Green light for bidirectional charging? Unveiling grid repercussions and life cycle impacts

• This study examines the environmental impacts of grid expansion depending on the charging strategy
• Compared to the uncontrolled case, a moderate increase in the share of bidirectional electric vehicles participating in arbitrage trading initially reduces the need for grid expansion
• However, with further increase in the share, the need for grid expansion grows massively
• Increased grid losses and higher grid expansion needs due to arbitrage trading of electric vehicles negatively impact their life cycle assessment
• This increased greenhouse potential can be overcompensated by increased use of renewable energy through bidirectional charging.

Study Objectives

The publication in the Journal Advances of Applied Energy investigates the environmental impacts caused by bidirectional charging strategies, such as Vehicle-to-Grid (V2G) or Vehicle-to-Home (V2H), on the future power distribution grid infrastructure. A life cycle analysis (LCA) was conducted to assess the future grid expansion needs until 2040 depending on the charging strategy. The subsequent comparison of resulting environmental impacts with potentially positive effects of bidirectional charging, such as emissions in vehicle operation, provides insights into the possible overall balance of large-scale implementation. Thus, the study provides insights into the role of bidirectional charging strategies in achieving climate goals.

Methodology

Using the power grid and energy system model “GridSim,” the grid expansion needs in the future distribution network were determined depending on the charging strategy. Data from 1,206 low-voltage networks from the year 2020, provided by Bayernwerk Netz GmbH, served as the basis for the case study. Three scenarios for the year 2040 with different charging strategies were simulated: price-optimized V2G charging, uncontrolled charging, and a mix of V2G, V2H, and uncontrolled charging. The scenario for 2040 assumes a high number of battery electric vehicles (BEVs) in Germany. The simulation results serve as input for a prospective life cycle analysis (pLCA) to quantify the impacts of different charging strategies on the greenhouse potential (Global Warming Potential, GWP) of the grid expansion needs. To contextualize the quantified results, they are compared with effects on the vehicle’s life cycle assessment. This includes determining and comparing the GWP of additionally required charging infrastructure and the operation of BEVs for the analyzed scenarios.

Results

The study shows that a scenario with purely price-optimized V2G charging leads to the highest grid loads, requiring significant expansion of low-voltage networks. This is due to higher simultaneous charging and discharging volumes, and associated grid losses. Compared to direct charging in the reference scenario, simulation results in the V2G scenario show 61% higher grid losses in 2040. In the mixed charging strategies scenario, these increase by only 9%. However, the need for grid expansion can be reduced in the mixed scenario. A sensitivity analysis of the national electricity mix shows that the ongoing defossilization of power generation can significantly reduce overall impacts in several categories, particularly fossil resource depletion and climate change.

On a technological level, bidirectional charging leads to net reductions in the operational emissions of BEVs. During times of renewable energy shortages and high electricity prices, BEVs can be used as flexible storage and feed-in units, representing a functional component of the energy transition. Compared to direct charging, emissions in the V2G scenario decrease by approximately 96 kg CO₂ equivalents per year per BEV (in the mixed scenario by approximately 30 kg CO₂ equivalents per year per BEV). Even considering the higher environmental impacts from charging infrastructure and grid expansion needs and losses, the high reductions during the operational phase can overall lead to a decrease in the greenhouse potential per vehicle.

The focus of this study is on the greenhouse potential. Other impact categories should be considered in further research. For a long-term sustainable design of electromobility, not only the environmental impacts during the vehicle’s operational phase should be considered, but also those associated with the production phase of BEVs should be reduced.

Overall, the study results contribute not only to research but also provide insights for industry, grid operators, and policymakers to understand and act on the potential positive and negative impacts of large-scale BEV integration. All results and conclusions are presented and discussed in detail in the open access paper “Green Light for Bidirectional Charging? Unveiling Grid Repercussions and Life Cycle Impacts” in the Journal Advances in Applied Energy.

Further Information

• What parameters influence the life cycle assessment of electric vehicles?
• What are the benefits of smart and bidirectional charging for users today and in the future?
• unIT-e² – Living Lab for Integrated E-Mobility
• unIT-e² project webpage
• GridSim – Electric Grid and Energy System Model for Distribution Grids – FfE