Storage of liquefied or cryogenic hydrogen in tanks is attractive when a high volumetric energy density is wanted. However, an essential part of this technology is the liquefaction process, which is expensive and requires 25-40% of the energy content of the hydrogen stored. Hydrogen has to be cooled down below -253°C to become liquefied. Moreover, liquefied hydrogen storage requires expensive (dewar) tanks which are designed to minimize heat transfer from the outside to the liquid, and often additional insulation of the tanks and storage facilities is used. Still, losses due to boil-off of hydrogen are 0.1-0.5% per day. However, the operational pressure is low, <10 bar, and after liquefaction the physical volumetric energy density of liquefied hydrogen is 2300-2950 kWh/m3. Tanks can therefore contain 0.1-100 GWh. Liquefied hydrogen is the preferred option when large amounts of hydrogen must be transported over long distances where no pipelines are available. Tanks can be loaded upon trucks or stored in ships.
The investment costs for liquefied hydrogen storage consists of two parts, i.e. the costs of the tanks and the costs of the liquefaction process. The costs of the tanks scale with the amount of hydrogen that can be stored (expressed in in kg or GWh), the costs of the liquefaction scale with the maximum hydrogen flow (expressed in tons/day or MW_H2). Since costs of liquefaction are usually the dominant factor, here MW_H2 is used as the unit of capacity of the installation.