Fuel cells are device capable to convert chemical energy into electrical energy. During the last decade fuel cell market had an expansion in specific market niches, such as automotive and backup power. My research activity was related to the development of fuel cell based power system for backup in telecommunication applications. Several installations done in the last years demonstrated that the technology can be used and features many advantages with respect to conventional battery uninterruptible power supply and diesel generators, related to cost reduction, availability and durability. The market of telecommunication equipment is continuously expanding, in particular in Asian markets, where the business of mobile phones is ramping up quickly. Many new sites are located in remote areas, where the main distribution of electrical energy is not available. The solution to power those sites involves renewable energy sources, that are often instable and with a low availability. Solutions for local energy accumulation are mandatory to perform power peak shaving and power backup. The same approach can be used to improve the robustness of smart grid applications, where the power is generated locally, in a number of small and distributed energy sources, and delivered to the network. Hydrogen can be used as energy carrier and as energy storage to power sites when the energy produced by renewable sources is less than the amount required by the load. The thesis explores the design of a power system, a device capable to generate hydrogen and store the compressed gas from renewable sources and to use the gas to generate electrical energy to supply the load.