Home batteries and time-of-use tariffs: charging cheap, using at peak

On a time-of-use tariff, electricity costs less at some times of day than others. A home battery can charge when power is cheap and run your home when it is expensive – with or without solar panels. This guide explains how that works in Great Britain, what the losses are and what to check before you buy. We don’t recommend any particular supplier or tariff: offers change often, and the maths below works for any of them.

Static and dynamic time-of-use tariffs

Time-of-use tariffs charge different prices at different times of day or on different days ¹. There are two broad types:

All new flexible time-of-use tariffs require a smart meter with half-hourly readings ¹.

Three ways to use a battery

1. Solar self-consumption – store daytime surplus and use it in the evening, instead of exporting it.
2. Tariff shifting – charge from the grid when the tariff is cheap and supply your home when the cheap period ends. The Energy Saving Trust notes this can happen automatically ².
3. Exporting stored energy – some suppliers offer export tariffs that pay more at certain times. Whether stored grid electricity counts for an export payment depends on your supplier’s terms and how your system is metered; check before you plan on it.

Exports from solar can earn money through the Smart Export Guarantee (SEG). Participating suppliers must offer a rate that is always above zero, for eligible technologies such as solar PV ³. When your battery is full, surplus solar can be sold through a SEG tariff ².

Efficiency eats into the price gap

Every kWh you store doesn’t fully come back out. With 90% round-trip efficiency and a charging price of 10p per kWh, each kWh you later use effectively costs about 11p (10 ÷ 0.9). The difference between cheap and peak rates has to be bigger than that loss – plus standby consumption – for shifting to pay.

That’s why efficiency matters more on a time-of-use tariff than for simple solar storage. In HTW Berlin’s 2026 test, battery efficiency ranged from about 88% to 97.1%, and standby draw from 4 to 64 W ⁴. See usable vs nominal capacity for what those figures mean over a year.

Power: can the battery fill up in time?

Cheap windows can be short. A battery needs enough charging power to fill up within them:

• A 10 kWh battery charging at 2.2 kW needs about 4.5 hours from empty to full – fine for a long overnight window, not for a single cheap half-hour.
• Of 22 batteries in our database with a stated charge power, 8 charge at 5 kW or more; the rest charge more slowly.
• Five models in our database explicitly advertise control based on dynamic prices; their charge power is 1–2.4 kW.

Also check the control side:

• Can the battery import tariff prices itself, or do you need a separate energy management system?
• Does the control work with your supplier’s tariff, or only with certain providers?
• Can you set it to discharge only to your own home, not to the grid?

Browse options in our list of home batteries for dynamic tariffs.

Costs and VAT

The Energy Saving Trust gives a range of £1,500 to £10,000 for a battery system, with around £4,600 for a 5 kWh system ². Certain electrical batteries qualify for the reduced VAT rate on energy-saving materials from 1 February 2024 to 31 March 2027 ⁵ – ask your installer to confirm that your installation qualifies and that the quote reflects it.

Compare the purchase price against a realistic yearly saving: daily kWh shifted × price gap after losses × days per year. Batteries age, so don’t assume year-one savings for the whole life – see lifespan and warranties.

Before you sign up

• Smart meter installed and sending half-hourly readings.
• Tariff terms read: peak prices on a dynamic tariff can be high, and a battery softens that but doesn’t remove it.
• Grid connection: adding a battery can move you from G98 to G99 – see AC vs DC-coupled batteries.
• MCS-certified installer: get at least three quotes ².