Depends completely on your Feed in Tariff (FIT) - if it is greater than what you are charged (as it is in my case 44C FIT, usage around 22c i think).
I am much better off using as little power as possible during the day (as i am generating at 44c) - so if i export 20kW i get $8.80 credited, then if i use 20kW once the sun is down, i pay $4.40 - so i'm $4.40 up for the day.
Conversely, if/when the FIT reduces to 6c - i am much better off using as much power as i can during the day, as when i use my own generated power, i am charged nothing. For example (assuming my load demand is spread over the day), i use 20kW, and generate 20kW, then power cost is zero for the day.
