That's going to double the demand for electricity.
While technically that's true in the sense of the demand for the power to propel vehicles being shifted from a liquid source to a pure electrical equivalent. I suppose that if you think of it, depending on how efficient a car engine vs the electric generators and the transporting and storing electricity, electric cars may or may not add to the problem.
PL/I -- "the fatal disease" -- belongs more to the problem set than to the solution set. -- Edsger W. Dijkstra, SIGPLAN Notices, Volume 17, Number 5