Try to compute differently: how much usable energy you milk from gasoline/diesel? How many fill-up you do per week on your car? Now compute it at national scale

Try to compute differently: how much usable energy you milk from gasoline/diesel? How many fill-up you do per week on your car? Now compute it at national scale and imaging it in electrical energy instead of chemical. That's the "most real" consumption you can compute... Another easier and raw/spannometric computation can be counting a 70/80% recharge per day per car. Results are far bigger than yours :-) And I forgot to mention that Australia is one of the few developed country with a very little mean density and population so you have many possible energy sources and few people who consume them...