How to size a home solar battery

4 min read

Published by QUOTES AND DEALS · Updated

14 September 2026

THE SHORT ANSWER

Size a battery around the energy your home can regularly store and use, then check its power output and backup design. Evening usage, solar surplus, seasonal conditions and reserve settings matter more than capacity alone.

Capacity and power are different.

Usable capacity, measured in kWh, is the amount of energy a battery can store for use. Power, measured in kW, affects what it can run at the same time. Ask about both, along with any reserve kept for outages.

Build a household energy picture.

Collect your bills or interval usage data, your existing inverter details and an idea of future loads such as an EV. Ask how the proposed battery will be charged in winter and what happens on days with little solar.

Decide what backup means to you.

An ordinary grid-connected system does not automatically keep your house running in a blackout. Ask which circuits are backed up, what extra equipment is included, the continuous and surge limits, and whether the system can recharge from solar during an outage.

Compare usefulness before subsidy.

Since May 2026, the federal certificate factor tapers for capacity above 14 kWh and again above 28 kWh. A larger subsidy is not a substitute for checking whether your home can use the extra storage.

Sources & further reading

DCCEEW: Cheaper Home Batteries Program ↗

General information, not a site-specific design or an eligibility decision. Confirm requirements with the relevant authority and your installer.

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