Environmental effects of vehicle-to-grid charging in future energy systems – A prospective life cycle assessment

Vehicle-to-grid (V2G) is increasingly recognized as a concept that uses battery electric vehicles (BEVs) as flexible storage options, enabling both charging and discharging of vehicle batteries. Applications of V2G aim towards technical and economic benefits from the system and end-user perspectives. Life Cycle Assessments (LCA) on BEVs indicate that charging strategies potentially reduce operational emissions. Besides evaluating environmental effects on the ‘technology level’, the literature recommends considering impacts on the ‘system level’ caused by a diffusion of the investigated technology. Since the future electricity mix per hour of (dis)charging is decisive for the impact of BEVs, systemic effects include repercussions of charging strategies on hourly electricity generation. When analyzing future scenarios, a prospective LCA (pLCA) allows us to consider technological developments. To assess the impact of charging strategies, the literature lacks a consistent framework that applies a pLCA approach and considers repercussions on the hourly greenhouse gas (GHG) emissions of electricity. The contribution of this article is the consolidation of the system and technology point of view when assessing V2G services. First, we present a framework that combines energy system modeling and a comparative pLCA to assess medium and long-term effects. To prove its suitability, the framework is exemplarily applied to evaluate two cost-minimized climate policy scenarios of Germany, i.e., with and without the option of V2G charging. The article outlines repercussions on the electricity system from 2025 to 2045 in an hourly resolution. This allows determining the impact per charging strategy on the technology level compared to conventional passenger cars in the second part of the study. Despite the insignificant effects on total GHG emissions by 2045, V2G charging accelerates decarbonizing electricity generation in the medium-term (2030–2035). When assessing the impact on BEVs, V2G causes substantial reductions. By 2030, operational emissions decrease between −50% and almost −200% compared to uncontrolled charging (144 kgCO2e/BEV). These potentials depend on the allocation of GHG savings reached through the secondary purpose of BEVs, i.e., a storage option for the energy system. With the ongoing decarbonization of electricity, however, the potential of V2G to reduce operational GHG emissions decreases, and the production phase gains importance. Regarding long-term contributions, substituting 117 GWh of stationary batteries indicates a reduction in raw material demands. Overall, combining the system and technology levels in a prospective assessment enhances the understanding of environmental effects caused by a large-scale diffusion of V2G charging. Researchers can further apply the outlined method for assessing use cases in other geographical scopes and time frames.