Choose the right battery capacity to maximize self-consumption and minimize grid reliance
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Average Household
Large Household
Look at your electricity bill or smart meter data to find your average daily usage in kWh. This is the foundation for sizing your battery.
Typical Australian household usage:
The key to battery sizing is understanding how much energy you use when the sun isn't shining (typically 5pm-7am). This is what your battery needs to cover.
Rule of thumb:
Evening/night usage is typically 50-70% of your total daily consumption. For a household using 30kWh/day, that's 15-21kWh overnight.
Most lithium batteries can safely discharge to 90-95% of their capacity. A 13.5kWh battery with 90% DoD provides 12.15kWh of usable energy.
Example: Tesla Powerwall 2 has 13.5kWh total capacity but 12.2kWh usable capacity (90% DoD).
Your battery should be matched to your solar system size. A larger solar system can charge a bigger battery during the day.
Recommended ratios:
If you want backup power during blackouts, consider which appliances you need to run and for how long.
Essential loads (typical):
A 13.5kWh battery can power essential loads for 3-5 days during an outage
The WA State rebate provides $1,300 per 10kWh up to 30kWh ($3,900 maximum). This creates natural sizing sweet spots:
If you're on a time-of-use tariff with Synergy or another retailer, a battery can shift your usage from expensive peak periods (3pm-9pm) to off-peak times, maximizing savings beyond just solar self-consumption.
Programs like Synergy's Battery Rewards allow your battery to participate in grid services, earning you additional income. This can improve your payback period by 1-2 years.
Our quote builder analyzes your usage patterns and provides tailored battery sizing recommendations
