Dynamic-cycle simulation of power-to-methanol-to-power system with reversible solid oxide cells: Multi-physics and techno-economic analysis

Power-to-Methanol-to-Power System (PMPS) has a great potential for fluctuating renewable power storage and flexible power generation. In this study, a dynamic-cycle model of PMPS is developed by coupling reversible solid oxide cells with methanol synthesis process. The system stores energy from fluctuating photovoltaic power in the form of methanol during the day and generates electricity at night using the methanol fuel generated in the daytime. It is found that reducing the CO₂ ratio in co-electrolysis from 60% to 30% increases CH₃OH production by 64% and doubles electricity efficiency due to the increased H₂ supply to methanol synthesis section. While in the fuel cell, reducing methanol supply rate from 500 to 200 SCCM increases power generation capacity by 110% with longer generating duration, and the electricity efficiency is improved from 30% to 61%. Besides, the optimized PMPS presents a round-trip efficiency of 78%, along with high conversion rates of carbon (97%) and hydrogen (84%), significantly exceeding that of the Power-to-Hydrogen-to-Power System (PHPS, the round-trip efficiency of 45%) under similar cell's inputs. Furthermore, our techno-economic analysis shows that the levelized fuel cost (0.49$ t⁻¹ CH₃OH) and levelized generating capacity cost (0.22 $/kWh) of PMPS are about 10% (4.8$ t⁻¹ H₂) and 74% of the PHPS, mainly due to the 16% lower capital expenditure of PMPS.