In short
- A battery stores surplus solar or cheap off-peak electricity for later, but the Energy Saving Trust says the savings won't always justify the cost on their own.
- Batteries are sized in kilowatt-hours of storage and kilowatts of power. The Energy Saving Trust says a typical home system might be 10 kWh.
- Most grid-connected systems shut down in a power cut. Backup power has to be designed in from the start.
- If your panels are on the Feed-in Tariff, Ofgem says you must tell your FIT licensee before battery storage is connected.
- Location matters for safety: installers follow manufacturers' rules and the BSI specification PAS 63100:2024, which steers batteries away from escape routes and living spaces.
How a home battery works alongside solar panels
Solar panels generate most around the middle of the day, when many households are out or using little power. Without a battery, any surplus is exported to the grid. With a battery, the surplus first charges the battery, and the stored energy is used in the evening or overnight. Once the battery is full, the rest is exported as usual.
A battery can also charge from the grid. The Energy Saving Trust explains that, on a smart time-of-use tariff, you can charge the battery when electricity is cheap and use it when prices are higher, with or without solar panels. It adds that a battery will save more if it is running a heat pump than if it is only storing extra solar energy.
- Batteries suit households that are out in the day and use most of their electricity in the evening.
- They can suit homes with a heat pump or an electric car on a time-of-use tariff.
- They are less useful if you are at home all day and already use most of your solar generation as it is produced.
- The Energy Saving Trust notes that using stored energy is less efficient than using electricity directly, so some energy is lost each time a battery charges and discharges.
Sizing a battery in kWh and kW
Two numbers describe a battery. Capacity, in kilowatt-hours (kWh), is how much energy it can store. Power, in kilowatts (kW), is how fast it can charge or discharge. A large battery with a low power rating may not be able to run a cooker, kettle and shower at once, so both numbers matter.
- The Energy Saving Trust says a typical home system might be 10 kWh, and that there is no exact formula. Your installer should size it from your own use.
- Usable capacity is less than the headline figure. The Energy Saving Trust explains that systems stop discharging at a set level, perhaps 20% of capacity, to protect the battery.
- A battery much bigger than your evening use, or bigger than your panels can fill on a typical day, may sit partly unused for much of the year.
- In winter, panels generate much less, so a battery sized to your summer surplus will rarely fill from solar alone between November and February.
Under the MCS solar standard, an installer quoting a battery with new panels must show the expected self-consumption with and without the battery, using the battery's assumed usable capacity. Ask for both figures, and ask for your half-hourly or monthly usage to be used if you have a smart meter.
Time-of-use tariffs and charging from the grid
Time-of-use tariffs charge different rates at different times of day. With a battery, you can charge at the cheaper times and avoid the more expensive periods. The Energy Saving Trust notes that some newer tariffs also let you sell electricity from your battery at peak times.
There is a catch with export payments. If the battery charges from the grid as well as from your panels, some of what you export may not be renewable electricity. The Energy Saving Trust explains that suppliers don't have to pay for non-renewable electricity exported under the Smart Export Guarantee, although some choose to, and some may ask you to show how you separate solar generation from grid electricity. Ofgem's guidance to suppliers covers how export from co-located storage charged from the grid should be treated.
- Look at your usageCheck when you use most electricity, and whether you could move some use, such as washing or EV charging, into cheaper periods.
- Compare tariff typesSome tariffs need a battery or a particular supplier. Check the conditions, not just the headline rates.
- Check the export rulesAsk your export supplier whether battery charging from the grid affects your export payments.
- Set the battery up properlyAsk the installer to set the charging schedule for your tariff and show you how to change it if you switch.
AC-coupled, DC-coupled and hybrid inverter systems
Solar panels produce direct current (DC), your home uses alternating current (AC), and batteries store DC. How the battery is connected decides how many conversions happen and how easy it is to add to an existing system.
| Arrangement | How it works | Often suits |
|---|---|---|
| AC-coupled battery | The battery has its own inverter and connects to your home's AC wiring, alongside the existing solar inverter. | Adding a battery to existing panels without touching the solar side. Slightly more conversion losses. |
| DC-coupled with a hybrid inverter | One hybrid inverter manages the panels and the battery. Solar can charge the battery directly as DC. | New solar and battery systems designed together, or replacing an old inverter. |
| All-in-one systems | The battery and inverter come as a matched package from one manufacturer. | Simpler installs where the product fits your power needs. |
A hybrid inverter can be a good choice if your existing inverter is near the end of its life. The Energy Saving Trust says inverters need replacing after around 12 years, so on an older system, swapping to a hybrid inverter can solve two problems at once. Ask installers to explain why they chose the arrangement in their quote.
Adding a battery to panels you already have
MCS says a certified installer can connect a battery to an existing solar system. Before quoting, the installer should check:
- The size, age and condition of the panels and inverter, and whether the inverter is still under warranty.
- Your consumer unit, earthing and space for any new isolators and meters.
- Your current export arrangement, MCS certificate and any Feed-in Tariff paperwork.
- Where the battery can safely go, and the cable route to it.
HMRC's VAT Notice 708/6 says the zero rate of VAT covers retrofitting a battery to an existing solar system in a home, until 31 March 2027.
A battery that can export counts as generation for the grid connection rules. Guidance from the Welsh Government on the Engineering Recommendations explains that a single installation up to 3.68 kW on a single-phase supply, or 11.04 kW on three-phase, can connect and then notify the network operator, with evidence sent within 28 days of commissioning. Above that, the installer must apply in advance under G99. The Energy Networks Association notes that the total includes electricity storage, so adding a battery to an existing solar system can push it over the limit. Your installer deals with UK Power Networks, the network operator for Kent.
If your panels earn Feed-in Tariff payments
The Feed-in Tariff closed to new applicants in 2019, but many homes still receive payments. Ofgem's guidance for FIT generators says you must notify your FIT licensee when battery storage is connected to an accredited installation.
- Ofgem says your payments won't be affected as long as your generation, and your export if it is metered, can still be accurately measured. If it can't, you can't be paid for that electricity.
- Generation must be measured separately from all other sources, which is why the battery's position in the wiring matters.
- Ofgem also says that if you have a smart meter fitted and currently receive deemed export payments, these stop and you are paid for the export the meter records instead.
- The Energy Saving Trust explains that you can't receive FIT export payments and Smart Export Guarantee payments at once, but you can opt out of FIT export payments, move to an export tariff and keep your FIT generation payments.
Will a battery keep the lights on in a power cut?
Not automatically. Grid-connected solar and battery systems are designed to stop operating when the grid goes down, so they don't feed power into cables that engineers may be working on. The Energy Networks Association's fast-track conditions, for example, require that generating units won't operate when there is a loss of mains. So in most homes, a power cut switches off the solar and the battery along with everything else.
Some systems offer a backup or emergency power function. This needs extra equipment to isolate your home safely from the grid before the battery supplies it, and it is usually limited to some circuits.
- Ask whether backup is included or an extra, and which circuits it covers.
- Ask how quickly it switches over, and whether the solar panels can recharge the battery while the grid is down.
- Check that the battery's power rating can run what you want to keep on, such as a fridge, lights and the boiler controls.
- Make sure backup is designed in at the start. It is often harder to add later.
Where a battery can safely go in your home
Home batteries are usually lithium-based and store a lot of energy, so siting matters. The Energy Saving Trust says batteries can be installed in garages, on external walls or in utility rooms, depending on the product. Manufacturers also set rules on temperature, ventilation, clearances and mounting.
The British Standards Institution published PAS 63100:2024, a specification for protecting against fire from battery energy storage systems in homes. Industry summaries of PAS 63100 describe it as:
- Favouring locations outside the living space, such as a garage, an outbuilding or an external wall, with suitable protection.
- Keeping indoor batteries away from habitable rooms and escape routes, and keeping escape routes unobstructed.
- Calling for fire detection where a battery is installed indoors, linked to a fire alarm system.
- Requiring warning labels at the consumer unit that show a battery is present.
- Restricting installation in lofts, roof spaces and other voids.
PAS 63100 applies to dwellings of up to 200 square metres of floor area, according to the published summaries. Ask your installer which standard they work to, where they propose to put the battery and why, and how to isolate the system in an emergency.
Battery lifespan, warranties and replacement
The Energy Saving Trust gives a typical battery lifespan of about 10 to 12 years, and MCS says that if you also have solar panels you can expect to replace the battery at least once during the life of the panels. Manufacturers usually state a lifespan in years or in full charge cycles, and most systems monitor battery health.
- Read what the warranty covers: years, cycles, and the capacity the battery should keep by the end of the warranty.
- Check whether the warranty requires an internet connection or registration.
- Keep the battery in the temperature range the manufacturer specifies, which matters in an unheated garage.
- Ask how the installer will handle a fault, and who removes and recycles the old battery when it is replaced.
Get quotes from local solar and battery installers
When you're ready, describe your project once and we'll pass it to vetted solar and battery installers who cover your part of Kent. They quote you directly, and nothing is booked until you accept.
Sources
- Energy Saving Trust: Battery storage (updated October 2026): energysavingtrust.org.uk/advice/battery-storage/
- Energy Saving Trust: Solar panels, costs, savings and benefits (updated October 2026): energysavingtrust.org.uk/advice/solar-panels/
- MCS: Battery storage for consumers: mcscertified.com/consumers/technologies/battery-storage/
- MCS: MIS 3002 Solar PV Systems standard, issue 6.0 (March 2026): mcscertified.com/wp-content/uploads/2026/03/MIS-3002_Solar-PV-Systems-V6.0-Final.pdf
- Ofgem: Feed-in Tariffs, information for generators: www.ofgem.gov.uk/environmental-and-social-schemes/feed-tariffs-fit/generators
- Ofgem: Smart Export Guarantee guidance for SEG licensees: www.ofgem.gov.uk/guidance/guidance-seg-licensees
- GOV.UK, HMRC: VAT Notice 708/6, energy-saving materials and heating equipment: www.gov.uk/guidance/vat-on-energy-saving-materials-and-heating-equipment-notice-7086
- Energy Networks Association: Connecting generation to the electricity networks (G98, G99 and G100): www.energynetworks.org/industry/connecting-to-the-networks/connecting-generation-to-the-electricity-networks
- Welsh Government: Connecting on-site generation to the grid, technical note: www.gov.wales/connecting-site-generation-grid-technical-note-html
- BSI: PAS 63100:2024, protection against fire of battery energy storage systems for use in dwellings: accord-checkout.bsigroup.com/products/electrical-installations-protection-against-fire-of-battery-energy-storage-systems-for-use-in-dwellings-specification
- Build It: New fire safety standards introduced for domestic battery storage systems: www.self-build.co.uk/new-fire-safety-standards-for-battery-storage/