Solid oxide cells (SOCs) have multiple advantages, including high efficiency and reversibility, but they are still characterized by low maturity and high investment costs. Their cost-effectiveness remains to be evaluated from an investment viewpoint for their ability to compete with mature and low-cost alkaline electrolysis (ALK). To this end, this study considers the application of SOC in the production of green hydrogen and electricity to decarbonize a refinery plant, a potential application scenario favoring the efficient SOC technology due to its requirement for stable operation and lack of inexpensive renewable electricity. A planning model is proposed to optimize the system configuration and minimize the system cost, based on which the acceptable cost threshold enabling SOC to compete with ALK is determined, defined as the unit investment cost of SOC at which substituting ALK with SOC will not increase the system cost. The results show that the high efficiency of SOC reduces the investment in renewable generation to fulfill the hydrogen demand, and its reversibility eliminates additional hydrogen-to-electricity and ammonia-to-electricity investments to realize long-duration energy storage. These factors enable SOC to compete with ALK at an investment cost of 11.6 CNY/W, three times the investment cost of ALK. Moreover, when SOC and ALK are combined, SOC can operate at a capacity factor above 75%, 1.5 times the capacity factor of ALK. This further boosts the threshold to 20.4 CNY/W, revealing that SOC and ALK, instead of competing, can work together to lower the system cost and drive commercialization of the emerging SOC technology.