What Size Solar Battery Do I Actually Need? (10kWh vs 13kWh vs 20kWh)

 It is the question every homeowner asks, and it is the one most likely to get a vague answer. Bigger is not automatically better. A battery that sits half charged every night is money parked on your wall doing nothing, and an undersized one leaves you buying grid power at peak rates. The right size is the one that matches how your household actually uses electricity after the sun goes down.

Here is how to work it out, what 10 kWh, 13 kWh, and 20 kWh each realistically cover, and why the changed 2026 rebate nudges most homes toward a particular size.

Start with your overnight usage, not your total usage

Your daily electricity use is not the number that matters. During the day, your solar panels are running the house directly. A battery only earns its keep from late afternoon through to the next morning, so the figure to find is how much power you use once solar stops producing.

You can pull this from your electricity bill or your meter data. Most Australian homes use roughly 40 to 60% of their daily electricity in the evening and overnight. As a rough guide:

• A smaller household using around 16 to 20 kWh a day might use 8 to 11 kWh of that after dark.
• A busy family home using 25 to 35 kWh a day might use 13 to 18 kWh overnight.
• A large home with a pool, ducted air con, and an EV can easily push past 20 kWh overnight.

The goal is a battery that comfortably covers a normal evening and overnight run, with a little headroom, without paying for capacity you will rarely cycle. It is also worth adding a small buffer of around 20% for capacity that fades slightly over the battery’s life. If you are unclear on the units, our explainer on kW vs kWh clears it up. Read More: https://www.greenlightsolar.com.au/what-size-solar-battery-do-i-actually-need-10kwh-vs-13kwh-vs-20kwh/