Blackout Protection

Why this isn’t automatic

The grid-tied solar inverters installed on most Australian rooftops shut down when the grid fails. This is a deliberate safety measure (anti-islanding) required by Australian standards - it prevents live household power being injected onto downed wires where linesmen might be working.

An add-on battery system doesn’t automatically override this. The battery needs to either:

1. Incorporate an automatic transfer switch (ATS) that disconnects the house from the grid before the battery forms its own local supply, or
2. Use a grid-forming inverter architecture that manages the disconnection and re-energisation safely

Without this, a battery system provides no backup capability whatsoever during a blackout - the battery may have capacity, but it cannot discharge without the grid reference.

Whole-home vs partial backup

Backup capability breaks down into two categories:

Partial backup (EPS circuit): The backup output covers a single circuit - pre-wired to essential loads like the fridge, phone chargers, some lights. The rest of the house loses power. This is simpler and cheaper to install, and is the approach used by many hybrid inverters (Sungrow, Growatt, Fronius in some configurations).

Whole-home backup: The entire house switches to battery supply during a blackout. The Tesla Powerwall uses a gateway device to achieve this - it disconnects from the grid and energises all circuits within milliseconds. Enphase’s IQ System Controller provides a similar capability with IQ8 microinverters. Whole-home backup costs more and requires switchboard work.

Transfer time

The speed of switchover matters:

• Milliseconds (< 20 ms): Seamless - most appliances don’t notice, computers stay on
• ~2 seconds: Some appliances restart, computers may lose unsaved work
• Manual: You physically connect an extension lead to a battery output socket

Tesla Powerwall 3 claims sub-second switchover for whole-home backup. Systems without dedicated gateway hardware typically have longer transfer times.

How long will it last?

With grid down and no solar charging: battery capacity ÷ average load. A 13.5 kWh battery powering a 500W average load (fridge, some lights, phone charging) lasts about 27 hours. Add solar charging and the backup can extend indefinitely as long as there’s sun.

Configuring a backup reserve - leaving, say, 20% of battery capacity reserved exclusively for blackout use - is important if you live in an area with frequent outages. Without it, a battery depleted from an overcast week may have nothing left when the grid fails.