But as far as I know we can’t build anywhere near enough hydro in Australia.
A study at the Australian National University (ANU) identified about 3,000 low-cost potential sites around Australia with head typically better than 300 metres and storage larger than one gigalitre (see Figure 3). The sites identified have a combined energy storage potential of around 163,000 GWh. To put this into perspective, a transition to a 100% renewable electricity system would need 450 GWh of PHES storage. The potential pumped hydro energy storage resource is almost 300 times more than required. Developers can afford to be very selective since only about 20 sites (the best 0.1% of sites) would be required to support 100% renewable electricity generation.
Emphasis mine.
Yeah, link rot.
I did some googling for you: https://www.ceem.unsw.edu.au/sites/default/files/documents/Low%20Emission%20Fossil%20Scenarios.pdf