Battery safety and siting: where one may and may not go

What the risk actually is

The government’s own review — commissioned by the Office for Product Safety and Standards and published in September 2020 — is measured about this, and worth reading in its own words rather than through either the industry’s or the internet’s.

It states that “even though few incidents with domestic battery energy storage systems (BESSs) are known in the public domain, the use of large batteries in the domestic environment represents a safety hazard.”

The mechanism it describes has three parts:

Heat. “Excessive heat generated deep inside a battery pack as cells fail and thermal runaway propagates through the pack.”

Pressure. Cell and pack failures generate “large volumes of gasses resulting from the rapid pressure build-up and vent release.”

Toxicity. Where lithium hexafluorophosphate meets humidity, hydrogen fluoride forms — described in the review as “an extremely strong acid with etching qualities”, with an immediately-dangerous-to-life concentration cited at 30 ppm.

That is the honest picture: rare, and serious when it happens. Which is exactly the risk profile that siting rules exist for.

Where a battery usually goes

Working through what the standard excludes leaves a short list, and it matches what competent installers propose anyway:

A garage — the common answer. Ventilated, separated from living space, accessible.

A utility room or plant space, subject to the REI 30 separation and detection requirements.

An external wall or ground mount, respecting the one-metre clearance from escape routes, doors and windows, and two metres from flammable materials. Check the manufacturer’s ambient temperature range: outdoor siting in a British winter is within spec for most units but not all.

Not the loft, a bedroom, the hallway your stairs run through, or a cellar you can only reach from inside the house.

The standards an installation should meet

From the government review and the building regulations:

Approved Document L’s own note is short and worth having: where on-site electricity generation or energy storage is installed, “the fire safety (including means of escape) and electrical requirements of the Building Regulations should be met”, following Approved Documents B and P, and manufacturers’ instructions should also be followed.

What to ask before the installation

1. “Where exactly will it go, and does that comply with PAS 63100?” Get the answer in writing. This is the single question that matters most on this page.
2. “What fire separation and detection are you providing?” REI 30 indoors, and BS 5839-6 detection where the location is not frequently visited.
3. “What is the manufacturer’s stated ambient temperature range?” Then compare it with where you are putting it.
4. “Who certifies the electrical work?” Approved Document P applies and a certificate should follow — see building regulations.
5. “Is there an accessible isolation switch, and do I know how to use it?” The London Fire Brigade’s suggestions recorded in the government review included a readily available and visible shutdown switch.
6. “Have you told my network operator?” If the battery can export, G98 or G99 applies as it does for the panels.

And tell your insurer

Not because we know they will care — the position varies and nothing is published centrally — but because a material change to the property that goes undisclosed is a bad thing to discover at claim time. The call costs nothing.