Key takeaways
- A battery can provide backup power during a power cut, but the system needs to be designed for it.
- Not every battery installation automatically works when the grid goes down.
- How much backup you need depends on what you want to keep running and for how long.
- Running only essential appliances needs much less battery capacity than running air conditioning or the whole house.
- A larger battery can provide longer backup, but the inverter must also be able to supply enough power for the appliances you want to use.
- Solar panels may be able to help recharge the battery during a prolonged outage, but this depends on how the system is configured.
- Work out your own numbers with the Battery Size Calculator.
Yes — a home battery can provide backup power during a power cut, but only if the system is designed and configured to do so.
This is important because simply having solar panels and a battery does not automatically mean your home will stay powered when the grid goes down. Some systems will switch off during an outage unless the battery, inverter and electrical setup are specifically configured for backup.
The other big question is how much of your home you want to keep running. Keeping the fridge, Wi-Fi and a few lights on is very different from trying to run air conditioning, cooking appliances and the whole house.
Why doesn't every battery work during a power cut?
This can be surprising. You might have solar panels generating electricity and a battery sitting fully charged, but when the grid goes down the system may still switch off.
This is mainly a safety issue. Your home must not continue sending electricity back into the grid while engineers may be working on it. A system designed for backup needs to be able to safely disconnect your home from the grid and then supply electricity to selected parts of the house independently.
You may hear installers use terms such as backup mode, EPS, islanding or backup gateway. You do not need to understand all of the technical language. The most useful question to ask is simply: “If the grid goes down, exactly what in my home will continue working?”
What do you want to keep running?
This is the best place to start. Rather than choosing a battery size first, decide what you actually want the battery to do during a power cut.
Essentials only
For many households, the priority is simply keeping the basics running. That might include the fridge and freezer, Wi-Fi, some lighting, phone charging and a few small devices. This type of backup needs relatively little energy, so even a modest battery can potentially keep essential appliances running for many hours.
Essentials + comfort
You may want a little more than the basics. This could include televisions, laptops, fans and additional sockets around the house. That increases the amount of electricity being used, so the same battery will not last as long.
Essentials + air conditioning
This is where the battery requirement can increase significantly. An air conditioner uses much more electricity than a router, light or fridge. Running one efficient bedroom AC may still be realistic with a suitably sized battery, but trying to run several air conditioners or other large appliances can quickly increase the amount of storage and inverter capacity required. That does not mean it cannot be done. It simply needs to be planned properly.
How long do you want the backup to last?
There is a big difference between wanting enough battery power to get through a short interruption and wanting the house to operate through the night.
- 4 hours — suitable for a shorter outage.
- 8 hours — enough to cover a longer evening interruption.
- 12 hours — more substantial backup.
- Overnight — designed around keeping selected appliances running until the grid returns or solar production starts again.
Our Battery Size Calculator lets you choose what to keep running and for how long, then estimates the energy and battery size you would need.
What could different battery sizes run?
The answer depends on your appliances, but as a simple idea:
| Battery size | What it might cover in an outage |
|---|---|
| 5 kWh | May be enough for essential loads such as fridge, Wi-Fi, lights and small devices for a useful period. |
| 10 kWh | Considerably more flexibility: longer backup for essentials, possibly comfort loads and some air conditioning depending on the system. |
| 15 kWh | More storage again, potentially suitable for longer backup or heavier loads. |
These are not fixed rules. They depend on your appliances, how the system is configured and how much charge the battery happens to hold when the outage begins.
A simple example
Imagine two homes both have a 10 kWh battery. The first household uses the battery only for its fridge, freezer, Wi-Fi, lights and phone charging during a power cut. The second household wants to run all of those things plus an air conditioner.
The first home could potentially keep its essential appliances running for much longer because its electricity demand is relatively low. The second home will use the stored electricity much faster. The battery is the same. The difference is what the households are asking it to power.
That is exactly the choice the Battery Size Calculator offers: essentials, essentials plus comfort, or essentials plus one bedroom air conditioner.
Battery size is only part of the story
Battery capacity, measured in kWh, tells you how much electricity can be stored. Power, measured in kW, tells you how much the battery and inverter can deliver at any one moment.
A household can have plenty of stored energy and still be unable to run several large appliances at the same time if the inverter cannot supply the power they demand together. Both numbers matter.
Can solar panels keep working during a power cut?
Potentially yes, but it depends on the system. Some correctly configured solar and battery systems can allow the solar panels to continue supplying the home and charging the battery while the grid is unavailable.
That can be particularly useful during a longer outage. If the battery is partly depleted overnight, solar production the following morning may help recharge it. This is not automatic, so ask your installer directly: “If the grid is down, can my solar panels continue running and recharge the battery?”
Do I need solar panels to have battery backup?
No. A battery can provide backup power without solar if the system is designed correctly. Without solar, the battery normally recharges from the grid.
Under Malta's current household electricity tariffs, there is generally little financial reason to install a battery without solar purely to reduce electricity costs. In that situation, the main reason is backup and resilience. Our guide on whether a battery actually saves you money in Malta covers the economics in detail.
What appliances should you avoid during a power cut?
Large electrical loads drain a battery quickly. Electric ovens, electric water heaters, several air conditioners running together, pool equipment and similar heavy appliances can empty even a large battery in a short time.
That is why backup systems are usually designed around selected circuits rather than the whole property. Limiting backup to the circuits that genuinely matter can make a smaller battery last far longer.
Questions to ask your installer
- Will the battery work when the grid goes down?
- Will it back up the whole house or only selected circuits?
- Which appliances can I use during a power cut?
- Can it run one air conditioner?
- How long should I expect the battery to last with my chosen loads?
- What is the maximum power the battery and inverter can supply?
- Can my solar panels continue operating during an outage?
- Can the solar panels recharge the battery while the grid is down?
- What happens when the battery reaches its minimum charge level?
How much battery backup do you need?
Start with what you want to keep running, then decide how long you want it to run for. The Battery Size Calculator takes both: essentials, essentials plus comfort or essentials plus AC, over 4 hours, 8 hours, 12 hours or overnight.
So, can a home battery keep the power on?
Yes.
But the system needs to be designed for backup, and the battery needs to be large enough to run the appliances you care about for the amount of time you want. The two questions to answer before you buy are:
“What do I want to keep running?”
“How long do I want it to run for?”