Contribution of waste heat recovery system to hydrogen power technology for land transportation

Hydrogen is one of the most important candidates for future energy supply systems. Currently, proton exchange membrane fuel cells (PEMFCs), solid oxide fuel cells (SOFCs) and hydrogen internal combustion engines (HICEs) are the major hydrogen energy utilisation technologies for land transportation. All the three technologies produce large amounts of waste heat. As a result, waste heat recovery (WHR) technologies have become increasingly indispensable for improving thermal efficiency. Hence, it is necessary to re-evaluate these three technologies after combining with WHR as a whole system. However, in former researches they are only compared without WHR. To fill the research gap, in this study how the WHR systems help improve the thermal efficiency of current and future HICEs, PEMFCs and SOFCs is studied and compared. In addition, the advantages and disadvantages of the three technologies coupled with WHR systems are re-evaluated. The results show that the proposed new collaborative design method of the HICE-WHR combined system can achieve a maximum efficiency of 63.7 %. The maximum electricity efficiencies of the combined system of PEMFC-WHR and SOFC-gas turbine-WHR can achieve 69.2 and 78 %, respectively. However, considering the end demand for mechanical energy, the maximum mechanical efficiency of the HICE-WHR combined system may be slightly higher than that of the PEMFC-WHR combined system. In terms of the cost and power density, the PEMFC-WHR combined system may have the most advantages among the three in the future, followed by the HICE-WHR combined system. These conclusions are opposite to the comparison of only the three technologies themselves, which provide a new perspective on the development of these technologies.