What are the fire risks associated with photovoltaic cells?

Understanding the Fire Risks of Photovoltaic Systems

When we talk about the fire risks associated with photovoltaic cells, we're looking at a combination of factors: electrical faults, material flammability, environmental conditions, and installation quality. While PV systems are generally safe and reliable, they are not immune to failure, and when fires do occur, they present unique challenges for firefighters and building occupants. The core risk isn't that the panels themselves are highly combustible; it's that they are always live electrical generators, and faults can lead to high-temperature arcs, sparking, and ignition of surrounding materials.

Let's break down the primary ignition sources. The number one culprit is DC arc faults. Unlike your home's AC wiring, a solar array generates direct current (DC) at potentially very high voltages (often 600V to 1500V for residential and commercial systems). If a connection becomes loose, a wire is damaged, or a connector fails, it can create an electric arc. DC arcs are notoriously persistent and can reach temperatures exceeding 3,000°C (5,432°F)—hot enough to melt glass, copper, and aluminum, and easily ignite roof decking, insulation, or dust accumulation. A study by the German Fraunhofer Institute for Solar Energy Systems found that in about 70% of PV-related fire incidents, an electrical fault, primarily arc faults, was the root cause.

Next, we have hotspots. These occur when a part of a solar cell is shaded or defective, causing it to act as a resistor instead of a generator. This localized overheating can degrade the module over time and, in severe cases, lead to thermal runaway, where the heat buildup accelerates uncontrollably. While modern modules have bypass diodes to mitigate this, failed diodes or poor manufacturing can render this safeguard useless. Data from underwriter laboratories suggests that hotspot temperatures can exceed 200°C (392°F) under fault conditions, posing a direct ignition risk to backsheets, which are often made of polymer-based materials.

The choice of materials in the module's construction plays a huge role. The front is tempered glass, which is not flammable. The real concern lies in the backsheet and the encapsulant (usually ethylene-vinyl acetate, or EVA). While these materials are designed to be self-extinguishing, not all are created equal. Some older or lower-quality modules used backsheets with a core of polyethylene terephthalate (PET) or polyvinyl fluoride (PVF), which have lower thermal stability and flame resistance. When exposed to sustained high heat from an arc or hotspot, they can pyrolyze (decompose) and release flammable gases, fueling a fire. The table below outlines common materials and their fire-related properties:

Component	Common Material	Key Fire Risk/Property
Front Cover	Tempered Glass	Non-flammable, but can crack and fall from heat.
Encapsulant	Ethylene-Vinyl Acetate (EVA)	Can decompose at ~350°C, releasing flammable gases.
Backsheet	Multi-layer (e.g., PET/PVF/Tedlar)	Flame retardancy varies; PET layers can melt and burn.
Frame	Anodized Aluminum	Non-flammable, but conducts heat to mounting structure.

Installation quality is a massive, often overlooked, factor. A system designed with the best components can still be a hazard if installed poorly. Think about it: these systems sit on rooftops for 25+ years, exposed to UV radiation, thermal cycling, wind, and rain. Poorly torqued MC4 connectors can loosen over time, creating resistance and heat. Wires routed without proper chafe protection can wear through their insulation. Inadequate grounding can leave nowhere for fault currents to go safely. The National Fire Protection Association (NFPA) notes that many fire investigations trace the origin back to workmanship errors during the initial install or subsequent maintenance, not a spontaneous failure of the photovoltaic cells themselves.

Then there's the firefighting challenge. For first responders, a burning building with a PV system is a nightmare scenario. The fundamental rule is "never cut into or spray water on an energized electrical conductor." But a solar array is energized whenever there's light—day or overcast. Even if the building's main breaker is shut off, the DC lines from the array to the inverter remain live at high voltage. This creates a "shock hazard zone" on the roof and in the attic where conduits run. Firefighters' standard tactics of ventilating the roof by cutting holes are severely restricted. Some departments resort to applying foam blankets or waiting for total darkness, which is hardly a rapid response. Statistics from the UK's BRE National Solar Centre indicate that although fires involving PV are rare (estimated at roughly 1 incident per 10,000 installations per year), when they happen, they result in 20-30% greater average financial loss due to increased firefighting complexity and collateral damage from delayed suppression.

Environmental factors add another layer. Bird nests under panels can introduce dry, flammable nesting material. Accumulated leaves and debris in commercial ground-mount systems are a real fuel source. In regions with high wildfire risk, like California or Australia, the presence of a solar farm or rooftop array can alter fire spread dynamics. While the panels might not be the initial fuel, the plastic components can burn, and the structural supports can fail, scattering debris. Moreover, hail damage or extreme wind events can physically crack cells and break electrical connections, creating latent faults that may ignite much later.

Mitigation is where technology and standards come in. The industry isn't standing still. We're seeing rapid adoption of module-level power electronics (MLPE) like microinverters and DC optimizers. These devices, attached to each panel, drastically reduce the high-voltage DC string wiring, limiting the available energy for an arc. Many also include rapid shutdown functionality, a code requirement in many countries (like NEC 690.12 in the US), which reduces the voltage in roof-run wires to a safe level within seconds of shutdown initiation. Furthermore, new testing standards like IEC 61730 and UL 790 specifically evaluate a module's fire classification (Class A, B, or C) based on its performance when exposed to flame on the roof under simulated wind conditions. Choosing Class A fire-rated modules is now a best practice for any roof-mounted application.

So, what does this mean for an owner or specifier? Due diligence is key. It means selecting high-quality components from reputable manufacturers with proven fire ratings. It means hiring certified, experienced installers who follow national electrical codes to the letter, paying special attention to connector installation, wire management, and labeling. It means considering system design choices—like using MLPE in high-risk environments or ensuring adequate access and pathways for firefighters are designed into the layout. It also means having a clear operations and maintenance plan to periodically inspect for physical damage, rodent activity, and connector integrity. The risk is manageable, but it requires respect for the technology's inherent electrical nature and a proactive approach to safety over the system's entire lifetime.