A home battery does not automatically mean your house will stay powered during a blackout.
True backup depends on the battery, inverter, switching equipment, backup architecture and — most importantly — what you actually need to keep running.
The right starting point is not “How big a battery should I buy?”
It is “What does the home need to keep doing when the grid disappears?”
Will My Battery Work During a Power Cut?
Sometimes.
A battery may be perfectly capable of storing and supplying electricity during normal operation but still shut down when the grid fails.
That is because normal grid-connected systems must disconnect safely from the electricity network during an outage.
Depending on the system, backup may require:
- EPS capability
- a backup consumer unit
- automatic switching
- a backup gateway
- suitable inverter functionality
- correctly designed grid isolation
Important
Battery storage and backup power are not the same thing.
Why Do Solar Panels Usually Shut Down Too?
Many homeowners assume that if the sun is shining, their solar panels will continue powering the house during a power cut.
In a standard grid-connected installation, that is usually not the case.
When the electricity network fails, the solar inverter normally shuts down to prevent electricity being fed into a grid that should be de-energised.
Without suitable backup equipment:
Grid fails → Solar shuts down → Home loses power
With a correctly designed backup system:
Grid fails → Home safely disconnects from grid → Battery and, where supported, solar can supply backup loads
The solar panels themselves have not stopped receiving sunlight.
The issue is whether the system can operate safely while disconnected from the grid.
Start With What Needs to Stay On
This should be the first design decision.
Think about what you would actually want during a power cut.
That might include:
- broadband
- fridge and freezer
- lighting
- heating controls
- selected sockets
- security systems
You may also want to keep running:
- heat pump
- cooking equipment
- larger household loads
- most of the property
Those are very different backup requirements.
A system designed to keep the router, fridge and lights running may need relatively modest power.
A system expected to maintain heating, cooking and most household circuits needs substantially greater capacity and output.
Design the backup around the loads, not the battery.
Different Levels of Home Backup
- Dedicated EPS Supply
- Some systems provide an Emergency Power Supply output. This may power a dedicated socket, a small number of selected circuits, or a separate backup consumer unit.
- Essential-Loads Backup
- Selected circuits are moved onto a dedicated backed-up consumer unit — typically lights, fridge/freezer, broadband, heating controls and selected sockets. This keeps demand manageable and preserves battery runtime.
- Partial-Home Backup
- A larger part of the property remains powered, but high-demand loads are deliberately excluded.
- Whole-Home Backup
- Most or all of the property's electrical circuits remain energised through a suitable backup gateway or switching arrangement.
Backup power does not have to mean all or nothing.
But there is an important limitation:
Whole-home backup does not mean every appliance can run at full power at the same time.
The battery and inverter still have power limits.
EPS vs Backup Gateway
- EPS — Emergency Power Supply
- Commonly provides a dedicated backup output. This can supply selected circuits, an essential-load consumer unit or a dedicated emergency socket. Practical where only certain loads need to remain powered.
- Backup Gateway
- Normally monitors the grid connection and automatically isolates the property when the grid fails. Once isolated, the battery system can create a local electrical supply for the backed-up part of the home. Can be used for wider backup arrangements, including whole-home backup.
These terms are often used in quotations without much explanation.
Neither approach is automatically better.
The right choice depends on what needs to stay powered, battery power, inverter capability, installation layout, budget and future plans.
Battery Capacity vs Backup Power
- Battery Capacity — kWh
- How much stored energy is available. It affects how long backup may last.
- Battery Power — kW
- How much electrical demand the battery and inverter can supply at one time. It affects what can run simultaneously.
Backup power makes the difference between kWh and kW especially important.
For example, a battery may contain plenty of stored energy but still be unable to support an oven, kettle, heat pump, immersion heater and EV charger all at the same time.
Backup duration is about energy. What you can run at the same time is about power.
What Can a Home Battery Actually Run?
The answer depends on usable battery capacity, inverter output, battery discharge power, number of loads operating, backup reserve and whether solar can contribute.
Lower-demand loads such as a broadband router, lighting, fridge/freezer, heating controls and small electronics can usually be easier to maintain for longer periods.
Higher-demand loads such as a kettle, oven, immersion heater, heat pump or EV charger can place much greater demand on the backup system.
A battery can have enough stored energy remaining but still reach its maximum power limit if too many large loads operate together.
Load Shedding
- Grid fails
- EV charger disabled
- Immersion heater disabled
- Essential household circuits remain powered
A good backup system does not always try to power everything.
Sometimes it is more useful to deliberately remove non-essential loads when the grid fails.
This is called load shedding.
The aim is to protect the loads that matter most and prevent unnecessary demand from draining the battery or exceeding the inverter’s output.
Sometimes the best backup system is the one that knows what not to power.
Backup Reserve
Many battery systems allow part of the stored energy to be reserved for a power cut.
For example, if the backup reserve is set to 40%, the battery may stop normal discharge once it reaches that level.
That leaves energy available if the grid fails.
There is a trade-off.
A higher reserve gives you more emergency capacity.
But it leaves less battery capacity available for reducing grid imports, tariff shifting, and storing and using solar.
Backup reserve is therefore a choice between everyday battery use and emergency resilience.
What Happens When the Power Goes Off?
- Grid failure detected
- Property disconnected from grid
- Backup supply established
- Selected circuits continue operating
In an automatic backup system, the process may happen very quickly.
The transition time depends on the system.
Some equipment may continue operating without interruption.
Other sensitive devices may reboot if the transfer takes long enough.
This is an important distinction:
Home battery backup is not always the same as a dedicated UPS.
If uninterrupted operation is critical for a particular device, that requirement should be considered separately.
Can Solar Keep Working During a Power Cut?
Potentially — but only if the system has been designed to allow it.
In a suitable backup architecture, solar PV may be able to continue generating while the property is operating independently from the grid.
That energy might supply household loads, recharge the battery, or reduce the amount of stored energy being used.
But system behaviour varies.
It depends on:
- solar inverter
- battery inverter
- backup gateway
- battery state of charge
- operating limits
- manufacturer design
Do not assume that solar will automatically continue operating simply because the home has battery backup.
Can Solar Recharge the Battery During an Outage?
- Battery supports home overnight
- Battery state of charge falls
- Sun rises
- Solar powers household loads
- Excess solar recharges battery
Some backup systems can allow solar PV to recharge the battery while the home is disconnected from the grid.
This can make a significant difference during a long outage.
But that behaviour is not universal.
Important questions include:
- Can the solar inverter operate in island mode?
- Can the battery accept charge during backup?
- What happens when the battery reaches its lower limit?
- Can the system restart itself after shutdown?
If extended backup matters, these details should be understood before the system is installed.
What Happens When the Battery Runs Flat?
If the battery reaches its minimum operating state of charge, the backup supply may shut down.
At that point, the property may lose power until the grid returns, solar generation becomes available, or the backup system can restart.
Different systems behave differently after deep depletion.
Some may be able to restart automatically when solar returns.
Others may require particular conditions before backup resumes.
This is why extended-outage behaviour matters just as much as the initial switchover.
What Is Black Start?
Black start refers to the ability of a system to restart without relying on an operating electricity grid.
In a home-energy context, this may mean a battery and inverter can restart an islanded system after it has completely shut down.
This can be particularly useful during a long outage if solar generation becomes available the following morning.
Black-start capability is not universal.
It depends on the equipment and system architecture.
Can a Heat Pump Run During a Power Cut?
Potentially.
But a heat pump changes the backup requirement significantly.
A heat pump can operate for long periods, particularly during cold weather.
That means both battery power and stored energy matter.
Consider:
- heat-pump electrical input
- outdoor temperature
- building heat loss
- heating demand
- hot-water demand
- remaining battery capacity
- other household loads
Winter is also the period when heating demand is usually highest and solar generation is often lowest.
Keeping a heat pump running during an outage is therefore very different from maintaining only lighting and broadband.
If heating backup is important, it should be designed into the system from the start.
Our sister site
For heat loss, heating-system design and heat pumps, see Heat Loss Hub — our sister site, run by the same team.
What About EV Charging During a Power Cut?
An EV charger can be a very large electrical load.
A typical home charger may draw around 7 kW.
Allowing that demand during an outage could drain a home battery rapidly or exceed the backup system’s available power.
For that reason, EV charging may be:
- disabled during backup
- limited to a lower power
- manually enabled only when required
A backed-up house does not necessarily need a backed-up EV charger.
Automatic vs Manual Backup
- Automatic Backup
- The system detects the outage and automatically transfers the backed-up circuits onto battery power. This can offer a much more seamless experience.
- Manual Changeover
- The homeowner may need to operate a switch or manually enable an emergency supply.
- Dedicated EPS
- A separate backup socket or circuit may become available when the grid fails.
Different systems can behave differently when the grid fails.
When comparing systems, it is worth asking:
What actually happens when the power goes off?
That can be just as important as knowing the battery capacity.
Backup Is About Resilience, Not Just Payback
Battery storage is often assessed through electricity savings, tariff optimisation, solar self-consumption and payback periods.
Backup power has a different value.
It may provide:
- internet continuity
- refrigeration
- heating
- home-working continuity
- security
- lighting
- comfort
- resilience
For some households, those benefits may be more important than whether the backup equipment produces a direct financial return.
Backup power is not always a financial investment. Sometimes its value is continuity.
Plan Backup Before the Battery Is Installed
Backup can often be added later.
But it may be simpler and more cost-effective to consider it before the original battery installation.
Retrofitting backup can potentially require:
- additional switching equipment
- backup consumer unit
- gateway
- new cable routes
- changes to electrical circuits
- equipment relocation
- additional labour
Even if backup is not being installed immediately, it is useful to ask:
- Is the battery capable of backup?
- Can a gateway be added later?
- Where would backup equipment go?
- Which circuits might eventually be backed up?
- Is the electrical layout suitable?
If backup might matter later, think about it before the first battery is installed.
What Should a Good Backup Proposal Tell You?
A backup-power quotation should make it clear what the proposed system can actually do.
Useful information includes:
- battery manufacturer and model
- usable battery capacity
- continuous backup power
- peak backup power where relevant
- inverter model and rating
- EPS or gateway architecture
- circuits included in backup
- circuits excluded from backup
- transfer method
- expected transfer behaviour
- backup reserve
- solar operation during an outage
- whether solar can recharge the battery
- load-shedding strategy
- behaviour when the battery is depleted
- restart or black-start capability
- future expansion options
Two systems using batteries with the same capacity can provide very different backup capability.
The backup architecture matters just as much as the battery itself.
Backup Power Visualiser
Energy Flow Hub is developing an interactive Backup Power Visualiser to make backup design easier to understand.
You will be able to select loads such as broadband, fridge/freezer, lighting, heat pump, oven, immersion heater and EV charger, and explore:
- total backup demand
- battery power requirements
- estimated runtime
- effect of removing large loads
- impact of backup reserve
- solar contribution
The aim is to answer a simple question:
What does your home actually need to keep doing during a power cut?
Common Backup Power Questions
Will my battery work during a power cut?
Only if the battery system and electrical installation have been designed with suitable backup functionality.
Will my solar panels still work?
Normally not in a standard grid-connected installation. Solar may continue in a suitable backup system that can operate safely while isolated from the grid.
What is EPS?
EPS stands for Emergency Power Supply and usually refers to a dedicated backup output from compatible equipment.
What is a backup gateway?
A gateway can monitor the grid and automatically isolate the property so a suitable battery system can provide backup power.
Can I back up my whole house?
Potentially, but battery capacity, inverter power and simultaneous electrical demand all need to be considered.
How long will the battery last?
It depends on usable capacity, household demand, backup reserve and whether solar can contribute.
Can my battery run a heat pump?
Potentially, if the battery and inverter have enough output power and sufficient stored energy.
Can I charge my EV during a power cut?
It may be technically possible in some systems, but EV charging is a large load and is often excluded or limited during backup.
What happens when the battery runs flat?
The backup supply may shut down until the grid returns or, in some systems, solar generation allows the system to restart.
What is black start?
Black start is the ability of a system to restart without relying on an operating electricity grid.
Explore Backup Power
Backup power is about much more than adding a battery.
Explore our guides covering:
- EPS vs backup gateways
- whole-home backup
- essential-load backup
- solar during power cuts
- backup runtime
- load shedding
- battery reserve
- black start
- heat-pump backup
- backup gateway comparisons
The better you understand what needs to remain powered, the easier it becomes to understand what the battery and backup system need to deliver.
Design Backup Around What Matters
A good backup system starts with the loads you need to keep running.
Only then should you work backwards to the battery capacity, power, inverter and switching equipment required to support them.
Design the backup around the loads, not the battery.