Millions of EVs charging at night and the in the middle of the day, and discharging in the morning and evening, goes a long way to balancing demand and generates a tidy profit for EV buyers, further encouraging adoption.
We will need, after enough generating capacity is built out, much cheaper storage than any car has. Cars have radically different requirements for their storage than the grid does: fast charging, fast discharging, lightweight, compact, collision tolerant. These make it much more expensive than alternatives.
The utility storage that will be built will necessarily be much cheaper, and store enormously more, than even a fully electric fleet could store. We are nowhere near a fully electric fleet, and barely moving toward one. The exact mix of utility storage we will have is impossible to predict, but it will be driven by the cost at the time it is being built.
We need to build factories for every kind of storage now, even though some will not be favored later. Demand will be high enough that more expensive ones that have factories ready will find buyers even if another will be cheaper "soon".
In California, charging at 40c/kWh during the day and discharging at 85c/kWh (for evening peak) would yield about $23 daily - or $8,400 annually.
Most Tesla's retain above 90% battery capacity after 100,000 miles [1]
Completely charging and discharging daily for one year is equivalent to 99,280 miles. A new Model 3 battery pack costs $15,800 [1] currently. 10% degradation is equivalent to $1,580.
Doing this currently would provide a ~7-year payback period on a Model 3.
[1] https://evannex.com/blogs/news/tesla-model-3-battery-degrada...
[2] https://www.slashgear.com/857917/replacing-the-battery-pack-...
I ask again - would you do that? Do you think your neighbors would do that? Do you think it's reasonable to base an entire power grid on that? What about if power starts to get cheaper on a particular day? Do you let the grid reach brownout status based on individual market pricing of individual actors?
Or do you just build some dedicated storage stations like any reasonably designed system?