Dangerous combination: Roofs and solar panels increase the risk of fire spread

Heat between the solar panels and the roof can become so intense that it becomes easier for fire to spread—despite the fact that the roof may contain flame retardants, a new PhD thesis shows. Illustration: Jens Steemann Kristensen

In recent years, solar panels have been spreading over an increasingly large part of the Danish building stock, and the energy crisis caused by Russia’s attack on Ukraine may lead to the installation of solar panels on roofs becoming a legal requirement. But the Danish legislation ignores the increased fire risk that solar panels entail.

The way the solar panels are installed can lead to violent roof fires that are difficult to put out as well as to large financial losses, according to the Association of Danish Emergency Management Services (Danske Beredskaber) and civil engineer Jens Steemann Kristensen, who has investigated the subject in his PhD thesis.

“A normal flat roof, designed according to current legislation, can resist most ignition hazards. However, in the event of a fire, the backside of the panels will deflect the flames and thus increase the heat radiated to the roof, which can then release a critical concentration of flammable pyrolysis gases. And then the fire can spread,” he explains.

No information has been systematically collected about roof fires and the impact of solar panels on fire behaviour, so no actual statistics exist. But according to Jens Steemann Kristensen, who is currently employed at the Danish Institute of Fire and Security Technology (DBI), several examples of roof fires spreading under solar panels installed on flat roofs have been observed abroad.

Danish authorities: Solar panels not an “unusually great fire hazard”

At the trade association Danske Beredskaber, Rasmus Storgaard, director of emergency services at Beredskab Øst, is in no doubt that fire spread is a real problem.

“The relatively large fires in building complexes with solar panels, which we have seen around the world, mean that we have to deal with the fact that fires spread—and that this happens faster under solar panels, where they’re also very difficult to extinguish. The authorities have not yet taken a stance on that matter today.”

The position of the Danish authorities has so far been that solar panels are not “considered ... an unusually great fire hazard,” as the Danish Housing and Planning Authority wrote to the Danish Association of Consulting Engineers (FRI) in 2020. Therefore, there is no legal requirement for the installation of solar panels to not impair fire safety of a building.

Ingeniøren asked the Danish Housing and Planning Authority on Tuesday whether, in light of the new research results, the authority will introduce rules for the installation of solar panels, but the authority did not answer by our deadline for publication on Wednesday afternoon.

We need solar panels

However, both Jens Steemann Kristensen and Rasmus Storgaard hope that the Danish authorities will take the problem seriously and quickly introduce rules to eliminate the risk of fire spread. This is because solar panels are needed, Jens Steemann Kristensen emphasizes.

“Solar panels are a great technology that is ideal to install on unused roofs. But if we don’t understand the increased risk of fire, then I’m afraid that fire safety may end up causing problems in the long run.”