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.
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.
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.