Multiphysical Analysis and Optimization of the Thermal Power Output of a Feedback Fuel Cell Vehicle

Abstract

In the context of the climate change, extensive research was conducted with the aim of reducing anthropogenic greenhouse emissions. While the shift from fossil energy carriers to renewable sources is essential for the advancing energy transition, some challenges are related to it. This includes long-term storing of the fluctuating renewable energy. For that matter, hydrogen is expected to play an important role in the near future. One way of converting the hydrogen to energy is by using a fuel cell. Electric vehicles powered by a fuel cell (FCEV) are becoming increasingly common for transportation. With the idea of coupling the transportation and energy sector, an FCEV could be used as a virtual power plant for energy feedback, thus making use of synergy effects between the two sectors. Unlike regular electric vehicles, which can also be integrated into an energy system via bidirectional charging, FCEVs generate heat as a byproduct. Utilizing this heat in addition to the electricity makes the FCEV a combined heat and power plant that could supply the energy demand of a household. In order to analyze the feasibility of the concept, a test stand was set up in the context of this work. The achieved thermal power outputs were relatively low with values in the region of 1kWth to 3kWth. For this reason, the present work aims for maximizing the thermal power output and the overall system efficiency with a view to a possible redesign of the system. This was done by creating a physical simulation model with MATLAB Simscape. With the model, the system behavior was analyzed in detail. In order to validate it, measurement data from various test drives and test stand experiments were evaluated. The simulated heat transfer rates through the two installed plate heat exchangers (PHE) showed an average deviation of 7.2% and 18.6%, respectively, in comparison to the measurement data. The investigations showed that the PHE in the test vehicle is capable of achieving thermal output efficiencies of 80% and above for an electric load of up to 30kWel, resulting in a thermal power transfer in the region of 12kWth to 14kWth. For loads higher than 30kWel, a larger PHE is needed for a similar efficiency. During the experiments, considerably lower efficiencies of 27% to 64% were recorded. Even though the integration of an FCEV into an energy system poses technical and infrastructural challenges, it is shown that the concept can be used for supplying the energy demand of a household partially or completely. This could be applied for grid peak loads or in times of low renewable energy production.