Optimal design and operation of solid oxide cell-based energy systems

Hua Liu

Research output: Book/ReportPh.D. thesis

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Abstract

Global warming has almost reached the 1.5°C target that climate scientists have set. Decarbonizing our society by replacing fossil fuel consumption is urgent and essential. Renewable energy, like wind power, could replace fossil fuels and decarbonize power generation, transportation, industry, utilities and other sectors. Denmark is building two energy islands to collect and distribute large-scale offshore wind power. However, fluctuating wind power supply challenges grid power balance management. To cope with the challenges, wind power could be converted to hydrogen and its carriers before sending it to the grid or users. The solid oxide electrolysis cell (SOEC) is a high-temperature electrolyzer that can convert fluctuating wind power into green hydrogen. Degradation is still one of the issues with SOEC in state-of-the-art configurations after decades of development. At the point of SOEC commercialization, it is particularly critical to understand SOEC performances under wind power fluctuations and degradation. These uncertainties affect SOEC heat balance and equipment duty at the system level. Further, SOEC systems' energy efficiency and economic performance are the most reliable metrics to evaluate such uncertainty and its effect. Also, both metrics are critical indicators of SOEC commercialization. This thesis clarifies concerns and identifies bottlenecks in SOEC commercialization. The economic and energy performance of SOEC systems is simulated, analyzed, and optimized considering degradation and power fluctuations.

Techno-economic analysis and optimization of the SOEC system yield several conclusions. (1) A durability stack test under fluctuating power and flow rates confirmed the robustness and flexibility of SOEC stacks. Meanwhile, SOEC dynamic operation did not introduce additional degradation compared to stable operation. (2) Degradation and dynamic operation changed the system heat balance and heat exchangers' duty. External heat integration could improve system efficiency and economic performance with uncertainties. Optimal operation strategies are proposed to minimize system energy consumption during degradation and power fluctuation. (3) Collaboration between academia, industry, and government could make green hydrogen production at SOEC cost-effective. Heat integration, super-grid integration, and SOEC development will make green hydrogen cheaper than grey hydrogen ten years from now. These results provide information for investors and decision-makers in relevant sectors. More stakeholders will be motivated to participate in green hydrogen development for decarbonization goals.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages296
Publication statusPublished - 2023

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