Blackouts and batteries: what really happens

A home battery does not protect your house from a blackout by itself. Backup power needs two things together: hardware built for it (a hybrid or backup-capable inverter, or an all-in-one system with a backup port), and correct wiring, a backup changeover device feeding a dedicated backup circuit or a whole-home transfer switch. Get both right and the system switches to island mode, keeping your essential circuits live and drawing down the battery until it empties or the grid comes back. Switchover time varies by inverter: some are rated well under a second, others are slower, so check the datasheet for the model you are quoted.

Without that backup hardware, a standard grid-tied inverter shuts itself down the moment the grid drops. That's a deliberate safety feature called anti-islanding, required under AS/NZS 4777.2, the grid-connection standard for inverters, and it means your solar panels stop producing anything usable during the outage too, even in full sun. A battery bolted on without a backup circuit does nothing when the lights go out either.

Does a battery automatically protect me from blackouts?

No. This is the most common mix-up buyers bring to a quote: assuming any battery keeps the fridge running once the grid drops. It only works if the inverter is backup-capable and an installer has wired a backup circuit for your essential loads. Ask for both, by name, before you sign, and confirm exactly which circuits the backup covers.

What is island mode?

Island mode is what a backup-capable system switches to during a grid outage: it disconnects from the grid and powers your backup circuit on its own, isolated from the fault outside. Essential circuits (or a backup circuit) are the specific loads, usually the fridge, some lighting and a few power points, wired through a dedicated sub-board so the system can carry them without the rest of the house drawing on the battery too.

Essential-circuits backup vs whole-home backup: what's the difference?

Most retrofits cover essential circuits only: enough to keep the fridge, some lights and a handful of sockets running. Whole-home backup, powering the entire switchboard, needs a bigger inverter again: at least 10 kW of rated backup output and a 63 A on-grid bypass. A typical 5 kW hybrid inverter cannot deliver whole-home backup no matter how large the battery paired with it is. If whole-home coverage matters to you, say so early, since it changes which inverter is even on the table.

How do I avoid overloading my backup circuit?

1. Know your inverter's continuous power rating and its surge rating, both are printed on the datasheet.
2. Don't start several heavy loads at once. Switching on the kettle, the oven and the aircon together during an outage drains the battery far faster than running the fridge and some lights alone, and can trip the inverter's overload protection.
3. Consider a manual transfer switch, or load-shedding on large appliances, so you can shed a heavy circuit deliberately instead of the system doing it for you.

A bigger load always means a shorter runtime, never a longer one. Runtime comes down to usable capacity against what you're drawing, so the fewer big appliances running at once, the longer the battery carries you.

If you're also weighing a VPP for the same battery, backup reserve and VPP participation pull in different directions: see is a VPP right for you? and does VPP cycling wear out your battery? before you set a backup reserve.

Where next

Where to place a battery in a Perth home

AS/NZS 5139 clearance rules, garage vs outdoor walls, and what installers check on-site.

How to size a battery for your usage

A step-by-step method covering evening usage and seasonal AC demand.

Synergy Battery Rewards: what the VPP pays

Activation events credit 70¢/kWh on top of DEBS exports, and signing up is a WA rebate condition.

Explore your options

Answer a few questions and see systems and installers that fit your home.