Whole-home vs essential backup: what you actually need
Most batteries can keep some power on in a blackout — but backing up your whole home is a much bigger ask than backing up a few essential circuits. Here is what separates the two, and what your system needs to deliver each one.
Key insight
Whole-home backup isn't a battery feature — it's an inverter feature, gated by battery size. It needs a hybrid inverter with a high-current changeover (around a 63 A on-grid bypass) and roughly 10 kW or more of continuous backup output, fed by enough battery to sustain that draw. A typical 5 kW hybrid can run essential circuits, but it cannot power a whole home no matter how big the battery is.
The two kinds of backup
Essential / backup circuits
A chosen set of circuits — usually lights, power points, the fridge, internet and maybe a fan — wired to a backup sub-board. Most hybrid systems, including 5 kW single-phase units, can do this. It keeps the basics running for hours without trying to power the whole house at once.
Whole-home backup
Everything stays on automatically — including high-draw loads like air-conditioning, an oven or an EV charger (within the inverter's limits). This needs a higher-output inverter, a high-current changeover, and a battery big enough to feed it. It costs more and not every system can do it.
What whole-home backup actually requires
Three things have to line up. Miss any one and you're back to essential-circuit backup:
A qualifying inverter
Around 10 kW or more of continuous backup output, with a high-current on-grid bypass (about 63 A) so the whole switchboard can transfer to battery. A 5 kW hybrid simply can't pass enough current to run the whole home.
Enough battery to feed it
A battery's continuous power scales with how many modules (kWh) are installed. A small stack can't deliver 10 kW even behind a big inverter — so whole-home backup has a minimum battery size, not just a minimum inverter.
The right phase setup
Single-phase and three-phase homes need different hardware (below). Three-phase backup also has to cover all three phases, which most homes have power split across.
Single-phase vs three-phase homes
This is where many quotes quietly fall back to essentials-only backup:
- Single-phase homes need a single-phase hybrid that actually reaches ~10 kW of backup. Only a couple of single-phase hybrids do (for example Sungrow's SH10RS and Fox ESS's KH10) — most single-phase hybrids top out around 5-6 kW, which is essentials-only. Because the load is concentrated on one phase, a single-phase whole-home setup also needs a larger battery to sustain the draw.
- Three-phase homes spread the load across three phases (roughly a third of the total on each), so most whole-home backup systems are three-phase. Many popular hybrids are three-phase-only for whole-home backup — they cover the whole house, but each phase is capped at its share of the inverter's output.
How much battery you need
There's no single number — it depends on the inverter output, your phase setup and the battery's chemistry. As a rough guide for a ~10 kW whole-home system:
- High-voltage stacks (the kind that deliver more power per kWh) generally reach whole-home output from around 13-20 kWh.
- Low-voltage stacks deliver less power per kWh, so they need more capacity — roughly 16-23 kWh — for the same backup output, with single-phase needing more than three-phase.
- Bigger inverters (e.g. 15 kW three-phase) or per-unit all-in-one batteries scale the requirement up again.
These are general ranges for sizing intuition — your installer should confirm the exact battery configuration for the inverter and backup level you want.
Which should you choose?
Essential backup is enough if…
- You mainly want lights, fridge, internet and power points to stay on
- You're on a budget or have a single-phase 5-6 kW hybrid
- Blackouts in your area are short and infrequent
- You don't need air-con or an oven running through an outage
Go whole-home if…
- You want everything to stay on seamlessly, including big loads
- You're sizing a 10 kW+ system with a larger battery anyway
- You work from home or rely on medical equipment
- You're happy to pay for the bigger inverter and battery
Before you sign a quote
Ask your installer to spell out, in writing, exactly which circuits are backed up, the backup power output (kW) during an outage, and whether it covers all phases. "Has backup" on a spec sheet doesn't mean whole-home backup.