In rich countries the electrical grid only needs to roughly double to power all transportation. The US did that in the 01960s, and China did it in the 02010s and probably will have done it again this decade.
This is why I genuinely suggest PV cells mounted into the bodywork of EVs. They'll "only" add 10-20 miles per (good weather) day depending on the specifics, but this is a significant fraction of the (mean) miles driven per day per vehicle, which means the necessary grid upgrades are much smaller.
Almost all those cars still need to be charged, the weather won't always be good, people don't generally choose to leave their cars parked in direct sun if they can help it, etc. — but as a systematic reduction in impact over the entire power grid, it's non-trivial.
