They are batteries too....
Further to BobLs excellent post....
-- EVs are storage batteries too
-- I'd imagine they benefit from not being charged to 100% every time, every day, but (perhaps) about 80%
-- Excess juice can be syphoned off 20 million cars into the vehicles that need it
I'd imagine most EV aren't simply dumb repositories. I'm vaguely aware that Teslas send a bunch of telemetry and diagnostics back home each night to The Great AI that does Something with it....
I'd also imagine that the government might set a base of information and open standards that need to be applied to all EV's, just like they did with OBD2 diagnostics. Since manufacturers refused to play nice with OBD diagnostics, governments forced them to. EVs nightly diagnostics might be the same.
SO!
--> Why not charge them up while the sun shines and the wind blows....
--> And suck them down to 60 or 80% when it doesn't....
--> Pay EV owners c/Kw
And everyone wins.
If one does expect a long trip, or set of trips, this coming day/week then log in to the management tool and select "fill er up!"....
In bobLs case, 20 million batteries is a lot of reserve... along with home batteries, home wind generators and other crafty micro generators.