of these arrays on warranty and insurance issues if the solar array is mounted over the top of an existing shingle roof.
This response is not intended to discuss the pros and cons of the concept of solar. Nor is it intended to critique Mr. Drewes’ observations, which were spot on. The hope is that this response will elaborate on the concerns he addressed and review a relatively new alternative to the pedestal-mounted solar array. This alternative is an array that mounts flush to the roof deck, allowing it to serve as roofing material. There are no shingles involved with the installation of a flush-mounted solar array except those around the perimeter of the array.
Under Mr. Drewes’ paragraph titled “A Force of Nature” he accurately expressed concerns about the additional weight added to the roof structure related to the solar array. With the pedestal-mounted array, not only is there weight added to the roof, the added weight is concentrated on the pedestals. This combines the entire weight of the solar array on relatively small areas of the roof structure. In contrast, the weight of the flush-mounted solar array is distributed uniformly across the surface of the roof. In addition, with the flush-mounted system, there is no need to be concerned that an installer might use fewer pedestals in order to reduce cost, thus increasing the weight at each of the mount points. Regardless, the ability of the roof structure to handle additional weight must always be determined, as any new system does change the total weight of the materials on the roof.
Mr. Drewes’ next observation is the change of wind loads on the roof surface because of the space between the bottom of the array and the roof surface and the height the array projects above the roof surface. The space between the surface of the roof and the underside of a pedestal-mounted array may vary from two inches to as much as nine inches. The height at the top surface of the array can project as high as 12 inches or more from the roof. The risk of unusual wind loads that a roof was not designed to handle becomes very real with the pedestal-mounted arrays, as Mr. Drewes pointed out. Flush-mounted panels minimize the potential additional wind load created by the panels themselves, creating no more wind load than a skylight would. The flush-mounted panel has a very low profile of about two inches above the surrounding asphalt shingles. On roofs with wood shakes or metal shingles, the panel might even be flush to the surrounding roof surface material, further minimizing the impact of wind on the array.
Lowering the height of a pedestal-mounted solar array wouldn’t necessarily provide a perfect solution to the wind-load concern. If the space under the pedestal-mounted array is too small, collection of debris under the array could inhibit roof drainage much like an ice dam, forcing the water up slope and under the shingles, resulting in leakage. There are no such drainage issues with the flush-mounted array. Since the flush-mounted panels are mounted directly on the roof deck surface and serve as the weatherproof surface (much like a skylight), there are no penetrations to caulk, no potential leaks and no shingles to damage or age underneath the array.
Another advantage of the flush-mounted array is that, when the time comes to replace the roof shingles, there is no need to remove the array before removing some of the shingles because there are no shingles under the flush-mounted array. This avoids the significant cost of removing and reinstalling the solar array in order to get at the shingles. There will be further future savings in that the roof replacement will cost less because the portion of the roof covered by the array will have no shingles requiring replacement.
As Mr. Drewes points out, there is always the danger of developing a leak around one of the array pedestals, the repair of which would require disassembly of a portion of the array to address that leak. Since there are no exposed penetrations under the flush-mounted array, this is never an issue. And, there are no shingle warranty issues with the flush-mounted solar panels.
Hopefully these observations shed additional light on the excellent article Mr. Drewes authored in the January/February publication. This is still a fledgling industry and we can be assured that as it matures, there will be many significant changes. Will we ever see solar panels on multi family structures? Your guess is as good as mine.