Battery
Home battery savings calculator
A battery does not make electricity — it moves it to a cheaper moment. This estimates how many units yours could move, what that is worth, and how long the cost would take to repay.
The calculator is free, needs no account, and keeps your figures in your own browser.
Open the battery calculatorAny solar estimate and home figures you have already entered are used automatically.
Where a battery earns money
Two places: storing surplus solar you would otherwise export for a few pence, and charging on a cheap overnight rate to avoid day-rate units. Both are priced from the rates you enter, hour by hour across a modelled year.
Size, reserve and losses
Usable capacity is reduced by any backup reserve you keep, and some energy is lost in every charge and discharge cycle. Power limits can also stop a battery filling during a short cheap window. The calculator shows several sizes together so diminishing returns are visible rather than assumed.
Honest about the limits
Degradation over the years, warranty terms, installation constraints and the value of backup power during a cut are not priced here. They can matter as much as the annual saving, so they belong in the conversation with your installer.
Common questions
- How much can a home battery save in a year?
- It depends on how many units it can move each day and the price gap it moves them across — surplus solar instead of a low export payment, or cheap-rate grid units instead of day-rate ones. The calculator counts the units the battery can realistically shift rather than applying a flat percentage.
- How long does a home battery take to pay back?
- Installed cost divided by the yearly saving. Where the saving is small or negative, the calculator says there is no payback instead of showing a very large number.
- Does a battery pay for itself on a single-rate tariff with no solar?
- Usually not, because there is no price gap to exploit. A battery earns money from difference — between import and export, or between cheap and standard rates — so the tariff matters as much as the hardware.
- What reduces the saving?
- Round-trip losses, a backup reserve you keep charged, charge and discharge power limits, and a battery larger than your daily pattern can fill and empty. Each of those is visible and adjustable.
- Is a bigger battery better?
- Only up to a point. Extra capacity beyond your daily surplus and evening demand sits unused for much of the year, so savings flatten while cost keeps rising. Comparing sizes side by side shows where that happens for your home.