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Geng et al. Carbon Footprints 2025, 4, 8 https://dx.doi.org/10.20517/cf.2025.02 Page 5 of 15

subsequent trips. Due to the variability of weekend travel and limited parking opportunities, the vehicle’s
participation in V2G is not considered during weekends. For the charging stage, it is assumed that the
vehicle charges through a private charger upon returning home. Based on these assumptions, the battery’s
operational profile, including output power and changes in the State of Charge (SOC), was modeled over
the vehicle’s entire lifecycle. This study focuses specifically on commuter vehicles, as they are well-suited to
both meet commuting needs and provide energy storage services. The model operated with a one-minute
time resolution and was implemented in MATLAB.

For EVs, prioritizing energy for daily commuting is essential, and only the surplus battery capacity beyond
this requirement can be utilized for V2G participation. Therefore, it is crucial to first model the vehicle's
commuting stage and define the constraints on the available battery capacity. The battery’s operational
profile during the driving stage is influenced by factors such as commuting duration, daily commuting
distance, energy consumption rate, and speed. In this study, it is assumed that the EV operates at a constant
speed. Variations in user behavior, particularly changes in daily commuting distance and commuting time,
affect the battery’s operational profile. To account for these impacts, the study independently modeled the
battery’s operational profile for different commuting periods and distances, and the results were
subsequently weighted according to the probability distributions in the LCA model.

[22]
FR services are crucial for maintaining the stability of the grid frequency . Fluctuations in electricity supply
and demand during grid operation can lead to frequency deviations, which, if significant, pose risks to the
safe and stable functioning of the grid. FR services help stabilize the grid frequency by providing real-time
charging and discharging in response to the grid’s scheduling. When the grid frequency exceeds the
standard value, the EV battery can absorb excess electricity through charging, thereby reducing the
frequency. Conversely, when the grid frequency drops below the standard, the EV battery can discharge
electricity to supplement the grid, raising the frequency. In this study, the operation of EV batteries
[23]
providing FR services was modeled using the droop model . According to the droop model, the EV battery
is only activated when the frequency deviation exceeds a predefined deadband threshold, and the dispatch
capacity is determined by the magnitude of the frequency deviation.

PSVF services are employed to mitigate long-term load fluctuations in the grid, alleviating grid congestion
[24]
and postponing the need for grid expansion . In this study, the process of EVs providing PSVF services
[25]
was modeled based on the time-of-use (TOU) tariff policy . EVs charge during valley load periods and
discharge electricity back to the grid during peak load periods. Through the differential in TOU tariff, users
can earn profits.

By considering the battery’s operational profile across different stages, the daily variation in the SOC of EV
batteries throughout the vehicle’s lifecycle can be calculated, as shown in Equation (1).

where SOC denotes the SOC of EV batteries at time t on day i (%), SOC denotes the initial SOC of EV
i,t
i,0
batteries on day i (%), ∆SOC denotes the SOC change of EV batteries during the daily commuting stage at
D,i,t
time t on day i (%), ∆SOC FR,i,t denotes the SOC change of EV batteries during the FR service stage at time t
on day i (%), and ∆SOC PSVF,i,t denotes the SOC change of EV batteries during the PSVF service stage at time t
on day i (%). The detailed calculation process for each sub-model is provided in the
Supplementary Material.