Home battery backup: will your battery work in a power cut?
You have solar panels on the roof, a battery storing electricity and an app showing how much energy you are using. It would be reasonable to assume that, if the street loses power, your home will simply carry on.
That depends on how your system was installed.
A home battery can help you use more of your solar electricity or buy energy during cheaper tariff periods. Keeping the house powered when the grid fails requires backup capability as well. That needs to be part of the equipment, electrical design and commissioning of the installation.
If you already own a battery, or are considering one, it is worth understanding exactly what would happen in a power cut before you need to find out.
Does every home battery provide backup power?
The Energy Saving Trust’s solar power fact check explains that battery storage does not normally provide power during a cut unless the necessary equipment and configuration are included.
There is a safety reason for this. A home energy system must not unexpectedly feed electricity back into a public network that has lost power. A suitable backup installation separates the protected part of your home from the grid, allowing it to operate independently within its limits.
That separation is often managed by a gateway or another approved switching arrangement. The battery and inverter then supply the circuits included in the backup design.
When comparing home battery installations, ask for the backup arrangement to be described in writing. A product brochure showing backup features does not confirm that those features are included in your quotation.
What can home battery backup actually power?
There are several possible arrangements, and the everyday experience can be quite different.
Arrangement | What it means during a power cut |
Battery storage without backup | The battery does not supply the home when the grid fails. |
Dedicated backup outlet | Suitable appliances connected to that outlet can be supplied within its limits. Ordinary household sockets are not automatically covered. |
Selected circuits | Agreed circuits, such as lighting and refrigeration, are connected to the backup supply. Other circuits remain off. |
Whole-home backup | The installation can supply the home’s connected circuits, subject to output, stored energy and any load management restrictions. |
Whole-home backup still has a power limit. It does not mean every appliance can run together for as long as you like.
The distinction is reflected in Sigenergy’s home battery backup guide, which separates backup outlets from installations supplying household circuits.
For a home with a three-phase supply, ask specifically which phases and appliances are supported. The phrase “whole home” needs to match the electrical arrangement in your property.
The battery brand alone does not answer the question
Even familiar products can have different installation options. Tesla’s UK guidance describes Powerwall 3 in a non-backup configuration. In that configuration it can store energy for normal use, but it does not provide backup power to the home during an outage.
For Sigenergy installations, its technical note on switching to backup mode describes the SigenStor and Sigen Energy Gateway working together to detect a grid failure and switch supply.
The useful question is therefore: “What does this particular installation include?” If you are comparing Powerwall options, our Tesla Powerwall installation guide explains the wider survey and installation process.
How long does home battery backup last during a power cut?
Start with two different numbers. Capacity, measured in kilowatt-hours or kWh, describes stored energy. Power, measured in kilowatts or kW, describes how quickly energy is being supplied.
For a simple illustration, assume a system can deliver 8 kWh to household appliances from the charge available when a cut begins. That is energy available after allowing for the system’s operating limits and losses, rather than the nominal figure on the battery label.
Average combined electrical demand | Calculation | Illustrative runtime |
0.4 kW | 8 kWh ÷ 0.4 kW | 20 hours |
1 kW | 8 kWh ÷ 1 kW | 8 hours |
2.5 kW | 8 kWh ÷ 2.5 kW | 3.2 hours |
These are arithmetic examples, not predictions for a particular home or battery. Appliances cycle on and off, demand changes, and temperature and equipment condition can affect performance. The backup inverter must also be able to support the appliances at each moment, including starting demand.
This is why deciding what matters most can be more useful than asking whether a battery will last “all day”. Lights, refrigeration and phone charging create a different requirement from electric cooking, heating and charging a car.
If your priorities have changed since installation, our guide to battery storage extensions explains how to assess additional capacity. Adding storage does not automatically add backup capability or increase the inverter’s output.
Can solar panels recharge the battery during a cut?
They can in a compatible system designed for that purpose. However, solar panels connected through an ordinary grid-dependent inverter will not necessarily keep generating useful electricity for your home when the network fails.
Tesla’s UK guidance for power cuts makes clear that solar recharging during an outage depends on the system configuration.
Ask whether your existing solar inverter is supported in backup mode, whether it is connected to the protected side of the installation, and what happens if the battery reaches its minimum operating level. Restarting from a depleted state is a separate question from continuing to run while energy remains.
When planning solar panels alongside storage, consider winter too. A system should not promise a full daily recharge from the roof during short, cloudy days.
Will backup still work if the internet goes down?
An internet outage and an electricity outage are separate events. Loss of the app connection does not necessarily mean the battery has stopped supplying electricity.
Tesla says in its system alerts guidance that Powerwall is expected to operate normally during a power outage without an internet connection. Remote monitoring and notifications can nevertheless be unavailable.
That statement should not be applied to every manufacturer or configuration. Sigenergy’s SigenStor Home single-phase manual describes limitations following prolonged loss of internet connectivity. Ask your installer what continues locally, what needs online services and whether extended disconnection creates restrictions for your model.
Powering the router also cannot restore a broadband network that has failed outside your home. Check communications separately from the battery’s electrical backup function.
Ask these questions before you buy
A clear proposal should explain which circuits are protected, whether changeover is automatic, the continuous and starting power limits, the energy available at your chosen reserve, and whether solar can recharge the battery while the grid is down.
It should also explain the handover: how you recognise a power cut, what to switch off, and how to get help if the system does not behave as expected. Ask for a supervised demonstration or commissioning record covering the agreed backup functions.
The government’s Be Ready power cut guidance recognises that suitably designed solar and battery systems can help keep essential appliances running. Keep wider preparations in place too, including a torch and a way to access important information.
Understand what your home could keep powered
If you live in Surrey, Berkshire, Hampshire or West London, contact Your Energy Your Way to discuss battery storage and backup for your home.
If you already have a system, share its model, your postcode and any installation documents or app screenshots. Tell us what you would most want to keep running, and we can explain the appropriate next step.
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