Winter Storm Readiness: Backup Gateways and What Stays On in a Power Cut
- A backup gateway detects an outage and disconnects the battery from the grid, so the home can run on battery.
- Not everything in the house is necessarily backed up. It depends on the configuration.
- Overloading the system can cause it to cut out, so reduce demand if that happens.
- Ofgem says network operators usually pay compensation automatically for long power cuts.
- The Priority Services Register is free and offers extra support during power cuts.
A home battery only keeps the lights on in a power cut if it was installed for backup. The device that makes this possible is the backup gateway, and what stays on depends on which circuits were wired to it.
What the gateway does
Tesla's system design page describes its Backup Gateway as the part that detects a grid outage and disconnects the battery from the grid, then switches the home to battery power. Disconnecting matters: it stops the battery feeding power back into a grid that crews may be working on.
Other brands use their own hardware for the same job, sometimes built into the inverter. The principle is the same, and an installer should be able to name the device in your system. For a longer explanation of the idea, see how whole-home battery backup works.
What stays on, and what does not
Whole-home backup and partial backup are different installations. Tesla says its recommended number of Powerwall units can support all appliances in a whole-home setup. In a partial setup, only the circuits wired to the backup side stay powered.
Even with a whole-home design, there is a limit. Tesla's backup troubleshooting guidance implies that overloading during backup can cause a brownout or blackout, and advises reducing connected loads and checking whether any load breakers have tripped. In a storm, that means switching off the big loads first.
Preparing before the first storm
How long the battery lasts depends on its size and what you run, which our guide on how long a battery lasts in a power cut works through. Preparing now is mostly about choices you can make in the app and on the wall.
- Know which circuits are on the backup side, and write them down.
- Check the backup reserve is set high enough for the season.
- Find out whether your system has a storm-forecast feature. Tesla lists one called Storm Watch, though we could not read what it does, so check the maker's page.
- Keep the app logged in and the home internet powered, if the app matters to you.
Do not rely on it for medical equipment
A battery is a convenience, not a guarantee. If anyone depends on powered medical equipment, plan with your network operator and clinician as well.
Compensation and support
If a cut lasts long, the network operator pays compensation, usually automatically. Ofgem's guidance lists £90 after 24 hours for a Category 1 storm and after 48 hours for a Category 2 storm. Report a cut by calling 105.
Households that depend on power can join the free Priority Services Register, run by the network operator, which gives power cut updates and a personalised plan. This is particularly relevant if anyone relies on electrically powered medical equipment, and a home battery is not a substitute for that support.
Common questions
Will my battery work in a power cut by default?
Not always. Backup needs to be part of the installation, and some systems need a backup gateway for it. Check how yours was configured.
Can I back up the whole house?
Whole-home designs exist, but the limit is the battery's power and capacity. Heavy loads can overload the system, so know what you can run at once.
Where do I report a power cut?
Call 105 or use your network operator's website. Ofgem says operators usually pay compensation automatically for qualifying cuts.
Related guides
Want to know which battery size fits your home?
Use our free calculator to get a size, savings and payback estimate.