Page 11 - North American Clean Energy September/October 2019 Issue

This unpredictability is a fundamental unknown associated with ballasted systems. On slightly sloped roofs, thermal dilatation and contraction can make the PV array shift slightly over time; adding a few anchors to make sure the array doesn’t crawl can be seen as a good practice.
When a racking starts to lift up under extreme wind events, it starts to react to wind in an entirely different way than when it was flat on the roof. Different racking manufacturers will have different tolerance to such lifting and bending
of their racks, so the project developer should inquire about maximum lifting that is allowed for a given product. More lifting means more unknowns.
Also, concrete blocks can degrade over time, especially if poor quality concrete is used. If blocks lose part of their weight, or break apart and fall of their ballast trays, the integrity of the solar array can be compromised.
Even anchors are not always fully
understood. It’s important to consider
eccentricity on anchors when engineering
a solar array. For instance, if the loads
are not applied directly over the central
axis of the anchor, forces applied on a
metal rail beside the anchor can become
C
a sort of lever. That will make the anchors
M
weaker than their maximum rated forces.
Y CM MY CY CMY K
Rail-based racking systems that can be mounted directly over the anchors, with very little surface touching the roof, will also reduce roof wear and tear, which is usually safer over time.
Manufacturers must also understand anchor placement, and how the racking system distributes the forces on the anchors. Done properly, this allows the installer to place fewer than one anchor per panel (which is more typical of “rack” or “tray” based racking systems that can use up to 2 anchors per panel).
As climate change provokes harsher weather events, hurricanes and more frequent stronger winds, project developers should thoroughly consider the advantages of anchors. To limit damages and risks associated with anchored systems, ask professional roofers (ideally the same team that installed the original roof ) to integrate the anchors into the roof. Offering a single
warranty on the entire roof system, including anchors, will help bring peace of mind to building owners.
In summary, because wind deflectors may bend and ballast blocks
may degrade over time, PV array lifting can change the aerodynamics
of a racking system, rare strong wind events will be more frequent in
the next decades, and new knowledge, science and Building Codes are
bringing better understanding of the effect of building size and shape
on a solar array, anchors are a compelling choice. Solar developers
should take time to investigate the option of anchoring their solar
GEN4_Dynapower_NACE.pdf 1 8/23/19 3:48 PM
Alexandre Vanasse is VP Business Development at Opsun. Opsun engineers, designs, and manufactures custom mounting systems for PV installations, for both rooftop and ground mount.
Opsun /// opsun.com
1SEAOC, “STRUCTURAL SEISMIC REQUIREMENTS AND COMMENTARY FOR ROOFTOP SOLAR PV ARRAYS PV1- 2012” and “WIND DESIGN FOR SOLAR ARRAYS PV2-2017”.
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