How long can a solar battery power a house?
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: divide the battery's usable kWh by how much power your house is drawing. A battery's size is measured in kWh [SB-S301, C]. If your home draws an average 1 kW overnight, a 10 kWh battery lasts about 10 hours; at 0.5 kW, about 20 hours [SB-S301, E]. Australian homes use 11–23 kWh across a whole day [SB-S220, C], so a 10–14 kWh battery often covers an ordinary night, but not a day without sun as well [SB-S220, E]. In a blackout it only runs your house if the system is set up for backup [SB-S301, SB-S303, C].
This page is about hours on one charge. For how many years a battery lasts, see how often solar batteries need replacing.
On this page: The sum / What changes it / Blackouts / Check your own / Ask your installer
The sum
Hours = usable kWh ÷ average kW your house draws [SB-S301, E].
| Usable battery | House draws 0.5 kW | 1 kW | 2 kW |
|---|---|---|---|
| 5 kWh | 10 h | 5 h | 2.5 h |
| 10 kWh | 20 h | 10 h | 5 h |
| 13.5 kWh | 27 h | 13.5 h | 6.75 h |
Our arithmetic [SB-S301, E]. Real runtime is a bit lower, because most batteries keep some charge in reserve and lose a little energy in conversion. We haven't found official reserve and loss figures for each model, so check the datasheet's usable kWh, not the total.
What changes it
- What's running. Runtime depends on how big your solar is, how much you use and which appliances are on [SB-S303, C]. Heating, cooling, ovens and hot water draw far more than lights and a fridge [SB-S303, E].
- The season. Use differs between summer and winter, and between peak and off-peak [SB-S305, C].
- Whether it was full. In winter your panels make less, so the battery may not start the night full [SB-S219, C].
- Battery age. Lithium-ion home batteries last about 10–15 years [SB-S300, C], and capacity falls over that time, so runtime shortens. How much it falls each year varies by model, so check the warranty terms with your installer.
If you're weighing a single large unit, check the Powerwall 3's usable capacity and Expansion units before you run the numbers: one unit holds 13.5 kWh, and Expansions take it to 54 kWh [SB-S052, SB-S070, C].
In a blackout
Most solar-only systems switch off in a blackout for safety [SB-S301, C]. A battery only powers the house in an outage if the battery and inverter are a backup (multimode or hybrid) setup [SB-S303, C]. Some backup setups cover only chosen circuits, so ask which ones [SB-S303, E]. Backup time follows the same sum: kWh ÷ what you run [SB-S303, E].
Check your own numbers
- On your bill or smart-meter data, find your use from about 5 pm to 7 am [SB-S305, E].
- Divide by the hours (14) for your average overnight draw [SB-S305, E].
- Divide the battery's usable kWh by that draw. That's your rough runtime [SB-S301, E].
Example (one case): 9 kWh overnight ÷ 14 h ≈ 0.64 kW. A 10 kWh battery ÷ 0.64 ≈ 15.6 hours, enough to reach morning [SB-S301, E].
Ask your installer
- The usable kWh, and how much is held in reserve [SB-S301, E].
- Whether the system gives backup in a blackout, and which circuits [SB-S303, C].
- Your overnight use in summer and winter from your own data [SB-S305, C].
The federal battery discount
The Cheaper Home Batteries Program gives a discount through certificates (STCs). Installs from May to December 2026 earn 6.8 certificates per usable kWh; from 1 January 2027 it's 5.7 [SB-S036, C]. The full rate covers the first 14 kWh, then 60% to 28 kWh and 15% to 50 kWh [SB-S036, SB-S001, C]. The rate is set by your installation date, not the day you sign [SB-S004, C]. The STC price moves, so there's no fixed dollar amount off. The battery must be on the Clean Energy Council approved list and be VPP-capable, and the installer must be accredited by Solar Accreditation Australia [SB-S003, C]. Check the current rules at cer.gov.au and dcceew.gov.au.
To check what size battery fits your nights, use our sizes guide. To find out how many years a battery lasts, see our replacement guide.
We haven't installed or used these batteries ourselves. This page is research from government pages, manufacturer documents and installer price lists, each linked and dated.
Rules checked 3 November 2026. Next scheduled check: before 1 January 2027 (STC step-down), and monthly for WA and NSW.