Since 2014
YOUR FREE SOLAR & BATTERY CALCULATOR
Big sunshine. Smaller bills.
Build your system. See the savings. Let’s make it happen.
Household estimates · Ergon Tariff 11 starting rates · Adjust to match your bill.
Use total household consumption. If you have no solar, find “average daily usage” on your bill.
Daytime means 6 am–6 pm.
1. Solar panels Off
2. Home battery Off
Stores spare solar for later. Switching on a battery also switches on solar.
Adjust your usage pattern, electricity rates & assumptions
Household starting rates: Ergon Tariff 11 from 1 July 2026: 28.895 c/kWh and $1.80508/day, including GST. Eligible regional feed-in tariff: 6.006 c/kWh. Checked 8 September 2026. Rates are editable and do not update automatically. Match them to your bill; this calculator does not model time-of-use, demand or controlled-load tariffs.
Commercial starting rates: Ergon Tariff 20: 30.663 c/kWh import and $2.14438/day supply, including GST, from 1 July 2026. This small-business tariff is not a large-industrial default. Around 20 c/kWh applies to an off-peak period on Tariff 22D, not its all-day rate. No export payment or demand/fixed charges are assumed initially. Enter your own rates on the same GST basis. No commercial export eligibility is assumed; export limit starts at 0 kW. Confirm export permission and any contracted export rate before changing these settings. This is an indicative flat-rate energy-cost estimate, not a complete commercial tariff comparison.
Demand and operating patterns: Enter existing monthly demand, metering and other fixed charges as one amount, excluding the daily supply charge already entered. The same amount is kept in all three scenarios; no peak-demand reduction is predicted. Real demand charges may change, so full bill savings need interval meter data and tariff modelling. Commercial usage assumes the same average daily load every day, including weekends; it does not model closures, shifts or weekday-specific tariffs. A daytime-weighted business profile is illustrative, not an industrial load survey.
How it works: An illustrative 365-day hourly model supplies the property from solar first, then charges the battery from spare solar, exports within the selected limit, and draws from the grid when needed. The battery stores solar that would otherwise exceed the export limit, and stores exportable solar only when using it later is worth more than the export credit. Battery savings include conversion losses and the export credits you give up. No grid charging or battery export is modelled.
Generation and usage: 4.2 kWh per installed kW per day is an editable modelling assumption before inverter clipping, not a measured Townsville forecast. A synthetic seasonal and cloudy-day pattern and illustrative hourly household or commercial profiles are used, with a solar DC/AC ratio of 1.2. Actual weather, roof orientation, shading, inverter limits, usage timing, degradation and battery reserve settings change results. Battery size means rated usable capacity; this model does not set aside a separate backup reserve.
Reading the results: Monthly values are annual totals divided by 12. Comparison rows show all three options at the chosen sizes, even when a system is switched off. A negative net bill is shown as an estimated credit; bars show payable bills only. Bill credits, rebates and concessions are excluded. If you already have solar, your grid-import reading alone understates total site usage. The model does not assess installation eligibility, connection approval or backup capability. A site assessment is needed for a system recommendation. Commercial sizing extends to 1,000 kW solar (1 MW) and 1,000 kWh usable battery storage (1 MWh); equipment and network constraints are site-specific.
Rate sources: Ergon residential tariffs · Ergon feed-in tariff · Ergon business demand charges