What size battery do I need?
The right battery is the one that covers the power you use after dark, without paying for capacity your solar can never fill. Answer five quick questions and we will suggest a usable battery size, show batteries we install at that size, and work out your federal rebate.
The sizes use our own Geelong figures from more than 4,500 installs since 2011. It takes about a minute, and you do not need to give us your details.
Battery size calculator
Battery size questions
What size battery do I need for my house?
Start with the power you use after dark on a typical day, because that is the job the battery does. Many Geelong homes use 8 to 15 kWh after dark, which points to a battery of about 10 to 16 kWh usable. Add more if you want blackout backup or charge an electric car at night. Most of our solar-and-battery customers now choose 20 kWh or more, partly because the federal rebate covers more of the first 14 kWh.
What is the difference between usable and total battery size?
Usable size is the energy you can actually draw from the battery. Total size includes a small reserve the battery keeps to protect itself. For example, one Sigenergy SigenStor module (BAT 10.0) holds 9.04 kWh in total and 8.76 kWh usable. The federal rebate and this calculator both use the usable figure.
Is a bigger battery always better?
Only if your solar can fill it. On an average day each kW of solar panels in Geelong makes about 3 kWh, and less in winter. A battery that rarely fills costs more without doing more. The rebate also tapers: the full rate applies to the first 14 kWh, 60% from 14 to 28 kWh and 15% from 28 to 50 kWh.
Will a battery keep my power on in a blackout?
It can, but backup has to be designed in. You can back up a few essential circuits, such as the fridge, lights and internet, or the whole home. Whole-home backup needs a bigger battery and more switchboard work. We check what your home needs on site before we quote.
Can I add a battery to my existing solar system?
Yes, in most cases. The battery must be on the approved list, installed by an accredited installer and compatible with your solar system. If your current inverter cannot run a battery, we can fit a battery with its own inverter alongside your panels. See adding a battery to existing solar for prices.
How much is the battery rebate for my size?
From 1 May to 31 December 2026 a battery earns 6.8 certificates per kWh of usable capacity, on a tiered scale. A two-module SigenStor (17.52 kWh usable) earns 109 certificates, about $4,142 at $38 each. The rate drops to 5.7 certificates per kWh from 1 January 2027. Try any size on our battery rebate calculator.
Want a battery sized from your real usage?
Related pages: Battery rebate calculator · Solar size calculator · Solar batteries in Geelong · Geelong price guide · Case studies
