A home battery is solar's most-debated add-on. Some installers push it on every quote. Others tell you to skip it. The truth, as usual, is in the maths — and it depends heavily on how and when you actually use electricity.
What a battery actually does
Without a battery, solar you generate but don't immediately use is exported to the grid for an SEG payment — typically 5–15p per kWh depending on tariff. With a battery, you store that surplus instead and use it after sunset, displacing grid electricity at 27–32p/kWh.
The arbitrage is the difference: roughly 15–25p saved per kWh you would have exported and now self-consume. 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 that already gives you cheap overnight rates (you'd be better off just charging from the cheap grid), if your daytime usage is already high (working from home with EV charging during the day), or if your solar generation is modest and you don't have much surplus to store anyway.
Battery sizing rule of thumb
For most UK homes, the sweet spot is a battery sized at roughly 2.5× your solar array — so a 4kW system pairs well with a 10kWh battery. Bigger isn't always better: you only benefit from capacity you actually fill, and oversized batteries push payback past their warranty.
Headline brands worth shortlisting: Tesla Powerwall 3 for premium integration, GivEnergy for value, Solis hybrid for retrofit simplicity. All come with 10-year warranties as standard.