A home battery is solar's most-debated add-on. Some installers push it on every quote; others tell you to skip it. The answer is in the maths, and it depends heavily on how and when you use electricity.
What a battery does
Without a battery, solar you don't use straight away is exported to the grid for an SEG payment, typically 5–15p per kWh depending on tariff. With a battery, you store that surplus and use it after sunset, displacing grid electricity at 27–32p/kWh.
The gap is your gain: roughly 15–25p per kWh you'd have exported and now use yourself. Over a year, a 10kWh battery on a 4kW solar system typically cycles 250–300 times, saving around £450–£650/year.
When the maths works
Batteries pay off best for households who:
- Use significant electricity in the evenings (cooking, EV charging, heat pump)
- Have a south or south-west facing solar array generating well
- Are on a high standard tariff (not Economy 7 or Octopus Tracker)
- Plan to stay in the property 10+ years
When to skip it
A battery doesn't pay off if you're on a time-of-use tariff with cheap overnight rates (you'd do better charging from the cheap grid), if your daytime usage is already high (working from home with daytime EV charging), or if your generation is modest and there's little surplus to store.
Battery sizing rule of thumb
For most UK homes, the sweet spot is a battery roughly 2.5× the size of your solar array, so a 4kW system pairs well with a 10kWh battery. Bigger isn't always better: you only benefit from capacity you fill, and oversized batteries push payback past their warranty.
Brands worth shortlisting: Sigenergy SigenStor for slick all-in-one integration, Fox ESS EP12 for value and UK support. Both come with 10-year warranties as standard.
