Pedro Anchustegui Balner, Environmental Systems Analysis

This thesis addresses two rarely seldom considered aspects of vehicle-to-grid (V2G) using life cycle assessment (LCA) – the EV charging equipment and the impact that the EVs have on the low voltage distribution grid. The thesis presents three papers and original work, aiming to answer four research questions on the environmental burden of the charging equipment and the power electronic transistors used, as well as the environmental impact of reinforcing the Swedish low voltage distribution grid.

The environmental burden of the charging equipment is calculated by carrying out an LCA of four different EV charging equipment options. Two such options represent the state-of-the-art bidirectional and today’s typical unidirectional designs, both modeled after existing designs. Between these designs there is a gap in power rating, directionality and transistor technology. Two additional equipment options are theoretically constructed to cover this gap and allow understanding of the impact of each change. The results show the state-of-the-art design has a lower climate change impact and material resource use than today’s current design. This is driven by production-related impacts of the charging equipment.

The production of power electronic transistors is assessed by first comparing two alternative production routes for silicon carbide (SiC) wafers. These wafers are used in the production of the transistors used by the state-of-the-art onboard charger. The production routes are: Acheson process, followed by physical vapor transport (PVT), or high temperature vapor deposition (HTCVD). It was found that the climate change impact of an SiC wafer can vary by a factor of 70, depending on energy supply mix and production route. Then, in an assessment at a packaged transistor level, the thesis shows that the climate change impact of an SiC transistor produced with the HTCVD route can be lower than that of an equivalent silicon transistor. Coupled with an improved performance and indirect benefits linked to SiC, using SiC MOSFETs instead of silicon IGBTs leads to lower impacts in an onboard charger.

The thesis assesses the impact of reinforcing the low-voltage distribution grid to allow home charging of a fleet composed of 100% EVs. Three charging strategies are assessed: charging directly when arriving home, charging optimized to follow the spot price, and a mixed strategy, where the EV fleet is split 70/30 between direct and optimized charging. Depending on the charging strategy followed, reinforcing the low-voltage distribution grid in Sweden requires the installation of between 3900 and 5700 MVA additional transformer capacity. The reinforcements needed by the low voltage distribution grid can have an impact of over 150 thousand tons of CO2-equivalents if a direct charging strategy is followed. In the mixed strategy, 30% of the fleet performing spot-price optimized charging reduces this impact by 50 thousand tons.

Overall, the thesis presents environmental impacts that can be expected in any V2G implementation. In doing this, it sets an environmental performance floor for V2G: the impacts of burden from the charging equipment and the necessary grid reinforcement. State-of-the-art charging equipment can reduce the environmental burden of the production and improve the efficiency during its use-phase. The role of the charging strategy followed by the EV fleet can set the V2G performance floor higher, as direct charging can significantly increase the impact of the reinforcement of the low-voltage grid.