Adding Batteries to Existing Solar System UK: Sizes, Costs & Compatibility

Quick answer: Adding batteries to an existing solar system UK-wide almost always means one of two routes: an AC-coupled battery (its own small inverter, works with any existing solar setup, roughly £4,500–£7,500 fitted for 5–10kWh) or a hybrid inverter swap if your current inverter supports a DC-coupled battery add-on (usually cheaper battery hardware but a bigger job, from about £5,500). Most retrofits use AC-coupling because it doesn't touch your existing, already-certified solar installation. Size the battery to your actual daily export, not the biggest one you can afford, and always confirm compatibility with your original installer or the battery manufacturer before ordering anything.

Don't guess: check your real export. This table is a starting point based on typical UK yields, not your actual numbers. If your solar was installed with an app (Solis, SolarEdge, Fox ESS or Tesla monitoring, for example), you can see your real average daily export from the last 12 months. Size to that figure, not the table. For a personalised recommendation that factors in your tariff and occupancy too, run our Battery Storage Calculator →.

• Identify your existing inverter make and model: it's usually on a sticker on the unit itself, or in your original installation paperwork
• Check the inverter's age: inverters over 8–10 years old are approaching typical replacement age anyway, which can tip the decision toward a hybrid swap instead of AC-coupling
• Confirm your consumer unit has spare capacity: a battery needs its own circuit, and older consumer units sometimes need an upgrade first
• Check your SEG or export tariff terms: most providers are fine with adding a battery, but some tariffs are written around solar-only systems, so it's worth a two-minute call
• Got a GivEnergy inverter? GivEnergy entered administration on 9 April 2026, and its administrator has said it will not honour hardware warranties. Ask installers about an AC-coupled battery from another brand rather than adding more GivEnergy kit
• Use an MCS-certified installer for the retrofit: this keeps your original installation's certification valid and is required if you want the addition itself to count for any future incentive scheme

About 5kWh (for example Myenergi Libbi or Sunsynk): £4,500–£6,800 fitted

About 10kWh (for example Fox ESS EP11): £5,500–£7,500 fitted

13.5kWh (Tesla Powerwall 3): £8,500–£11,500 fitted. A hybrid inverter swap usually starts from about £5,500, depending on the battery

Can any solar inverter have a battery added later?

In practice, yes, even older, non-hybrid inverters can take an AC-coupled battery, because it connects independently at the consumer unit rather than through the inverter itself. The exception is very old or unusual inverter models that an installer may struggle to find monitoring compatibility for; a quick model check with the battery manufacturer avoids surprises.

Will adding a battery affect my existing SEG export payments?

Not usually, most SEG tariffs are based on metered export, and a battery still allows export once it's full. It's worth confirming with your specific SEG provider, as a small number of older tariff terms were written before batteries were common.

Is it cheaper to add a battery now or wait?

Battery prices have been falling gradually year on year, but retrofit labour costs haven't. If your solar system is already exporting a meaningful amount you're losing to the grid for free, the payback clock is running now. Waiting for a slightly cheaper battery rarely outweighs the savings missed in the meantime.

Do I need the same brand of battery as my existing inverter?

No, not for an AC-coupled retrofit, that's the main advantage of this route. Because the battery has its own inverter built in, it doesn't need to match or communicate with your existing solar inverter's brand. A DC-coupled hybrid swap is more brand-dependent, since the new inverter needs to be compatible with your existing panels.