RE "South Australia’s last coal-fired power plant had closed, leaving the province of 1.8 million heavily reliant on wind farms and power imports from a neighboring region. " So - now they import power from places that use coal fired power stations and they have grid stability problems. NOT quitting coal at all. Id ask what is the price of their power KWh?
If you keep reading, that was the situation seven years ago before the giant Tesla battery that solved their stability problems.
The biggest problem is that SA is pretty flat[3] and doesn't have good sites for dams. They have a grand total of 3MW of hydroelectric capacity, which means they rely on Victoria (and soon NSW) for renewable energy when peak demand exceeds wind/solar generation, as well as their own gas generators and Victoria's coal plants. The big battery can respond faster than the interstate interconnects (which are far away) and the gas generators (which are expensive to run and only turn on when spot prices are high), which lets it fill the same role a big flywheel would in a coal/nuclear plant.
[0] https://hornsdalepowerreserve.com.au/
[1] https://www.aer.gov.au/wholesale-markets/wholesale-statistic...
[2] See https://en.wikipedia.org/wiki/File:Electricity_generation_SA..., which is a year-by-year collection of the data from https://www.energy.gov.au/data/australian-electricity-genera...
[3] https://en-au.topographic-map.com/map-wwnx/South-Australia/?...