Does every home battery provide blackout backup?
No. Standard grid-connected solar shuts down when the grid fails unless a compliant system can isolate the home or selected circuits from the network and operate safely as an island. This anti-islanding behaviour prevents a normal grid-connected inverter from feeding a network that is meant to be de-energised.
A battery can be installed purely for bill management with no backup at all. Treat backup as a separate design requirement when comparing quotes.
What are the four practical levels of battery backup?
| Backup level | What it usually means | Main trade-off |
|---|---|---|
| No backup | Battery operates while the grid is available but stops supplying the home during an outage. | Lowest backup complexity, but no blackout resilience. |
| Essential circuits | Selected loads such as fridge, lights, internet and a few outlets remain powered. | Preserves energy and reduces required inverter power. |
| Partial-home backup | A broader group of circuits remains available, with large loads excluded or actively managed. | More convenient but requires more power and careful circuit selection. |
| Whole-home backup | Most or all household circuits remain available subject to battery/inverter limits and load management. | Highest electrical and inverter demands. “Whole home” does not mean unlimited simultaneous power. |
Why do usable battery kWh and backup inverter kW both matter?
Usable kWh tells you how much stored energy is available. Backup kW tells you how much electrical power the system can deliver at one time.
A 20 kWh battery can contain plenty of energy but still be unable to start or run several high-power appliances together if its backup inverter output is limited. Likewise, a powerful inverter cannot make a small battery last all night if the household keeps drawing heavy loads.
What are surge loads?
Some motors, pumps, compressors and appliances draw a brief higher current when they start. The battery system therefore has both a continuous output rating and, where specified, a short-duration surge capability.
Air conditioners, pumps and refrigeration equipment should be checked against the actual backup design rather than assumed safe because their normal running power appears low enough.
Is backup automatic?
Many modern home battery systems use automatic transfer or gateway equipment so selected circuits are isolated from the grid and restored from the battery after an outage is detected. Other designs may involve different switching arrangements or manual actions.
Ask the installer to explain the proposed sequence in plain English: what switches automatically, what the homeowner may need to do, how quickly backup becomes available and what happens when grid supply returns.
Can rooftop solar recharge the battery during a long blackout?
Sometimes, but not automatically. The system needs to support solar generation while islanded and must be able to control solar output as household demand and battery state of charge change.
This can greatly extend outage duration on a sunny day, but it should be demonstrated for the proposed inverter and battery combination. An AC-coupled retrofit, microinverter system or older solar inverter may behave differently from an integrated hybrid design.
Why are three-phase homes more complicated?
A three-phase supply does not automatically mean the battery backs up all three phases. Some systems protect one phase or selected circuits, while other products and designs can support broader three-phase backup.
Large three-phase loads may also be excluded from backup. Ask which circuits and phases remain energised, not simply whether the salesperson calls the system “whole-home”. Read the phase decision guide ↗.
How long will the battery run during a blackout?
Runtime depends on usable stored energy, the battery state of charge when the outage begins, the average backed-up load, conversion losses and whether solar can recharge the system while islanded.
A small essential-circuit load can last far longer than electric heating, cooking, pool pumps or EV charging from the same battery.
Estimate outage runtime from the loads you plan to keep on.
Use the battery-runtime calculator to compare usable battery energy with an estimated backup load.
START MY ASSESSMENTWhat should a backup quote state explicitly?
- Exactly which circuits and phases are backed up.
- Usable battery capacity in kWh.
- Continuous and surge output available in backup mode.
- Whether transfer is automatic and what manual steps may be required.
- Whether solar can continue generating and recharge the battery while islanded.
- Any appliances the installer recommends excluding or load-managing.
- How a backup reserve state of charge is configured.
Sources and further reading
Editorial references checked: 5 October 2026Source labels identify who published each reference, not an independent endorsement. Confirm current requirements and exact product terms before purchasing.
- Government sourceSolar Victoria: What you need to know about backup power ↗: Victorian guidance on islanding, priority circuits and backup-capable battery systems.
- Government sourceAustralian Government: Batteries ↗: Anti-islanding, backup configurations, capacity and solar/battery operation during outages.
- Government sourceSolar Victoria: Power outages and all-electric homes ↗: Outage planning and backup considerations for electrified Victorian homes.