Optimized Smart Charging of Electric Bus Fleets for Greenhouse Gas Emission Minimization

The EU has set the goal to reduce the greenhouse gas emissions of the transport sector. The electrification of the public transport sector in Europe is underway to contribute to this goal. By 2030, approximately 90 % of new sales of buses have to be zero-emission vehicles, e. g., electric buses. Compared with conventional fossil driven buses, they have the advantage of reducing local noise pollution and avoiding local greenhouse gas emissions. However, when one considers the full lifecycle, the emissions for electricity generation have to be considered. The greenhouse gas emissions stemming from electricity generation fluctuate depending on the share of the different types of generation. As the expansion of renewable energy sources in Europe continues, the overall potential for a reduction of greenhouse gas emissions increases, but so does the volatility of the generation. Therefore, the targeted timing of electricity consumption, e. g., charging processes, can contribute to an overall emission reduction in the electricity and the transport sector. Based on an exact solution approach we identify the greenhouse gas emission minimization potentials for three charging strategies of an electric bus fleet with 80 buses and compare them to an uncontrolled fleet charging strategy. The optimizations run over 3 years of historical price and CO2emission factor data for electricity. When minimizing the procurement cost of electricity at the day-ahead and intraday power markets, cumulative greenhouse gas emissions can be reduced by 23.5 % and, when minimizing the emissions directly, up to 31 % can be reduced. A further reduction can be achieved with a holistic scope, if the bus depot feeds electricity back to the grid at suitable times.