Home Cost Australia

Solar System Size Calculator

Estimate the solar system size you need from your daily electricity use, the share you want to offset, your own peak-sun-hours and system losses.

Share of daily use to cover. e.g. 80

Enter a value for your own location — we do not assume one. e.g. 4.2

Inverter, wiring, soiling, temperature. e.g. 15

Your estimate

Enter your values and select Calculate to see the estimate.

The formula

Required DC size (kW) = daily use × offset ÷ (peak-sun-hours × (1 − losses))

Peak-sun-hours describe how much usable sun your location gets on an average day. We deliberately do not assume a value for your city — enter one for your area. Losses account for inverter efficiency, wiring, soiling and temperature.

No invented irradiance

Because peak-sun-hours vary widely by location and season, this tool asks you to supply the figure rather than fabricating a city default. A local installer or a dated public dataset can refine it.

How to improve the estimate

Use your annual electricity use divided by 365 for daily use, pick a realistic offset (100% rarely means 100% self-consumption), and confirm peak-sun-hours for your postcode with an installer.

How we calculated this

This estimate uses transparent inputs and a fixed formula. See our methodology for how ranges, sources and assumptions work.