Abstract: Disclosed is a water electrolysis system that improves durability by preventing performance degradation inside a water electrolysis stack. According to the present invention, in order to reduce electrode degradation in a water electrolysis unit cell, which can frequently occur in the starting and stopping stages of a process for producing hydrogen from the water electrolysis system, power of a constant current is supplied to the water electrolysis stack and electrolyte circulating water is heated while being circulated in the water electrolysis stack in the starting stage of the water electrolysis system. Also, when performing a stopping process, power of a constant current is supplied to the water electrolysis stack and electrolyte circulating water is cooled while being circulated in the water electrolysis stack. Accordingly, it is possible to improve durability by preventing performance degradation inside the water electrolysis stack.

Abstract: An eco-friendly energy storage system for frequency regulation, includes: a water electrolysis apparatus and a hydrogen storage apparatus for performing discharge of surplus power for a power system; a fuel cell power generation apparatus for performing charge of deficiency power; and a control device for controlling charge and discharge by detecting a system frequency for controlling charge and discharge of the system, comparing the system frequency with a frequency reference value, and reflecting a frequency regulation amount calculated on the basis of a hydrogen storage amount of the system.