What Size Solar Battery Do I Need?

In one minute to know: What Size Solar Battery Do I Need?

Most Aussie homes land between 7–13 kWh of usable storage. Start by listing your blackout must-haves (fridge, Wi-Fi, lights), add a few “nice-to-haves,” then check your evening usage. Match your needs to a battery size that covers both your bills and outage goals.

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Step 1: List your essentials (blackout must-haves)

The critical loads you want alive during an outage, typically:

Fridge/Freezer ❄  — ~100–200 W while running

Wi-Fi + a few lights ᯤ  — ~100 W combined

Garage door / TV / PC  ☐ — occasional short bursts

Covering these essentials first drives your system design and inverter choice.

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Step 2: Add “nice-to-haves”

Be honest about what you’ll really use in a blackout:

• Everyday extras — TV, PC, microwave

• Heavy loads — ducted air-con, hot water, electric shower (these usually need whole-home backup and a larger inverter)

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Runtime examples for 7, 10 and 13 kWh (idealised)

• 7 kWh (Compact) — entry-level backup

• 10 kWh (Popular) — covers most homes

• 13 kWh (Extended) — for longer outages or higher evening use

Runtime examples:

Scenario	Approx. load	7 kWh	10 kWh	13 kWh
Essentials only	~0.25 kW	~28 h	~40 h	~52 h
Essentials + TV/PC	~0.5 kW	~14 h	~20 h	~26 h
Essentials + more	~0.75 kW	~9 h	~13 h	~17

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3 rules of thumb

1 Start with essentials

Add comfort once critical loads are covered.

2 Check your evening peak

Cooking, hot water and heating/cooling can spike usage.

3 Bigger solar ⇒ more battery value

More daytime surplus improves utilisation.

When comparing quotes, insist on apples-to-apples: usable kWh (not just nominal), backup output (kW) continuous vs surge, official inverter compatibility, and written inclusions (switchboard works, brackets, bollard, weatherproofing).