Design concept and the performance of a metal hydride hydrogen storage tank in totalized hydrogen energy utilization system

We have proposed the Totalized Hydrogen Energy Utilization System (THEUS) for applying to commercial buildings. THEUS consists of fuel cells, water electrolyzers, metal hydride tanks and their auxiliaries. The basic operation of the THEUS is as follows: In the nighttime, hydrogen is produced by water electrolysis and stored in metal hydride tanks. In the daytime, it conducts fuel cell power generation using the stored hydrogen to meet the electric power demand of a building. The chilled and hot water generated in this process are also utilized. It is also possible to use the electric power from renewable energy. That is, THEUS has not only the load leveling function but the function to stabilize the grid system. The metal hydride tank is an important component of THEUS as hydrogen storage. The tank was designed as a thermally driven type, which be able to absorb/desorb hydrogen at normal temperature and pressure and utilize the endothermic reaction during hydrogen desorption as chilled water for air-conditioning. The tank with 50 kg ABS type metal hydride alloy was assembled to investigate the hydrogen absorbing/desorbing process. The experimental results of the heat utilization ratio using this metal hydride tank are about 43%. Since the reaction heat is consumed to heat and to cool the tank up to the temperature of possible heat utilization. The heat utilization ratio can be improved by reduced the heat capacity of the tank and exchanging heat with multiple tanks.