1. No backup function
The inverter is designed for grid-connected use only. In an outage it shuts down, and adding a switch alone may not make this equipment suitable for backup.
Already installed solar and storage?
Panels. Battery. Power cut. Still in the dark?
It’s an unpleasant surprise: the battery is sitting there, the panels are on the roof—and the lights have gone out. Often, the equipment hasn’t failed. The system may simply never have been designed to provide backup power.
The key distinction: a battery stores energy; backup equipment lets the system safely supply your home when the grid is down. They are related, but one does not automatically mean the other.
Why this catches people out
“Solar and battery” doesn’t always mean “backup.”
A standard grid-connected inverter needs to see a healthy grid supply. If the grid fails, anti-islanding protection makes it disconnect. That helps prevent household generation from energising a section of network that engineers may have isolated to repair. A battery connected to a system without backup capability can shut down too, even if it is charged.
Backup requires equipment that can safely separate the relevant home circuits from the public network, then form a stable local supply. Depending on the system, that might involve an EPS output, a compatible gateway or transfer switch, specific wiring, and a dedicated set of backed-up circuits. The design must keep the home’s local supply isolated from the network.
This is why backup can add cost: there may be additional hardware, electrical work and design choices. But it is a requirement worth discussing early, so you can decide whether it matters to your household before the quote is agreed.
What might be installed?
Three common situations
2. Backup-capable, not set up
The inverter may support emergency operation, but the compatible gateway, transfer arrangement or backed-up circuits may not have been included in the original installation.
3. Limited backup is fitted
You may have an emergency socket or a few selected circuits, rather than whole-home backup. High-demand appliances may be excluded or exceed the system’s output.
These are examples, not a diagnosis of your installation. Different brands use different terms and arrangements. A “backup” label on an app or inverter is not enough to confirm which parts of the property will stay live.
Start with the paperwork
Find out what you actually have.
- Find the inverter and battery make and model in your handover documents, quote or monitoring app.
- Look for terms such as EPS, Emergency Power Supply, backup output, island mode, gateway or essential-load circuits.
- Check the installation drawings or circuit schedule to see whether any sockets or circuits are specifically identified as backed up.
- Ask the original installer to confirm what happens when grid power is lost, and what equipment would be needed to add backup.
Please don’t experiment inside the equipment. Don’t remove covers, alter wiring or try to create an island yourself. Ask a qualified installer to inspect the design and explain it safely.
If backup matters to you now
A retrofit may be possible—but it needs a proper check.
Whether an existing system can be upgraded depends on the exact inverter and battery, whether compatible backup equipment is available, how the property is wired, the earthing and protection arrangements, which circuits you want covered, available space, and any relevant network requirements. In some cases, a modest emergency socket may be practical; in others, the equipment or wiring may need more substantial changes. Some systems cannot be upgraded economically.
Ask an installer to set out, in writing:
- Which circuits would remain powered—and which would not.
- The continuous and peak power available to those circuits.
- Whether solar can recharge the battery while the grid is off.
- How the system starts or restarts if the battery runs low.
- The estimated usable energy, expected loads and assumptions behind any runtime estimate.
- The full retrofit cost, including any required electrical work or approvals.
Be specific about the essentials: perhaps lighting, refrigeration, communications and a few small sockets. Heating, hot water, cooking and EV charging can use far more energy or exceed the backup output. A battery’s capacity is not a promise that every appliance will work.
The questions people ask first
Quick answers
Does no backup mean my battery is faulty?
Not necessarily. The battery may be working exactly as designed, while the system has no backup mode or no transfer equipment and backed-up circuits installed.
Can I add an EPS switch to any system?
No. A switch or gateway must be compatible with the inverter and system design. It cannot turn every grid-only inverter into a backup inverter.
Will backup keep my whole house running?
Not automatically. Some installations support only an emergency socket or selected circuits. Ask for the exact circuits and load limits.
Will solar refill the battery during the outage?
Only if the inverter and backup arrangement support it in island mode. Available charging also depends on daylight, weather, shading and system settings.
For the longer explanation of anti-islanding and safe isolation, see What happens to solar panels during a power cut? For wider household planning, read our calm three-day power-cut plan and the official UK Government power-cut guidance.
Buying a system now? Ask the backup question before you sign.
Ask the salesperson to show you what happens when the grid fails, which circuits are covered, what extra equipment is included and what the realistic runtime assumptions are. That makes it easier to compare like with like—and decide whether backup is worth the added cost for your home.
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