Design and optimization of solar-driven reversible solid oxide cell-based polygeneration system for residential buildings

Solar-driven polygeneration systems have the potential to significantly reduce global carbon emissions. However, the inherent variability of solar energy and the volatility of building energy demands result in extreme complexity in supply-demand matching of energy. Reversible solid oxide cells (rSOCs), which can store electricity as fuels in solid oxide electrolysis cell (SOEC) mode and generate electricity and heat using the stored fuels in solid oxide fuel cell (SOFC) mode, are well-suited to address this challenge. Previous relevant studies considering matching of energy supply and demand are relatively limited and are not able to achieve complete electricity self-sufficiency on solar energy. This study developed a completely electricity self-sufficient solar- driven rSOC-based polygeneration system composed of an rSOC, photovoltaic (PV) device, parabolic trough collector (PTC), and other balance of plants for residential buildings, without additional electricity supply and storage equipments. The system operation strategy based on hourly supply-demand matching of electricity was proposed: PV-SOEC-PTC mode for polygeneration of electricity, hydrogen, and heat in case of sufficient solar energy, and PV-SOFC or SOFC mode for cogeneration of electricity and heat in case of insufficient or no solar energy. Crucially, this study devised a method to optimize the sizing of the key energy-supplying components (PV device, rSOC, and PTC). The optimized system demonstrated an annual polygeneration efficiency of 68.61 % at a total cost rate of 0.7782 USD/h, which represents a 2.57% increase and a 46.1 % decrease in comparison to a system in which the PV capacity was maximized to meet the peak demand. The hourly efficiencies of hydrogen production and power generation of rSOC, and polygeneration of the system were in the ranges of 89.00 %- 99.70 %, 50.15 %-73.46 %, and 34.68 %-88.64 %, respectively. Furthermore, the total hydrogen surplus of 454 kg during spring, summer, and autumn was sufficient to offset the hydrogen deficit of 235 kg in winter, ensuring year-round self-sufficiency of electricity.