Do solar panels work in a power cut? On their own, no. When the grid goes down, a standard solar system shuts down with it, even in bright sunshine. That surprises most people, and it is the single most asked question we see about solar and power cuts. The good news is that it is fixable, and you do not always need a new system to fix it.
The Short Version (Read This First)
What happens to your solar in a power cut, and what changes it:
- A normal grid-connected solar system switches itself off the moment the grid fails. This is a safety requirement, not a fault.
- Having a battery does not automatically mean having backup. Most batteries shut down with the grid too.
- To keep power on you need extra equipment that safely separates your home from the network.
- There are two levels: a few essential sockets, or a whole-home changeover.
- Many existing systems can be upgraded without replacing the panels.
01Why Your Solar Panels Switch Off in a Power Cut
Every grid-connected solar inverter in the UK is required to disconnect automatically when it detects that the mains supply has failed. It is built into the equipment and it cannot be switched off.
The reason is straightforward. When the network goes down, engineers have to work on lines they expect to be dead. If thousands of homes kept pushing solar power back into those lines, those lines would not be dead. The inverter shutting down is what makes the network safe to repair.
So on a bright afternoon, with a roof full of working panels, your lights still go out. Nothing is broken. The system is doing exactly what it was designed and certified to do.
This catches people out after they have already bought. A solar system is sold on savings, and backup during a power cut is rarely discussed. Plenty of people only discover it the first time the street goes dark.
02Having a Battery Is Not the Same as Having Backup
This is the part that causes the most confusion, and it is worth being blunt about.
A home battery stores electricity so you can use it later, usually to avoid buying expensive power in the evening. That is what it is for, and that is what it is sized and priced around. In a power cut, a battery on its own does the same thing your panels do: it detects that the grid has gone and it stops.
So you can have a full battery, a sunny roof and no lights. The energy is there. There is simply nothing in the system allowing it to be used safely while the network is down.
If backup matters to you, it has to be asked for specifically, and it usually means an extra piece of equipment alongside the battery.
03What Actually Keeps the Lights On
What you need is a device that can disconnect your home from the grid, confirm the separation is safe, and then let the battery run your circuits on its own. Different manufacturers give it different names, but it does the same job.
There are broadly two levels, and the difference matters more than the brand.
A backup circuit, or a few essential sockets
The simpler option. One dedicated circuit or a small number of sockets stay live when the grid is down. You decide in advance what goes on it: usually the fridge and freezer, the router, some lighting, and somewhere to charge phones. Everything else in the house stays off.
It is cheaper, simpler to install, and for most households it covers what actually matters during a few hours without power.
A whole-home changeover
The fuller option. A device sits between your home and the incoming supply, and when the grid fails it switches the whole house across to the battery. You carry on more or less as normal, within the limits of what the battery can deliver.
It costs more, needs more work at the consumer unit, and it is not always the right answer. A battery is a finite amount of energy, and running the whole house through it empties it far faster than running a fridge and a few lights.
A point worth knowing before you choose: the switchover is not always instant. Some systems take a few seconds to transfer, which is fine for a fridge and inconvenient for a desktop computer. If you work from home, ask specifically how long the gap is.
Not sure what your system can do?
Tell us what you have and we will tell you plainly whether backup can be added.
Ask us about backup →04Can My Existing System Be Upgraded?
In many cases yes, and without touching the panels on the roof. What decides it is the battery and inverter you already have, and how your consumer unit is arranged.
In practice we add backup to FoxESS and Sigenergy battery systems. Most need one extra piece of equipment — a gateway — which watches the grid and switches your home over to the battery the moment it drops.
Whether yours can take one depends on three things: the exact model you have, how your home’s electrics are arranged, and your warranty. That is why we check before quoting rather than after.
It can matter who installed your system. Battery manufacturers may limit your warranty if work is done by someone they have not approved. If we did not fit your system we look at the equipment and the paperwork first, and we only go ahead if it is safe and will not put your cover at risk.
05What Is Involved, and What It Costs
Before the day. We survey your home and agree with you what you want kept running in a power cut — the whole house, or just the essentials. That choice drives everything else.
On the day. Your electricity goes off briefly while everything is connected safely, usually one to one and a half hours depending on your wiring and your system. We tell you beforehand so you can plan around it.
At the fuse box. Depending on the house we may fit a small extra unit beside it, and some homes need additional safety equipment so everything stays protected while the grid is down. Anything needed is explained at the survey, before you commit to anything.
Before we leave we test the changeover properly and show you how it works.
We do not put a price on this page, and that is deliberate. The cost turns on which gateway your battery needs, whether your consumer unit needs work, and whether you want the whole house backed up or only the essentials. A number here would be a guess about your house, and you would be right not to trust it.
The survey gives you a fixed figure before you commit.
06What It Will and Will Not Run
Backup is not the same as carrying on as though nothing happened. A battery holds a fixed amount of energy, and anything that draws heavily will empty it quickly or simply refuse to start.
As a rule, lighting, a fridge and freezer, a router, a television and phone charging are comfortable. Anything that makes heat is the problem: electric showers, ovens, immersion heaters and some tumble dryers can draw more in a few minutes than the rest of the house uses in hours.
There is no honest single answer, and anyone giving you one has not looked at your house. It depends on three things:
- How full the battery is when the cut happens.
- What you are running. Lights, the fridge and the router use very little. Kettles, heaters and cookers use a lot.
- The weather. In daylight your panels can keep topping the battery up, which is the part people forget.
At the survey we look at your battery size and what you want kept on, and give you an honest idea of what to expect. You can also set the battery to hold some charge back in reserve for emergencies.
Best left off backup, or used sparingly: electric showers, ovens and hobs, immersion heaters, heat pumps and EV chargers. Running a lot of things at once can overload the system and trip it out altogether.
The ones that catch people out:
- Gas central heating. The boiler still needs electricity. It only runs if it is on a backed-up circuit — which surprises almost everyone.
- Anything with a motor. Fridges, freezers, pumps and power tools need a burst of extra power to start, and occasionally that surge is too much.
- Circuits you did not back up. If you chose essentials-only, everything else is simply off.
- Broadband. Your router can stay on, but if the street cabinet has lost power too you will have no internet and no landline regardless.
- A brief flicker. Some systems take a moment to switch over, so clocks and computers may reset.
Worth being plain about: battery backup is not a guaranteed uninterrupted supply. It should not be relied on for medical or life-support equipment.
07Is It Worth It?
That depends on how often your power actually goes out, and what it costs you when it does.
For most homes, power cuts are rare and short, and backup is a comfort rather than a necessity. It is worth more if you are somewhere with an overhead supply and a history of outages, if you work from home, if there is medical equipment in the house, or if you keep livestock or a freezer full of stock you cannot afford to lose.
It is worth less if you are in a dense urban area on an underground supply that has not failed in years.
We will tell you honestly which of those you are. If backup is not worth the money for your situation, we would rather say so than sell it to you.
Frequently Asked Questions
Do solar panels work in a power cut?
No, not on their own. A grid-connected solar system is required to shut down automatically when the mains supply fails, even in full sunshine. It is a safety rule, not a fault: it keeps the network dead while engineers repair it. To have power during a cut you need a battery plus equipment that safely separates your home from the grid.
Why do solar panels not work in a power cut?
Because the inverter disconnects itself the moment it detects the grid has gone. If it did not, your roof would keep pushing electricity into lines that engineers expect to be dead. Every grid-connected inverter sold in the UK does this, and it cannot be turned off.
Will my solar battery work in a power cut?
Usually not, unless it was set up for it. A battery is normally there to store cheap or self-generated power for later, and it shuts down with the grid like everything else. Keeping it running during an outage takes an extra device alongside the battery. If nobody mentioned backup when your system was quoted, assume you do not have it.
Can I use my solar battery during a power cut if I add something?
In many cases yes. The usual route is to add a backup device that isolates your home from the network so the battery can run your circuits safely. Whether yours can take one depends on the battery and inverter you already have, so it needs checking against your actual system rather than assumed.
What happens to solar panels during a power cut?
They stop producing usable power. The panels themselves are undamaged and still generating voltage in the sunlight, but the inverter stops converting it, so nothing reaches your sockets and nothing goes to the grid. When the supply returns, the system restarts on its own, normally within a few minutes.
Will backup run my whole house?
It can, but it is often not the sensible choice. Running everything empties a battery far faster than running the essentials, and heavy loads such as electric showers and ovens may not start at all. Most households get better value from a single backup circuit covering the fridge, the router and some lighting.
Do plug-in solar panels work in a power cut?
No. Plug-in panels push power into a normal socket through a small inverter, and that inverter follows the same rule as any other: no grid, no output. They are not a backup solution and are not designed as one.
Does my system need replacing to get backup?
Usually not. In most cases the panels stay exactly where they are and the work is at the battery and consumer unit end. Whether your existing equipment can take backup is the first thing to establish, and that is a question about your specific system rather than a general one.
Matthew has over a decade of UK solar experience, helping homeowners and businesses make clear, confident renewable-energy decisions, from first visit to switch-on.
