Is a solar battery worth it?

What the battery is trying to solve

Solar panels generate most during the day. Many homes use most electricity in the morning and evening. A battery helps by storing surplus daytime solar for later use.

That can reduce imports from the grid. It can also reduce export income, because less surplus is sent out. The financial question is whether the import saving gained is worth more than the export income lost and the battery cost added.

The cost hurdle

Energy Saving Trust says battery storage tends to cost around £5,000 to £8,000. That is a serious extra cost on top of the solar PV system.

If the battery adds £6,000 and saves an extra £250 a year, simple payback on the battery alone is long. If it saves much more through high self-use or smart tariff use, the picture can improve.

Where batteries fit best

Batteries tend to make more sense when evening use is high, import rates are high compared with export rates, and the household can use the stored energy regularly.

They may also be attractive for non-financial reasons, such as backup capability. Be careful here. Not every battery provides whole-home backup during a power cut. Ask exactly what is backed up, for how long and at what power.

How to model it

Run solar-only first. Then add the battery cost and a cautious self-consumption uplift. If the payback gets worse, the battery may still be useful, but it's not improving the pure financial case under those assumptions.

• Try a 10 to 15 percentage-point uplift as a careful case.
• Try 20 to 30 points only if your usage pattern supports it.
• Check whether the tariff rewards or restricts battery export.
• Ask about battery warranty, usable capacity and cycle life.