Liquefied hydrogen storage

An alternative to compressed hydrogen storage is storing liquefied hydrogen or converting to hydrogen carriers. Conversions require additional energy, however, and some forms (ammonia and liquid hydrogen) require continuous cooling. Promising storage or transport options include:

• Liquefying hydrogen by cooling it to cryogenic temperatures (below -252.8°C) and storing or transporting it in tanks or other containers.
• Converting hydrogen into liquid ammonia, which has greater density than hydrogen, and can thus be easier to store or transport in containers.
• Converting hydrogen into organic liquids or semi-solids called liquid organic hydrogen carriers (LOHCs), which are particularly useful for transporting hydrogen over long distances.

Liquefied hydrogen storage has a much higher density compared to compressed hydrogen storage. This higher density also increases the volumetric energy density. Liquefied storage needs to be kept at temperatures below -252.8°C. It is estimated that 30-40% of the hydrogen energy content is used for the liquefication process (compared to 15% in the case of compressed gas storage). In addition, the low temperatures needed to store and transport hydrogen require that all related mechanical elements such as valves or tanks resist hydrogen embrittlement. Ships transporting liquefied hydrogen storage either assume significant levels of evaporation due to the cold and lightness of the fluid or improve the insulation of the load or even invest in complex cryogenic systems.

As an alternative to liquefied hydrogen storage and transport, LOHCs, such as benzyl toluene, can help reduce the technical requirements described above. Last, hydrogen derivatives (e-methane or e-methanol) represent alternatives to transport hydrogen to consumption hubs. Ammonia is an even cheaper option (Liebreich, 2022; Usman, 2022).

The ability to store and transport hydrogen offers flexibility to the energy system and allows supply to be connected to demand. The location of supply and demand centres will determine the suitability of liquefied hydrogen storage. Liquefied hydrogen via ammonia or LOHCs is easier to store in large quantities and transport over long distances than electricity. Therefore, these two options are suitable for international hydrogen trade.