How Bidirectional Charging Strategies contribute to Achieving a Climate-Neutral Energy System
The publication in the Journal of Applied Energy examines the impacts of Vehicle-to-Grid (V2G) strategies on the future energy system. As part of the unIT-e² project, a prospective Life Cycle Assessment (LCA) was conducted to investigate the effects of various charging strategies on the Global Warming Potential (GWP) of electricity generation in Germany. The results demonstrate V2G’s contribution to reducing greenhouse gas (GHG) emissions in the energy system and potentially lowering the operational GHG emissions of electric vehicles. Thus, the study provides insights into the role of V2G in achieving climate goals.
Study Objectives
V2G allows battery electric vehicles (BEVs) to be used as flexible storage options, enabling controlled charging and discharging of vehicle batteries. V2G applications aim for technical and economic benefits from the perspective of the system and end-users. LCAs of BEVs suggest that charging strategies can reduce operational GHG emissions. Besides evaluating environmental impacts at the “technology level,” impacts at the “system level” caused by the dissemination of the studied technology must be considered. These systemic effects include the impacts of charging strategies on hourly electricity generation. To comprehensively assess the effects of charging strategies, a methodological framework is needed that consistently integrates future developments at both the technology and system levels. A prospective LCA (pLCA) allows for considering technological developments in analyzing future scenarios.
Methodology
The methodological contribution of this article lies in consolidating the technology and system perspectives for evaluating new use cases in the energy system. The study combines energy system modeling with a comparative pLCA, enabling the assessment of medium- and long-term effects of charging strategies in the energy system. The subsequent application of the methodology evaluates two cost-minimized climate policy scenarios for Germany. In the “V2G scenario,” BEVs can be used as flexible storage options, while the “reference scenario” excludes this option. The two scenarios are simulated with the linear optimization model ISAaR for 2025 – 2045. The second part of the study examines how the systemic impacts in the V2G scenario affect the LCA of the technology, i.e., the footprint of BEVs. Determining emission factors in hourly resolution allows for considering the influence of different charging strategies. By comparing to conventional cars (ICEVs), the ecological payback time (“break-even”) can ultimately be determined.
Results
The study shows the impacts of V2G on the GWP of German electricity generation in hourly resolution. As shown in Figure 1 (left), the widespread availability of V2G can accelerate the integration of renewable energies (RE) in the medium term (years 2030 – 2035). Although both scenarios achieve climate goals by 2045, different impacts on storage needs in the energy system arise. Figure 1 (right) shows the installed storage capacity per scenario. Compared to the reference scenario (without V2G), using BEVs as flexible storage options can substitute 117 GWh of stationary battery storage in Germany. This indicates a long-term reduction in resource demand in the V2G scenario.

At the technology level, V2G significantly reduces the operational GHG emissions of BEVs. As shown in Figure 2 (left), the greatest potentials for GHG reduction occur in 2030: Compared to uncontrolled charging (144 kgCO2e/BEV), annual operational emissions decrease by up to 200% through V2G, reaching negative values (-141 kgCO2e/BEV). These potentials depend on the allocation of emission savings achieved through the secondary purpose of BEVs, i.e., the storage option for the energy system. If this secondary purpose is considered (“system expansion”), more emissions are displaced (negative values) than incurred through charging. If the secondary purpose is not considered (“physical allocation”), V2G savings are comparable to unidirectional controlled charging (V1G). The ecological break-even, i.e., the time or mileage until the higher footprint in BEV production is offset, thus significantly depends on the charging strategy. As shown in Figure 2 (right), this point is reached after 3 years for uncontrolled charging, 2.7 years for V1G, and 2.5 years for V2G (commissioning in 2025 and average German driving profile).
The results strongly depend on assumptions in energy system modeling (e.g., RE expansion, BEV availability) and driving behavior (in this case, average German driving profile). Similar to systemic impacts, the study shows that with increasing RE share in electricity generation, the potential for reducing operational emissions through V2G decreases in the long-term. The production phase thus gains importance. Manufacturers should focus on reducing environmental impacts in BEV production and the supply chain.

Conclusions
Overall, combining system and technology levels in a prospective assessment improves the understanding of the environmental impacts arising from the penetration of new use cases in the energy system. The study demonstrates this using the example of a large-scale application of V2G strategies in the German energy system. Results show a medium-term contribution to accelerated RE integration by applying BEVs as flexible storage capacity. Although the reference scenario without V2G availability also reduces GHG emissions from power generation in the long-term with stationary storage, V2G can achieve potential resource savings by utilizing existing vehicle batteries. When the impacts on power generation are considered in the LCA of BEVs, a reduction potential of up to 200% of operational emissions is evident. Overall, the results depend on the scenarios’ assumptions and the charging behavior. Researchers can apply the method presented in the paper and the hourly emission time series for subsequent studies to evaluate use cases in the energy system.
All results and conclusions are presented and discussed in the Open Access paper “Environmental effects of vehicle-to-grid charging in future energy systems – A prospective life cycle assessment” in the Applied Energy Journal.
The developed method is also applied to evaluate the combination of charging strategies (Multi-Use). The results are published in the Open Access paper “Prospects of electric vehicle V2G multi-use: Profitability and GHG emissions for use case combinations of smart and bidirectional charging today and 2030” in the Applied Energy Journal.