Backup
Blackout backup: essential circuits or the whole house?
A lot of people assume solar keeps the lights on in a blackout. It doesn't. A standard solar system shuts down when the grid goes down, so it can't push power into lines that line workers might be repairing. To keep anything running you need a battery set up for backup.
Essential circuits
The installer moves a few chosen circuits onto a separate backed-up supply. Typically that's the fridge, some lights, the internet and a few power points. When the grid drops, those circuits switch over to the battery in a fraction of a second.
- Works with a standard 5 kW hybrid inverter.
- Costs less, and the battery lasts much longer in an outage because it's only running the essentials.
- Air-con, ovens and other big loads stay off until the power is back.
Whole-home backup
The whole switchboard runs from the battery when the grid is down.
- Needs a larger inverter, usually 10 kW or more, because everything in the house can switch on at once.
- Costs more to wire, especially on an existing house. On a new build it's far cheaper to plan in from the start.
- Drains the battery much faster if you run air-con or cooking appliances through an outage.
How long will it last?
Divide the usable battery capacity by what's running. A fridge, lights, internet and a TV might average under 0.5 kW, so a 13 kWh battery would run them for a day or more, with solar topping it up during daylight. A ducted air-con alone can draw 3 to 5 kW, which could empty the same battery in an evening.
Things to decide before the install
- Which circuits matter to you: medical equipment, fridges and freezers, the garage door, a home office.
- Whether you want the battery to keep a reserve for outages instead of emptying it every night. That costs some everyday savings, but means there's always something there.
- Three phase: some three-phase inverters limit backup power on each phase, so the backed-up circuits need spreading across the phases.
Backup is set up in the wiring, so it's much easier to include on install day than to add later. If you think you'll want it, say so at the quote.
Want the numbers for your house?
Send us your latest Synergy bill and we'll size a system from your actual usage, show every rebate as its own line, and tell you what we can and can't offer before you sign anything.