3. Comparison with other storage technologies: hydrogen in all its states

3.1 Liquid storage

In liquid form, at 20 K and atmospheric pressure, hydrogen has a density of 71 kg·m ^–3 . Under these temperature and pressure conditions, 5 kg of hydrogen can be stored in a 70-liter tank. This storage technique would therefore be highly suitable for storing hydrogen in a small volume. However, hydrogen at a temperature of 20 K has to be stored in a cryogenic tank which, according to current scientific advances, cannot be perfectly thermally insulated. This means that evaporation is inevitable, which can lead to a leakage rate of 0.5 to 1% by volume per day, depending on the storage volume.