How Much Does a Home Battery Actually Save?

On the worked example below, a 5kWh home battery with 3.7kWp of solar saves about £318 a year for a household with an electric car on an EV off-peak tariff, about £201 a year for a household without a car on Economy 7, and about £126 a year on a standard variable tariff.

A battery saves money in two separate ways, and the second only works if your tariff has cheap hours:

1. Time-shifting your own solar — storing midday surplus and using it in the evening.
2. Charging off-peak from the grid — filling the battery overnight at a cheap rate and using it at peak times.

The worked figures use a 3.7kWp solar system generating 3,600kWh a year, a 5kWh battery that loses about 10% of what it stores, a household using 3,500kWh a year before any car charging, the Ofgem price cap electricity rate of 26.32p per kWh, and a 12p per kWh export rate. They are the figures our electricity and battery calculator gives for the same inputs. Your savings depend on your usage, roof and tariff.

One cycle a day: a 5kWh battery can deliver at most 1,825kWh a year if it fills and empties once every day. Stored solar and off-peak charging share that capacity, so their savings can't simply be added together. Where they compete, the worked figures give the capacity to whichever is worth more per kWh.

VAT assumption: 26.32p is the cap for 1 October to 31 December 2026 and assumes no VAT on household electricity, which applies until 31 March 2027. When VAT returns the import price rises, which increases the battery saving rather than reducing it. Ofgem announces the next cap, for January to March 2027, on 25 November 2026.

Storing your own solar electricity saves the import you avoid minus the export payment you give up, allowing for about 10% losses, which is about 11.7p for each kWh put into the battery at a 26.32p import price and a 12p export rate.

Industry estimates from secondary sources put the share of solar a home uses at 30% to 50% without a battery and around 70% with one. They are estimates, not measurements.

Worked example: a 3.7kWp system generating 3,600kWh a year, with self-use rising from 40% to 70%, sends 1,080kWh into the battery instead of the grid. After losses, 972kWh comes back out. That is 972kWh × 26.32p of import avoided, minus 1,080kWh × 12p of export given up: £126 a year. It uses 972kWh of the battery's 1,825kWh yearly capacity.

If your export rate is lower, this saving is bigger: on a 3p export tariff each kWh put into the battery saves 20.7p, or £223 a year. Most of this saving comes between spring and early autumn, when there is surplus solar to store.

These figures assume the VAT-free 26.32p import price; with VAT back on electricity after 31 March 2027, each stored kWh saves more.

Charging a battery overnight at an off-peak rate and using the electricity at peak times saves the gap between the two prices on every kWh, which is about 17p per kWh with an 8p EV off-peak rate and a 26.32p peak rate once about 10% charging losses are allowed for.

The 8p figure is the Intelligent Octopus Go off-peak rate (11:30pm to 5:30am), checked in September 2026. That tariff requires a compatible electric car and charger; the cheapest overnight rates are often tied to owning an EV. Other time-of-use tariffs have different cheap hours and prices.

With an electric car, the battery charges off-peak first. A kWh bought at 8p costs about 8.9p after losses and replaces a 26.32p kWh, saving 17.4p. A kWh of stored solar also replaces a 26.32p kWh, but storing it means giving up 12p of export for every 0.9kWh you get back, so it saves only 13p. When the overnight rate is that cheap, the battery's space is worth more filled from the grid than from the roof, and the solar is better exported.

Worked example: the battery takes 2,028kWh a year at 8p (£162) and delivers 1,825kWh — its full one-cycle-a-day capacity — in place of electricity at 26.32p (£480). That saves £318 a year. With no room left, storing solar adds nothing on top. That is why a household on a cheap EV tariff may get little extra from storing solar: the battery is already doing something more valuable with the same space.

Without an electric car, the overnight tariff most households can get is Economy 7. Rates for Flexible Octopus Economy 7, average of the 14 GB regions, paying by Direct Debit, from 1 October 2026: 14.19p per kWh overnight and 32.65p in the day (Octopus Energy tariff data, checked September 2026). Here the order reverses: stored solar saves 19.3p per kWh against the day rate, more than the 16.9p from charging at 14.19p (about 15.8p after losses). So the battery takes 972kWh of solar first and fills the remaining 853kWh of its yearly capacity off-peak.

The catch is the day rate: every kWh the panels and battery don't cover costs 6.33p more than on a standard tariff. Without a battery this household would pay £283 a year on a standard tariff and £413 on Economy 7, so it would stay on the standard tariff. With the battery, Economy 7 costs £82 a year, a saving of £201 a year: £126 from storing solar and £75 from charging off-peak once the higher day rate is paid for.

The split is indicative, not precise. The one-cycle-a-day limit is applied over the whole year. In reality a summer day might do both — charge overnight, use it in the morning, then refill from the panels — while a winter day might have no solar to store at all. The totals are a reasonable guide; the division between the two mechanisms is rougher.

This assumes VAT-free prices on both rates. VAT adds the same percentage to the off-peak and peak prices, so the gap between them — and the saving — grows when VAT returns.

Yes — a home battery on a time-of-use tariff still saves money in December because it charges from the grid at the cheap overnight rate, even though solar panels produce very little surplus in winter.

According to the European Commission's PVGIS model, a south-facing 3.7kWp system in the East Midlands produces about 131kWh in December, around 4kWh a day, against about 437kWh in May. A home uses that small winter output as it is generated, so there is almost nothing left over to store.

That is why the off-peak mechanism matters. It works on a dark, wet December day exactly as it does in June, because it doesn't depend on the panels at all.

A battery saves much less on a standard variable tariff because every hour costs the same, so it can only save by storing surplus solar — about £126 a year in the worked example, against about £318 a year for a household with an electric car on an EV off-peak tariff.

With one flat price there is no cheap electricity to store and nothing to gain by shifting grid use. In winter, when there is little solar surplus, the battery sits mostly idle.

The saving from a battery depends on the owner choosing a time-of-use tariff. Without a car, switching to Economy 7 raises the worked saving to about £201 a year. If you won't switch — because you prefer a fixed deal, or the cheap tariffs need an EV you don't have — expect a fraction of the headline figures installers quote.

On the worked example, a 5kWh retrofit battery costing £3,500 to £5,500 installed takes 12 to 18 years to pay for itself with an electric car on an EV off-peak tariff, 18 to 28 years without a car on Economy 7, and 28 to 44 years on a standard variable tariff — longer than a typical 10-year battery warranty in every case.

Those ranges divide the typical quoted retrofit price (Heatable and Home Energy Quotes cost guides, checked September 2026) by the yearly savings above — £318, £201 and £126 — rounded up to whole years. Without solar, a household with no car saves about £87 a year on Economy 7, a payback of 41 to 64 years.

They use the VAT-free 26.32p price for October to December 2026; higher import prices once VAT returns would shorten them. They also assume the battery keeps its full capacity, which it won't — batteries lose capacity with age, which lengthens payback. Warranty length is not the same as battery life, but a payback that runs past the warranty depends on the battery outlasting it.

Payback isn't the only reason people fit a battery. See battery storage pros and cons for what the numbers don't price, premium export tariffs, the VAT deadline and when to walk away.