This paper presents the design of a hydrogen based emergency back-up system for telecommunication applications, providing 5 kW power for 5 h. The system is composed of a water electrolysis unit, a hydrogen buffer tank, a metal hydride tank and a polymer electrolyte membrane fuel cell (PEMFC). In particular, the paper describes the design of the hydrogen generation and storage section and the various options that have been studied, based on technical and economical considerations of state-of-the-art hydrogen technologies. The water electrolyser produces 0.5 Nm(3) H-2/h at 10 bar pressure. The 1 m3 conventional medium pressure tank has a capacity of approximately 6 Nm(3) H-2 and the metal hydride tank a capacity of 15 Nm(3) H-2. Particular attention is paid to the integration of the hydrogen storage and the fuel cell, with respect to optimizing heat exchange. (C) 2003 Elsevier Science B.V. All rights reserved.