Infigen to supply Tesla, page-21

Have a look at the NEM interconnect logs and you can see the power exchange between the eastern state markets.
http://nemlog.com.au/interconnector/

These allow the states to exchange power as the market ebbs and flows. The power from Lake Bonney is sent into the grid in SA and if there is a demand in VIC/NSW/QLD the Interconnects can distribute any excess north.
That said IFN has got assets in various states to supply customers with firming added in the form of gas turbines and LB BESS so they can supply contracts to wholesale customers.