Fires in Photovoltaic Systems: Lessons Learned from Fire Investigations BRE research meeting
Over the past decade the number of new photovoltaic (PV) system installations has increased sharply throughout the world. With this growth, the associated risks grew significantly. This included an increase in the number of fire incidents involving PV systems. For example, it is estimated in the UK we have suffered over 90 fires directly attributed to PV systems. This has drawn the attention of the fire safety community and facility managers.
This article will assess some of the fire risks associated with of PV system installations based on fire investigations conducted in the UK, it is based on a meeting held at the BRE, Watford, which examined the root causes of PV fires.
The growth of photovoltaic system roof installations has been a result of public incentives for green energy. Some of the fire incidents associated with PV systems involved large roof fires and were often followed by an interior compartment fire. Some of these fires even resulted in the loss of the structure. The investigations into these fires revealed that DC arcing and the ignition of combustible roof insulation, often polyurethane or polystyrene foam, were often contributing factors in these fires.
The losses that have resulted from these events could have been reduced by implementing a risk analysis approach in the early design stages of these installations. This should include evaluating the fire risk of the most common failures associated with a PV installation, such as cell mismatch, DC arcing, and localized fires in connection boxes or PV modules.
At the same time, in England there was a short time period for building owners to access the public incentives, before they closed. This resulted in compression in the timing for engineering, procurement, and construction of these projects, which resulted in the lack of standardization for the specific PV materials. This along with the inexperience of installers led to an undervaluation of the fire risk associated the PV system and the building housing the installation.
The available data on PV plant fires includes fire incidents ranging from fires in an electrical connection, to a limited fire of few PV modules, to a large fire on the roof of the building spreading inside through the skylights.
The chart above refers to the number of incidents related to fires of various magnitudes that involved the PV system installations in England.
Further analysis of the data shows the number of fires peaked in 2012 following the first wave of installations. Since these fires involved new installations, the lack of qualifications of designers/installers played a role in these fires. This included the incorrect management of shading, the exposure of plant components to substandard conditions (heavy water condensation under the panels), low quality components, crushing of cables during the installation, under-evaluation of typical DC current behaviour, and mismatch of PV cells.
The research also highlighted that, fires are more likely to occur within the first two years of installation, or after six years of installation. The first likely to be caused by poor design or installation, the second by age/wear/tear.
Additionally, after 2012 the number of fires involving PV system installations has dropped as the market for PV-related services decreased. This has led to a better qualified workforce to install these systems. At the same time, better product standards and an increase in national regulations have also helped. Moreover, after the first relevant fires occurred, most PV panels producers started to include fire resistance requirements in the installation procedures.
Based on this assessment, the following common fire scenarios were observed:
- A building compartment fire spreading through openings and propagating to the roof
- Fire starting in PV modules installed on a roof with fire spreading to the building compartment.
- Additionally, PV plant components on a roof or on a building façade could:
- Alter the spread of fire outside or throughout the building.
- Result in combustion products interfering with the smoke and venting systems.
- Be an obstacle to firefighting operations.
- Introduce a safety hazard to firefighters as a result of the presence of energized electrical components.
The most common components identified are DC isolators – this would suggest that buildings need a PV maintenance schedule, to check and assess the condition of components within the installation. Why? Well the photo below shows an installation which the customer had called an engineer in to examine, as it was ‘smelling funny’. This picture was taken shortly before a fire that caused over £150,000 worth of damage to a domestic property:
Anything wrong with this? – Look at the isolator on the left – it is an AC isolator being used on the DC side. This caused the fire below:
A preventive fire risk assessment on the PV installation and roof configuration could easily identify the inherent dangers associated with coupling a strong fire load with an almost unavoidable ignition source. Also, skylights or the smoke evacuation systems can be a pathway for internal fire spread.
Based on the results of investigations of fires that occurred in PV system installation in England, there is a need for a comprehensive review of the fire and building regulation requirements for PV roof installations. Specifically, these requirements should address combustible insulating and roof materials located below active PV system components.
BRE are suggesting the flow chart above be followed in the event of a thermal event being witnessed or the risk assessment suggesting a thermal event is a high risk.
They key suggestion is maintenance and servicing of systems – which can only be a good thing!