What size battery for a 10 kW solar system?
How this site makes money. We don't earn money from any links on this site yet. If that changes, we'll update this notice first. We don't compare every battery, installer or energy plan in the market. How we make money
Short answer: for most homes with a 10 kW system, size the battery to what you use from late afternoon to morning, not to the panels. Your panels make about 36.0–42.0 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 10 kW homes look at 13–20 kWh first [SB-S219, SB-S220, E]. Your bill decides it.
On this page: What 10 kW makes / How big a battery / How many batteries / The discount by size / When it won't fill / Ask your installer
Already have a 10 kW system on the roof? Adding a battery often means a hybrid inverter or a second, battery inverter [SB-S304, C], so start with adding storage to panels you already have.
What a 10 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 10 kW (yearly average) |
|---|---|
| Brisbane / Adelaide | about 42.0 kWh |
| Sydney | about 40.0 kWh |
| Melbourne | about 36.0 kWh |
| Hobart | about 35.0 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].
What size battery for a 10 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 40.0 kWh a day that uses 12 kWh while the sun is up has about 28.0 kWh spare [SB-S219, SB-S220, E]. If it uses 12 kWh overnight, a battery of about 12–17 kWh is the fit [SB-S219, SB-S220, E].
Going past 14 kWh on 10 kW
A 10 kW system has more spare solar, so a bigger battery can fill: about 36 kWh a day in Melbourne and 40 in Sydney on average [SB-S219, E]. But the discount per kWh falls past 14 kWh [SB-S001, SB-S036, C]:
| Usable battery | Certificates (May–Dec 2026 installs) |
|---|---|
| 14 kWh | 95 [SB-S036, SB-S001, E] |
| 20 kWh | 119 [SB-S036, SB-S001, E] |
| 28 kWh | 152 [SB-S036, SB-S001, E] |
So going from 14 to 28 kWh doubles the storage but adds only about 60% more certificates [SB-S036, SB-S001, E]. Go bigger only if your bills show big evenings, such as air con or an electric car charged at night [SB-S305, E].
Which brand steps fit 13–20 kWh? Sigenergy 2 modules, 17.52 kWh [SB-S060, E]; FoxESS 4 modules, 18.64 kWh [SB-S054, E]; Alpha ESS 2 modules, 18.6 kWh [SB-S074, E]; Powerwall 3 plus one Expansion, 27 kWh [SB-S052, SB-S070, C].
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].
Modular batteries let you start small and add modules later; FoxESS adds 4.66 kWh at a time, from 9.32 to 41.93 kWh [SB-S054, C]. See how FoxESS modules build up in size.
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 10 kW system makes less, so a battery that fills in summer may not fill in July [SB-S219, E]. If you have a smaller system, see the 6.6 kW battery guide. If yours is bigger, read our page on a battery for a 13 kW system.
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 see how battery sizes step up from small homes to big ones, read our sizes guide.
Rules checked 3 November 2026. Next scheduled check: before 1 January 2027 (STC step-down), and monthly for WA and NSW.