Overhead transmission lines will send the electricity generated by Sun Cable to Darwin and feed into the state’s power grid, but Griffin said two-thirds of the power would be exported to Singapore by high-voltage direct current undersea cables.From what I can see, it's nominal capacity will be 10GW, if you assume 10% losses, that still leaves 3GW for NT domestic consumption.
I didn't know someone was going to be building the world's largest aluminium smelter in Darwin because there is no way the current population will use 3GW between now and 2030, inclusive.
The NT could probably do more for reducing emissions by upgrading it Channel units to Combined cycle because from what I can work out, all their thermal fossil fuel power generation is from open cycle gas turbines, so the 1000C waste heat is just being lost. Close cycle units recover the heat to make steam and get roughly 50% more generational capacity.
If Singapore can make this work (assuming its not actually some BS), then there is no reason why solar power stations should be built in western SA, NT or even WA and power transmitted to the east coast grid and go along way to help resolve the evening peak issue. But is a 3000 HV line worth the cost for a few hours a day? Unlikely.