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.
"The following is not for the weak of heart or Fundamentalists." -- Dave Barry