There has been studies around the world including Warwick university on V2G and the effects of degradation. The results are may/may not harm the performance, may have a neutral effect on the battery or does not significantly degrade the battery.
However we all know that current battery cell chemistry including lithium degrade overtime and different charging scenario’s have a impact more than others, i.e fast vs slow.
That said, I wouldn’t want to use what I consider my transport lifeline, as a portable powerplant for the grid or anyone else for that matter, other than myself.
The grid, on a large scale should be adopting battery storage plants at windmill farms, so not to pay the operator of these farms to turn them off when demand is low or when the wind blows above a certain speed. The same goes for solar farms, where battery storage should form an important aspect of these farms. Recycled batteries would also play an important role in these area’s. Relying on every man and his EV is not the answer.
The current number of Motability customers with EV’s is around 30,000,have non biderectional chargers. The cost to upgrade these customers would be a huge sum of money from a scheme perspective, with costs no doubt passed onto us. Of course its unlikely, as Motability have met their pledge of providing those that are able, with a facility to charge the vehicle. However, I guess they could offer a bi-directional charger as part of a non standard install.
Home battery storage, with or without solar, along with 2 rate tariffs would IMO be the best way to go 🙂