Solar Photovoltaic Guide
SCOPE
This white paper covers solar photovoltaic (PV) systems when installed on buildings or ground mounted with the goal of providing information related to operation, hazards, failures, and general risk management considerations. The paper does not include utility scale systems or solar thermal systems.
INTRODUCTION
Converting solar energy into electricity is not a new idea. The earliest United States patent for this technology was issued in 1888. Though the efficiency of PV devices was initially very low, only 1 to 2 percent, and has improved with changes in materials, the core idea remains: convert the energy contained in sunlight to electrical energy for use in the built environment.
The PV panels are constructed of semiconductor materials, primarily silicon, polymers, metals, and glass. The panels may be rigid or a flexible film. Most installations use a rigid panel. The panels sandwich the semiconductors and electrical components between a top layer of glass and a bottom layer, or backsheet. The backsheet itself may be multiple layers of polymer sheet material. When the sun impacts the solar cells inside the panel, electrons are dislodged from the semiconductor material, creating an electrical current. The current from all the cells is combined to form the panel output, then the output of all the panels is combined to form the system output. The theoretical total output depends on the number of panels and the efficiency of the panels.
Since the panels generate direct current electricity (DC), an inverter is employed to convert this power to alternating current (AC) and synchronize the power with the local utility signal. This allows the PV generated electricity to work with the utility power and to flow back into the grid when the power produced at the site exceeds usage. Power output varies with the time of year and the time of day. PV power uses the same electric infrastructure as all other electric power sources.
In the 1990s, government at various levels began providing financial incentives to install solar PV systems and passed laws and regulations related to how much renewable energy power companies must have in their power generation totals. These incentives and requirements have driven a rapid expansion of installed PV capacity. According to the Solar Energy Industries Association, the installed PV nameplate capacity went from 2,094 Megawatts (MW) in 2010 to 140,005 MW in 2022. The US Energy Information Administration (EIA) estimates that solar power contributed approximately 2.8% of all power generated in 2021, up from 0.1% in 1990.
Several major fire losses have been associated with PV installations, either directly or indirectly. A significant warehouse fire loss occurred in 2013 in New Jersey, in which the presence of the PV system contributed to a change in firefighting tactics and ultimate loss of the facility. A more recent loss occurred at a bottling facility in Arizona, in which a fire involving panels on the roof spread under and in the panels destroying a significant portion of the system. Amazon temporarily turned off all PV systems on all their buildings after experiencing at least six fires at various facilities in one year.
Relevant published standards include:
• FM Global Property Loss Prevention Data Sheet 1-15, Roof-mounted Solar Photovoltaic Panels
• FM Global Property Loss Prevention Data Sheet 7-106, Ground-mounted Solar Photovoltaic Power
• NFPA 70, National Electrical Code
• NFPA 70B, Standard for Electrical Equipment Maintenance
• NFPA 1, Fire Code
RISKS AND HAZARDS
Solar PV panels are solid state devices, meaning there are no moving parts, and the failure rate is very low. In a 2017 report, the Department of Energy estimated the failure rate at 0.05%. Panel failures are typically associated with a manufacturing defect, though the panels can be damaged by extreme weather. Even so, there are several hazards associated with solar PV installations that need to be considered, ranging from panel ground faults and fires to structural failure of the support system, which may include the roof.
ROOF MOUNTED SYSTEMS
For systems mounted on the roof of a building, there are several risks that need to be considered. In particular, the ability of the roof to carry the additional loads imposed by the system should be evaluated. The individual panels and supports may not weigh much, but the aggregate weight of several thousand panels and supporting structure, cables, conduit, etc. as found in large installations can be significant. Poorly laid out systems may impede roof drainage, which can lead to ponding and subsequent roof collapse. Because of the geometry of the panels to the roof, higher snow accumulations can be experienced because of drifting.
The system needs to be secured to the roof in some manner. Unsecured systems can move across the roof in high wind conditions, damaging conduit, and wiring, as well as the roof cover. Many systems use a simple concrete block ballast. Other systems use fasteners through the roof cover and into the structure below. The securement should be designed for anticipated wind loads and earthquake loads as applicable to the site.
The roof cover should also be evaluated prior to installation of the system. It is extremely difficult and expensive to replace the cover after a PV system has been installed. Serious consideration should be given to installing a new roof cover around the PV panels if the anticipated remaining service life of the roof cover is less than the anticipated service life of the PV system.
Fire is a major concern for roof mounted systems. The geometry of the panels to the roof tends to intensify the fire, and access limitations can hinder manual firefighting. Detection delays exacerbate these issues. When the roof deck or cover is combustible, especially on the light roofs common in the southwest United States, the fire department may decline to directly attack a fire involving PV systems. This could lead to a complete loss of the facility.
GROUND MOUNTED SYSTEMS
Ground mounted systems have fewer considerations than roof mounted systems because they are supported directly on foundations. Many times, these systems are incorporated as part of covered parking, and the structure is engineered as a canopy with the PV panels constituting the “roof”. Other systems are mounted on supports close to the ground. These systems should also be engineered for relevant wind, snow, and earthquake loads.
Because they are close to the ground, these systems also present a security risk, and adequate isolation of the systems components should be provided. This may be accomplished by fencing the installation, or by mounting the inverters and other components in secured enclosures in areas where fencing the entire installation is not practical. In some instances, the canopy-style installation may be in a public parking lot.
PANEL FAILURES
Failures can occur in three general phases of service. These are the start-up phase, the in-service phase, and the end-of-life phase. Many failures can reduce the power output of the panels or prevent power output. From a property protection perspective, failures that lead to ignition or other hazardous conditions are primarily of concern. Ground faults are one such failure. These can occur within the panels or in the associated wiring because of deterioration or improper installation or maintenance. Various other internal panel issues can lead to hot spots and an ignition of the backsheet.
The relative hazard of ignition is dependent on the location of the system. A roof mounted system poses the highest risk because a fire involving the backsheet exposes the roof cover. The cover can then ignite, and fire can grow in the shielded area under the panels. Not only is there a more vigorous fire due to the close surfaces, but manual firefighting can be hindered by the panels even if the fire department chooses to fight the fire aggressively. This leads to a larger fire than would be experienced without a PV installation present. Ground mounted systems tend to have less combustible material below and greater clearance from the backsheet, as well as better access for manual extinguishment efforts. Vegetation could be an issue and the space under the panels should be maintained appropriately.
CABLING ISSUES AND CONDUIT RUNS
Power is transmitted from the panels to combiner boxes on the roof, then to inverters that may be on the roof or on the ground. Wiring can be run in conduit or exposed as allowed by NFPA 70. All wiring and conduit runs should have adequate provision for expansion and contraction due to temperature swings over the course of a year. This can be accomplished with 90-degree offsets in the conduit run, creating a section that can absorb dimensional changes. This provision should also be applied to the interface between the roof cover and the panel structure. Exposed cabling should be secured to prevent it from being blown around in high wind conditions, which could lead to mechanical damage and fire.
INVERTERS
DC power produced by the PV panels is inverted to AC power for use and transmission on the electrical grid. Large units are typically mounted at ground level adjacent to the building or inside the building in an electrical room. The inverter and associated switchgear serve as the main disconnect point for the PV system. These installations require the same inspection, testing and maintenance as the rest of the electrical system (e.g., infrared scans, periodic cleaning and exercising of breakers, etc.) as described in NFPA 70B, as well as inspection testing and maintenance unique to the PV installation.
FIRE DEPARTMENT
It is important that the responding fire department is aware of the PV installation and has developed a pre-fire plan. This should include complete information on the location of all equipment related to the system, including position and coverage of the PV panels, location and operation of the inverters and switchgear, and safe roof access points. There is no guarantee that the fire department will choose to attack a roof fire due to safety. Even if the switchgear is off, the panels will still generate power as long as sufficient light is present. An unprepared department may delay firefighting until safety can be determined, and this could lead to a large loss.
GUIDANCE
• Ground mounted systems are preferred to minimize the fire risk.
• Where systems are installed on existing roofs, a structural analysis should be completed to ensure the structure will support the additional loads. A new roof cover may also be advisable in some circumstances.
• Proper design and installation of the system in accordance with the requirements of FM Global 1-15, NFPA 70, and any state or local laws is essential. Only qualified contractors should be retained.
• Consider installation of a fire detection system for roof mounted PV, such as linear heat detection.
• Panels selected should be of good quality design and construction as determined by independent testing. Once such independent testing organization is PV Evolution Labs (PVEL) https://scorecard.pvel.com/
• Notify the property insurance carrier and have the plans reviewed prior to installation.
• Work with the local fire department to develop a pre-fire plan.
• Inspect, test, and maintain the system in accordance with NFPA 70B.
CONCLUSION
Solar PV systems serve an important and growing role in the total power generation of the world. With the focus on clean energy sources and government incentives in place, installation of these systems is likely to accelerate. While there are positive aspects to these systems, the risks and necessary risk management can’t be ignored. Site-specific evaluations before and after installation, and careful review of plans prior to installation, can help minimize the risks.
Sigma 7 Paragon Risk Engineering can provide risk analysis and loss prevention services (Solar PV Roof System focused visits or plan review for new Solar PV Roof System Installations) for owners and operators of sites that utilize Solar PV Roof Systems.
Sigma7 Paragon Risk Engineering is a worldwide risk engineering provider with over 200 engineers in 35 countries with extensive industry experience and technical expertise. We are fully independent of any insurance company or broking entity and are part of the Sigma7 group of companies, with colleagues working in other specialized areas such as forensic post loss accounting, Business Interruption pre-loss assessments, worldwide /security threat monitoring, on line e-training for site personnel and financial/risk due diligence.
For more information about how Sigma 7 Paragon Risk Engineering Consultants can help protect your facility from the risks of Solar PV Roof Systems, contact us at.
REFERENCES AND RESOURCES
https://www.smithsonianmag.com/sponsored/brief-history-solar-panels-180972006/
https://www.eia.gov/energyexplained/electricity/electricity-in-the-us-generation-capacity-and-sales.php
https://www.nrel.gov/news/program/2017/failures-pv-panels-degradation.html
https://www.gses.com.au/what-causes-solar-pv-fires-and-how-to-prevent-them/
https://www.cnbc.com/2022/09/01/amazon-took-solar-rooftops-offline-last-year-after-fires-explosions.html
https://galeassociates.org/knowledge/from-our-blog/building-enclosure-design-consulting/considerations-for-snow-loads-on-roofs/
https://www.nj.com/burlington/2013/09/dietz_and_watson_warehouse_fire_solar_panels_make_battling_blaze_much_harder_officials_say.html
https://scorecard.pvel.com/top-performers/
FM Global Property Loss Prevention Data Sheet 1-15, Roof-mounted Solar Photovoltaic Panels (January 2023 revision)
FM Global Property Loss Prevention Data Sheet 7-106, Ground-mounted Solar Photovoltaic Power (January 2023 revision)
NFPA 70, National Electrical Code (2023 edition)
NFPA 70B, Standard for Electrical Equipment Maintenance (2023 edition)
NFPA 1, Fire Code (2021 edition)
