If you already have solar panels, you don't need to start again to get a battery. In most Northern Ireland homes a battery can be added to the system you've got. The part most guides skip is what happens to your ROC payments — and if your system earns them, that part matters more than which battery you pick.
The short answer
- Yes, you can usually add a battery. Either alongside your existing inverter, or by replacing the inverter with a hybrid unit that runs the panels and the battery together.
- If you get ROC payments, the design decides whether they stay safe. Where the battery sits in relation to your generation meter, and whether it can charge from the grid, both matter — and Ofgem will not approve a change in advance.
- A battery added to existing solar in your home is 0% VAT until 31 March 2027.
- NIE Networks needs to know. A battery connects under the same G98/NI and G99/NI rules as your panels.
Two ways to add a battery
1. Keep your inverter and add a battery alongside it
The battery comes with its own inverter and connects into your house wiring on the AC side. Your existing solar inverter carries on exactly as it does now. It's usually the least disruptive route, and the one to look at first if your inverter is still fairly young.
2. Replace the old inverter with a hybrid
A hybrid inverter runs the panels and the battery from one unit. Sigenergy's SigenStor goes further — hybrid inverter, battery, backup, energy management and optional DC EV charging in one tower. This route makes most sense when your inverter is getting old anyway: one fitted in 2012 is fourteen years old this year. It's also the route that sets a house up best for adding more storage or an EV charger later.
But if your system earns ROCs, read the next section before choosing it.
If you get ROC payments — read this before you buy anything
Ofgem's guidance is plain that adding storage to an accredited station can affect whether it keeps receiving support, or how much it receives. Storage isn't banned: ROCs can continue, provided your station's genuine renewable generation can still be measured accurately and the electricity is still used or supplied in a permitted way.
In practice that comes down to your generation meter. Your ROCs are worked out from its readings, so it must only ever count electricity your panels made. In Ofgem's own example of a battery sitting before the generation meter, the battery can only be charged by the panels. If a battery could fill up from the grid overnight and then discharge back through your generation meter, that meter would record grid electricity as solar generation — which is exactly what the rules exist to prevent.
That matters most for the hybrid route. A hybrid inverter goes where your old inverter was, so its output runs through the generation meter. If it's allowed to charge the battery from the grid, you have a problem. There are proper ways to handle it — limiting the battery to charging from the panels only, or changing how the system is metered — and which one fits depends on how your system was accredited in the first place.
No approval in advance
There is no way to get Ofgem's go-ahead before the work is done. Changes are assessed case by case once they've been made and notified. So the design has to be right first time, not corrected after a payment has been queried.
What Power NI asks for when a battery is added
- An installer's report on headed paper: what the battery is for, whether anything else changed, when it went in (with the G98/NI or G99/NI commissioning certificate), how the electricity is used, and whether the battery can charge from the panels, the grid or both.
- An updated schematic diagram showing the correct generation meter.
- Nameplate photos of the inverter or inverters, and of the battery (make, model and serial number).
- The installer's invoice.
- Which of Ofgem's co-location scenarios matches your setup.
- A declaration that you, as the generator, sign and send.
We prepare the installer's report, the schematic and the certificates, and help you with the rest if you want it. The declaration itself is yours to sign.
Changing the inverter as well
Your original NIE Networks application recorded a declared net capacity for the system. Power NI recommends replacing an inverter like for like — without increasing that figure. If a new inverter does increase it, an amended application goes to NIE Networks and Ofgem needs the updated figure.
NIE Networks: the battery counts
Which application your system needs depends on its total installation capacity:
- G98/NI — up to 16 amps per phase: 3.68 kVA on a single-phase supply, 11.04 kW on three-phase. This covers most homes.
- G99/NI Fast Track — up to 60 amps per phase, with each inverter limited to 32 amps per phase and export limited to 16 amps per phase. NIE Networks changed the Fast Track rules on 1 May 2026.
- G99/NI — anything above that.
A battery with its own inverter adds to that total, so adding one to an existing system can move you out of G98/NI. We handle the NIE Networks side either way.
Starting small and adding more later
Several of the people who've asked us about batteries this year wanted the same thing: start with what they can justify now, and add more when the car or the heat pump arrives. The battery systems we fit all allow for that:
- Sigenergy SigenStor — battery modules stack to 48 kWh in the same tower.
- EcoFlow PowerOcean — starts with a single 5 kWh battery and grows to 45 kWh, with the longest warranty we fit: fifteen years, to 70% capacity.
- Hinen — 14.4 kWh modules, up to six per inverter, to 86.4 kWh.
If you're trying to choose between them, we've compared all three in Hinen vs SigenStor vs PowerOcean.
VAT and cost
HMRC's energy-saving materials rules zero-rate a battery retrofitted to existing solar panels in a home. The zero rate runs until 31 March 2027.
We price battery additions at survey rather than from a list, because the cost depends on which route suits your system, how big the battery is, and whether anything else needs changing. Our published solar and battery package — from £6,750 — is for new systems.
Adding a battery usually means you export less and use more of your own electricity. If you're weighing up what that's worth, our guide to export payments in Northern Ireland explains how export is paid here — and Power NI's current rate of 9.64p per kWh runs until 30 September 2026, with new rates due to be published towards the end of September.
What to have ready before you call
- A photo of your inverter's nameplate — make, model and, if you know it, the year it went in.
- Whether you get ROC payments, and from whom.
- Whether your supply is single-phase or three-phase (we can check).
- A year's electricity bills, or your supplier app's usage figures.
- Where a battery could go: garage, utility room or an outside wall.
Where these facts come from: Ofgem, co-location of electricity storage under the RO (version 6); Power NI's renewables team guidance on adding a battery and changing an inverter; Power NI tariff rates; NIE Networks, connecting generation; HMRC VAT Notice 708/6. All checked 18 September 2026.
Questions people ask
Can I add a battery to my existing solar panels?
In most homes, yes. Either a battery with its own inverter is added alongside your existing solar inverter, or the old inverter is replaced with a hybrid unit such as Sigenergy's SigenStor that runs the panels and the battery together. Which suits you depends mostly on the age of your inverter and whether your system earns ROCs.
Will adding a battery affect my ROC payments?
It can. Ofgem's guidance says storage can affect whether an accredited station keeps receiving support or how much it receives. ROCs can continue if the station's genuine renewable generation can still be measured accurately. Ofgem assesses each change case by case after it has been made and notified, so the design has to be right first time. Power NI asks for an installer's report, an updated schematic, nameplate photos and a declaration you sign.
Can I charge the battery from the grid if I get ROCs?
It depends on how the battery is connected in relation to your generation meter. Your ROCs are worked out from that meter, so it must never record grid electricity as solar generation. In Ofgem's example of a battery sitting before the generation meter, the battery can only be charged by the panels. We check how your system was accredited at the survey and tell you which arrangement applies.
Is there VAT on adding a battery to existing solar panels?
No. HMRC's energy-saving materials rules zero-rate a battery retrofitted to existing solar panels in a home, and the zero rate runs until 31 March 2027.
Can I add more battery capacity later?
Yes, with the modular systems we fit. Sigenergy SigenStor battery modules stack to 48 kWh, EcoFlow PowerOcean grows from a single 5 kWh battery to 45 kWh, and Hinen uses 14.4 kWh modules, up to six per inverter, to 86.4 kWh.