Global warming impact of electric city buses in Chile: Critical stages of their fabrication and use

Abstract

The government of Chile has pledged that 100% of the city buses fleet will be powered by electricity by 2040. Since the fabrication processes of electric vehicles and electricity generation are not emissions-free, process analysis appears as a valuable tool to quantify their implications towards the optimization of the industrial processes in terms of better use of resources and recycling. This work aims to quantify the global warming potential and identify critical stages in the fabrication and use of electric and diesel city buses in Chile by process simulation of: (i) metallurgical processes (aluminum, copper and steel), (ii) thermoelectric power plants, and (iii) diesel production plants. A total of 618 kg of aluminum, 187 kg of copper and 11,538 kg of steel are required for the fabrication of an electric bus, while for a conventional bus are required 61 kg of aluminum, 10,354 kg of steel and 268 kg of cast iron. The results indicate that 12.94 tons of CO 2,eq per ton of aluminum, 1.22 tons of CO 2,eq per ton of copper and 1.38 tons of CO 2,eq per ton of steel are generated, with the major contribution to emissions coming from the Hall-Héroult process, the electrorefining stage and the iron blast furnace, respectively. A natural gas power plant in Chile produces 1.0 kg of CO 2,eq per kWh generated, which corresponds to 0.51 kg of CO 2,eq per km driven for electric buses. The processing of crude oil in the United States (main supplier of diesel in Chile) generates 0.61 kg of CO 2,eq per litre of diesel produced, corresponding to 1.38 kg of CO 2,eq per km driven for conventional buses. These results are in good agreement with previous reports which suggest that the positive impact of switching to electricity-powered vehicles is strongly correlated with the carbonization-level of the electricity grid related to buses fabrication and charging.