A town in a valley under a heavy evening sky, hills beyond

Battery storage

A battery stores midday power for the evening.

We price every estimate with a battery and without one, so you can see what it adds to the price, what it adds to the saving and how long each takes to pay back.

See both on my estimate When a battery pays
Every estimate priced
With and without
Battery on the estimate
+⁠£4,500
Capacity priced
10 kWh

How it works

Spare power at midday, used after dark.

Whatever is running in the house takes the roof’s power first. Around midday a roof often makes more than the house is using, and without a battery the rest is exported to the grid. A battery catches that spare power instead, and the house draws on it after dark, when it would otherwise be buying from the grid.

Whether that pays comes down to the gap between two prices: what you pay for a unit and what you are paid to export one. The example estimate assumes 30p bought and 16p exported. Every unit stored and used at home instead of exported is worth roughly the difference. Tariffs and export rates vary by supplier, so yours may differ.

How export payments work
A house at night with panels across its dark roof and warm light inside

Battery storage

Battery, or not. We price both.

Panels make most at midday. Most homes use most in the evening. A battery moves one to the other, and whether that pays depends on when you are home, what you pay per unit and what you are paid for export.

What your roof makes What your home uses Stored at midday Used after dark
  • What your roof makes
  • What your home uses
  • Stored at midday
  • Used after dark

Usually worth it when…

  • your evening use is high
  • you’re out most of the day
  • you’re on a time-of-use tariff
  • an electric car charges overnight

Often not when…

  • someone is home through the day
  • the array is small for the house
  • your export rate is already strong

On your estimate, 10 kWh adds £4,500, and we show the payback both ways. The choice stays yours.

See both on your estimate

Both ways

The example estimate, with and without.

On the example roof in Exeter (EX4), a 6.2 kWp array costs £7,200⁠–⁠£8,900 installed without a battery and £11,700⁠–⁠£13,400 with a 10 kWh one. At a £1,500 yearly bill, the home uses 28 per cent of what the roof makes without the battery, and 48 per cent with it.

That changes where the saving comes from. Without the battery it is about £460 off the bill and £620 exported, about £1,080 a year, paid back in about seven years. With it, about £780 off the bill and £450 exported, about £1,230 a year, paid back in about ten. The battery’s own share is about £150 a year for £4,500, so on its own it would take about 30 years to repay. Both sit side by side on your estimate.

Battery or no battery: the sums

Choosing one

How a battery is sized and placed.

Capacity matched to your evening use, not the biggest box on the list.

  • 01

    Matched to your evenings

    Sized to what you use after dark. Too big and it sits partly empty; too small and spare midday power still goes to the grid.

  • 02

    A place for it to live

    A garage, a utility room or an outside wall. The surveyor looks for the spot while they are there.

  • 03

    Priced both ways

    With and without, side by side, on the same estimate. On the example estimate, 10 kWh adds £4,500.

  • 04

    Manufacturers we see on quotes

    Tesla Powerwall, Sigenergy, Fox ESS and Sunsynk, for example. We weigh them on how well they match your evenings.

The batteries we see on quotes

Battery storage · questions

Asked about batteries.

01Does a battery change what I’m paid for export?

Yes. Power stored in the battery is used at home instead of exported. On the example estimate, export income falls from about £620 to about £450 a year, while the saving off the bill rises from about £460 to about £780.

02Can I add a battery later?

Yes, and it’s worth telling us now. Planning for one can change the inverter we choose and leave room for it.

03Does a time-of-use tariff change the answer?

It can. Prices on a time-of-use tariff change through the day, usually cheapest overnight, and a battery is more often worth it on one.

04Will you tell me to buy one?

No. We price the system with a battery and without, show the payback of each and leave the decision with you.

05What warranty do the batteries you price carry?

A ten-year manufacturer’s warranty, with a share of their capacity guaranteed to the end of it. The manufacturer’s own terms say how large that share is.

Every question

From the guides

Read more before you decide.

Every guide explains one part of the job in plain English.

A quiet street of terraced houses with front gardens

Money · 5 min read

Export payments, in plain English

How the Smart Export Guarantee works, what has to be in place before payments start, and why part of a solar saving is export income.

Read the guide

Keep reading

The rest of the service.

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