A modular, regenerative fuel cell system that includes a plurality of dedicated or reversible electrochemical cell stack modules, where each such module is devoid of major fluid systems, is provided. The inventive system allows a user to specifically and effectively tailor the system to the demands of a particular application. If additional electrolysis capability and/or additional power are needed, only electrolysis cell stack modules and/or fuel cell stack modules are added to the system. The use of unnecessary or duplicative support equipment is avoided thereby rendering this system more cost effective and efficient.