In short
- PV cabling stays live in daylight, and faults at connectors and inverters can start fires.
- PAS 63100:2024 sets out where batteries in dwellings shouldn't go – including sleeping rooms, escape routes and lofts.
- On blocks of flats, check cable routes through compartments, roof construction, isolation and fire service information.
- Update the fire risk assessment when PV or batteries are added.
The fire risks of solar PV
Rooftop solar PV is generally low risk when designed and installed well. The risks come from:
- DC arcing at poorly made or damaged connectors, isolators and cables
- Inverter faults
- Roof fires spreading across combustible roof coverings or insulation beneath the array
- Firefighter hazards – PV cabling can't simply be switched off while the sun is shining
- Cable routes through the building that breach compartmentation if not properly fire-stopped
Installations should follow BS 7671 (the IET Wiring Regulations, which include requirements for PV systems) and recognised installation standards, and insurers may have their own requirements.
The fire risks of battery storage
Battery energy storage systems (BESS) usually use lithium-ion cells, which can fail through thermal runaway – releasing heat and toxic, flammable gases. The risk depends on the battery chemistry, the size of the system, its management system and, above all, where it's installed.
PAS 63100:2024 – batteries in dwellings
PAS 63100:2024, published by BSI, sets fire safety requirements for installing battery storage in homes. Its location rules say batteries should not be installed in places including:
- Rooms intended for sleeping
- Escape routes, including protected stairs, corridors and lobbies
- Firefighting lobbies, shafts and stairs
- Voids, roof spaces and lofts
- Cupboards that open into sleeping rooms
- Cellars or basements without access to the outside
- Outdoors within 1m of escape routes, doors, windows or vents, or within 2m of stored flammable materials
Larger systems
Batteries in plant rooms, car parks or commercial buildings need a building-specific assessment of separation, ventilation, detection, suppression, access and how a battery fire would affect evacuation. Fire services have also published guidance on larger battery installations.
What to check on a block of flats
- The roof – what's under the array, and could fire spread across it?
- Cable routes – are penetrations through compartment walls and floors fire-stopped? See compartmentation surveys.
- Isolation and labelling – can the system be isolated, and is that clearly signed for firefighters?
- Inverters and batteries – where are they, and are they kept out of escape routes?
- Information for the fire service – for high-rise buildings, include PV and batteries in the plans and premises information box. See premises information box requirements.
- External walls – PV on façades or balconies is an external wall attachment and should be considered in the FRAEW.
When to update your fire risk assessment
Solar PV and battery storage fire risk should be assessed early. Update the fire risk assessment before a significant PV or battery installation goes in, and again once it's complete. It's far cheaper to fix a cable route or battery location at design stage than after installation.
Blocks of flats: ownership and maintenance
On blocks of flats, PV systems may be owned by the freeholder, a resident management company, a third-party energy provider or individual leaseholders. Whoever owns the system, the responsible person still needs to understand it for the fire risk assessment. Make sure there's a maintenance contract, regular inspections of connectors and isolators, and clear records – and that contractors installing cables through the building fire-stop every penetration they make.
Information for firefighters
Firefighters need to know that PV is present, where it is, where the isolators and inverters are, and whether there's battery storage. Clear signage at the main entrance and on the plans helps them work safely.
Our EV, solar and battery fire risk assessments cover proposed and existing installations in blocks of flats, offices and commercial buildings.
How we can help
We match each project to a qualified specialist and confirm the scope, the named professional and a fixed fee before you commit.
Sources
- BSI – PAS 63100:2024 Protection against fire of battery energy storage systems for use in dwellings
- Battery Design – PAS 63100:2024 summary
This guide is general information based on the law and guidance in England as at 8 November 2026. It isn't legal advice – for advice on a specific building, get in touch.