In order to mitigate carbon dioxide emissions and the dependence on fossil resources, several advanced sustainable processes for massive hydrogen production are currently studied throughout the world. Among them, High Temperature Electrolysis (HTE) of water steam seems to be a promising process. Achieving low hydrogen production costs is a parallel priority besides the accomplishment of process scale up. Studying the economic elements of HTE, major cost contributions appear to be the electrolyser investment and electric consumption. The investment contribution is directly linked to the electrolyser capital cost and lifespan. Both parameters should be simultaneously considered. A sensitivity study is carried out to help establish R&D targets for the electrolyser investment – lifespan pair. Besides, compromises are required between the overcost due to electrolyser cell replacement and the electricity consumption overcost caused by the electrolyser cell performance impoverishment along time. Several scenarios are proposed in order to examine these compromises. Results have a direct impact on the maintenance policy.