Assessing fluctuating wind to hydrogen production via long-term testing of solid oxide electrolysis stacks
Hua Liu, Jens Valdemar Thorvald Høgh, Peter Blennow, Xiufu Sun, Yi Zong, Ming Chen
Abstract
The Danish government plans two energy islands to collect offshore wind power for power distribution and green fuel production. Wind power is often criticized for lacking stability, which challenges downstream fuel synthesis processes. Solid oxide electrolysis cells (SOEC) are promising for green hydrogen production on a commercial scale, but the impact of fluctuating power on SOEC remains uncertain. This paper explores the feasibility of a Wind-SOEC coupled system by conducting a 2104-h durability test with the state-of-the-art Topsoe TSP-1 stack. Three periods of steady operation and two periods of dynamic operation were conducted. Wind power fluctuation was simulated during the dynamic period, and two control strategies were used to handle it. The constant flow (CF) and constant conversion (CC) strategies maintain the feedstock flow rate and conversion ratio of steam-to‑hydrogen, respectively. Compared to steady operation, the stack shows no signs of additional degradation in dynamic operation. Thus, the TSP-1 stack has been proven robust and flexible enough to handle fluctuating wind power supplies under both operation strategies. Further, stack performance during dynamic periods was compared and analyzed by removing degradation effects. Accordingly, SOEC stacks with CC control will consume less external heat than CF to maintain a heat balance. Nevertheless, SOEC systems with CF and CC control strategies may have different efficiency or hydrogen production costs. Tech-economic analyses will be needed to investigate control strategies at the system level.