How can you reduce the risk of solar panel roof fires?


To reduce the risk of a solar panel flat roof fire, measures should be taken to prevent electrical arcing1, as this is the major factor that could cause an outbreak of fire.

Arcing occurs where conducting parts in the solar panel flat roof system become separated and current flows across the gap between them through ionisation of the air. These high voltage electrical arcs can produce extremely high temperatures exceeding 6,000°C and, as a Roof mounted PV system is based on direct current (DC) rather than alternating current (AC), the arcing can be sustained. The high temperatures generated can ignite nearby materials causing fire to breakout and spread across the roof.

Faults with electrical connections leading to arcing could be caused by manufacturing errors, damage to equipment during transportation, or when in operation on the roof, and by poor installation of the solar panel system on site. Therefore, the selection of a quality system manufacturer and experienced installation team can help reduce some of the risks associated with arcing and roof mounted solar PV fires. Specialised equipment specifically designed to enclose key equipment is also available. It can prevent any arcing that may occur from causing a fire to further reduce fire risk.

Once the solar panel system has been selected and installed, maintenance is important to ensure that all equipment is regularly checked and any issues causing concern are rectified. Cleaning is also required, as a build-up of contaminants in the form of oxides on electrical connections leads to the generation of resistive heat that can eventually break down materials and lead to arcing.

Does the presence of solar panels effect the behaviour of roof mounted Solar PV fires?

Solar panels affect the fire dynamics of a flat roof. This means that should a fire break out, regardless of its origin, the panels could increase the severity and damage caused by that fire.

The speed of fire spread across a roof with solar panels can be influenced by the gap between the panels and the roof. If the panels are below a certain height, known as the critical gap distance, then the fire may spread more rapidly. In tests2 the acceleration of the flame front was up to 38 times faster with solar panels than without, highlighting the importance of ensuring the correct gap height for solar panels is achieved during installation.

The angle of the solar panels also plays a part as the panels can re-radiate heat from a fire back down onto the roof surface generating hot spots. Solar panels could hinder the effort to put out a roof mounted solar PV fire and their presence also adds additional fire load to the roof.

These changes in the fire dynamics mean that, even if all the steps are taken to lower the risk of the solar panels themselves starting the fire, a fire from a different source could be more destructive, and harder to extinguish, due to solar panels being in place.

How can fire-resistant roof boards help to further mitigate the risk of solar panel fires?

Given the risks of a roof mounted Solar PV, fires cannot be completely eliminated. The use of fire-resistant roof boards between the waterproofing membrane and insulation layer incorporates a layer of fire resistance into the roof to help slow down the spread of fire and potentially limit damage, should a fire occur on the roof.

DensDeck® Roof Boards are comprised of a gypsum core and fibreglass mats, both of which are classified as non-combustible. The embedded facers form the first line of defence against a fire followed by the gypsum core.

DensDeck® Roof Boards are used as a component in over 398,487 flat roof assemblies that achieve a FM Approvals (FM) Class A fire performance. These assemblies are assessed to higher standards than required by building regulations and can give specifiers reassurance that they are selecting a proven system to help mitigate the risks posed by roof mounted Solar PV fires.

If you would like to find out how selecting DensDeck® Roof Boards as part of your flat roof specification can help reduce the impact of roof mounted Solar PV fires, please contact us today for detailed project advice and guidance.

1 Fault tree analysis of fires on rooftops with photovoltaic systems – Journal of Building Engineering 29 Nov 2021
2 Experimental study of flame spread underneath photovoltaic (PV) modules – Journal of Building Engineering 7 May 2020

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