Electrochemical CO2 reduction (ECO2R) is being considered as a potential solution to the problem of managing excess electricity from renewable energy generation. In this study, ECO2R system coupled with a renewable energy generation system is designed and evaluated for commercial applicability. Mathematical models of the various components of an ECO2R system leading to methanol as the product are developed and compared with experimental data. A two-stage stochastic programming model that minimizes the overall cost of the coupled system is formulated to determine the optimal capacity of the system under uncertain weather conditions. The optimal design is carried out for two regions with different weather patterns: Denver, USA and Munich, Germany. The result of the optimized design shows that the ECO2R system is economically feasible at a methanol price of 550 USD/ton. In addition, the two-stage stochastic programming approach proves to be an effective way to address uncertain weather conditions in the design.