Here's a report that is over 5 years old. lt is based on a study...

Here's a report that is over 5 years old. lt is based on a study using 250 watt panels. Today's panels are around 450 watts so the outcome today would be much more significant .

Australia’s estimated total potential for rooftop solar is 179 gigawatts with an annual energy output of 245 terawatt-hours – exceeding current electricity consumption on the main grids in Australia.

This report explores Australia’s potential for rooftop solar – providing estimates of both the nation’s available roof space, and our solar potential. It concludes that Australia is currently only using five per cent of available roof space and has the potential of 179 gigawatts with an annual energy output of 245 terawatt-hours.

https://www.cefc.com.au/insights/market-reports/how-much-rooftop-solar-can-be-installed-in-australia/