Solar and battery payback: is a battery worth it?

Adding a battery to solar panels typically costs £2,500 to £5,000 when both are fitted together, and saves an extra £150 to £450 a year. A battery lets you use more of your own solar power, rising from about 40% without a battery to around 75% with one. Whether it is worth it depends mostly on how much electricity you use in the evening and whether you use a cheap overnight tariff.

This guide explains how batteries change the sums, when they are worth it and when they are not.

Why a battery helps solar

Solar panels produce most of their power in the middle of the day, when many homes are empty or using little. Without a battery, a typical home uses about 40% of its solar power and exports the rest to the grid under the Smart Export Guarantee, at rates of around 4p to 15p per kWh.

Electricity you buy from the grid costs about 26p per kWh. So each unit of solar you use yourself is usually worth more than each unit you export. A battery stores the spare daytime power and releases it in the evening, so your self use rises to around 75%.

A simple worked example

Here is how the sums work, in words rather than invented numbers.

1. Start with your solar output. A 4 kWp system on a south facing Dorset roof produces about 1,000 kWh per kWp a year. Multiply that by the system size to get your yearly generation.
2. Without a battery, you use about 40% of that generation. The rest is exported at your SEG rate, often around 12p per kWh on a good fixed tariff.
3. With a battery, you use about 75%. The difference between the two shares is the solar you now keep instead of exporting.
4. Value that shifted solar. Each unit you keep saves you the grid price of 26p per kWh, but you lose the export payment for it. So each shifted unit is worth the gap between the grid price and your export rate.
5. Add off peak charging. On a time of use tariff, the battery can also charge overnight at around 8p per kWh in winter, when solar output is low, and power your home during the expensive part of the day.

Put together, most homes see an extra £150 to £450 a year from a battery. Divide the cost of £2,500 to £5,000 by your expected yearly saving to get a rough payback for the battery on its own. The whole solar system without a battery typically pays back in 8 to 14 years.

Our free solar estimate gives you a rough figure for your own home.

Time of use tariffs

Smart time of use tariffs charge less overnight and more at peak times. This is where batteries really earn their keep, especially in winter:

• In summer, the battery mostly stores your own solar.
• In winter, when panels produce less, the battery can charge cheaply overnight at around 8p per kWh and cover your evening use.

If you also have an electric car or a heat pump, a time of use tariff and battery can work well together. See our pages on EV chargers and air source heat pumps.

When a battery is worth it

• You use a fair amount of electricity in the evening and at night
• Someone is out at work during the day, so solar would otherwise be exported
• You are happy to switch to a time of use tariff
• You are fitting solar now, so the battery shares the installation and scaffold visit
• You have, or plan to get, an EV or heat pump

When it may not be worth it

• You are home all day and already use most of your solar as it is generated
• Your electricity use is low overall
• You have a very generous export tariff, which narrows the gap between exporting and using
• Your solar system is small and there is little spare power to store

Export or store?

It is not all or nothing. A good battery and inverter can be set to store solar, export at certain times, or charge from the grid overnight. Some export tariffs pay more at peak times, so smart settings can let you sell stored power when it is worth more. Ask your installer what control the system gives you and which tariffs it works with.

Sizing your battery

Most homes choose 5 to 10 kWh. Bigger is not always better. A battery that never fills or never empties is wasted money. As a rough guide:

• Look at how much electricity you use from late afternoon to the next morning
• Match the battery to that, within what your solar can realistically fill
• Think ahead if you plan to add an EV or heat pump

An installer should look at your bills or smart meter data before recommending a size.

Adding a battery later

If you are not sure now, ask for a hybrid inverter with your solar. It makes adding a battery later simpler and often cheaper. Bought on its own, a fitted battery typically costs £3,000 to £6,000. Batteries fitted to homes also have 0% VAT until 31 March 2027, whether fitted with solar or later.

Warranties

Batteries typically come with a manufacturer warranty of 10 to 15 years, often guaranteeing a share of the original capacity at the end. Check:

• the length of the warranty and the capacity it guarantees
• whether there is a limit on the number of charge cycles
• who handles a claim if the installer stops trading
• whether the workmanship warranty is insurance backed

Solar panels themselves typically last 25 to 30 years, so you may replace a battery once during the life of your panels. If payment comes up, ask your installer about payment options.

For more on the cost of the panels themselves, read how much do solar panels cost in Dorset, and find out more about battery storage. Homes in towns like Poole and Weymouth often pair solar with a battery.

Next steps

Get a rough cost and saving for solar, with or without a battery, using our free estimate tool. Then request quotes and we will pass your details to up to 3 local MCS certified installers.