I watched an interview with a person representing the electrical utilities in the United States and the question was posed about the strain that electric cars will place on the grid.
He responded that the grid will need some work as demand ramps up - but not as much as people think. Certainly, he said, not as much as was required when central air conditioning became available to home owners in the 1960s and '70s.
Full information here:
http://www.autoline.tv/show/2013?play