Whole-home backup vs essential-circuit backup

First, the uncomfortable truth about batteries and blackouts

Here is the conversation I have on driveways all over the Sunshine Coast: a storm took the power out last summer, the neighbours' lights stayed on, and now you want a battery so yours do too. Completely reasonable. But the detail matters, because not every battery system keeps anything on in a blackout.

A standard grid-connected solar and battery system shuts down when the grid fails. That is a safety feature, not a defect, because the system must not push power into lines that workers are repairing. Keeping your home live during an outage requires specific hardware: an inverter with a backup function, often called EPS or emergency power supply, plus the switchboard work to carve out what gets backed up.

So the real question is not "does the battery have backup?" but "what exactly stays on, for how long, and what did that capability cost?" That is the whole-home versus essential-circuit decision, and it is one of the most important choices in any battery quote.

Why your battery and inverter set hard physical limits

Two numbers govern everything in an outage. The first is your inverter's backup output, measured in kilowatts. That is how much power it can deliver at once. If the inverter can supply 5 kW in backup mode and your ducted aircon plus oven wants 8 kW, something is not turning on, no matter how big the battery is.

The second is battery capacity, measured in kilowatt-hours. That is the fuel tank. A 10 kWh battery running 1 kW of load lasts about ten hours. Run 5 kW of load and you get about two. Every appliance you keep on during an outage is draining the same tank.

There is also a subtlety people miss: motor loads like pumps, compressors and aircon units draw a big surge when they start, several times their running power. An inverter that handles the running load can still stumble on the start-up surge. Good system design accounts for this. Optimistic brochures do not.

The good news is that solar keeps helping. A properly configured system recharges the battery from your panels during a daytime outage, which is how well-designed homes ride out multi-day events. But overnight, the tank is the tank.

Essential-circuit backup: the sensible default

Essential-circuit backup means we nominate a handful of circuits at the switchboard and wire only those to the inverter's backup output. When the grid drops, those circuits carry on, usually so seamlessly you only notice because the microwave clock survived.

What goes on the list? The fridge and freezer, first and always, because a blackout that costs you a full fridge of food has a real dollar value. Then lights, or at least the key living areas. Then the internet router and NBN box, because modern life, work and even phone calls run through them. Then a couple of power points for phone charging, the TV, and a fan.

What stays off: the big-draw items. Ducted air conditioning, electric ovens, pool pumps, electric hot water. Not because we are mean, but because they would flatten the battery in a couple of hours and can exceed the inverter's backup output anyway.

The honest appeal of this setup is that it matches what outages actually require. Blackouts here are usually hours, occasionally a day or two after a serious storm. Cold food, light, information and communication cover about 90 percent of what a family genuinely needs in that window, at a fraction of the cost of backing up everything.

Whole-home backup: what it takes to do properly

Whole-home backup means the entire switchboard, or close to it, stays live when the grid fails. Done properly it is excellent, and done properly it is a bigger project: more inverter capacity or multiple inverters, more battery, a backup gateway or changeover arrangement, and more involved switchboard work.

Even then, physics still applies. Most whole-home systems include load management, which automatically sheds the biggest appliances when the battery runs low or the load exceeds what the inverter can deliver. "Whole home" in practice usually means "everything, with the big things managed," and any installer promising unlimited everything is skipping the fine print.

The cost difference is real. You are typically adding capacity and hardware specifically for a capability you use a few times a year, so it needs to be worth it to you. For some households it absolutely is: medical equipment, home businesses that cannot stop, tank pumps for water, hinterland properties where outages run long. That is a rational purchase, not an indulgence.

If you are unsure, here is a practical middle path: start with a generously sized essential-circuit setup, and have the installer design the board so more circuits can move onto backup later. Good wiring today keeps tomorrow's options open.

What a real outage actually looks like

With a typical 10 to 13 kWh battery and essential circuits, a household that behaves sensibly, fridge closed as much as possible, lights used normally, devices charging, will ride out an overnight outage with capacity to spare, and with decent sun the next day the system recharges and does it again. Multi-day storm events become an inconvenience rather than a crisis.

With whole-home backup and normal habits, the same battery drains far faster, which is exactly why load management exists. The families who do best in extended outages are the ones who treat backup power like camping with excellent facilities rather than pretending nothing happened.

Set expectations with everyone in the house before storm season, not during the blackout. Know which circuits are backed up, know roughly how long the battery lasts, and know that the aircon is a fair-weather friend. A backup system you understand is worth twice one you do not.

How to decide, and how we do it

Ask yourself three questions. How often does your area actually lose power, and for how long? What in your house genuinely cannot stop, as opposed to what would be nice? And what is the premium for whole-home backup on your specific quote, because the gap varies a lot between systems and brands.

Suburban homes with rare, short outages usually get the best value from essential circuits done well. Hinterland and storm-exposed properties, homes with medical needs, pumped water or home businesses lean towards whole-home with load management. There is no universally right answer, only a right answer for your house.

When we design a backup system, the circuit selection is a conversation, not an assumption, and every backed-up circuit is clearly labelled at the switchboard so anyone in the house knows exactly what stays on. If you want a straight recommendation for your place, ask us for a quote and we will walk the board with you and put it in writing.

Common questions