Based on projected electric vehicles (EV) penetration in the near future, EV batteries could provide significant energy storage for the electric power grid by giving and taking energy when needed. This bidirectional charging could provide a wide range of ancillary services to the grid. The use of EV battery capacity for grid storage has been heavily discussed and modeled in recent years, but few studies have tested the impact on the battery themselves. The Hawaii Natural Energy Institute has partnered with Florida Solar Energy Center to test commercial Lithium ion battery under Vehicle-to-Grid (V2G) and Grid-to Vehicle (G2V) conditions to forecast their durability.

Battery degradation is extremely important to EV technologies and is a function of several factors, such as electrode chemistries, operating temperatures, and usage profiles (i.e. driving only vs. drving and vehicle-to-grid applications). The goal of this research was to assess such impact. The battery test plan used two separate experiments: a cycling experiment to assess the impact of both V2G and G2V charging strategies as well as a calendar aging experiment to assess the impact of temperature and SOC. We concluded that the simplistic approach adopted by current V2G pilot studies, namely that an EV is discharged and charged without consideration of battery degradation is not economically viable because of the impact additional V2G cycling has on battery life. However, a smart control algorithm with an objective of maximizing battery longevity can mitigate this and make V2G/G2V viable strategies. In such approaches, the control algorithm would only allow access to the battery’s stored energy if there were no adverse effects on battery longevity. This relies upon the development of accurate battery prognostic models and further advances in understanding the causes, mechanisms and impacts of battery degradation.

Point Person: Kathy McKenzie

 

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