Transient simulation and experimental validation of a solid oxide cell module in electrolysis and polygeneration mode

Abstract

The transition to a low-carbon mobility relies on a significant expansion of the hydrogen refueling infrastructure, and in particular of the security of its supply. These challenges can be addressed by a system capable of hydrogen production using renewable electricity when available, and from e.g. natural gas or biogas when not. In the European project SWITCH, a system with reversible Solid Oxide Cell (SOC) technology is being developed and evaluated for this purpose. It produces hydrogen in water-electrolysis mode using renewable electricity. If this is not available, the continuous production is secured by switching into fuel cell / polygeneration-mode, in which electricity and hydrogen are produced simultaneously. For that, the system must be able to switch rapidly between these two operating modes, implying that its behavior is transient in nature. The extent to which fast transients and mode changes lead to conditions that put the system at risk are unknown for this technological approach. Therefore, this contribution focuses on analyzing the behavior of the core of the system, its SOC module, by means of a transient simulation model, which is experimentally validated. The model comprises the individual SOC stacks, piping and insulation. It accounts for heat transfer, flow distribution, electrochemistry and reaction kinetics, thereby enabling temperature and voltage profiles at the cell, stack and module levels. The model is validated via experimental results, that include switching between different hydrogen production rates in electrolysis mode, transient U-i curve characterization in fuel cell mode, as well as switching between its electrolysis and polygeneration mode. Finally, the model is applied to predict an air flow rate for improved spatial and temporal temperature gradients, to simulate the operation beyond the experimental scope. Furthermore, the simulation enables insights into the transient effect of different mode-switching strategies on the internal temperature gradients and how to reduce them.