Just how much electricity is this and where does this number come from? Doing some simple arithmetic we get:
1000 watt-hours is 1 unit of electricity as billed by utilities which is one kilowatt-hour (kWh)
45,000 gigawatt-hours = 45,000,000,000,000 Watt-hours (Wh). The average Australian household uses 16 kilowatt-hours (kWh) per day. If the number of households is 8.1 million. 16Kwh multiplied by 8.1 million is 129,600,000 kWh which is 129,600 mWh. This figure is per day, so we multiply by 365 to get 47 304 000 000 mWh per year, or 47,304 gWh per year. So our answer a little larger than the 45,000 gWh, but not too bad for an estimate.
Incidentally, the 16 kWh per day is about 480 kWh per month which comes to 5,840 kWh or 5.8 mWh per year. It might be useful to look at your energy bills and see how you could reduce your consumption.