Most this electricity will come from overnight charging.
When rates are lower overall and specifically for electric car charging.
Currently, most of our electrical grid is idle overnight.
The USA can convert over 50% of our cars to electric without building a single extra power plant.
Wake up every morning with a fully charged car using American energy without having to go to the gas station.
Natural gas, hydro,nuclear, and renewables combined can more than handle future electric needs.
I bought that malarkey once, too. I built an all electric house with a geothermal heat pump for heat. It had a "smart meter" to sell me this great low cost electricity at night. It was a complete disaster. I quickly found out that my family (and most people) use electricity when they WANT to use electricity, not when the power company wants to sell it to them.
The energy density of batteries, in both mass and volume, will have to get an order of magnitude better (that's TEN TIMES BETTER), before electric cars will become feasible for most people.