SOLAR PV · BATTERY STORAGE · EMERGENCY BACKUP
Solar Panels and Batteries: Will Your Home Still Have Power During a Power Cut?
Why having solar panels and battery storage doesn't necessarily mean your home has emergency backup power.
You have solar panels on your roof, a battery storing electricity and an inverter managing everything. So, when the electricity network goes down, your home should automatically switch over to battery power. Right?
Unfortunately, for many homeowners, the answer is no.
At Speedy Fit, we've spoken to customers who have had solar panels and battery storage installed for several years and genuinely believe their homes are protected against power cuts.
The reality is that many of these systems were installed purely to reduce electricity bills, not to provide emergency backup power.
When the grid fails, their inverter may shut down, leaving the house without electricity even though the battery is fully charged.
Why does a solar inverter shut down during a power cut?
Most conventional grid-connected solar inverters are designed to stop supplying electricity when they detect a failure of the public electricity network.
This essential safety feature is known as anti-islanding protection. It prevents the inverter from continuing to energise the electricity network when engineers may be working to restore the supply.
Having a battery connected to your system doesn't automatically change this behaviour. Even some hybrid inverters that support battery storage cannot supply your home during a power cut unless the correct backup facilities have been installed and commissioned.
Standard solar and battery systems versus EPS backup
These examples show the important difference between a normal grid-connected installation and a system that has been correctly configured for emergency backup.
Standard solar and battery system
During a grid power cut
The grid-connected output shuts down. Without a configured backup supply, stored battery energy cannot power the household circuits.
Solar and battery system with EPS
During a grid power cut
The backup system operates independently of the grid and can supply selected circuits within its rated capacity.
Important: These diagrams illustrate operating principles, not electrical wiring arrangements. Solar generation during an outage depends on the inverter's capabilities and operating conditions.
What is EPS?
EPS stands for Emergency Power Supply. Certain hybrid inverters have a dedicated EPS or backup output that can supply electricity independently of the grid.
However, having an EPS connection on an inverter does not mean it has been connected to your home's electrical installation.
Depending on the equipment and installation, backup power may be provided through a dedicated emergency socket, a separate essential-loads consumer unit, a suitable manual changeover arrangement or a manufacturer-approved automatic backup system.
Each arrangement has different capabilities and requirements. Some systems switch over automatically, while others require the homeowner to operate a changeover switch.
Whole-house backup or essential circuits?
Many homeowners assume that backup power means everything in the house will continue operating normally. That is not necessarily practical.
Electric showers, immersion heaters, ovens, heat pumps and other high-demand appliances can quickly exceed the inverter's available backup output.
For many properties, a dedicated essential-loads consumer unit is a more sensible solution. It might supply selected lighting, refrigeration, broadband equipment and certain socket circuits.
The circuits must be assessed against the inverter's continuous output, starting-current capability and the battery's available energy.
Why earthing and electrical protection matter
Emergency backup power is not simply a matter of connecting two wires from the inverter to the consumer unit.
When the public electricity supply fails, the installation's earthing and neutral arrangements may need to operate differently.
Depending on the supply characteristics, inverter design and backup configuration, additional switching, protective devices and an earth electrode may be required.
The design must prevent backfeeding into the public network and ensure that protective devices operate correctly during backup operation.
How long will your battery last during a power cut?
Battery capacity is normally expressed in kilowatt-hours (kWh), while inverter output is expressed in kilowatts (kW). These measure different things.
For example, a battery containing 10kWh of usable stored energy could theoretically supply a constant 1kW load for approximately 10 hours.
In practice, backup duration depends on inverter losses, reserve settings, temperature, state of charge and the appliances operating.
A battery that's nearly empty when a power cut occurs may provide very little backup time. Some systems allow a minimum battery reserve to be maintained for emergencies.
Can an existing solar and battery system be upgraded?
Quite possibly, but it depends on the equipment already installed.
Some hybrid inverters already have an EPS output that has never been connected. Others require a manufacturer-specific backup interface or switching device. Some cannot provide backup power without replacing equipment.
Before recommending an upgrade, an installer should assess the inverter model, battery compatibility, existing consumer units, earthing system, desired essential circuits, switching arrangements and electrical protection.
How can you tell whether your system has emergency backup?
Start by checking your original installation paperwork for references to EPS, backup supply, essential loads, changeover switching or emergency power.
You can also check the manufacturer's documentation using the exact inverter model number.
However, finding EPS listed in the inverter specifications is not proof that your installation has been configured to use it.
The most reliable confirmation is documented commissioning and a successful functional test of the backup arrangement.
Don't wait until the next power cut to find out
If you have solar panels and battery storage, it's worth establishing exactly what your system can and cannot do.
A battery that reduces your electricity bills is useful, but it isn't necessarily an emergency power supply.
Speedy Fit undertakes solar PV, battery storage and electrical installation work across Worthing and West Sussex. We can assess existing installations to establish whether emergency backup is technically possible and what additional work may be required.
Not sure whether your solar battery has backup power?
Contact Speedy Fit to discuss an assessment of your existing installation.
Contact Speedy FitNo fake smiles, no fake promises — just professional, honest work.