Benefits of external heat sources for high temperature electrolyser systems

High Temperature ELectrolysers (HTEL) operate around 1073 K with steam at 1073 K. Water is previously heated up in the Balance of Plant by the hot outlet gases and optionally by electrical heaters. If liquid water is fed to the system, vaporisation needs are covered by electrical heating, which leads to a low system efficiency of 89% vs. HHV. Using steam instead of liquid water would suppress vaporisation needs, thus increase the efficiency. This work aims to analyse the potential benefits of a steam supply. Calculation is performed without considering the energy required to preheat water. Results show that feeding the system with low-temperature steam instead of liquid water enables a system efficiency jump of 18%. Further increasing the steam temperature to 933 K negligibly impacts the system efficiency and is therefore unnecessary. It is concluded that a low-temperature steam source is sufficient to increase significantly the HTEL system efficiency.