My time-of-use rate plan for PG&E (EV2-A) drops to its cheapest price at 12am–I'm guessing that's the cause of the spike. I start my car charging at 12:05am. I wish they offered an even more dynamic rate plan.
Dynamic tariffs (aka real-time or wholesale plans) are becoming more common in the UK an EU. These are usually priced by 30-min periods and announced 24h in advance. More modern utilities will offer apps that control when your car is charged (in exchange for cheaper rates). But I agree, optimizing this is fun too. I'm building support for configuring Tesla Powerwall systems based on dynamic tariffs.
If you have the option, the best time to charge your car would be during the day when there is abundant solar.
In the long run, it makes sense to consume power when renewables can supply it, instead of having to store it in a battery and use it later.
In the short term however, renewables can't scale up in demand, so you're actually likely to require that the load is served from dispatchable power, which is probably either gas, hydro, or battery.
I don't think there's really any good time to charge it then. If solar was ever underutilized, I would assume there would be no gas in the mix at that point in time, but there is no such time.
On gridstatus, you can see how much renewable power is being curtailed (purposefully lowering output below what could be produced): https://www.gridstatus.io/live/caiso
Its... several GW in the middle of the day recently. So, this suggests charging EVs during this time would actually allow for better utilization of available renewables.
Another metric you can look at is if the grid scale batteries are currently charging or not. If they are charging, this suggests there is excess capacity available (or at least inexpensive capacity). The hours when grid batteries are charging are probably also good hours to charge EVs.
