A home battery saves money by charging when electricity is cheap and discharging when it is dear. Enter the usable capacity, your peak and off-peak rates, how many times a year it cycles and the battery cost to estimate the saving and payback.
A battery on its own earns money from the gap between cheap off-peak and expensive peak electricity, so a wide rate spread and a tariff with cheap night units are what make it pay. Paired with solar it does more, storing daytime generation for the evening rather than exporting it cheaply. Batteries are not cheap and last around ten years, so the payback is often close to the lifespan; see solar battery storage and time-of-use tariffs for the detail.
Common questions
Is a home battery worth it?
It depends on the price gap between peak and off-peak electricity and how fully you cycle it. A 5kWh battery cycled daily on a wide rate spread saves a few hundred pounds a year, which can take most of its ten-year life to pay back the upfront cost.
How much can a battery save per year?
Take the usable capacity, multiply by the difference between your peak and off-peak rates, and multiply by how many times a year it cycles. A 5kWh battery at a 19p spread cycled 300 times saves about £285 a year.