If you had solar panels fitted a few years ago, there’s a good chance they came without a battery — most systems installed before energy prices climbed did. Now, with electricity costing far more than it used to and export rates well below the old Feed-in Tariff, a lot of solar owners are asking the same question: is it worth adding a battery to what I’ve already got?
We retrofit batteries to existing solar systems regularly, so we’re not a neutral party. But the honest answer is that it’s worth it for some homes and not others — and it’s easy to work out which you are. Here’s how to think it through.
Why so many solar owners are adding batteries now
When your panels generate more than you’re using — usually in the middle of the day — that surplus goes to the grid. Under the old Feed-in Tariff you were paid reasonably well for it. Today, most people export for a fraction of what they pay to buy electricity back in the evening. A battery closes that gap: instead of selling your solar cheaply at midday and buying expensive power at 7pm, you store your own generation and use it when you’d otherwise be paying peak rates.
How much more of your own solar you’d actually use
Without a battery, a typical home uses only around 40% of what its panels generate — the rest is exported. Add a battery and that self-consumption usually rises to somewhere around 70–80%. In plain terms, you keep far more of the free electricity you’re already producing rather than handing it to the grid. The bigger the gap between your daytime generation and your evening usage, the more a battery does for you.
Will a battery work with your existing system?
Almost always, yes — but how it’s fitted depends on what you have. A battery can be “AC-coupled,” which means it’s added alongside your existing solar inverter without replacing it, and that’s the usual route for a retrofit. Alternatively, if your inverter is ageing or due for replacement anyway, a hybrid inverter can run both the panels and the battery together. A good installer will look at your current inverter, its age and your consumer unit, then tell you the cleanest option rather than forcing a one-size-fits-all answer.
If you’re weighing up which battery, our comparison of Tesla, GivEnergy and Sunsynk is a useful starting point.
What size battery do you need?
Bigger isn’t automatically better. The right size is roughly the amount of electricity you use in the evening and overnight, once the sun is down — because that’s what the battery is there to cover. Oversize it and you’re paying for capacity you’ll rarely fill; undersize it and you’re still buying peak power. Our free size estimator gives you a sensible starting point before anyone visits.
What about backup during a power cut?
This one is worth being clear about, because it’s often misunderstood. A standard battery does not automatically keep your lights on in a power cut — for that, the system has to be set up specifically for backup, with the right inverter and wiring. If keeping essentials running during an outage matters to you, say so up front, because it changes the specification. It’s very doable; it just isn’t automatic.
When adding a battery might not be worth it
- Very low evening usage. If you’re genuinely out most evenings and use little power once it’s dark, there’s less for a battery to save.
- A much older system. If your panels or inverter are near the end of their life, it can make more sense to plan a fuller upgrade than to bolt a battery onto ageing kit.
- You’re moving soon. The savings build up over years, so if you’re selling up shortly the payback window is tight.
None of these are dealbreakers for most homes — but a straight installer will tell you if you’re one of them rather than selling you a battery anyway.
Getting it done properly
A retrofit battery still needs doing to the same standard as a new installation: fitted by an MCS-certified installer, notified to your Distribution Network Operator where required, and backed by proper workmanship and product warranties. It’s a straightforward job for an experienced team, but not one to cut corners on — the battery is the most significant single component, and it has to be installed and configured correctly to be safe and to perform.
Talk to a local installer
We’re an MCS-certified installer based in Wimborne, covering Dorset, Hampshire and Wiltshire, and we retrofit batteries to existing solar systems as well as fitting new ones. If you’d like a straight answer on whether it’s worth it for your home — including if it isn’t — request a free, no-obligation quote and we’ll take a look at your current setup.
Not sure where to start? Our free suitability checker and battery storage page are a good first stop.