The short answer
Size follows your evening usage, not your roof
Solar sizing is mostly about roof space and daytime generation. Battery sizing is different — it's about how much electricity you use after the sun goes down, and how much of that you want the battery to cover. Two homes with identical solar systems can need very different battery sizes.
Starting points
Typical ranges by household
Small household
Lower evening usage, mainly self-consumption.
Often around 5-7 kWh.
Typical family home
Evening cooking, appliances and some backup circuits.
Often around 10-13 kWh.
Larger household or EV
Higher evening load, more backup circuits, or charging an EV overnight.
Often 13 kWh+.
What actually decides the size
Four things we check during your assessment
- Evening and overnight usage — read from your electricity bill or smart meter data, not guessed.
- Existing or planned solar — how much you're currently exporting unused during the day, which is what the battery would otherwise be storing.
- Backup goals — whether you want specific circuits (fridge, lighting, internet) to keep running in a blackout, since backup capacity is designed separately from day-to-day savings capacity.
- Inverter compatibility — some batteries pair more simply with your existing inverter brand than others, which can affect the practical size options.
A system sized purely to "cover everything" is often oversized and paid for capacity that rarely gets used. We size from your actual bill and routine, not a generic industry figure.
Also worth reading
The federal battery rebate, explained — how the Cheaper Home Batteries Program reduces the upfront cost once you've settled on a size.