Efficiency Potentials of Fuel Cell Propulsion Systems

A clear transition from carbon-based energy sources and energy carriers towards renewable and carbon-free energy carriers is necessary in order to meet the climate goals set in the Climate Change Conference in Paris 2015. Hence, the consistent decarbonisation of all sectors of our economy is mandatory, e.g. in mobility and transport, for households and in industry. Electricity and hydrogen are the only two energy carriers that can be produced and used in an emission-free cycle. Particularly in mobility and road transport, battery electric vehicles for short range and fuel cells electric vehicles for long range and fast refuelling are offering the possibility for a complete decarbonisation. When high driving range is required, fuel cell vehicles achieve lower costs at high production volume compared to battery electric vehicles. Moreover, fuel cell vehicles feature significant advantages regarding rare resources and recycling. However, high improvement potentials especially concerning overall efficiency, costs, industrialisation, materials etc. are still existing.

As a starting point this paper provides an overview of the status of technology of fuel cells and hydrogen in mobility and road transport. Regarding efficiency analyses, the focus is put on a novel method for evaluating the fuel cell system efficiency using energy and exergy analyses. This innovative approach is based on sophisticated exergy analyses to determine efficiency potentials from fuel cell stack up to fuel cell system level including the auxiliaries – BoP components. In addition, the results are structured into physical, chemical and kinetic efficiency potentials. In this context examples for passenger car as well as for heavy duty applications are presented. As the thermal management of FC propulsion systems is decisive for enabling high efficiencies this method further allows detailed thermodynamic investigations for a single component as well as for entire propulsion systems on a scientifically established basis. Furthermore, the well-to-wheel as well as life-cycle CO₂ emissions of FCEVs in comparison to other powertrains are analysed. This comparison includes passenger cars, busses and trucks.