Tax incentives, power buy-back programs, and ever-increasing utility bills help justify the cost of solar panel installations for home and business owners. The cost-benefit analysis and the return on “solar investment” look attractive on paper over a 20-year period; However, the underlying risks of rooftop solar panels are generally not well known to homeowners and insurance companies.
Some of the risks associated with solar installations can be particularly serious in areas of North America that experience very cold temperatures and cold and ice in winter. Solar panels placed on roofs that are not structurally sound can cause the roof to collapse or water intrusion. Solar panels are subject to large fluctuations in temperature, exposure to humidity and freeze-thaw cycles. Direct exposure to the external environment accelerates wear and increases the likelihood of component failure. Since there is currently no uniform standard in North America to provide advice for the structural design, installation and maintenance of solar panels, the risks vary on a case-by-case basis depending on the characteristics of the project, including size, location and installation approach.
For residential properties, some risks arising from solar panels on the roof, such as damage caused by a hazard (for example, fire, windstorm and hail) may be covered by a standard home insurance policy, as they are generally considered to be part of the property. However, for commercial buildings, loss of business interruption resulting from a solar panel failure may not be covered by a standard policy. Therefore, commercial buildings are generally at a potentially higher risk of damage from rooftop solar panels than residential buildings, although statistical studies in this area are limited.
Solar farms share similar environmental risks with rooftop-mounted solar panels, for example, hail, freeze-thaw, and wind damage. However, they are exposed to additional losses such as frost heaving, broken foundations and significant movement due to varying soil moisture or flooding. The development of solar farms may present a risk of forest fires over a large area, although there are some ways to mitigate this risk. Given the amount of land required for a solar farm, aesthetics, proximity to residential areas, and the potential impact on risk to wildlife can also be concerns when developing a solar farm.
Many engineering standards require consideration of ice loading for structures sensitive to ice. ASCE 7 defines ice sensitive structures as “structures for which the effect of an atmospheric icing load (i.e. freezing rain) governs the design of part or whole structure ”. For structures such as steel power towers, guyed masts, ski lifts, etc., radial layers of ice can form around structural members, increasing their weight, internal stresses and windy faces. . As stated earlier, there is no generally acceptable structural standard for the design of solar panels. However, forensic experience and site inspections conducted after ice storms have shown that solar racks can be classified as ice sensitive structures. This not only affects the design of the solar racks (support frames), but can also change the ultimate load applied to the support structures / foundation system.
Photovoltaic systems are generally designed for a lifespan of 20 to 25 years; however, in cold regions the effective life expectancy of floor mounted systems may be shorter due to certain aggressive environmental conditions. Frost heave can affect power generation and even the stability of solar racks. At subzero temperatures, the water in the soil freezes, and the volume of soil around footings, for example micropiles, increases. This results in an upward movement of the solar racks. Depending on the type of soil, this cyclical frost heave motion can occur at a rate of 1/64 “to 3/4” of an inch per day for a recessed foundation under certain weather conditions. The risk of frost heave is higher in clay and silt and lower in sand and gravel, according to the US Army Corps of Engineers.
Frost heave causes structural deflection and angle changes of the solar panels. Non-uniform deviations of the sole system can cause failure or deformation of connections, shelving systems, disconnection of conductors and / or grounding in frozen ground. Appropriate design of PV systems for the possible impact of frost heave can reduce the risk of damage. For example, footings or micropiles can be designed below the frost line according to building code recommendations; However, determining the frost heave force on piles is difficult, although 15 psi is a generally recommended value. However, the piles can be pushed out of the ground even if they are driven below the frost line.
PV systems mechanically attached to sloped residential roofs typically weigh between 2 and 4 pounds per square foot. This is not a considerable weight, as an intact and well-designed roof should support this extra load with little to no modification. However, changing the structural systems or loads of an existing building may require code upgrades that may affect the original building design due to more stringent requirements. The gravity loads of ballasted PV systems on flat roofs are considerable and can place an additional 5 to 30 pounds per square foot on the roof framing for which detailed structural analysis is required.
The main challenge for both installation methods is that the weight of the solar panels is not evenly distributed over the roof and can have critical local effects on some structural elements. If detailed drawings for the location of the panels are not produced, the actual roof loads will differ from the design loads as repositioning of the solar panels on the roof at the construction stage is likely.
Water intrusion and water accumulation
Solar panels on a sloping roof are attached to the roof frame using mechanical fasteners. For existing buildings, this means that many holes must be drilled in the roof system. Anchor holes are usually sealed to prevent water leakage into the building. However, seal performance is a factor in installation accuracy and long term behavior of the sealant’s exposure to environmental elements. Vibration of panels due to wind forces, as well as thermal expansion / contraction cycles, can cause joint failure and water intrusion.
On flat roofs, solar racks can disrupt the water drainage path to roof drains depending on their support configuration. The ballasted solar racks are also spaced in parallel rows on the roof and can cause rainwater or snowmelt buildup between the modules. Puddles can occur in these strip regions which can lead to accelerated delamination, cracking and sagging of the roof and ultimately water intrusion into the building.
Assess the risks in advance
Installing solar panels on flat or sloped roofs can change roof geometry and capacity, especially taking into account exposure to environmental loads. Snow load, ice load, wind load (plus wind over ice), additional dead load, water accumulation, drainage obstruction and water intrusion not only influence structural design of buildings, but can also affect their long-term functionality.
The risk of damage to buildings with roof mounted solar panels is simply higher due to the presence of the panels. Insurers may unknowingly bear a considerable portion of this risk, and homeowners may be unaware of the risk exposure. The lack of a uniform engineering standard, which includes all aspects of design and installation, especially for flat roofs, adds more complexity to the liability arising from solar panels.
Footing movement due to frost heave can lead to permanent damage to solar rack and power generation. Wind damage to solar parks is likely due to the complexity of the wind design and the effect of vortex which can place excessive uplift load on the panels.
Simply put, the design of solar farms or rooftop solar panels is a multi-faceted issue that should be evaluated by qualified engineers and insurers should know if the property includes any rooftop solar panels to take into account. take into account the potential risks.
Ben Daee and Sadegh Khosravi are engineers at JS Held, a global consulting firm providing specialist technical, scientific, financial and advisory services.
The views and opinions expressed in this article are those of the author and do not necessarily reflect those of pv magazine.
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