[Read more here: RenewEconomy--South Australia already at 57% wind and solar in 2016/17]
This is in fact quite a big deal. Two north German laender (states), Schleswig-Holstein and Mecklenburg-Vorpommern, have reached 100% renewables, but they are well connected to the rest of Germany as well as by HVDC lines to Denmark, Norway and Sweden. Surplus electricity can easily be sold outside their regions, and if the wind stops blowing, they can buy electricity in.
South Australia on the other hand is almost an "island grid". There are two interconnectors to the Victorian grid, but one is small and connects with western Victoria where the grid is already inadequate. If demand on the interconnector gets too high, the switches trip and the interconnector is shut down. The grid operators in SA have to be careful not to rely too much on being able to sell surplus power to Victoria or to buy when there is a deficit in South Australia. (The reason for this inadequacy is that the state electricity grids used to be entirely separate, as they were run by public enterprises owned separately by each state.)
So South Australia has the highest renewables penetration of any large-scale "island grid" anywhere. (Hawaii has a population less than half South Australia's, and until recently has been using diesel to provide electricity.) How SA copes with being an island grid will provide lessons for the rest of us, because if they can do it, so can we. They are building the world's largest battery bank, and there are strong rumours of a 110 MW CSP plant by SolarReserve in the state's north.
Note that this rapid roll out of renewables in South Australia has happened and is happening despite the hostility of the Commonwealth government and the Murdoch press. SA has been ruled by the Labor Party, but there is a state election next year which the so-called "liberal" Party might win, in which case the rise of renewables in SA will come to a screeching halt.