Entire fleet is not going to switch to electric in 2022, Mercedes-Benz will start offering electric versions of their models in 2022, some other manufacturers are targeting to switch to EVs around the same time span. So in the beginning of 2020s we'll see gradual process of switching to EVs for all car manufacturers. 5 years is plenty of time for electricity providers to prepare their grids, especially considering that their investments will probably pay off with an interest, since they are gonna increase sales as more cars become electric.
Plus most of the charging probably will be scheduled at the time when electricity usage is less and providers offer better pricing. For example in some areas in US you can get free nights rate, at night there is less strain on the grid and abundance of wind power makes it possible.
Mercedes is going to update its lineup, not replace every single car in the world overnight. Countries have time to build out their network of charging stations.
