(373as) Optimal Design and Operation of Solid-Oxide Cell Systems Considering Chemical and Physical Degradation Under Seasonal Variation

Solid oxide cell (SOC)-based energy systems are undergoing extensive investigation for decarbonizing the electric grid. One essential requirement for the effective application of SOC systems is their flexible operation in both electrolysis and fuel cell modes [1], i.e., rapidly transitioning from producing H₂ in electrolysis mode to generating power in fuel cell mode, ramping up/down H₂ or power demand as needed. Therefore, steady-state analysis of these systems is insufficient to determine optimal operation for process analysis. Dynamic optimization of these systems is challenging due to the need to account for multiple time scales [2]. For SOC systems, process operational variables such as temperature, concentration, etc., have time scales of seconds to minutes, while microstructure-level chemical degradation of the SOC has time scales of months to years. Furthermore, dynamic optimization also needs to take into consideration physical degradation [3] due to high-temperature operation that can limit the useable lifetime of SOC stacks, thus increasing the number of stack replacements.

Due to the time-varying performance of the SOC system caused by chemical degradation, it is necessary to optimally plan operating profiles over its lifetime. Models of chemical degradation [4] have been developed by considering dominant degradation mechanisms in the SOC electrodes and electrolyte. A model of physical degradation has been developed by considering the temporal evolution of residual stress with time. Synergistic effects of physical and chemical degradation have also been modeled. For dynamic optimization of these multi-scale systems, a quasi-steady state discretization approach has been developed for dynamic optimization over 20,000 hours of operation. The levelized cost of hydrogen (LCOH) is minimized by considering various modes of operation such as potentiostatic and galvanostatic operation, as well as operation when both cell terminal voltage and current density are optimized. In addition to optimizing the LCOH for a given cumulative H₂ demand, optimization is also undertaken by considering seasonal variation in H₂ demand and electric load. Long-term operating trends ranging from cell-level considerations such as spatial temperature profiles, optimal voltage, and current density to system-level decisions such as heat integration, H₂ production rate, etc., are optimized. Additional design considerations include the optimal number of cells in the SOC stack and the resultant stack replacement lifetime. The dynamic optimization considering long-term operation under seasonal variation shows an interesting interplay of seasonal operating decisions over the course of a year and multi-year design considerations.

Acknowledgements:

This work was conducted as part of the Institute for the Design of Advanced Energy Systems (IDAES) with support from the U.S. Department of Energy’s Office of Fossil Energy and Carbon Management (FECM) through the Simulation-Based Engineering Program.

Disclaimer:

This project was funded by the Department of Energy, National Energy Technology Laboratory an agency of the United States Government, through a support contract. Neither the United States Government nor any agency thereof, nor any of its employees, nor the support contractor, nor any of their employees, makes any warranty, expressor implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof, or any of their contractors.

References:

[1] Jiang (2016). Challenges in the development of reversible solid oxide cell technologies: a mini review. Asia‐Pacific Journal of Chemical Engineering, 11(3), 386-391.

[2] Bhattacharyya, D., Rengaswamy, R., & Finnerty, C. (2009). Dynamic modeling and validation studies of a tubular solid oxide fuel cell. Chemical Engineering Science, 64(9), 2158-2172.

[3] Clague, R., Marquis, A. J., & Brandon, N. P. (2012). Finite element and analytical stress analysis of a solid oxide fuel cell. Journal of Power Sources, 210, 224-232.

[4] Giridhar et al. (2024) Optimal Operation of Solid-Oxide Electrolysis Cells Considering Long-Term Chemical Degradation [Manuscript in preparation]