Efficiency of low-temperature adsorptive hydrogen storage systems

• Efficiency of adsorptive hydrogen storage at cryogenic temperatures is determined.
• Efficiency is between 65 and 81% for short storage times.
• Efficiency drops with increasing storage time, long-term storage not meaningful.
• Efficiency of uncooled storage increases with system size and heat of adsorption.

This study presents a thermodynamic analysis of adsorptive hydrogen storage systems at cryogenic temperatures, focusing mainly on the efficiency of the storage system. Four different operation modes, differing in the process used to release the hydrogen and the availability of cooling during storage time, are examined. A sensitivity analysis was performed to determine the dependency of the efficiency on several input parameters including storage time, enthalpy of adsorption, energy required for cooling, and system size. It can be concluded that the energetic efficiency of the hydrogen storage system not considering production and usage steps ranges from 65 to 81% for short storage times, depending on the energy effort and hydrogen losses of the applied operation mode. The storage time has the most noticeable impact on efficiency and cryo-adsorptive hydrogen storage is not suitable for long storage times due to the increasing cooling effort or hydrogen losses. For short storage times e.g. hours, cooling during storage time may be omitted due to the low hydrogen losses.