Metal Hydride Storage Systems: State of the Art Analysis and Integration in FC-based Energy Systems

The technology of metal hydride hydrogen-storage systems has already reached a mature stage and several systems from different manufacturers around the world are now available for purchase. The main reasons for this development can be found in their intrinsic safety features, lower energy consumption and smaller size as compared to other more consolidated hydrogen storage technologies, such as hydrogen compression or liquefaction. However, metal hydride systems also present some drawbacks which limit their range of applications, above all their weight and poor kinetic performance. Therefore, in this paper metal hydride based hydrogen-storage technology is reviewed in order to assess its performance, and several commercial systems are surveyed and compared to other well-established technologies. Particular emphasis is given to the design constraints which must be taken into account when devising a proper layout for a FC-based energy system, with metal hydrides used to supply hydrogen to the FC. In order to achieve optimal efficiency, the thermal energy required by the storage system should be recovered from the system waste energy, and the most suitable accessories (batteries, supercapacitors) should be integrated in the system so as to extend its kinetic capabilities. The authors have cooperated to the development of such an integrated system within two research programs (DEMAG, FEMAG) financed under the 6th EU Framework Programme. Details of the system layout implemented are given and discussed.