Infrastructural requirements for indirect and direct electrification of road transportation

Licentiatavhandling, 2024

This thesis analyzes the integration of electricity and transportation systems for a future in which transportation is increasingly electrified. The focus is on exploring the infrastructures required for the indirect electrification of heavy transportation and the direct electrification of passenger vehicles. The work is motivated by both the increased number of electrified vehicles and a lack of knowledge as to the impacts on the electricity system. The papers included in this thesis develop and apply two different energy systems models.

The first model, which is a cost-minimizing, linear, optimization model for hydrogen refueling stations, was developed to compare the cost-efficiencies of three electrolysis-based systems for providing hydrogen to refueling stations for heavy road transportation:  a decentralized, off-grid system for hydrogen production from wind and solar power; a decentralized system connected to the electricity grid; and a centralized grid-connected system with hydrogen transported to refueling stations. The results show that for most of the studied geographic regions, the decentralized grid-connected system gives the lowest costs for hydrogen delivery, while the standalone system entails higher hydrogen production costs. In addition, the centralized system entails lower costs for production and storage than the grid-connected decentralized system, although the additional costs for hydrogen transport increase the total cost.

The second model, the REGAL model, is an open data-based model designed to create a synthetic representation of a low-voltage (LV) grid for a country-size geographic area. This thesis presents the results of calibration and validation against real-world data for the synthetic grid generated by the model. For a region with area >350 km2, an average deviation from real-world data of less than ±10% was achieved. For an average area of 1 km2, the error was 44.5%, which means that the model is not suitable for analysis at this geographic scale. However, the level of accuracy is deemed sufficient for initial estimations of hosting capacity for larger geographic areas, such as a region or a country.

The REGAL model is used to investigate power system violations linked to exceeding the operational limits (thermal capacity and voltage magnitude) of the Swedish LV grid when electric vehicle (EV) charging is added at different EV shares of the passenger vehicle fleet. Three charging strategies are assumed: direct; cost-minimized (based on an electricity spot price); and mixed charging (a mix of the first two charging strategies). The results show that the number of violations increases with the fleet share of EVs, regardless of the charging strategy, albeit slowly at first. As the fleet share of EVs increases, the number of violations introduced with each additional EV is higher. Most violations occur in areas with a high population density. The charging strategy affects both how often and to what extent the operational limits of the grid are exceeded. On average, the direct charging strategy has a higher frequency (i.e., how often limitations are exceeded) and amplitude (i.e., by how much the limits are surpassed) of violations compared to the other charging strategies. However, when EVs follow the cost-minimizing charging strategy, a stronger coincidence is seen for the EV charging, yielding higher peaks of the maximum load in some areas and, thereby, a higher peak amplitude of power system violations, as compared to direct charging.