[oil pan 4]

About 8 to 12 years ago I remember seeing pipe dream news articles about vehicle to grid fairly often.
Saying that it was never alive is probably more accurate.

Why no vehicle to grid:
Cost.
Range.
Wear.
Power.
Negotiations.

Cost. Most electric vehicle owners are cheap. For it to be effective vehicle owners will need at last a 240v 20 amp circuit to charge their vehicle. It appears around half of electric vehicle owners charge with 120v power.

Range. If the power company controls when your vehicle charges and puts power on the grid is your car going to be charged when you need it?

Wear, convince people this isn't going to wear out their traction battery.

Power. How much power are the vehicles going to put on the grid, too little there's no point.

Negotiations. Who pays for it, how's it going to work, when is it going to work? This would require auto makers and power companies to sit down and talk to each other.
They don't appear to have any interest in each other.

Equipment. Then once you do all that you have to figure out what equipment is going to be used, how its going to work, who is going to use it, where they are going to use it. Are the cars going to have this built in or will it be external.
Is it something that can only be added to new vehicles or will it be a seperate piece of equipment.

I think the best way it would work is to base it on the CHAdeMO protocol. Because you are tapped straight into the vehicles battery and there are up to 50kw of power available.
Unless there is a blocking diode in the vehicle that prevents back flow of battery power to the CHAdeMO.