What's the best battery for a 6.6 kW solar system?
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Short answer: for most homes with a 6.6 kW system, size the battery to what you use from late afternoon to morning, not to the panels. Your panels make about 23.8–27.7 kWh a day across Melbourne to Brisbane, averaged over a year [SB-S219, E], and Australian homes use 11–23 kWh a day [SB-S220, C]. The federal discount pays the full rate on the first 14 kWh of usable storage, then less [SB-S001, SB-S036, C], so many 6.6 kW homes look at 10–14 kWh first [SB-S219, SB-S220, E]. Your bill decides it.
On this page: What 6.6 kW makes / How big a battery / How many batteries / The discount by size / When it won't fill / Ask your installer
What a 6.6 kW system makes
Averaged over a year, 1 kW of panels makes about 3.5–5 kWh a day, depending on where you live [SB-S219, C].
| City | Typical a day from 6.6 kW (yearly average) |
|---|---|
| Brisbane / Adelaide | about 27.7 kWh |
| Sydney | about 26.4 kWh |
| Melbourne | about 23.8 kWh |
| Hobart | about 23.1 kWh |
Our arithmetic from energy.gov.au's per-kW table [SB-S219, E]. You'll make more in summer and less in winter [SB-S219, C]. On a sunny day, energy.gov.au puts a 6.6 kW system at about 26 kWh in Sydney, 28 in Brisbane and 23 in Hobart [SB-S220, C].
What size battery for a 6.6 kW system?
Work it out in three steps [SB-S219, SB-S220, E]:
- Find your night use. Your bill or smart-meter data shows daily use; check summer and winter separately [SB-S305, SB-S220, C]. Your installer or retailer can split it by time of day.
- Find your spare solar. Daily solar minus what you use while the sun is up. Only the spare can charge the battery [SB-S219, SB-S220, E].
- Pick the smaller of the two. A battery bigger than your spare solar won't fill; bigger than your night use won't empty [SB-S219, SB-S220, E].
Worked example only, use your own numbers: a Sydney home making about 26.4 kWh a day that uses 8 kWh while the sun is up has about 18.4 kWh spare [SB-S219, SB-S220, E]. If it uses 12 kWh overnight, a battery of about 12–14 kWh is the fit [SB-S219, SB-S220, E].
Is 6.6 kW enough to fill a battery?
Often, but not every day. A 6.6 kW system averages about 23.8 kWh a day in Melbourne and 26.4 in Sydney [SB-S219, E]. If you use 8 kWh during the day, that leaves about 16–18 kWh spare on an average day [SB-S219, E], enough to fill a 10–14 kWh battery. On grey winter days it may not fill [SB-S219, E]. That's why batteries over about 14 kWh are often hard to justify on 6.6 kW: you pay for storage that only fills in summer, and the discount per kWh drops after 14 kWh [SB-S001, SB-S036, E].
Which brand steps fit 10–14 kWh? Powerwall 3 is 13.5 kWh in one unit [SB-S052, C]. FoxESS gets 13.98 kWh with 3 modules [SB-S054, E]. Sungrow SBR gets 12.8 kWh with 4 [SB-S137, E]. Two Sigenergy modules make 17.52 kWh [SB-S060, E], which may be more than 6.6 kW fills in winter.
How many batteries?
Most home batteries are modular: you choose a number of modules, not separate batteries. Step sizes differ: Sungrow SBR 3.2 kWh, FoxESS 4.66, Sigenergy 8.76, Alpha ESS 9.3, Powerwall 3 13.5 [SB-S137, SB-S054, SB-S060, SB-S074, SB-S052, C]. Pick the brand whose steps land closest to your number [SB-S219, SB-S220, E].
The discount by size
Installs from May to December 2026 earn 6.8 certificates per usable kWh up to 14 kWh, then 60% of that to 28 kWh, then 15% to 50 kWh [SB-S036, SB-S001, C]. So the first 14 kWh earns the most per kWh. The rate drops from 1 January 2027 [SB-S036, C].
When it won't fill
In winter your 6.6 kW system makes less, so a battery that fills in summer may not fill in July [SB-S219, E]. If your winter evenings are big, a bigger solar system, like 10 kW, adds spare power: see our guide to sizing a battery for 10 kW of panels. Bigger again? We also cover batteries for 13 kW systems.
Before you book, ask your installer whether to mount it in the garage or outside.
Ask your installer
- How much spare solar your system makes in summer and winter, from your own data [SB-S305].
- The battery's usable kWh, and how many certificates the quote assumes for your install date [SB-S004].
- Whether your inverter can take a battery, or you need a hybrid or a second inverter [SB-S304, C].
Next step: get quotes
Ask at least two accredited installers for a written quote that shows the model, usable kWh and the certificate count.
To compare smaller and bigger setups, see every battery size, step by step.
Rules checked 3 November 2026. Next scheduled check: before 1 January 2027 (STC step-down), and monthly for WA and NSW.