What causes solar panel fires? A study of where PV fires start
A Bridgehill research study by Thor Brubakken reviews incident records and published research to show where solar PV fires start, why components fail and how fire spreads on roofs.
Recorded solar panel fires most commonly start in the electrical system around the panels: connectors, DC cables, DC isolators and inverters. In none of the seven published incident series reviewed in a new Bridgehill study is the PV module itself the most frequently reported starting point.
The study, Fire causes in photovoltaic systems by Thor Brubakken, combines the PV Fire Intelligence incident register with published investigation reports, research and fire-service material to examine where PV fires start, why components fail and how fire spreads on roofs.
Where do solar PV fires start?
A key finding of the study is a component profile Bridgehill derived from a published synthesis of rooftop PV fire data (Ong et al., 2022). Once fires with an unidentified or unrelated cause are excluded, connectors account for 25.4%, isolators for 22.4% and inverters for 20.9%. PV modules follow at 14.9%.
Individual incident series point the same way. Connectors and DC cables account for 30% in a German insurance investigation series, about 25% in Swedish data and 23.1% in UK insurer data for 2025.
Australian data shows a different pattern. DC isolators account for 54% of incidents in one Queensland series and 50% in a Western Australia subset. A UK investigation report by BRE also ranks DC isolators first, followed by DC connectors.
A burned panel is not necessarily where the fire started. Because each dataset uses its own population and categories, the study reports the figures side by side rather than combining them into one global ranking.
Where PV fires start: component profile
Key findings: Four published datasets, four different populations
- Connectors and DC cables, Germany
- 30%
- IFS insurance investigation series (n = 244)
- DC connectors and cables, Sweden
- ~25%
- Elsäkerhetsverket 2018–2024, fires and incipient events (n = 155)
- DC connectors and cables, UK
- 23.1%
- QBE insurer analysis of PV-involved fires, 2025 (n = 212)
- DC isolators, Queensland
- 54%
- QFES PV-involvement series 2014–2018 (n = 100)
Why do PV system components fail?
The component tells you where a fire started. The root cause explains why. The study points to poor electrical contact, damaged insulation, moisture ingress, unsuitable equipment and product defects, all of which can lead to overheating or arcing.
Connectors are a clear example. Joining connector halves from different manufacturers, known as cross-mating, and poor crimping in the field are documented sources of overheating and arcing. With DC isolators, poor installation can allow moisture in and lead to arcing inside the switch.
In a German analysis by Fraunhofer and TÜV, installation faults and planning or design faults together accounted for 55% of identified root causes.
Identified root causes of PV fires and heat damage
How solar panels affect fire spread on roofs
A component fault explains where a fire may start. The roof construction, the module layout and nearby combustible material influence whether a small fire becomes a building fire.
In a UK Building Safety Regulator program of 11 large-scale experiments on pitched roofs, every tested configuration incorporating PV showed greater flame spread than the control.
In Norway, RISE Fire Research carried out 29 experiments on the cavity behind PV modules on pitched roofs. Both the size of the gap and the size of the initial fire affected fire spread, and larger initial fires could spread even with a 12 cm gap.
Both results apply to the assemblies tested. Together they show that the fire performance of the complete roof and PV assembly needs to be assessed, not only the electrical installation.
What the percentages do and do not show
The figures describe how recorded incidents are distributed within each dataset. They do not show how likely a connector, inverter or PV system is to catch fire. That would require data on the installed population and time in operation.
How a dataset is defined also changes the answer. In Danish data, the same nine wiring and joint cases make up 13.6%, 16.4% or 23.7% of the total, depending on whether battery-related and unreported events are included.
About the study
Fire causes in photovoltaic systems: A combined analysis of incident records and research evidence is a retrospective descriptive study by Thor Brubakken, published by Bridgehill in October 2026.
It draws on PV Fire Intelligence, an incident and research evidence base operated by Bridgehill. The base covers 885 public incident records and 279 research catalogue entries across 71 countries and territories, alongside seven published report series from Germany, Sweden, the UK, Denmark and Australia.
The study has not undergone independent peer review. Bridgehill develops FireBlock fire-protection products, and this commercial interest is disclosed in the report. The study does not independently validate any Bridgehill product or performance claim.
Frequently asked questions
What causes most solar panel fires?
There is no single global answer. Connectors and DC cables are prominent in several published series: 30% in a German insurance investigation series, approximately 25% in Sweden and 23.1% in a 2025 UK insurer dataset. In some Australian datasets, DC isolators dominate. Underlying faults include poor electrical connections, incorrect installation, moisture ingress and equipment defects.
What is cross-mating of solar connectors?
Cross-mating means joining connector halves from different manufacturers. A physical fit does not mean the electrical connection is suitable. Published research describes overheating in cross-mated connector pairs and arcing from poor field crimping. Norwegian guidance from NEK specifies connectors of the same type and manufacturer.
Do these percentages show how likely a component is to catch fire?
No. They describe how recorded incidents are distributed in each dataset, not the probability that a given connector, inverter or PV system will catch fire. Estimating that would require data on the installed population and time in operation.
Do solar panels affect how a roof fire spreads?
Experimental research indicates they can. In a UK program of 11 large-scale experiments on pitched roofs, every tested configuration with PV showed greater flame spread than the control. Norwegian research by RISE Fire Research found that the size of the gap beneath the modules and the size of the initial fire affected spread. These results apply to the tested assemblies.
How can the risk of PV fires be reduced?
The study points to correct connector matching and termination, suitable switching equipment, appropriate environmental protection and documented verification of the installed system. Separately, the roof and PV assembly should be assessed to limit fire spread if a fire does occur.
Has the study been peer reviewed?
No. The study was published by Bridgehill, which develops FireBlock fire-protection products, and this commercial interest is disclosed in the report. It does not independently validate any Bridgehill product or performance claim.
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