Nissan LEAFs and e-NV200 at V2G station in the UK

Nissan LEAFs and e-NV200 at V2G station in the UK

A research team at the University of Hawaii at Manoa examined the impact of bi-directional charging between electric vehicles and the grid (V2G), and pretty much came up with the result one would expect - that it hurts the EV's battery; finding that constant use brings the expected lifespan of a battery pack to under 5 years.

Laboratory tests were performed using Panasonic's 18650 NCA cells.

According to the study, additional cycling (charging and discharge) of the EV's battery, decreases its capacity and increases resistance, which in general would make V2G uneconomical.

This has been, in the past - and in conjunction with smaller capacity batteries especially, one of the largest hurdles to V2G tech being more widely adopted.

The difference of capacity drop seems big according the University's research:

"The team concluded that a V2G step twice a day increased battery capacity loss by 75% and the resistance by 10%. This step once a day accelerated the capacity loss by 33% and the resistance increase by 5%. Forecasts based on the measurement results indicated that that V2G implementation would decrease the lifetime of the battery packs to under 5 years.

The team also found that calendar aging influenced the cells little enough that it was beneficial to charge the cells twice a day instead of once. Charging twice per day resulted in 5% less capacity loss and similar resistance increase compared to once per day."

source: Durability and reliability of electric vehicle batteries under electric utility grid operations: Bidirectional charging impact analysis via Green Car Congress