people don't generally park their cars on the 8th floor. They park them in a parking lot, so that's where you would put the outlets. Power grids will have to expand to deal with the excess demand, but the transition to electric vehicles is happening slowly, so there's plenty of time to do so. Also, since electric vehichles are basically just giant batteries, they pair very well with solar and wind power. As solar power makes up a larger percentage of total power generation, it will become much cheaper to charge vehicles during the day when most of them are sitting in office parking lots. This will significantly reduce the "duck curve" problem, and make solar power even more effective than it currently is.