I like the idea of the buses providing power back to the grid when they're not being used in the late afternoon, but the article's author seems to think that even privately-owned passenger cars should be participating in this as well.

I'm not sure how practical that would be, though. For school buses it's easy, because you know exactly the range of times during the day, every (week)day, when they're going to be out on the road. Late afternoon/evening use as a grid source is perfect, because they've already brought all the kids home, and won't be needed until the next morning, and there's plenty of time to charge them back up after they've sent energy to the grid.

But for my own private vehicle, I don't use it on a schedule. Well, sure, there's some scheduled use, but there's also random unplanned use, or even just random planned use that might not conform to when the grid wants to pull from my battery. If I'm leaving at 6pm to start a 3-hour drive to visit out-of-area family for a few days, for example, I certainly don't want the grid pulling from it, say, from 3pm to 6pm.

And on top of that is battery wear and tear. I would assume that, all else being equal, a car participating in a vehicle-to-grid program will need its batteries replaced sooner (maybe much sooner) than a car that isn't. And given how utilities seem to want to pay less and less for power that residential solar sends back to the grid, I can't imagine any paltry sum they pay for vehicle-to-grid use would offset the very real costs to the car's owner.