Why your solar switches off when the power goes out.

The 30-second take

• Anti-islanding makes a grid-connected inverter disconnect automatically when the grid fails.
• It is required under AS/NZS 4777.2 and built into every compliant inverter sold in Australia.
• The purpose is to protect line workers from a rooftop system re-energising a dead line.
• It cannot be disabled — an inverter without it could not be legally connected.
• Backup power works by disconnecting from the grid first, then supplying the house through an isolated circuit.

What “islanding” means

An island, in electrical terms, is a section of network that stays energised after it has been cut off from the main grid. If the street supply fails but a rooftop solar system keeps exporting, that section of line is still live — an island of power in a network everyone believes is dead.

Anti-islanding is the protection that prevents this. The inverter continuously monitors the grid’s voltage and frequency, and when those fall outside acceptable limits it disconnects, typically within a couple of seconds.

Why it is not optional

When a fault occurs, distribution workers isolate the affected section and work on conductors they have confirmed are dead. A solar system feeding into that section creates a lethal hazard in a place safety procedure says is safe.

That is why the requirement sits in AS/NZS 4777.2, the standard governing how inverter energy systems connect to the grid in Australia, and why compliant inverters implement it in firmware rather than as a user setting. An inverter that could be talked out of anti-islanding could not be legally connected to the network.

“The feature that frustrates you during a blackout is the feature that lets someone climb a pole afterwards.”

How backup systems work around it

Backup does not disable anti-islanding — it satisfies it. A backup-capable system physically disconnects from the grid at the switchboard, confirms the separation, and only then forms its own stable supply for the isolated circuits.

Because the house is genuinely islanded from the network at that point, no electricity can flow back into the street. This is why backup requires dedicated wiring and a suitable inverter, and why it cannot be retrofitted with a software change.

What you will actually notice

• A brief interruption at changeover. Even good backup systems take a moment to disconnect and re-form supply. Sensitive electronics may reboot.
• Automatic reconnection. When the grid returns and stays stable for a set period, the inverter reconnects on its own. You do not normally need to do anything.
• Occasional nuisance dropouts. Voltage or frequency excursions on a weak network can trigger anti-islanding briefly. Frequent dropouts are worth reporting — they may indicate a network issue or an inverter set up outside your area’s parameters.

If keeping power during outages matters to you, that is a design decision to raise before you buy, not after. Our blackout guide covers what it takes.

Read next

• Do solar panels work in a blackout?
• What a battery actually keeps running
• How solar panels work
• Solar battery cost in Australia

Sources

• standards.org.au — AS/NZS 4777.2 grid connection of energy systems via inverters
• cleanenergycouncil.org.au — buying solar