Usually, no: standard grid-connected solar panels stop supplying your home during a power cut. Adding a battery does not automatically change that. You need a compatible inverter, a properly installed backup arrangement and enough stored energy to run the appliances you want to keep on.
The useful question is not simply “does this battery have backup?” It is “what will still work in my home, for how long, and what happens when the battery runs low?” Here is how to turn those questions into a clear installation brief.
Why do solar panels stop working when the grid fails?
A normal grid-connected inverter is designed to stop feeding electricity into the network when the mains supply fails. This protective behaviour is commonly called anti-islanding. Your panels may still be in daylight, but that does not mean your sockets have a usable electricity supply. The Energy Saving Trust’s solar fact check confirms that powering a home through an outage requires an off-grid arrangement or additional equipment.
A backup system creates a safely separated supply for the circuits it supports. Its switching, earthing and electrical protection need to work correctly without relying on the normal grid connection. The IET’s explanation of island-mode operation describes why this needs specific electrical design. It is not a DIY wiring change or an app setting that can make any installation backup-ready.
What does a home battery need for backup power?
The complete system matters: battery, inverter, backup switching equipment and the circuits connected to it. “Backup-ready” or “EPS” — emergency power supply — should prompt questions about what is actually included in your quote.
Ask for the supported circuits, maximum continuous output, starting-load capability and changeover behaviour in writing. Confirm whether switching is automatic or manual, whether additional equipment is needed and what happens when mains power returns. For an existing installation, start with the exact inverter and battery model numbers rather than the brand name alone.
Our battery storage installation service includes discussing backup as an additional design requirement. It should never be assumed to come with every battery installation.
Essential circuits or whole-home backup?
Start with what you genuinely need: perhaps some lighting, refrigeration, a router and selected sockets. Keeping a short priority list makes the installer’s assessment more useful than asking to run everything unchanged.
A dedicated backup socket, selected household circuits and a whole-home changeover arrangement are different installation scopes. A socket only supplies suitable appliances connected to it. Selected-circuit backup leaves other circuits off. Whole-home backup can offer broader coverage, but the system’s power and energy limits still apply.
An electric shower, cooker, heat pump or EV charger can substantially change the design brief. Tell the installer about these loads even if you plan not to use them in an outage. For example, agreeing to postpone EV charging may leave more energy available for household essentials.
How long will a battery last during a power cut?
Two separate figures matter. Kilowatt-hours (kWh) describe stored energy; kilowatts (kW) describe how quickly the system can supply it. A battery may have enough energy for several hours but still be unable to start or run a particular combination of appliances.
Here is an illustrative calculation, not a Sunergy installation result or a product specification. Assume 6 kWh of stored energy is available above the battery’s shutdown limit when the cut starts. Allow 10% for discharge conversion losses: 6 × 0.90 = 5.4 kWh delivered to the AC side.
| Average backed-up load | Calculation | Illustrative runtime |
|---|---|---|
| 300 W (0.3 kW) | 5.4 kWh ÷ 0.3 kW | 18 hours |
| 1,000 W (1 kW) | 5.4 kWh ÷ 1 kW | 5.4 hours |
| 2,000 W (2 kW) | 5.4 kWh ÷ 2 kW | 2.7 hours |
These estimates assume no solar recharge and a steady average load. Additional system standby consumption, temperature and battery ageing can reduce runtime. Actual conversion efficiency also varies. The table does not confirm that a particular inverter can support these loads or their starting surges.
Use measured consumption for your chosen appliances where possible. Our guide to choosing home battery capacity with an EV tariff explains everyday sizing; outage planning adds a separate requirement for reserve energy and supported circuits.
Can the panels recharge the battery during an outage?
Sometimes, but this must be confirmed for the proposed system. For example, Tesla’s UK Powerwall guidance explains that solar recharging during a cut depends on the configuration. It also warns that excessive appliance demand can overload the backup supply. Those capabilities should not be assumed for another manufacturer’s equipment.
For retrofit projects, ask whether your existing solar inverter will operate on the backed-up supply and whether solar can restart the system after a low-battery shutdown. Do not plan on uninterrupted recharge through cloudy weather or overnight. Even a suitable installation needs enough generation to cover running appliances and replenish the battery.
How should you balance backup reserve and bill savings?
A battery used heavily for everyday savings may have little charge left when an unexpected outage starts. Where supported, a backup reserve keeps some energy available for that possibility. A larger reserve leaves less capacity for routine tariff shifting or solar self-consumption.
Agree the priority before commissioning. If you mainly want battery-only off-peak charging, compare that daily-use plan with the backup option separately. Neither a cheap overnight tariff nor a fully charged battery guarantees a working supply when the grid fails.
Frequently asked questions
Can I add backup to a battery I already own?
Possibly. Ask an installer to assess the exact equipment, manufacturer-supported options and existing wiring. An inverter replacement, extra switching equipment or circuit changes may be necessary; some systems will not offer a suitable upgrade route.
Will my Wi-Fi and gas boiler keep working?
Only if their electrical supplies are included and the backup system can support them. A powered router cannot guarantee that the provider’s network remains available. A gas boiler also needs electricity for its controls and other components, so include heating requirements in the survey.
Is battery backup the same as an uninterruptible power supply?
Do not assume so. Ask for the manufacturer’s transfer-time specification and confirm suitability for sensitive equipment. Equipment may restart during changeover. If someone relies on electrically powered medical equipment, agree an outage plan with their healthcare or equipment provider rather than relying on a general home battery promise.
Who should I contact about a local power cut?
Call 105 to reach your electricity network operator. National Grid’s power-cut guidance also links to its Midlands outage checker and advice for people who are medically dependent on electricity. Keep reporting details and your installer’s system handover instructions accessible offline.
Planning battery backup in Nuneaton and the Midlands
Sunergy Renewables is based in Nuneaton and helps homeowners across Warwickshire, Leicester, Leicestershire and the wider Midlands assess solar and battery options. Send your postcode, existing equipment details and a short list of the appliances you want to keep running.
Ask Sunergy about a battery backup assessment so we can discuss the installation scope, limitations and an appropriate quote for your home.
