How Many Electric Vehicles Can Off-Peak Power Charge?

Does anyone know how many kilowatt-hours we in the U.S. dump back to ground each night? If so, please comment, and add a link to the source. Cycling coal plants shortens their lives and adds to the cost of maintenance, and is therefore unappealing. But I’m having the devil’s own time coming up with this datum.

The use of off-peak power is directly relevant to the case for EVs. If we’re curtailing off-peak wind in the middle of nowhere, that’s one thing, but if we’re dumping power near population centers, that’s another.

On a related matter: wasn’t there a study from some government lab (Lawrence Berkeley? Argonne?) a couple of years ago that concluded that charging EVs would be very inexpensive since most of the extra generation would come from running gas turbines longer and it would make better use of the transmission and distribution infrastructure? I can’t find that either.

Thanks.