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Hawaii study finds vehicle-to-grid discharge detrimental to EV batteries

Mon May 15, 2017 6:48 pm

Via GCC, but comes as no surprise: ... 5-v2g.html

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. . . .

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. 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.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

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Re: Hawaii study finds vehicle-to-grid discharge detrimental to EV batteries

Mon May 15, 2017 6:59 pm


Well, as Nissan has shown us, there is a wrong way to handle batteries. I would not be too quick to dismiss the idea of V2G as acknowledge the devil in the details.
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Re: Hawaii study finds vehicle-to-grid discharge detrimental to EV batteries

Mon May 15, 2017 11:42 pm

Tesla co-founder and first CEO Martin Eberhard on electric vehicle grid storage: "You can get about 90% of the value not by allowing the vehicle to put energy onto the grid, but rather just allowing the grid to have precise control of the charging of the vehicle."


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Re: Hawaii study finds vehicle-to-grid discharge detrimental to EV batteries

Tue May 16, 2017 12:06 am

I recall seeing a post I believe in a Leaf FB group of a guy in a Japan w/Nissan's Nichicon V2H box having lost quite a bit of capacity in his Leaf. I forget how many capacity bars he was down.

IIRC, it was enough to qualify him for a warranty replacement. :) Wish I could find the post.

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