Vehicle to grid battery degradation impact

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Insinööritieteiden korkeakoulu | Master's thesis
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Master’s programme in Energy Storage
58 + 9
Electrification of the mobility sector is necessary to make a lasting impact on emissions from an otherwise entirely dependent fossilized fuel sector. A key component to electrification is ensuring that electric vehicles do not disrupt an already complex energy grid system. This thesis focuses on vehicle to grid (V2G) scenarios in which EVs are used to supplement peak demand periods in the grid while also smartly controlling when the battery is charged up again. This raises the question of, how does the extra charging and discharging affect the battery life? Currently EV manufacturers offer warranties anywhere from 8-10 years when the battery gets to 80% of its original capacity. This metric is compared overall to several usage profile and vehicle to grid (V2G) scenarios to determine the effects on battery degradation with the goal to demonstrate and understand its impact on the battery. Six weekday usage profiles, with weekend profiles considered, were constructed taking into account driving and charging habits when compared to grid data dictating peak energy demand periods. These profiles were outfitted into an AMESIM model, including a semi-empirical battery ageing model, calibrated to a 71 kWh battery electric vehicle (BEV) using a temperature estimation, charger, a generic nickel manganese cobalt (NMC) battery and driving cycle array. Finally, parameter effects within these profiles, such as power level, state of charge (SOC) limits, and frequency, were hypothesized on and compared in terms of capacity loss. After running the model for 1 year, the results show that V2G does not significantly add battery degradation versus simply driving and charging on a normal use schedule. There is a 0.35% capacity loss percent difference between the reference no V2G scenario and the heaviest V2G use case, of 2 V2G discharge cycles per day. Over 10 years this would be about 12.5% versus 16.0% capacity loss, still within 20% of the original capacity. These results support the usage of V2G and demonstrate that the battery capacity loss is limited and upon the use of smart SOC management could even be less than non V2G scenarios.
Santasalo-Aarnio, Annukka
Thesis advisor
Guglielmi, Paolo
Melotte, Jietse
vehicle to grid, smart charging, bidirectional charging, usage profile, battery degradation, peak demand
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