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Page 6 of 15 Geng et al. Carbon Footprints 2025, 4, 8 https://dx.doi.org/10.20517/cf.2025.02

Battery degradation model
One of the key factors limiting users’ participation in V2G is the additional battery degradation, which
results in extra economic costs for the user. From an environmental perspective, the additional battery
degradation associated with V2G also leads to increased GHG emissions related to the materials and
manufacturing of EV batteries. Therefore, it is crucial to analyze the battery degradation that occurs when
EVs participate in V2G. In this study, a data-driven empirical model was developed to quantify the battery
degradation throughout the vehicle’s lifecycle. The model incorporates both calendar aging and cycle aging,
[26]
with the calculations outlined in Equation (2) .

Q = Q + Q (2)
l,i
l,cyc,i
l,cal,i
where Q denotes the capacity loss of EV batteries on day i (%), which is measured by State of Health
l,i
(SOH); Q denotes the capacity loss caused by calendar aging on day i (%); and Q l,cyc,i denotes the capacity
l,cal,i
loss caused by cycle aging on day i (%).
When the battery's SOH reaches the End-of-Life (EOL) threshold and the vehicle itself is still operational,
the user will replace the battery. The battery degradation model quantifies the frequency of battery
replacement throughout the EV’s lifecycle, both with and without V2G participation. The detailed
calculation process for the battery degradation model is provided in the Supplementary Material.

Life cycle assessment of V2G technology
This study employed the LCA methodology to evaluate the additional lifecycle GHG emissions of V2G
technology. The global warming potential (GWP) midpoint factor from the ReCiPe 2016 method was used
to assess GHG emissions . Using V2G-based EV distributed energy storage introduces two additional
[27]
GHG emissions compared to directly using grid electricity. The first source comes from the materials and
manufacturing of related equipment, including bidirectional chargers and EV batteries. The second source
is electricity losses during charging and discharging due to the battery’s round-trip efficiency. Additionally,
for plug-in hybrid electric vehicles (PHEVs), participating in V2G causes additional battery degradation,
which leads to increased fuel consumption and corresponding GHG emissions.

Life Cycle GHG Emission (LCE) is adopted as the evaluation metric to assess the additional GHG emissions
resulting from V2G technology. LCE refers to the GHG emissions generated per kilowatt-hour of electricity
discharged from an energy storage system and is widely used in the environmental impact analysis of energy
storage technologies [20,28] . The detailed calculations for the LCA model are provided in the
Supplementary Material.

Input data
The additional GHG emission of V2G technology is determined by multiple factors. On one hand, the EV’s
energy storage potential is shaped by technical specifications and user behavior. On the other hand, the grid
and end-use loads, as the demand side for energy storage, determine the amount of energy storage services
provided by scheduling strategies and policies. Given the substantial regional heterogeneity of these factors,
this study analyzed the additional GHG emissions of V2G technology across various cities in China,
considering multiple perspectives.

China’s EV market exhibits significant regional variation. To capture this heterogeneity, a multidimensional
database was developed using 2023 EV sales data in China . The database characterizes the market by
[29]
spatial distribution, vehicle types, powertrain configurations, and battery chemistries. It covers 337 cities
across 31 provinces, excluding Hong Kong, Macau, and Taiwan. Vehicle types are categorized into cars (C),