The article linked above says that Tesla considered V2G and rejected it. But it doesn't say why specifically. It mentions that some people are concerned about battery degradation, which some have mentioned here. I wonder if Tesla might be concerned with how this would affect range? In a solar economy, everything gets charged up during the day, and the batteries are drawn down at night. If you have solar plus Powerwall this is what happens. Your Powerwall is at its lowest SoC in the morning just before your solar panels start producing. V2G would mean that your 300-mile car might have only 200 miles, or 100 miles, or 50 miles of range when you need to go to work. Of course, you could theoretically set a limit on how much power you let the utility take from your car, but that limits the value of the whole V2G system. The article says cars will be storing 350 GWh by 2025 and 1 TWh by 2030, but the actual amount available for use at night will depend on how low people are willing to let their range drop.
It still could provide some nighttime power, but probably nowhere near the numbers above. If you own a Tesla with a 75 kWh pack, maybe you'd be willing to let the utility take 25 kWh and have a usable range of 200 miles instead of 300. But if you own a Leaf with 100 miles of range, you probably don't want to give up any of that range. If half of all EVs are Teslas and half of Tesla owners are willing to give up 1/3 of their range for the good of the environment, that figure of 1 TWh by 2030 equates to about 84 MWh available for the grid. So the usable amount for V2G is about 8% of the total.
I'd happily give half of my range to V2G, but that's only because I bought the LR battery before I decided to move to an island where the farthest I'm ever likely to drive in a day is 50 miles total, and that might happen once or twice a year.
In short, the numbers in the article for total available energy are vastly inflated by looking at the size of the batteries without considering how much of that energy owners are realistically able to give up.
