Home batteries

A home battery stores electricity so a household can use it at another time. MCS, the scheme that certifies small renewable installations, gives the example of energy made at midday by solar panels being used in the evening.

Three ways to add one

MCS describes three routes. Many people, it says, add a battery when they get solar panels fitted, so the installer can design the panels and battery as one system.

A certified installer can also connect a battery to panels that are already on the roof.

A battery can work without panels too. MCS says it can be charged overnight on an off-peak tariff and the stored electricity used later in the day.

Sizing a battery

MCS suggests two questions to start with. How much energy do you want the system to store, and how much should it deliver at once?

If you have solar panels, or plan to, MCS says to check that the battery suits that setup.

How long a battery lasts depends on its type and how often it is fully charged and discharged, according to MCS. Manufacturers usually, MCS says, give an estimated lifespan, either in years or as a number of full charge cycles. It adds that a home with solar panels can expect to replace its battery at least once during the life of the panels.

Choosing an installer

MCS keeps an online list of certified installers. It suggests checking an installer's certification three times: when you get a quote, before you sign the contract and before the work starts.

When an MCS installation is finished, you should receive an MCS certificate within 10 working days. MCS also says you will get a handover pack with details of the products and the workmanship warranty.

In England, Approved Document P lists the electrical work in a home that has to be notified to building control. It includes installing a new circuit and replacing a consumer unit.

Electricians registered with a competent person scheme may self-certify that work, GOV.UK explains, so building control does not need to check it. The Registered Competent Person Electrical register lists electricians registered to work in homes in England and Wales.

Telling the network operator

A distribution network operator, or DNO, is the company that carries electricity from the national transmission network to homes and businesses in its area. MCS describes seven of them, covering fourteen districts.

MCS's guidance for installers says a battery connects under one of two sets of technical rules, called G98 and G99. Where G98 applies, the installer can notify the operator within 28 days of installation.

Where G99 applies, an application goes to the operator before installation. MCS says this covers storage over 3.68kW. It adds that a battery fitted with solar panels is likely to come under G99, and that a fast-track form exists for some combined systems.

Your electricity bill shows a long reference called the MPAN. MCS says its first two digits identify your network operator. Ask your installer which rules apply and who will send the form.

Safety

In 2020 the government published a research report on home battery storage. It said makers can reduce risk by allowing only qualified installers, and by setting out where a battery goes, how far it sits from anything that burns, and its fire detection and ventilation needs.

The same report stressed fitting a battery as its maker recommends, including where it goes and how much space it needs around it for ventilation.

The Office for Product Safety and Standards publishes product recalls on GOV.UK. One recall there, dated March 2021, covered some home batteries fitted as part of solar panel systems, because they could overheat and catch fire.

At the end of its life

MCS says most battery storage systems monitor their own health and will alert you when a replacement is needed. Some companies, it adds, handle the recycling or disposal of worn-out batteries.

The Office for Product Safety and Standards warns that a lithium-ion battery dumped in a household bin can catch fire, particularly if it gets wet or damaged. The battery collection points in shops are for portable batteries.

GOV.UK defines a portable battery as sealed and under 4 kilograms. A sealed battery that is not portable counts as an industrial battery.

A producer of industrial batteries must take a waste one back free of charge from any end user in three cases: when it supplies that user with new batteries, when the waste battery is a chemistry the producer sells, or when it cannot be returned to another producer. Producers must also tell end users how to return them.

GOV.UK says it is illegal to send waste industrial batteries to landfill or for incineration.

Useful links