For purely hypothetical discussion, I was asking myself how big electrical production increase would be needed for a first-world country when switching all cars from fossil fuel to EV only. I made the calculation myself for the country I live in (Italy, though the reasoning in principle would be valid for any chosen country), but the result is somehow unconvincing to me. So I would like to share my reasoning here and read you comments about it. Please note this is a very rough estimation, so please point out lack of precision in the calculation only when really matters to the general result, keeping in mind this is a very high level calculation.
In the examples I will reference data from 2019 which are the most recent complete dataset I was able to find.
The annual consumption of fuel for transportation was 7.3 million metric tons in gasoline and 23.8 million metric tons in diesel. The energy content is 46.9 MJ/kg for gasoline and 45.8 MJ/kg for diesel. The energy content sums up to about 344 PJ and 1090 PJ respectively. Converting to Wh (for easy comparison with electric consumption data) the total is just short of 400 TWh.
I found out that the efficiency of an internal combustion engine mounted on a vehicle is something around 20% - 35%, so I assumed an average value of 30% for the sake of simplicity. So the real energy that goes to motion is around 120 TWh. The efficiency of a full electric vehicle seems to me to be around 75%, so the electricity needed to charge that hypothetical EV fleet would be a little less than 160 TWh.
In the same year 2019, the electricity consumption in Italy was 320 TWh. So the conclusion of all this reasoning is that a country should roughly add 50% of its electrical production to support a full transition to electrical mobility.
Instinctively this seems way too much: have I made any serious error in my assumptions or calculations? Or is this basically a correct conclusion?