Study Says Vehicle-to-Grid Discharge Detrimental To EV Batteries

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Results of a study by a team at the Hawaii Natural Energy Institute, SOEST, University of Hawaii at Manoa, suggest that the additional cycling to discharge vehicle batteries to the power grid in a vehicle-to-grid (V2G) scenario, even at constant power, is detrimental to EV battery cell performance. This additional use of the battery packs could shorten the lifetime for vehicle use to less than five years, the researchers said in a paper published in the Journal of Power Sources.

By contrast, the researchers found that delaying the grid-to-vehicle (G2V) charge in order to reduce the impact on the power grid had a negligible impact on the cells at room temperature, but could be significant in warmer climates.

The Hawaii team performed laboratory testing on commercial Li-ion cells to investigate the impact of bidirectional charging on Panasonic 18650 NCA   batteries (used in the Tesla Model S). The researchers investigated the effects of V2G/G2V combined with different charging schedules (1 or 2 charges a day, immediate or delayed charging) and different charging currents (level 2 or fast charging). Further, the effect of calendar aging at different temperatures was also investigated in a second set of experiments.

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Extrapolation of model parameters for (a) the cycle aging experiment and (b) the calendar aging experiment. Errors bars represent 95% confidence bounds on fitting parameters for both models plus the experimental observed maximum variation between cells. Dubarry et al.
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