Ethanol–electric propulsion as a sustainable technological alternative for urban buses in Brazil

The option of fitting electric motors to vehicles that are more efficient and quieter than internal combustion engines has been hampered considerably, looking only at the use of conventional batteries supplying electricity. This is basically due to low gravimetric and volumetric energy densities of these devices that result in shorter autonomy, in addition to more weight and less usable space in the vehicle. An alternative that could make electric motors more attractive for vehicular applications by replacing batteries as the main electricity source is the fuel cell. Hydrogen is the main fuel used in these cells, but the hydrogen storage systems developed so far are heavier and bulkier than their equivalent for conventional liquid fuels such as diesel, gasoline and alcohol, despite heavier energy densities compared to batteries.This paper reviews technological aspects of fuel cells, the main storage systems for hydrogen and other energy sources, data on fuel use and the types of vehicles most commonly used in the Brazilian road transportation sector, followed by an overview of the insertion of hybrid ethanol–electric buses in Brazil.