Solar batteries: costs and choosing a size

A solar battery stores spare electricity from your panels so you can use it later. It can be useful if you’re out during the day and use more electricity in the evening.

Would a battery help you?

Start with how much spare solar electricity you have and when you need it. A battery may let you buy less electricity from the grid, but it adds to the installation cost and loses some energy when charging and discharging.

Ask for a comparison of the same solar panels with and without a battery. If you already have panels, your monitoring app and electricity bill can help the installer choose a suitable size.

How much does a solar battery cost?

Energy Saving Trust gives a broad range of £1,500 to £10,000, depending on capacity and the work needed. Its example for a typical 5 kWh battery is around £4,600. Ask for the full fitted price, including any changes to your inverter or wiring.

What size should you choose?

Battery capacity is measured in kWh, the same electricity unit shown on your bill. Ask for the usable capacity: the amount you can normally draw from the battery. It may be lower than the size advertised.

A larger battery is only useful if you can regularly charge it and use the stored electricity. In winter, your panels may not produce enough spare electricity to fill it.

Also ask how much power it can supply at once. This affects which appliances it can run together.

Will it work in a power cut?

Some batteries offer backup power, but many standard installations switch off with the grid. If backup matters to you, ask:

• Which lights, sockets and appliances will keep working?
• How long could they run?
• Will backup start automatically?
• Can the panels recharge the battery during the power cut?
• Is extra equipment or wiring included in the price?

Have the installer demonstrate the backup safely and leave instructions. Electricity reserved for emergencies is not available for everyday use.

Questions before you buy

• What is the usable capacity and full fitted price?
• How much electricity is lost during charging and use?
• How long is the warranty, and what does it cover?
• Does the app have a subscription charge?
• Can I use the electricity tariff I want?
• Who provides repairs and support?

See whether a battery could be worth the extra cost. If you already have a battery that has stopped working, visit the fault and repair guide.