SunWiz reported on 7 September 2026 that batteries around 41 kWh represented roughly a third of Australian installations in April. By July, no single size held more than about five per cent in its analysis.
The figures come from SunWiz Luminate, a monthly sample of installation activity from hundreds of installers in each market. Its coverage and composition affect how closely the results represent the wider market.
Capacity incentives changed
The Cheaper Home Batteries Program initially applied the same certificate factor across eligible usable capacity. The taper introduced on 1 May 2026 reduced support for additional capacity in the higher bands.
From 1 May 2026 the certificate factor began tapering with installed capacity. The Clean Energy Regulator (opens in a new tab) sets the bands as 100 per cent of the factor from 0 kWh up to 14 kWh, 60 per cent for every kilowatt hour above 14 and up to 28 kWh, and 15 per cent for every kilowatt hour above 28 and up to 50 kWh. The stated aim, per the Department of Climate Change, Energy, the Environment and Water (opens in a new tab), is to hold the discount near 30 per cent across a range of system sizes as battery costs fall.
For a 41 kWh system, 13 kWh falls in the 15 per cent band. That changes the discount calculation. The timing is consistent with an incentive effect, but the reported distribution alone cannot establish why each household chose its system.
| Usable capacity band | Share of the certificate factor from 1 May 2026 |
|---|---|
| 0 kWh to 14 kWh | 100 per cent |
| Above 14 kWh to 28 kWh | 60 per cent |
| Above 28 kWh to 50 kWh | 15 per cent |
Distribution versus average
SunWiz reports an average system size of roughly 27 kWh, down about a tenth across the quarter. The average conceals the wider spread of sizes: fewer installations cluster around one configuration.
Stock planning and quoting depend on the configurations customers buy. Suppliers should compare their own sales mix with the reported distribution before changing package sizes or inventory.
The spread across the mid-20s and low-30s does not, by itself, show whether systems were sized to household consumption.
Sample limitations
This newsroom recorded in August that the sharp fall in battery registrations after 1 May was partly a reporting artefact, because installers have twelve months to create certificates and recent months are always incomplete when first published. That caution was about the certificate registry, and it stands.
SunWiz Luminate draws directly from a monthly installer sample rather than certificate registrations. It avoids that specific certificate-creation lag, but coverage, reporting and sample composition still limit how closely it represents the whole market.
The series also measures a different outcome: the mix of battery sizes, rather than total certificate registrations. The two should not be treated as interchangeable.
Quoting after the taper
Review quotes that still use pre-May discount assumptions. In a 40 kWh system, the final 12 kWh receives 15 per cent of the certificate factor. Confirm the applicable installation date and current scheme settings before presenting the discount.
Quotes held open across a rule change need the same check: the installation date, not the quote date, determines the applicable settings.
For WA households, sizing still needs to account for consumption, solar surplus, tariffs and backup needs. The taper affects price; it does not determine the right capacity for a home.
