Investigation into the hydrogen production performance of a novel 5-kW hybrid-system composed of a solar steam generator directly connected with conventional solid oxide electrolysis cells

Abstract

Coupling solar energy with solid oxide electrolysis cell has the potential to reduce electricity consumption and improve energy conversion efficiency. This study introduces a pioneering 5 kW direct-connected hybrid system that couples a solar steam generator with solid oxide electrolysis cells utilizing conventional electrical energy for the electrolysis process. The successful demonstration of hydrogen production showcases promising results. When the solar irradiation power is 2.26 kW, the inlet water flow rate is 1.23 kg/h under operations at 700 °C, the hydrogen production efficiency of the system reaches 95.2 %, and the steam conversion ratio approaches 92 %, giving a cumulative hydrogen production yield of 5,840 NL in 6.3 h. The solid oxide electrolysis system is further tested under different operating conditions of the stack and solar irradiation. The experimental results show that a greater operating temperature is conducive to more efficient hydrogen production, while more water vapor at the cathode leads to a larger steam conversion ratio. The results indicate that increasing the irradiation power is beneficial to hydrogen production while decreasing the irradiation power will lead to fluctuations of hydrogen yield. In addition, the system efficiency (45.3 %) is higher than that of a photovoltaic alkaline water electrolysis (12.6 %) or photovoltaic proton exchange membrane electrolysis (14.76 %) system at the same irradiation power. Under the same electrolysis power and cathode inlet temperature, the total power consumption of a traditional solid oxide electrolysis system is significantly greater than that of the proposed hybrid system. The comparison shows that the saved electricity of the proposed hybrid system can account for about 30 %. Therefore, the proposed hybrid system has significant efficiency and power savings advantages.