Battery storage · Guide
Do solar panels work in a power cut?
Usually not. A normal grid-connected solar system switches itself off when the grid goes down, even on a sunny day. That’s deliberate: it’s a safety feature, not a fault.
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Why they switch off
Why solar panels switch off in a power cut.
Whether you keep any power depends on your equipment. Some batteries and inverters can run a backup socket, chosen circuits or the whole house, but only if they’re designed and installed for it.
Your inverter turns the panels’ power into electricity for your home. It’s built to disconnect as soon as it loses the grid supply. This is called loss of mains protection, or anti-islanding.
The rules come from the Energy Networks Association (ENA): Engineering Recommendation G98 for smaller systems and G99 for larger ones. They apply across England, Wales and Scotland.
The reason is safety. If your panels kept feeding the local network during a cut, they could keep a line live that should be dead. MCS calls this islanding and says it “presents a potential danger to those working on the network”.
One thing doesn’t switch off. Panels produce electricity whenever there’s daylight, so the cables from the roof stay live during a power cut.
Adding a battery
What a battery changes.
A battery doesn’t keep the lights on automatically. On many systems it goes off with the inverter. As one inverter maker puts it, “not every battery is automatically blackout-capable”.
For a battery to help, three things have to line up:
- The equipment supports backup. The manual may call it backup, emergency power supply (EPS) or off-grid mode. Some hybrid inverters have a backup output built in.
- It’s wired for backup, to a socket or circuits in your home, with the right switching and earthing.
- It’s set up for backup. On some systems, the battery won’t switch to backup if it’s already at its minimum charge in everyday mode.
Backup types
The three types of backup.
- A single backup socket. One dedicated socket, sometimes labelled EPS. You plug in essentials, such as the fridge or phone chargers. A few inverters offer one with no battery, but it only works while the panels are producing enough.
- Backed-up circuits. Chosen circuits, such as lights, the fridge, the router and the boiler, go on a separate backup board. When the grid fails, a changeover device switches them to the battery. Citizens Advice notes that most gas boilers need electricity to start.
- Whole-home backup. The whole house switches over to the battery and panels.
Limits
What backup can and can’t do.
- There’s a power limit. Go over it and the system shuts down with an overload fault. Fridges and washing machines need extra power to start, and that counts too.
- It lasts as long as the charge. Once the battery reaches its minimum, backup stops until the panels can recharge it. On short winter days they may add very little. See do solar panels work in winter?
- You can keep a reserve. Some systems let you hold back part of the battery for power cuts. Not running it flat every night is kinder to the battery too. See how long do solar batteries last?
- There may be a short break. Some systems switch over without one. Others pause briefly, so some equipment may restart.
- Don’t rely on it for medical equipment. One manufacturer prohibits connecting medical equipment to its backup output. If someone at home depends on it, join your network operator’s Priority Services Register. Ofgem says operators must offer people on it extra help.
For how much backup a battery can give, see what size solar battery do I need?
Installation
Backup has to be installed properly.
Backup makes part or all of your home a small island, cut off from the grid. It must be done safely.
- A proper changeover. G99 says the switch that separates your home from the grid must break the neutral as well as the live, and a changeover switch must be fail-safe and interlocked, so nothing can feed onto the network.
- Earthing. The IET explains that in island mode the network’s neutral-earth link “cannot and must not be relied upon”. A local earth electrode is normally needed.
- Protection that still works. Inverters supply only limited current into a fault, so the IET says an RCD is needed to disconnect faults in time, tested in island mode.
- The regulations. BS 7671, the IET Wiring Regulations, has a chapter for homes that generate and store electricity, and G99 points battery systems that island to the IET’s Code of Practice.
The details depend on your supply and equipment. Don’t try to set up backup yourself, and never feed your home’s wiring from a generator or power station through a socket.
Power back on
When the power comes back.
Under the grid rules, your inverter can only reconnect once the grid has been back within limits for at least 20 seconds. Give it a few minutes in decent daylight.
If it doesn’t come back:
- Look at the inverter. Note any red light or error code.
- Check the fuse board. If the solar breaker or RCD has tripped, switch it back on once. If it trips again, leave it off and call an engineer. See solar panels tripping the RCD or fuse box?
- Check the isolators by the inverter. If one is off, read solar panel isolator switches before switching it on.
- After lightning, check any surge protector. On most, a red indicator means it needs replacing.
- Check the app last. Your router lost power too, so monitoring may take a while to reconnect.
For more checks, see solar panels not working? Don’t open any equipment. If you smell burning or see scorch marks, keep clear and call an engineer. If there’s any sign of fire, call 999.
Before winter
Before the winter storms.
Storms bring more power cuts. Ofgem defines its storm categories by bad weather, including lightning, causing many times the usual number of network faults. A little preparation helps:
- Know where your inverter, isolators and solar breaker are.
- Save 105, the free power cut number for England, Scotland and Wales.
- If you have backup, check what’s connected to it and how much reserve it holds.
- After a storm, look from the ground for slipped panels or loose cables. Never go on the roof. Keep away from fallen power lines: call 105, or 999 if there’s immediate danger.
How we help
How we can help.
We install solar batteries across England, Wales and southern Scotland. If you already have a battery or hybrid inverter, we can check what it can do in a power cut and explain your options. We also repair systems that don’t come back after an outage, whoever fitted them. You get a clear written quote before any work starts.
Sources: Energy Networks Association EREC G98 and G99; MCS; the IET (Wiring Matters) and BS 7671; Ofgem and Power Cut 105; Citizens Advice; inverter makers’ backup guides.
Questions
The things people ask before they ring.
Not answered here? Call 0800 156 0191, Monday to Friday, 9:00am–5:00pm.
Why don’t solar panels work in a power cut?
The inverter must disconnect when it loses the grid. Under ENA’s G98 and G99 rules, this loss of mains protection stops your panels feeding lines that engineers expect to be dead.
Will my solar battery work in a power cut?
Only if it has a backup function and has been wired and set up to use it. Check your manual for backup, EPS or off-grid mode, or ask an engineer.
Why are my solar panels not working after a power cut?
The inverter reconnects by itself, but only after the grid has been stable for at least 20 seconds. If it hasn’t after a few minutes in daylight, check the solar breaker or RCD and the isolators. If a breaker keeps tripping, call an engineer.
Is solar battery backup worth it?
It depends on how often you lose power, what you need to keep running and what your equipment can do. The Energy Saving Trust describes a battery’s main job as storing spare solar or cheap-rate electricity to use later, so treat backup as an extra.
Ready when you are
Solar not back after a power cut?
We’ll call you back to talk it through, and you get a clear written quote before any work starts. Mon–Fri 9:00am–5:00pm.