If your solar panels went on a few years ago, they almost certainly came without a battery. Now the evenings are dark early and a battery looks sensible. The question we hear most is simple: will it work with what I already have?
Usually it will. But how it works depends on a handful of things, and a couple of them can change the plan. Here is what we look at when we survey an existing system. If you want the wider question of whether a battery is worth having, our guide to adding a battery to existing solar panels covers that. This page is about compatibility.
The short answer
Nearly every grid-connected solar system can have a battery added. The panels are rarely the problem. The inverter, the wiring and the paperwork are where the detail sits. Think of it as two routes: add a battery alongside what you have, or replace the inverter with one that handles panels and battery together. Both are normal, and a good installer will tell you which suits your house.
1. What type of inverter do you have?
This is the first thing we check, because it shapes everything else.
- A string inverter, usually a box on a wall in the loft, garage or utility room. This is the most common older setup. It works well with an AC-coupled battery, which connects on the house side and leaves your inverter alone.
- Microinverters, small units under each panel. These also suit an AC-coupled battery, since the panels are already producing AC power before it reaches the house.
- Optimisers with a central inverter. Many of these systems can take a battery, but the choice of compatible models is narrower, so it is worth checking the make and model before you fall for a particular battery.
Not sure what you have? The model number is on the inverter or in your handover paperwork. A photo of the inverter and your consumer unit is often enough for a first answer.
2. How old is the inverter?
Panels tend to outlast inverters. If yours is close to ten years old, it is worth thinking about now. Fitting an AC-coupled battery to an inverter that fails in two years means you are back with an engineer to deal with it.
In that case replacing the old inverter with a hybrid at the same time can be the tidier job: one new unit looks after both panels and battery. We explain the difference in our guide to hybrid inverters. If the inverter is healthy and fairly young, there is usually no reason to touch it.
3. Do you have a generation meter or the old Feed-in Tariff?
If your system was fitted under the Feed-in Tariff, you will have a generation meter that records what the panels produce. Tell your installer at the start. For many systems an AC-coupled battery leaves that metering as it is, but anything that replaces or rewires the inverter needs checking against the tariff arrangements first. This is a good example of why a proper survey beats a guess from a photo.
4. Single-phase or three-phase supply
Most homes are single-phase, and most home batteries are built for it. If you have a three-phase supply, the battery and inverter need to match, and the options are different. It is easy to see on the consumer unit or the meter tails, and we check it on every survey.
5. The consumer unit and the wiring
A battery adds a new connection to your electrics. Your consumer unit needs space for it, with the right protection, and the cable runs between the battery, inverter and unit have to be sensible. Older consumer units sometimes need replacing, which is better known about before a battery is ordered. If you want backup power in a power cut, that changes the wiring again, so say so early. Our guide to solar in a power cut explains what backup does and does not cover.
6. Where the battery will live
Batteries need a sensible spot: a garage, utility room or similar, with space around them and not in a bedroom or an escape route. Many older solar homes have the inverter in the loft, and the battery will not go there. It usually means a short run of cable down to a better location. We cover siting in our guide on whether home batteries are safe.
7. Approval from your network operator
Adding a battery changes how your property exports and imports, so your local network operator usually needs to be told or asked. We handle this paperwork. The detail is in our guide to DNO approval, G98 and G99.
When a battery is not a simple bolt-on
A battery is not a sensible next step if the inverter is already failing, if the roof needs work, or if the panels are producing well below what they should. In those cases we would sort the underlying issue first, and we will say so. If you are not sure the system is healthy, your monitoring app is a good place to start. Our guide to reading your solar monitoring shows what to look for.
Why use an MCS installer
The battery should be fitted by an MCS-certified installer, and ours are our own employed teams, not subcontractors. That matters on a retrofit, because the person who surveys your system should be the person accountable for how the battery works with it afterwards. You can read more about what we fit on our battery storage page.
Talk to a local installer
If you have solar on your roof and want to know what a battery would involve, we can look at your actual system and give you a straight answer, including when the answer is to wait. We cover Dorset, Hampshire and Wiltshire from our base in Wimborne. Request a free, no-obligation quote.