This is a very interesting topic but in it infancy depending on HEV and EV market development. Control of distributed energy resources under some constraints is a hot topic. Enclosed, you will find a preliminary study we have done in this context.
Social belief is based on utilizing V2G aiming at improving efficiency of operation, while until now, all evidences in practices show that employing them for long term applications is not economic. I would like refer you to 2 papers entitled as follows:
1. Economic assessment on V2G frequency regulation regarding the battery degradation
2. Evaluating the impact of V2G services on the degradation of batteries in PHEV and EV