Assessing Damages to Residential Solar Roof Systems
Solar is hot! We've all been at the gas pump lately and experienced the rise in energy costs. This, combined with yearly improvements on solar photovoltaic (PV) components efficiency is driving a boom in the residential solar roof market. As we take part in this energy revolution, we will be learning how these components perform after years of wear and tear, weather events and other exposures that lead to damages and failure of these new infrastructure elements.
There are two main types of residential solar roof systems that are being developed: solar shingles and roof mounted solar panels. The roof mounted solar panels are the typical installation we see in most roofs where these are mounted on top of existing roofs. The natural progression to this system consists in shingles that already have the solar cells embedded, creating a complete solution that serves as a roofing material as well as a solar panel. These are being developed primarily by companies like GAF and Tesla. Being that both of these systems are permanently attached to the structure, they're typically covered within most residential homeowners insurance policies.
The basic operation of solar cells consists of individual silicon cells wired in series and usually protected by tempered glass with an anti-reflective coating. These cells are laid on a back-sheet with several layers of lamination that support them. The solar cells convert energy from the sun into direct current (DC) electrical power, which can be stored, but its often converted to AC current by an inverter as it directly feeds the residence.
How long will my panels last?
Most manufacturers provide a 25-year warranty. Some published studies have found that after 20 years most roofs will still be generating energy to over 90% of their original production capacity. In an energy research study that evaluated over 250 homes for over four years, only two homes were found to experience failure. In both of these cases, the inverter that converts solar power into electrical power was found to be the causation for the failures. Nonetheless, the main hazards that could damage PV solar panels are windstorms, hail and snow, earthquake and fire exposure.
Wind Assessments:
When assessing damages related to wind, it's important to first evaluate design parameters. Approval Standard for Flexible Photovoltaic Modules FM 4476 (for systems directly adhered to the roof surface), Approval Standard for Rigid Photovoltaic Modules FM 4478 (for systems mounted on racks or rails) provide guidance for roof mounted panels after 2010. This means that this standard can be used as a reference to obtain the system uplift resistance rating as well as with the current edition of ASCE 7. Additionally, it is recommended to evaluate the manufacturer specifications and the ICC Evaluation Report if available, as they will very likely provide uplift resistance rating details.
In the field, check the perimeter of the module array by checking the corner areas and perimeter zone for bonding with the roof membrane. SEAOC PV2-17 states that the edges of arrays tend to be more flexible and easier to peel upward by wind than the interior portions, so it's important to investigate these carefully.
In the field its recommended to investigate the connections between the PV modules and the framing system, including the supports, fasteners, clips, couplings and adhesives. Most spot checks are recommended in the corners and perimeter areas looking for weak connections between the systems, while also checking for corrosion, fatigue cracks and displacement of the racks that connect panels.
领英推荐
After Hurricane Irma, FEMA published the Rooftop Solar Panel Attachment: Design Installation and Maintenance advisory, which has detailed recommendations for design, installation, maintenance and preparation of rooftop solar panels as it relates to wind resistance.
Hailstorms:
Neither ASCE 7, IBC, ICC AC428 nor FM 4478 provide wind-borne debris requirements for solar panels. FM 4478 recommends that designers specify panels that have a damage rating of VSH (very severe hail). Nonetheless, hail carries a lot less momentum than other windborne debris with considerably larger size under hurricane force winds, which means that airborne debris is probably the main risk factor that could damage the solar cells. The following image shows an example of a PV Module damaged by wind-borne debris during Hurricane Irma (ISVI, 2017)
Earthquakes
For seismic load concerns, greater focus is given to lateral forces. Small lateral displacement is generally allowed and accounted for in design codes, but significant lateral movement can cause damage to the solar cells. Generally speaking, the design loading for the elements of wind are greater than lateral earthquake loads so it is very unlikely for a solar panel to experience damage from an earthquake event by itself, unless of course, the structure where it is attached to displaces or collapses in a manner that would compromise the integrity of the solar system.
Fires
It's probably intuitive to think that fires can be very common on these roofs due to the presence of electrical components. Luckily, the solar industry has made it very unlikely for fires to develop due to malfunction of their designs. If there is a fire, it is more common to be relative to inadequate grounding of the electrical wiring. Grounding is achieved by having a copper wire that gets embedded to the ground that serves as a path for the current to dissipate in the ground if there's a malfunction. These wires are installed very similarly to those of your A/C Units, lanais and pool pumps. Nonetheless, fire risk is moderate due to the flammability of roof materials. Also, fire can originate from outside the solar system and then ignite it. This sequence can spread the fire further than if the solar system was not present.
Sources:
Note: Not legal or insurance advise.