Free tools

Battery-only payback calculator

See how long a home battery takes to pay for itself on your tariff. It charges in your cheapest rate and powers your home the rest of the time, worked out for every 30 minutes of a whole year.

About your new system
Illustrative only: battery ageing varies with use and temperature. Check the battery warranty for a better assumption.
Energy lost charging the battery and getting it back out.
About your electricity usage
Use the total shown across bills or statements for the latest 12 months, including any car charging. You can take the car off below.
This describes your home, not the car.

About your existing electricity tariff
New system variables
Choose yes if you intend to use grid arbitrage by exporting remaining battery energy, for example during the evening.
Enter the fixed export cap if your DNO has applied one. Leave blank if there is no limit or you do not know.
Financials
Optional. Enter the installed cost to compare payback with leaving this money in a savings account.
Applied equally to import rates, export payments and standing charges in the long-term estimate. Enter 0 for prices held flat.
Optional comparison. Interest compounds annually on the installation money kept in savings; tax is not included.

How this is calculated

This is the solar and battery calculator without the panels. Your home's use is spread over every 30 minutes of a calendar year using the daily pattern you choose, with more used on winter days than summer ones, following measured data for homes. The battery charges from the grid in your tariff's cheaper rate and powers your home at other times, within its size and charge and discharge limits, and it keeps its charge from one half hour to the next. Without the battery you pay your current tariff; with it, the tariff you'll be on.

The battery is assumed not to power your car. The car's charging is priced at the rates you entered it against and shown as its own line on each bill, but it's left out of the saving and the payback. Treat the result as a planning estimate rather than a quote.

Common questions

Does this include solar panels?

No. It looks at a battery on its own, charged from the grid. If you're adding solar too, use the solar and battery calculator, which works out both together.

How does it work out what the battery saves?

We work through every 30 minutes of a whole year, which is 17,520 steps. Your home's use follows the daily pattern you pick, with more used on winter days than summer ones, as measured in real homes. The battery fills up in your tariff's cheapest rate and runs your home the rest of the time, as far as its size and power allow. The saving is the difference between your bills with and without it.

Why does it ask about my car?

Most yearly bills include charging the car, so we take that off to find your home's use. The battery is assumed not to power the car, which is how most home set-ups work. The car's charging still shows on both bills, but it doesn't change what the battery saves.

Why do capacity loss and price rises matter?

A battery holds a little less each year, so it saves a little less. Prices rarely stay flat either. Both are applied year by year over 25 years before the payback is worked out.

Adding solar too? Try the solar and battery calculator →