If you had solar panels fitted a few years ago and you’re only now considering battery storage, the good news is that adding a battery afterwards is entirely normal and usually straightforward. The slightly more complicated news is that how it’s done, and what it means for any existing payments you’re receiving, depends on the details of your original installation.
How retrofitting actually works
There are two general approaches to adding a battery to an existing solar system, and which one applies to you matters more than most people realise. As explained in Sunsave’s guidance on adding a battery to an existing solar system, AC coupling adds the battery, complete with its own inverter, onto the household’s AC side, working alongside your existing solar inverter rather than replacing it. DC coupling, by contrast, typically sits on the panel side and usually requires a hybrid inverter, which in a retrofit situation often means replacing a solar inverter that’s still working perfectly well.
For most retrofits, AC coupling is the more practical route, precisely because it leaves your existing, functioning solar inverter in place rather than disturbing a system that doesn’t need fixing. DC coupling tends to make more sense in situations where your existing inverter is already near the end of its warranty, or is showing signs of age, and would need replacing before too long anyway.
Retrofitting also raises the same fire safety siting question that applies to any battery installation, regardless of whether it’s new or added later. Under PAS 63100, the British Standard covering fire safety for battery energy storage systems in dwellings, a retrofitted battery needs exactly the same careful consideration of location as a new one, ideally in a garage, outbuilding, or suitably fire-separated utility space, not simply squeezed in wherever there’s a spare wall next to the existing inverter.
Solar panels installed a few years ago? Worth a quick recheck
A retrofit is also a sensible moment to have your existing solar installation itself given a once-over, not just the new battery. Roofs and fixings that were perfectly sound when panels went up several years ago can change over time, and mounting brackets, cabling, and the inverter itself all benefit from a check as part of adding new equipment to the system, rather than assuming everything’s exactly as it was on day one.
If your solar was installed under the old Feed-in Tariff scheme
This is the part that catches a lot of people out, and it’s worth understanding properly before any work starts. If your solar panels were installed under the Feed-in Tariff, or FiT, scheme, which closed to new applicants back in 2019 but still pays out to existing accredited households, adding a battery doesn’t affect your generation tariff, since that’s based on the total electricity your panels produce, which doesn’t change just because you’re now storing some of it.
Export payments are a different matter. According to Ofgem’s own guidance for FiT generators, any household adding a battery to an existing FiT system, whether new or retrofitted, needs to formally declare it to their FiT licensee, typically by providing a schematic showing exactly where the battery sits within the installation. Many older FiT systems are paid on a “deemed” export basis, meaning your supplier assumes a fixed percentage of your generation is exported rather than measuring it directly. Where a battery is added incorrectly, or without the right metering in place, there’s a real risk of complications with that arrangement, including the possibility of grid-charged electricity being mistakenly counted as solar generation. A bi-directional meter, correctly installed, prevents exactly that problem.
None of this means adding a battery to a FiT system is a bad idea, for most households it still makes sense. It does mean it has to be done properly and declared correctly, rather than treated as a simple bolt-on with no wider implications. Skipping the declaration, or having it done incorrectly, risks a dispute with your FiT licensee further down the line over payments that were made on an inaccurate basis, which is a considerably more stressful conversation to have after the fact than getting the paperwork right from the outset.
If you’re on the Smart Export Guarantee instead
If your solar system is newer and you’re on the Smart Export Guarantee rather than the legacy FiT scheme, the situation is generally simpler. SEG payments are based on actual smart meter readings of what you export, rather than a deemed assumption, so adding a battery that reduces how much you export and increases how much you use yourself is simply reflected in your next reading, without the same declaration requirements that apply to FiT households.
Why a properly certified installer matters even more for a retrofit
Because of the FiT and metering considerations involved, a retrofit is arguably a job where installer competence matters even more than on a brand new system. The Microgeneration Certification Scheme’s dedicated battery installation standard, MIS 3012, requires MCS-certified installers to assess the existing system properly before adding storage, including how the retrofit interacts with any existing accreditation, not just how to physically wire it in.
GU Solutions is a NICEIC Approved Contractor and Domestic Installer, and for FiT households in particular, that means handling the declaration to your FiT licensee correctly and making sure your existing payments are protected throughout the process, not just fitting a battery and leaving the paperwork to you afterwards.
What to check before you commit to a retrofit
Before agreeing to a retrofit, it’s worth asking whether the installer recommends AC or DC coupling for your specific system, and why. If you’re on the FiT scheme, ask directly how they’ll handle the declaration to your licensee, and whether a bi-directional meter is included as part of the installation. And ask how they’ve assessed your existing solar inverter’s condition and remaining warranty, since that has a real bearing on which coupling approach makes sense for you.
A good installer will walk you through all of this clearly, because protecting an existing FiT arrangement while adding genuinely useful new capability is exactly what a well-handled retrofit should achieve. It’s also worth asking where they’re proposing to site the battery and why, given the fire safety siting rules that apply regardless of whether it’s a new system or an addition to an existing one, and whether they’ll be giving your existing panels, mounting, and inverter a quick health check while they’re already on site.
Getting a retrofit that protects what you already have
Retrofitting battery storage is entirely possible for the vast majority of existing solar systems around Basingstoke, Old Basing, Chineham, Oakley and Sherborne St John, but the right approach depends on your existing inverter, your export scheme, and how the installation is declared.
If you’d like your existing solar system properly assessed before adding a battery, GU Solutions is the first port of call. As NICEIC Approved Contractors and Domestic Installers, we’ll make sure any existing Feed-in Tariff or SEG arrangement is protected, and that the retrofit itself is done to the right standard from day one.
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