It surprises a lot of people: if there’s a power cut, a standard solar and battery system switches off too — even in bright sunshine, even with a full battery. If you’ve assumed solar means you’d keep the lights on when the street goes dark, this is worth understanding before you buy — because keeping power during an outage is absolutely possible, it just has to be designed in.
Why solar shuts down in a power cut
It’s a safety rule, not a fault. When the grid goes down, engineers may be working on the lines. If your panels kept pushing electricity out onto that network, it could put those workers at risk. So every grid-connected system in the UK is required to shut off automatically the moment it detects the grid has failed — it’s called anti-islanding, and it exists to protect people. That’s why a normal system, however large, goes quiet in an outage.
So what’s the point of a battery?
A standard battery still charges from your solar and saves you money day to day — but on its own it won’t power your home during a cut, for that same safety reason. To keep running through an outage you need the system set up specifically for backup, sometimes called EPS (Emergency Power Supply). With the right inverter and wiring, the system safely disconnects from the grid and runs your home from the battery and panels in “island” mode — legally and safely, because it’s isolated from the network.
Whole home, or just the essentials?
Backup usually comes in two flavours. A whole-home setup keeps everything running, within the battery’s limits. A more common and affordable approach is an essentials circuit — your fridge, freezer, broadband, some lights and sockets — which covers what actually matters in an outage without needing a huge battery. Which one suits you depends on how much you want to keep running, and for how long.
Which sockets does EPS actually power?
On an essentials setup, only the circuits that were deliberately wired into the backup supply — typically the fridge and freezer, the broadband router, and a handful of lights and sockets. Everything else stays off until the grid comes back. It is worth knowing which sockets those are before you need them, so ask for them to be labelled at handover. On a whole-home setup the house runs as normal, limited by how much the battery is holding and how much you draw at once, so heavy loads like an electric shower or an oven can still be more than the system will carry.
What you need for it to work
- A backup-capable inverter — not all inverters offer this, so it has to be chosen deliberately.
- The right wiring and a changeover device so the home can safely island from the grid.
- Enough battery capacity for what you want to keep running, and for how long.
The key point: this has to be specified at the design stage. It’s far simpler to build in from the start than to add later — so if backup matters to you, say so up front.
Can backup be added to a system you already have?
Often it can, but it depends on what is already on your wall. Some hybrid inverters have a backup output built in and need only the extra wiring and a changeover device fitting. Others have no backup capability at all, in which case adding it means changing the inverter, which is a larger and more expensive job. Battery brands differ too — a Tesla Powerwall needs its Backup Gateway to run the house in an outage, and other manufacturers have their own equivalent.
There is no honest one-size answer here, because it comes down to the specific inverter and battery you have. If you already have solar or storage and want to know whether backup can be added, call us on 01202 985888 with the make and model of your inverter and battery and we will tell you where you stand. See also our comparison of home batteries from Tesla, BYD and Sunsynk, which covers how each one handles backup.
Is it worth it for you?
Backup earns its keep if power cuts are more than a rare annoyance — if you’re rural or on a line that goes down in storms, if you work from home and can’t afford to lose connectivity, or if someone in the house relies on powered medical equipment. If your area almost never loses power, you might reasonably decide a standard battery is enough and skip the extra. There’s no wrong answer — just make the choice knowingly.
Talk to a local installer
We’re an MCS-certified installer covering Dorset, Hampshire and Wiltshire, and we design battery storage with or without backup depending on what you need. If keeping the lights on in an outage matters to you, tell us early and we’ll spec it properly — request a free, no-obligation quote to talk it through. Already have solar? See our guide to adding a battery to an existing system.