Do solar panels work in a power cut? (UK backup power explained)

No, a standard grid-tied solar system does not keep your home powered in a power cut, and even adding a battery doesn't change that on its own. UK grid-connected inverters are required by law (the G98/G99 connection rules) to shut down within about two seconds of losing the grid, a safety feature called anti-islanding that protects engineers working on the lines. To keep the lights on during an outage you need specific backup hardware: a battery paired with a backup gateway, or an inverter with EPS (Emergency Power Supply / island mode). Without that, your panels and battery sit idle until the grid returns.

This is a genuine myth-buster, because "I've got solar, so I'm covered in a blackout" is one of the most common misunderstandings about home solar. Here's exactly why standard systems switch off, and exactly what you'd need if backup power matters to you.

The myth, and the safety reason behind it

It feels obvious that panels making electricity should power your house when the grid drops. The reason they don't is safety, and it's non-negotiable.

When the grid goes down, engineers may be working on those same power lines to fix the fault. If your solar system kept pushing electricity out, it could energise lines that everyone assumes are dead, creating a lethal risk for those workers and for the network. This unwanted, isolated live section is called an "island", and preventing it is called anti-islanding.

So every compliant grid-tied inverter is built to detect the loss of grid voltage or frequency and disconnect itself within a couple of seconds. It's not a fault or a limitation someone forgot to fix. It's a deliberate, mandatory protection, and it applies to your battery too if the battery inverter has no backup capability: the whole system stands down to keep the lines safe.

G98 and G99: the rules that switch you off

Anti-islanding is mandated in the UK by the grid-connection standards G98 and G99, which govern how small-scale generation (like home solar and batteries) connects to the distribution network:

• G98 covers smaller systems, up to 3.68 kW per phase of export, on a "fit and inform" basis: the installer notifies your Distribution Network Operator (DNO) after commissioning.
• G99 covers larger or more complex installations and requires a formal DNO application and approval before work begins.

Both require the inverter to disconnect on loss of grid, typically detecting an out-of-range voltage (roughly below 207V or above 253V) or frequency (below 47.5Hz or above 52Hz) and shutting down within about two seconds. Whichever route your system connects under, the anti-islanding behaviour is the same: no grid, no output, unless you have backup hardware designed to isolate safely and carry on.

So what does keep the power on?

To ride through a power cut you need a system explicitly designed for backup, which means two things working together:

• A battery, so there's stored energy to draw on when the grid is down (and, in daylight, to be topped up by the panels).
• A way to safely disconnect from the grid and run as a self-contained island, either an inverter with EPS (Emergency Power Supply) built in, or a separate backup gateway (sometimes called an automatic transfer switch or backup box) fitted alongside.

When the grid fails, the backup gateway or EPS-capable inverter does the clever part: it physically isolates your home from the grid (so you can't back-feed the dead lines and break the anti-islanding rule), then switches the battery over to power your home as a safe, standalone island. When the grid returns, it reconnects and hands back over. This is how you get both compliance and backup: you're not defeating anti-islanding, you're isolating properly so it's safe to keep running.

Critically, a battery alone is not enough. If your battery inverter has no EPS or backup gateway, the battery will also sit idle in an outage, for exactly the same anti-islanding reason. Backup is a feature you have to specify and pay for, not an automatic side-effect of having storage.

Partial vs whole-home backup

Not all backup is equal, and this is where honest expectations matter:

• Partial (essential-loads) backup is the common, affordable setup. A dedicated backup circuit powers a chosen set of essentials, for example lights, the fridge and freezer, the router, and some sockets, while the rest of the house stays off. It's sized to the battery and inverter's output, so you plan around running the important things, not everything at once.
• Whole-home backup powers the entire house during an outage. It's possible but demands a larger battery, a more capable inverter, and careful design so a sudden big load (an electric shower, an oven, an EV charger) doesn't exceed what the system can deliver. It costs more and isn't necessary for most homes.

For most UK households, partial backup of the essentials is the sensible target: enough to keep the fridge cold, the lights on, and the internet up through a typical outage, without paying for a system big enough to run the whole house off-grid.

What backup won't do, and the honest limits

Set expectations before you spend:

• Panels alone still won't power you in daylight. Even in bright sun, without a battery and backup hardware the anti-islanding rule shuts the inverter down. Backup needs the battery and the isolation kit, not just the panels.
• There's usually a brief switchover gap. Some systems have a momentary interruption (a fraction of a second to a few seconds) as they detect the outage and switch to island mode. Anything needing a truly seamless supply (certain medical equipment) may need a dedicated UPS instead.
• Backup power is limited by battery capacity and inverter output. You'll run the essentials for as long as the battery lasts (topped up by solar in daylight), not indefinitely, and not high-power appliances all at once on a partial-backup setup.
• It must be specified up front. Retrofitting backup to an existing battery isn't always straightforward, so if backup matters, tell your installer at the design stage.

Do you actually need backup?

Worth asking honestly, because backup adds cost. The UK grid is, for most homes, highly reliable, and prolonged outages are uncommon in most areas. So the case for backup is strongest if you:

• Live somewhere with frequent or long outages (some rural areas, overhead-line networks).
• Rely on power for something important (home working, medical needs, a home business).
• Simply value the peace of mind and are already installing a battery, where adding EPS or a gateway is a smaller incremental cost.

If none of those apply, plenty of homeowners get a battery purely for the day-to-day bill savings, storing cheap or solar electricity for peak times, and accept that a rare power cut will still leave them dark. That's a perfectly reasonable choice. The battery lifespan and value trade-offs are covered in how long does a solar battery last? and what size solar battery do I need?.

The practical takeaway

Solar alone won't keep your home running in a power cut, and that's by design, for the safety of people working on the network. If backup power matters to you, specify a battery plus EPS or a backup gateway from the start, decide whether you want essential-loads or whole-home backup, and be clear on the limits. If it doesn't, a standard system still does its main job: cutting your bills whenever the grid is up. Either way, the starting point is understanding your roof: our roof check and savings calculator size up the generation side, and an MCS-certified installer covering your postcode can design the backup side properly.

Frequently asked questions

Do solar panels work during a power cut?

No, not on their own. UK grid-tied inverters are required by the G98/G99 connection rules to shut down within about two seconds of losing the grid, a safety feature called anti-islanding that stops your system energising power lines while engineers work on them. To keep power during an outage you need a battery plus backup hardware (an EPS-capable inverter or a backup gateway); panels alone, even in bright sun, will shut off.

Why do solar inverters switch off when the power goes out?

For safety. When the grid fails, engineers may be working on the lines, and if your inverter kept exporting it could energise lines everyone assumes are dead. Anti-islanding, mandated by the G98/G99 standards, forces the inverter to disconnect within about two seconds of detecting an out-of-range grid voltage or frequency. It's a deliberate, legally required protection, not a fault.

Will a solar battery power my house in a blackout?

Only if it's set up for backup. A battery on its own follows the same anti-islanding rule and sits idle in an outage unless its inverter has EPS (Emergency Power Supply) or you've fitted a backup gateway that safely isolates your home from the grid and runs it as a standalone island. Backup is a feature you specify and pay for, not an automatic result of having a battery.

What's the difference between partial and whole-home backup?

Partial (essential-loads) backup powers a chosen set of essentials, such as lights, the fridge, the freezer and the router, through a dedicated circuit, and is the common, affordable option. Whole-home backup powers the entire house but needs a larger battery, a more capable inverter, and careful design so big loads don't overwhelm it, and it costs more. For most UK homes, partial backup of the essentials is the sensible target.

Is there a gap when the power switches to backup?

Often a brief one. Many backup systems have a momentary interruption, from a fraction of a second to a few seconds, while they detect the outage and switch to island mode. For most appliances that's unnoticeable, but anything needing a truly seamless supply (some medical equipment) may need a dedicated uninterruptible power supply (UPS) instead. Ask your installer about the switchover behaviour of the specific system.

Related

• How long does a solar battery last?
• What size solar battery do I need?
• Solar inverter types explained
• Solar battery storage in the UK
• Is my roof suitable for solar?
• Estimate your savings