Techno-economic optimization of power-to-methanol with co-electrolysis of CO2 and H2O in solid-oxide electrolyzers

Power-to-methanol processes with co-electrolysis in solid-oxide electrolyzer provides a promising approach to deal with two problems: large-scale renewable electricity storage and carbon capture and utilization. In this paper, a large-scale power-to-methanol system with solid-oxide electrolyzer co-electrolysis technology is studied. System-level heat integration and techno-economic assessment are performed by using a multi-objective optimization platform. The results indicate that there is a slight trade-off between the overall energy efficiency and methanol production cost. The system can achieve a high energy efficiency (72%) and carbon conversion efficiency (93.6%), with the annual CO2 utilization reaching 146.7 kton. However, its economic cost is high. SOE stack price, stack lifetime, and electricity price are crucial to the economic competitiveness of the system. By reducing the cost of SOE stack, extending its lifetime and reducing electricity price, the payback time can be shortened to 3–5 years. A stable supply of renewable electricity is necessary for the project investment. When the annual available hours of renewable electricity drop from 7200 to 3600, the payback time of the project increases to 21 years. Methanol synthesis with SOE co-electrolysis has an outstanding heat integration performance. The system can recover heat in a Rankine cycle to enhance the overall energy efficiency.