Solar
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21 Aug 2026
Adding a battery to an existing solar system
Fitted between 2011 and 2019 with no storage? Your roof has been giving most of it away. Whether you can add a battery is a narrower question than people assume.
If you had solar fitted between about 2011 and 2019, there is a good chance your roof has spent every summer since giving away most of what it makes. Adding a battery is the fix. Whether you can is a narrower question than people assume.
There are a lot of these houses across Lancashire. Panels went up under the old feed in tariff, the installer said nothing about storage because home batteries were barely a product yet, and the system has quietly worked ever since.
The problem is what happens at one in the afternoon in June. The panels are producing more than the house is using, the surplus goes back to the grid, and you are paid a modest amount for it. Then at seven in the evening the panels have stopped, the house is at its busiest, and you buy that electricity back at a considerably higher rate.
A battery closes that gap. This page is about whether one can be added to what you already have.
Octopus Energy, May to July 2026 against the same months last year
630%
Rise in battery only installations
Battery only means people who already had panels adding storage afterwards. It is the fastest growing part of the domestic market, and it is almost entirely made up of households doing exactly what this page describes.
The short answer
Usually yes. It depends on your existing inverter, and there are three routes.
1
AC coupled
A separate battery with its own inverter, wired in alongside the existing system. Your original setup is left completely alone. This is the usual answer for a retrofit and the least disruptive.
2
Hybrid inverter swap
Replace the existing inverter with one that handles panels and battery together. More work, tidier result, and often sensible if the original inverter is near the end of its life anyway.
3
Battery ready already
Some later systems were fitted with a hybrid inverter from the start, in which case the battery simply connects to what is already there. Worth checking before assuming anything.
Six things that decide it
What inverter have you got, and how old is it
The single biggest factor. It will be a box somewhere near the consumer unit, in a loft, a garage or a utility, with a make and model on the front. Photograph the label and you have answered most of the question in one go. Inverters typically need replacing at some point in their life anyway, and if yours is approaching that, a hybrid swap starts to look like better value than an AC coupled addition.
Are you still on the feed in tariff
This one matters and it is frequently got wrong. Adding storage does not end your feed in tariff payments. Under the old scheme most domestic systems are paid an export element on a deemed basis, meaning it is assumed you export a set proportion regardless of what you actually export. Storing more of your own generation does not reduce that payment. Check your own agreement rather than take our word for it, but the common fear that a battery will cost you your tariff is usually unfounded.
How much do you use after dark
A battery should be sized against your evenings, not against your array. A large system with an undersized battery still exports most of its surplus. An oversized one is money sitting idle. Ten minutes with a smart meter app will get you close enough to have a sensible conversation.
Where would it physically go
These units are substantial and they are heavy. Garage, utility, plant room or an external wall are all normal. The location affects the cable run back to the consumer unit, the ventilation, and occasionally whether the wall itself is suitable. It is worth deciding early because it shapes the design.
What tariff are you on now
This is what makes a battery useful in January rather than only in June. A time of use tariff lets the battery charge from cheap overnight grid electricity as well as from the roof, which gives it a second job through the months when your panels are contributing rather than providing. Not every setup is configured for it, so ask.
Do you want backup during a power cut
Most batteries do not provide backup on their own. It usually requires additional equipment and additional wiring, and it is the thing most often assumed and least often quoted. On a Tesla system that function comes from the Backup Gateway rather than from the battery. If it matters to you, say so at the start and make sure it appears on the quote.
What to find before you ring anybody
Five minutes of digging will save a survey visit and get you a far more useful first answer.
Go and look for these
A photo of the inverter
The label with the make and model on it. This answers most of the question on its own.
Roughly when it was installed
The year is enough. It tells us what generation of kit you are on.
Your feed in tariff paperwork
If you can find it. It confirms whether your export is deemed or metered.
Your annual electricity use
On any annual statement, in units. This is what the battery gets sized against.
When it is not worth doing
We would rather say this now than after a survey.
- If your array is very small. Below a certain size there is not enough surplus to be worth storing, and the money is better spent adding panels first.
- If somebody is home all day, every day. You are already using most of what you generate directly, which is better than storing it. The gain from a battery is correspondingly smaller.
- If the array is badly shaded and nobody has looked at why. Fix the generation problem before buying somewhere to put generation you are not producing.
- If the existing system has a fault. More common than you would think on systems fitted over a decade ago. Worth establishing that everything is working properly first.
Get a straight answer
Send us a photo of your inverter, the year the panels went up, and your annual electricity use. That is enough for us to tell you which of the three routes applies to your house and whether it is worth pursuing.
Free, no obligation
A photo of your inverter answers most of the question.
If a battery is not the right answer for your house, we will say so. We would rather tell you now than sell you something that disappoints you.
Battery only installation growth figure published by Octopus Energy and reported by Solar Power Portal, August 2026, covering May to July 2026 against the same period the previous year. Feed in tariff arrangements vary by agreement and by generation, so check your own paperwork or ask your tariff administrator rather than relying on general guidance.
