There have long been critics of the idea of widespread use of electric vehicle (EV) vehicle-to-grid (V2G) technologies for a variety of reasons, but largely in relation to the potential damage done to EV batteries, and thus reduced battery lifespan.
New research from the Hawaii Natural Energy Institute at the University of Hawaii at Manoa seems to clearly support this assertion — the extra cycling that accompanies use of an EV battery for grid balancing, even when at constant power, reduces EV battery cell performance significantly.
The researchers note, though, that simply delaying the charging of EVs as a means of balancing the grid would have only a “negligible” effect on EV batteries, and could thus represent a better option. However, this could prove to not be the case in environments warmer than “room temperature.”
Green Car Congress provides more: “The Hawaii team performed laboratory testing on commercial Li-ion cells to investigate the impact of bidirectional charging on Panasonic 18650 NCA batteries. 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.”
“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.”
The new work is detailed in a paper published in the Journal of Power Sources.