Power-cut protection
Keep your core equipment running when the grid goes down
Solar panels alone will not do it. This guide explains what will, for a home and for a business, and what each level costs.
Why solar switches off in a power cut
A standard solar inverter is built to follow the grid. When the grid fails, the inverter must disconnect within a fraction of a second. This is a condition of connecting to the network in the UK, and it protects engineers working on lines they believe are dead.
The result surprises many owners: in a power cut on a sunny day, a house with panels on the roof has no electricity. A battery does not change this by itself. Many battery systems are fitted without any backup output, because their job is to save money, not to cover outages.
To have power in a cut you need three things:
- Stored energy: a battery big enough for what you want to run, for as long as you want to run it.
- An inverter that can work alone: one with a backup or emergency power (EPS) output.
- A safe changeover: something that separates your circuits from the grid first, by hand or automatically.
Five levels of protection
Match the protection to what you cannot lose
You do not have to back up everything. Most homes and businesses mix two levels: a small unit that never drops the critical items, and a larger battery for everything else that matters.
UPS
An uninterruptible power supply sits between the socket and one device or rack. There is no break at all. A 1,500VA business unit costs roughly £700 to £800 and gives minutes at full load, enough to ride through a short cut or shut down cleanly.
Portable power station
A battery and inverter in one box, from about 1 kWh for £700 to 4 kWh for £2,800. Plug appliances into it during a cut. Some models pass mains through and switch over in milliseconds for anything left plugged in.
Essential circuits
A hybrid inverter with a backup output feeds a few chosen circuits or a dedicated socket. Changeover takes from a fraction of a second to a few seconds. On a system that supports it, the add-on backup box costs about £460 plus fitting.
Whole building
A backup gateway at the meter isolates the grid and the battery runs everything, up to its power limit. A 13.5 kWh battery with gateway is typically £7,500 to £10,500 installed. Solar keeps charging the battery during the cut.
Off-grid or generator hybrid
A battery bank with solar and a generator input. Sized to run for days and to refill itself. Common for remote sites and for businesses where a long outage would be very costly.
Start from your appliances
List what must stay on and for how long. The finder turns that into a battery size and shows the systems that fit your budget.
Price ranges checked 12 November 2026.
For homes
What to protect at home
- Heating. A gas or oil boiler cannot fire without electricity for its controls and pump.
- Fridge and freezer. Food is usually safe for a few hours with the doors shut. A long cut is different.
- Broadband and phones. Digital landlines stop working when the router loses power.
- Lighting in the rooms and stairs you use most.
- Medical equipment such as a CPAP machine, stairlift or powered bed.
- Pumps for drainage, a well or a sewage treatment plant.
How much battery is that?
A fridge freezer, boiler, router, LED lights and phone charging use about 2.8 kWh in 24 hours. Allowing for inverter losses, look for at least 3.2 kWh of battery to cover a full day. Kettles, ovens and electric showers are a different scale: one 3 kW kettle boil uses little energy, but it needs an inverter that can deliver 3 kW.
Join your network operator's Priority Services Register. It is free. Follow the equipment supplier's advice on backup power, and call 105 to report a power cut.
For businesses
Protecting core equipment at work
A cut costs a business more than the electricity it did not use: lost sales, spoiled stock, corrupted data and staff who cannot work.
Cannot drop for a second
Servers, network equipment, tills and card terminals, CCTV recorders, door access, process controllers.
Use: a UPS on each item or rack. A battery system behind it extends the running time.
Must be back within minutes
Refrigeration and freezers, phones, essential lighting, heating controls, pumps.
Use: a battery with automatic switchover feeding an essential-loads board.
Can wait
Air conditioning, ovens, most machinery, electric vehicle chargers.
Use: nothing, or a generator if a long outage would stop the business.
A worked example
A small shop or office with a server, network cabinet, one till, CCTV and an alarm draws about 350 W all the time.
| Cover needed | Energy used | Battery to look for |
|---|---|---|
| A working day (8 hours) | 2.8 kWh | 3.1 kWh or more |
| A full day (24 hours) | 8.4 kWh | 9.3 kWh or more |
| A weekend (60 hours) | 21 kWh | 23.3 kWh or more |
Add a display fridge and the full-day figure rises to about 13 kWh. Refrigeration is usually the largest load on the list, so check its rating plate.
Points that catch businesses out
- Keep the UPS. Most battery changeovers take long enough to restart a computer. A small UPS on the server and network bridges that gap.
- Three-phase supplies. Larger premises need three-phase backup equipment or a single-phase essential-loads board. This needs a site survey.
- Start-up surge. Compressors and motors draw several times their running power for a moment. The inverter must cope with it.
- Test it. Switch off the incoming supply once a year, on a quiet day, and check that everything you expect stays on.
- Insurance and stock. Ask your insurer whether backup power changes your cover for spoiled stock or business interruption.
Before you buy
Seven questions to ask an installer
- Will this system supply power in a power cut, as quoted?
- Which circuits stay on: a socket, chosen circuits or the whole building?
- How long does the changeover take, and is it automatic?
- What is the maximum power in backup mode?
- Will the solar panels keep charging the battery during a cut?
- Does the price include the network operator notification and the earthing that backup operation needs?
- Who honours the warranty if the manufacturer stops trading?
The last question matters. Read our note on what happened to GivEnergy owners.
See how the system types differ
Diagrams of on-grid, hybrid, automatic switchover and off-grid systems, with what each does in a cut.
System types comparedTalk it through
Tell us what you need to keep running and we will suggest a sensible level of protection.
Contact us