Energy and environmental analysis of a flexible Power-to-X plant based on Reversible Solid Oxide Cells (rSOCs) for an urban district

This study proposes the modeling and the performance assessment of a grid-connected Reversible Solid Oxide Cell (rSOC) plant that is the core system of a polygeneration flexible hub between the national electric grid and the local microgrid of an urban residential district. The system is designed to integrate a thermal storage unit based on phase change material with the rSOC stack by mzedeans of heat pipes. At times of low electricity price, the plant produces hydrogen via electrolysis fed preferentially by a dedicated wind farm. Hydrogen is stored as compressed gas and used for the public transportation and electricity production during peak-demand hours. The goal of the study is to investigate the performance and environmental indicators of this novel rSOC configuration and to identify which operating strategy best fits with the analyzed district application. The operating points of the overall system are mapped with a steady-state model and interfaced with thermal storage and loads by a time-resolved dynamic model. The feasible schedules of the system are defined considering the rSOC switching dynamics between fuel cell and electrolysis, and constraints on plant self-sufficiency for both heat and hydrogen vectors. Simulations at different levels of hydrogen demand for mobility (ranging between 10 and 1,000 ton/year) were performed. Results showed an annual efficiency range of 55-70% (including heat to DH) of the polygeneration plant. The environmental analysis showed that the rSOC plant emits 5-50% less CO2 than the current energy system (gas boilers, grid electricity, diesel buses), when electrolysis is fed by grid-electricity with the present UK carbon intensity in case of wind power shortages.