An uninterruptible power Supply (UPS) based on hydrogen technologies has been designed, manufactured and tested. The system consists of a proton exchange membrane fuel cell running on hydrogen and oxygen, a gas storage section and a water electrolyser for hydrogen and oxygen production. The UPS is of fail-safe design, completely silent and very reliable, thanks to the complete absence of moving parts. The prototype has an output of 5 kW for a maximum period of 5 It. A 3 kW advanced alkaline electrolyser produces 0.6 N m(3)/h hydrogen and 0.3 N m(3)/h oxygen at 1.5 MPa. which are stored in metal hydride tanks of 21 N m(3) H-2 capacity and a cylinder stack, respectively. Upon grid power interruption. the fuel cell takes up the load, with the help of a battery during the first minutes of operation. The results of the operation of this prototype are presented and discussed. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.