FRISSBE outlines comprehensive safety measures to mitigate fire risks in PV systems, emphasising the importance of proper installation and maintenance

Installing a photovoltaic (PV) system on the roof of a building introduces new fire risks to the building.

First, the PV installations have been shown to increase the chances of ignition through the failure of any of the electrical components of the system.

Second, the PV installation can increase the consequences of a PV-related fire.

It has been shown that within the area covered by the PV system, fires can spread faster and to a greater extent.

However, once the fire reaches the edge of the PV-covered area, the spread typically slows down significantly and often stops after a relatively short distance.

Thus, PV systems increase both the probability and the consequences of a roof fire, and, consequently also the fire risk, as it is defined as probability times consequence.

In addition, a PV system on a roof will cause a change in firefighting tactics because it creates a substantial physical hindrance and because precautions must be made when fighting a fire in the proximity of a permanent current-carrying installation.

Effective safety measures

To successfully mitigate the consequences of PV-related fires and reduce the probability of them, effective safety measures need to be put in place.

If the proposed safety measures are to adequately serve their purpose, their effectiveness should be confirmed via reference to sound data from reliable scientific experiments or statistics.

Until there exists sufficient knowledge about the mechanics of fire risks and how to mitigate it, a precautious approach in the design should be applied.

In terms of PV installations on flat roofs, the risk can be mitigated through reduced ignition probability and reduction of consequences.

Good components and products, as well as installation practice and maintenance are all necessary for achieving risk reduction on the side of probability.

The material selection, as well as the quality and layout of the roof construction are cornerstones concerning fire consequence reduction and firefighter safety.

For limiting the consequences of a fire, it has been shown in experiments that the roof membrane type and the type of PV panels play a minor role compared to the type of insulation material.

Thus, for both renovation and newbuilds, the main recommendation is to use non-combustible insulation materials to avoid the insulation material contributing to the fire and prevent spread to the building below.

If other solutions are considered, these solutions should show a similar robustness in experiments where the entire system (roof segment and PV modules) is tested as it will be built, and at a scale that involves several modules.

Ensuring a safe implementation of REPowerEU

As part of the REPowerEU plan, the EU Commission has defined an ambitious strategy for making the installation of rooftop solar energy compulsory for all new buildings over a certain size.

This is now being implemented via the Energy Performance of Buildings Directive (EPBD) requiring solar energy installations on most buildings in the future.

This will result in the unprecedented transformation of the European building stock and a significant uptake in photovoltaic (PV) panel technology on rooftops.

This transformation has the potential to have significant benefits from a climate and energy perspective, but it will also bring new safety challenges that should be anticipated and addressed upfront.

A fault tree analysis by Mohd et al. (2022) of fires on rooftops with photovoltaics estimated that the expected number of fires is 29 fires per installed GW of PV per year.

This indicates that tens of thousands of fires related to PV systems are to be expected per year in the EU alone.

Given that the expected number of fires is so large, this guideline aims to provide guidance on how to avoid the consequences of a PV fire on a roof becoming significant.

Further to that, Clean Energy Associates (CEA) has performed more than 600 safety audits for rooftop PV installations around the globe, and it found that 97 percent of the systems had safety concerns related to ignition hazards.

Based on these investigations, it can be hypothesized that at least one ignition event is inevitable in the lifetime of any PV installation.

These results are in line with findings by FM Global, which has reported that they continue to see ignitions and fires in buildings that follow their recommendations.

The key objective will be to provide the right conditions to ensure a safe large-scale rollout of PV systems.

Recommendations from the insurance industry are generally applied for large industrial and commercial projects such as shopping malls.

Nevertheless, these fire safety measures should also apply to high-rise and high-risk public buildings such as schools, museums, and hospitals.

Note that recommendations from insurance companies have yet to be considered by national regulations and EU legislation.

As numerous aspects govern the fire dynamics of a roof with a PV installation,  assessing the fire risk of a PV installation solely based on the assessment of individual materials and components of the individual products can lead to erroneous conclusions.

Rather, it is essential to treat the PV installation as a system composed of several parts namely the panels, mounting equipment, and the roof buildup to assess the fire risk correctly.

All configurations with panels installed flat or at an inclined angle have proven to increase the extent of fire spread beyond what is expected on a roof without the PV system, and this has been evidenced both in real fires and in experiments.

Considering this, the PV Guideline by the FRISSBE team at the Slovenian National Building and Civil Engineering Institute (ZAG) focus on the four aspects: Ignition hazards, fire dynamics, roof construction and firefighting operations.

Recommendations for safe PV installation

In terms of the roof buildup for buildings with PV installations, a major distinction should be made between retrofits and new buildups.

For retrofitted roofs, research has shown that a typical buildup with EPS and membrane on top of the roof base requires a mitigation layer to prevent involvement of the EPS, which is strictly necessary to avoid a very large fire.

Following most insurance standards, this mitigation layer typically consists of a layer of non-combustible insulation with a new roofing membrane on top.

As the system behaviour is key for PV fire safety, it is recommended that the performance of the mitigation layer is confirmed via reference to sound experimental or statistical data.

For a new roof, one should avoid the use of highly combustible insulation on top of the roof base.

It is recommended to use a more fire-safe alternative, such as non-combustible insulation, with a roof membrane on top.

The recommendation for non-combustible insulation is based on publicly available test results, which show that the spread across membranes that the PV modules facilitate is independent of the type of membrane and that the ensuing fires are significant enough to involve combustible insulation materials in the fire.

The fire risk with PV panels on roofs is higher compared to roofs without panels, necessitating systemic-level fire safety assessments.

The fire dynamics in PV-related fires are primarily influenced by parameters such as gap height, panel inclination, roof buildup, and array configuration, rather than the panel type itself.

Close placement of PV panels to the membrane facilitates flame spread, involving all types of membranes.

Consequently, using non-combustible insulation materials and mountings is recommended for significant risk reduction.

Additional links:

Read Fire Safety Guideline for Building Applied Photovoltaic Systems on Flat Roofs by ZAG by clicking here.

Listen: New Guideline for PV Fire Safety with Grunde Jomaas by clicking here.

This article was originally published in the July 2024 issue of International Fire & Safety Journal. To read your FREE digital copy, click here.