The battery is absorbing or providing short bursts of energy, thus providing grid stability, rather than than providing significant net energy. This then allows the use of renewables which might have short term variations int their output.

The big energy producer is the huge number of rooftop solar installations which everyday Australians have been putting on the roofs of their houses and wind. There are periods in summer when South Australia has surpassed 100% solar generation [1], the excess being exported to the East. These periods will continue to become more frequent, until they merge and South Australia is 100% renewable. They are the leaders, but the rest of the country is following.

By happy coincidence the most southern state and least sunny, Tasmania, is already 100% renewable due to abundant hydro, but they also have lots of wind being near the Southern Ocean.

[1] https://reneweconomy.com.au/south-australias-remarkable-100-...

A very small capacitor can stabilize a much larger supply. I totally believe that .1% fast response source and drain could have a stabilizing effect that is measurable.

For example: a battery that large could easily absorb a voltage spike that would cause a grid fault or brownout. Those tend to cascade and not having them immediately has a large effect on grid stability.

I can just imagine that getting a reliable power grid without batteries would mean you would have to supply extra power at all times to account for any shortfall. Now you just have to provide power until some natural gas generators can spool up.