Abstract
Hybrid propulsion systems are a realistic alternative to actual systems due to their lower consumption and emissions. Using two energy sources the converter of chemical energy can be designed and optimised focused on the energy conversion process. The adaptation to road and driver conditions can be then made at high efficiencies. The paper considers different types and combinations of the main components of hybrid systems, considering especial energetic aspects. Advantages of fuel cell vehicles can be obtained when the fuel is directly converted in electrical energy using an accessible fuel, if possible obtained from renewable sources. An other major competitor is the gas turbine combined in a serial configuration with the electrical driveline.