[David]

If we just look at total electric generation and how much electricity it would take to replace a given number of gasoline powered cars with electric cars it looks impossible to achieve without doubling or more our current electric generation.

But there's more to it than that. There's a large swing between daily peak electric use which is typically around 5-6pm and minimum electric use around 4am. The minimum use lines up with when most people would be charging their car at night. So we wouldn't need much more generation, we'd just need to use the generation available during current minimum use.

Once there's a smart grid system running where cars are communicating with the grid, the cars can be used for power storage so the grid can alternate between charging a car and drawing power from the cars when the extra load is needed.