Continuing my overbuilding work...
While V2G would probably work at 20x solar and 10x wind using only 2 million of California's 30+ million cars and light trucks there's the possibility that robo vehicles might to a large extent wipe out the number of cars plugged during all hours of the day. The V2G resource may disappear because most cars would be in service during busy parts of the day.
Moving to 20x solar and 20x wind would increase penetration to 89% while increasing the post-EV charging cost of electricity by only one cent, four to five. On only four days out of the year would direct supply from PV panels and wind turbines failed to have provided enough input to cover demand.
On the very worst day demand (with no EV charging) would have been 618,390 MWh. 20x solar plus 20x wind would have generated 568,340 MWh. A shortage of 50,050 MWh. On the worst day of the year solar and wind would have provided 92% of grid demand.
California could provide that amount of electricity from existing hydro.
Of course this is only one year. A multi year study would be needed to see if there are more severe supply stresses.
I'm working on getting offshore wind data for California. If so, I can probably model offshore which I think will lower the overall amount of wind and solar needed.