The storm hits at 6 pm and the street goes dark. You glance at the battery on the garage wall, expecting your home battery backup to keep the lights on. Sometimes it does. Sometimes the whole house goes quiet anyway.
If you are weighing up home battery backup for Adelaide and Sydney homes, the key point is that blackout protection is a feature of how the system is wired, not something every battery does automatically. This guide explains what keeps running, what does not and what to ask before you buy.
Key takeaways
- A home battery only powers your house in a blackout if it has backup capability. Many newer systems do, but not all.
- Solar panels without a battery shut down when the grid fails.
- Backup comes in levels. Only the top level charges from solar during the outage.
- Essential circuit backup lasts far longer than whole-home backup on the same battery.
- Runtime is roughly usable battery energy in kWh divided by your average load in kW. Heavy appliances drain it fast.
Does a home battery keep the power on during a blackout?
Only if it has backup capability. Without it, a battery can shut down when the grid fails, because grid-connected solar must switch off for safety. A backup-capable system disconnects from the grid and powers the circuits it is wired to supply, from essentials like the fridge and lights up to the whole home.
Why solar panels alone do not help in a blackout
Rooftop solar without a battery shuts down during a grid outage. This is a safety rule, not a fault. Energy Matters cites AS/NZS 4777 as the requirement, and RACV explains that grid-connected systems must stop so power does not flow back into the grid.
A battery changes this only if the system can island. Islanding means your home is isolated from the grid and runs on its own. RACV notes that many newer systems include a blackout option but not all do, so check the specification with your installer. A battery without a backup option may not work when mains power fails.
The four levels of home battery backup
Not every backup system behaves the same way. SolarQuotes founder Finn Peacock describes four levels, from no backup at all to full backup that keeps charging from the sun.
The four levels of home battery backup
0
Level 0No backup. Nothing runs in a blackout.
1
Level 1Some backup, with reduced battery capabilities.
2
Level 2Full backup, but no solar charging during the outage.
3
Level 3Full backup, and the battery charges from solar while the grid is down.
Source: SolarQuotes, Beating Blackouts: 4 Levels of Home Battery Backup (first published November 2022, last modified April 2026). Bar heights are illustrative.
Level 3 matters most in a long outage. Without solar charging, a daytime blackout on a poor solar day could leave you without power at night. SolarQuotes also warns that whole-of-house backup can drain the battery faster if nobody realises an outage has started. Backup capabilities should be written into your contract.
What happens in the first minute of a blackout
The sequence below shows what a backup-capable system does when the grid fails. The exact switchover time depends on the model. Energy Matters says systems usually switch in under a second, while RACV, in a December 2024 article, says power to the home can be cut for about 30 seconds. Ask for the figure for your exact system in writing.
What happens when the grid fails
1. The grid drops outMains power fails across your street.
2. Solar without backup shuts downGrid-connected solar must switch off so power does not flow back into the grid.
3. A backup-capable system isolates your homeIt disconnects from the grid and runs on its own. Sources put the switchover between under a second and about 30 seconds.
4. The battery supplies your chosen circuitsThat means essential circuits or the whole home, depending on how it was wired.
5. Solar recharges the battery, if the system allows itOnly Level 3 systems charge from solar during the outage.
Illustrative sequence. Sources: Energy Matters (July 2026), RACV (December 2024), SolarQuotes.
Essential circuits or whole home: which backup should you choose?
This is the biggest design decision in any home battery backup system. Essential circuit backup powers only pre-selected circuits. Whole-house backup powers every circuit, but it needs a much larger battery. The comparison below uses third-party estimates from Energy Matters, so treat the figures as a guide, not a quote.
| Essential circuits | Whole house | |
|---|---|---|
| What it powers | Pre-selected circuits, usually the fridge, lights, Wi-Fi router, phone chargers and one or two other appliances | Every circuit, including air conditioning, oven, washing machine, hot water and EV charger, if the battery has enough capacity |
| Typical battery size | About 5 to 10 kWh | About 10 to 30+ kWh, with a multi-mode inverter |
| Estimated runtime on 10 kWh | About 24 to 48 hours | About 6 to 12 hours |
| Air conditioning and oven | Not powered | Can run, but drain the battery quickly |
RACV adds that heavy appliances like electric ovens can drain a battery within a few hours. That is why limiting backup to the circuits you really need is often the safer choice.
Estimated cost range of backup, by type (AUD)
Essential circuits: about $8,000 to $18,000
$8,000 to $18,000
Whole house: about $15,000 to $30,000 or more
$15,000 to $30,000+
$0$10,000$20,000$30,000+
Source: Energy Matters, July 2026. Third-party estimates for most homes. Your quote will differ with brand, size and wiring.
How long will your battery last in a blackout?
A simple estimate for home battery backup is runtime in hours equals usable battery energy in kWh divided by your average load in kW. A 10 kWh battery running an average 0.8 kW load lasts about 12.5 hours before any solar recharge. Use the estimator below with your own numbers.
Blackout runtime estimator
About 12 h 30 minFrom 10 kWh at 100% charge with an average load of 0.8 kW, before any solar recharge.
Illustrative estimator with example inputs. It ignores solar recharge, reserve settings and inverter losses, so real runtime will differ. A formula from simple arithmetic, not a prediction for your home.
Three things shorten that number. A larger average load, a battery that was not full when the outage began, and big single appliances such as ducted air conditioning. Solar can extend runtime on a sunny day, but winter, cloud and panel orientation limit how much it adds.
A circuit priority test to use before you design backup
Sort every circuit into three groups before you talk to an installer. This keeps the battery for what matters. Your installer wires the circuits at the design stage, so decide first, not after the install.
| Keep on | Nice to have | Leave off |
|---|---|---|
| Fridge and freezer Lights Wi-Fi router Phone chargers |
Television Laptop and home office Ceiling fans Short microwave use |
Ducted air conditioning Oven and cooktop Electric hot water Pool pump EV charger |
Moving a circuit from the right-hand column to the left is what turns a 24 hour battery into a 6 hour one. Compliance and installation rules also affect where the battery and backup equipment can go. Our guide to residential energy storage system components, costs and compliance covers them.
Questions to ask your installer before you sign
- Does this exact battery and inverter combination have backup capability, and is it written in the quote?
- Which circuits will be backed up, and can I change them later?
- What is the inverter output in kW, and which appliances can run at the same time?
- Can the battery charge from my solar panels during a blackout?
- How long is the switchover, and which devices will need restarting?
- Can I set a backup reserve, and does any virtual power plant program use that capacity?
- Is the battery on the Clean Energy Council approved list, and who installs it?
When battery backup is not the right move
Backup is not automatically worth paying for. If outages in your area are rare and short, a battery without backup wiring may suit you better, because it still shifts your daytime solar into the evening. Compare the extra cost of backup against how often you lose power.
Be careful if anyone in your home relies on essential medical equipment. RACV states that a solar battery is not an uninterruptible power supply and is not suitable for people who rely on essential medical equipment. Speak to your medical equipment supplier about a dedicated solution.
Finally, do not expect a small battery to run ducted air conditioning, an oven and hot water all night. It will drain in hours.
Frequently asked questions
Will my home battery work in a blackout?
Only if it has backup capability. A battery without a blackout option may not work when mains power fails. Many newer systems include backup, but not all, so confirm it in writing before you buy.
What does a home battery keep running in a blackout?
It keeps running the circuits it is wired to back up. With essential circuit backup, that is usually the fridge, lights, Wi-Fi router and phone chargers. With whole-house backup, it can also include air conditioning, hot water and an EV charger if the battery has enough capacity.
How long will a home battery last in a blackout?
Runtime is roughly usable battery energy in kWh divided by your average load in kW. Energy Matters estimates about 24 to 48 hours on a 10 kWh battery for essential circuits and 6 to 12 hours for the whole house. Heavy appliances shorten it sharply.
Do solar panels work in a blackout without a battery?
No. Grid-connected solar systems must shut down in a blackout so power does not flow back into the grid. A backup-capable battery can keep your home running and, on a Level 3 system, charge from your panels.
Is there a delay when the power goes out?
Yes, sometimes. Energy Matters says systems usually switch in under a second, while RACV says power can be cut for about 30 seconds. The delay depends on the system, so ask your installer for the figure.
Can a battery run my air conditioner in a blackout?
Only with whole-house backup and enough capacity. Essential circuit backup does not power air conditioning. Even on whole-house backup, an air conditioner drains the battery quickly.
Plan your backup before the next storm
The right home battery backup design starts with your circuits, your usage and your budget. To compare options for your home, see our solar and battery systems page and try the savings and rebate calculators.
UR Local Solar reviews your electricity usage, roof, goals and budget before recommending a solar or battery solution, with service teams in Adelaide and Sydney. When you are ready, book a free battery assessment and ask about backup in your quote.
Sources
- SolarQuotes, Beating Blackouts: 4 Levels Of Home Battery Backup (first published November 2022, last modified April 2026)
- Energy Matters, Whole-House Backup vs Essential Circuits (July 2026)
- RACV, Solar batteries and blackout protection (December 2024)
