Effects of concentrated solar–integrated packed-bed thermal energy storage operation on solid oxide electrolysis cell performance

The use of renewable energy in the context of green hydrogen production requires suitable energy storage technologies to compensate for intermittent wind and solar resources. High-temperature electrolysis is a promising way to produce hydrogen as it has the highest electrical efficiency by using steam instead of liquid water compared to low temperature electrolysis. Here, a part of the total energy demand is substituted by thermal energy. For a sustainable and continuous process operation with concentrated solar energy, a high-temperature thermal energy storage heating air and steam is required to operate the high-temperature electrolysis above 800 °C. In this study, the charging and discharging behavior of a packed bed thermal energy storage with a capacity of 17.46 kWh is experimentally tested and a utility scale storage numerically analyzed. The storage is charged with superheated steam from a solar cavity receiver and discharged with ambient air or steam flow. The storage discharge temperature profile results in a change in the electrolysis operating state and therefore, a change in the reagent flow rate. This changes the hydrogen production capacity during the discharge period. Adjusting the thermal energy storage discharge flow rate maintains an electrical conversion efficiency of 97 %. Furthermore, additional electric heating or exothermal operation of the electrolysis is avoided. Additionally, an electrolysis cooling rate of greater than −0.3 K/min can be maintained.