Impact of electrified bus transport on the electricity system of Gothenburg - Can electric buses provide a service to the electricity system?

Abstract

The electrification of public bus transport is regarded as an important step in decarbonising metropolitan areas, yet little is known about its effects on the energy system of cities. Assessments in previous research do not explicitly account for the interconnection between electrified public bus transport and the energy system. This thesis studies how battery electric buses (BEBs) and the city energy system affect each other. To study electric buses in this context their driving and corresponding charging demand must be understood. This thesis aims to understand the impact of electrified bus transport on the energy system of Gothenburg, Sweden. A three-part method is employed. First, a model creates a network of electrified inner-city buses in Gothenburg and determines their time-resolved electricity demand for charging. Second, the charging of buses is matched to an electricity cost profile, and charging is delayed such as to minimise electricity costs for charging while fulfilling all transport demand in the network. Third, the electricity demand of the BEBs is added to a cost-minimising linear optimisation model of a city energy system. It models dispatch and investments in the energy system in a scenario with net zero CO2 emissions from heat and electricity generation in the city, and limitations in electricity import capacity. In the energy system model, the charging of the buses is delayed such as to reduce the total city energy system cost. The findings suggest that, although peaks in electricity demand of buses and the city overlap in time, BEBs have negligible impact on composition and operation of the energy system. However, benefits can be derived from delaying charging of buses to low electricity cost events, reducing the buses’ charging cost and the afternoon peak in the BEBs’ electricity demand. The findings also show a synergy between the fast charging bus network and the generation from photovoltaic solar power, where a part of the demand from the charging of buses during the day can be satisfied by generation within the city.