Home battery storage: cost, size and funding

Home battery storage lets a house bank electricity and spend it later, so power bought cheaply overnight, or made by solar panels in the day, is on tap when it is actually wanted. In the UK a typical home battery is around 10 kWh and costs roughly £5,000 to £8,000 fitted, with a 5 kWh unit near £4,600, on Energy Saving Trust figures. The Warm Homes Loan funds one up to £15,000. Whether it pays back turns almost entirely on the tariff you charge it from.

That is the part most sales pitches skip. So the sizing and the tariff come first here, and the loan comes after.

What a home battery actually costs

Prices scale with capacity, but not in a straight line, because a chunk of the bill is the inverter, the fitting and the labour rather than the cells. The Energy Saving Trust puts a 5 kWh battery at around £4,600, while a typical home system of about 10 kWh tends to land in the £5,000 to £8,000 band once installed. Battery-only jobs sit at the higher end of that. Adding cells to a system that is already going in costs less per kWh than a standalone retrofit later.

One relief works in your favour. Qualifying home battery installs carry 0% VAT until 31 March 2027, a genuine saving on the headline figure that disappears when the relief reverts. If a battery is on your list, doing it inside that window keeps a slice of the cost off the invoice. Our solar cost breakdown shows how the same relief lands when panels and a battery go in together.

Usable kWh versus total capacity

Here is the number that trips people up. A battery is sold on its total capacity, but you never get all of it. Manufacturers hold back a slice to protect the cells and lengthen their life, so the figure that matters is the usable capacity, the energy you can actually draw before the battery cuts out. Read the spec sheet for that line, not the badge on the front.

Modern lithium iron phosphate units give up most of their rated capacity, so the gap is smaller than it once was, but it is rarely zero. Size to the usable number and to the electricity you genuinely shift each day. A house with modest evening use gains little from an oversized bank, because the top slice seldom empties and then refills. Too small and you are back buying peak power before bedtime. The solar and battery calculator works this in usable kWh, which is the honest way to size it.

Where a battery pays: time-of-use tariffs

A battery does not make electricity. It moves it in time, and the profit is the gap between the price you pay to fill it and the price you avoid, or earn, when you empty it. On a flat tariff that gap is nothing. On a time-of-use tariff it can be large.

The mechanism is simple. Overnight, when demand is low, some suppliers price off-peak power at around 7p a unit on their smart tariffs, against a peak rate several times that. Charge the battery in that cheap window, then run the house from it through the expensive early evening. Every unit you shift is the difference between the two rates, banked. Pair that with solar and you fill the battery for free on a bright day and lean on the cheap overnight rate when the sun does not show.

Exporting is the other half. Under the Smart Export Guarantee, suppliers pay for units you send back to the grid, though each sets its own rate rather than working to a fixed national figure, so the number varies by deal. Some time-of-use tariffs let a battery export at the peak, turning stored cheap power into a payment. That only stacks up on the right tariff, which is why the tariff choice matters as much as the hardware.

Standalone or paired with solar

A battery works without panels. On a smart tariff a standalone unit charges cheap overnight and discharges through the peak, and that arbitrage alone can carry the case in a home with high evening use. No generation is needed for it.

Paired with solar the logic changes. Panels make power in the middle of the day, when a typical household is out and using least, so without storage much of it exports for a modest rate. A battery captures that midday surplus and holds it for the evening peak, which lifts the share of your own solar you actually use rather than sell cheap. That is why the two are so often quoted together. The solar panels guide and the battery storage pillar go deeper on the pairing and the kit.

How the Warm Homes Loan funds it

Battery storage is one of the measures the Warm Homes Loan Scheme is built to fund, with a loan cap of £15,000. Solar carries the same £15,000 cap, so a household fitting both can borrow against each measure rather than squeezing one number. You do not apply to the government. You borrow from an approved lender, and a grant of up to 20% of the loan reduces the balance the lender charges interest on, which is how the rate comes down over a 3 to 10 year terms.

Timing is the catch worth knowing. Public loans are expected from September 2026, so for now the route exists on paper more than at the counter. The full mechanics sit on our Warm Homes Loan Scheme page. Run the payback before you borrow, because a battery financed at a rate above the saving it earns is a slow loss, however clean the technology.

Common questions

Before you sign anything, put your own evening usage, your tariff and the usable capacity into a payback sum. A battery that shifts a fixed block of units each day across the gap between the off-peak and peak price earns a predictable sum a year, and that figure, not the brochure, tells you whether to buy now, wait for the loan, or fit it alongside panels.