Another way to see it : cars are parked about 95% of the time. If you allow V2G for 5 million cars to deliver 7 kW each to the grid, they can power the country

Another way to see it : cars are parked about 95% of the time. If you allow V2G for 5 million cars to deliver 7 kW each to the grid, they can power the country for about 7 hours with zero other mean of electricty production - assuming a 50 kWh battery in the car. A 50 kWh car will power a typical home for a few days to a few weeks for energy efficient homes. When full electrification of cars is done the grid will look very very different.