The reasons why the import of green energy will play a decisive role in supplying Germany and other industrialised countries in the future were explained in the first section of this chapter. To realise the import of large amounts of green energy from regions with a particularly high renewable energy potential to Germany, the transport of green, hydrogen-based energy carriers is necessary. In addition, transport infrastructures are also needed to supply individual consumers and connect them to storage facilities. In this section, the most important options for the transport of hydrogen and its derivatives are presented.
The transport of gaseous hydrogen is currently mainly carried out with the help of so-called tube trailers. Thereby, compressed gaseous hydrogen is stored in bundles of tube-shaped pressure tanks. These tube bundles are installed on truck trailers but can also be used for hydrogen transport by freight trains. In recent years, the maximum transport capacity of a single truck could be significantly increased by raising the storage pressure up to 500 bar (see illustration below). If the transport capacity needs to be increased further, liquid hydrogen trailers equipped with a cryo tank are a possible option. Due to the significantly higher volumetric energy density, the amount of energy transported per trailer can be almost quadrupled by using liquid hydrogen.
Options for the transport of hydrogen by road by Adolf et al. (2017) (CC BY-SA)
Transportation via shipsThere are already a number of possibilities for transporting hydrogen derivatives via ship. For example, tankers that are currently used to transport fossil oil can also be used to transport LOHCs by ship. Liquid ammonia and methanol are currently transported in large quantities with corresponding tankers, so that existing infrastructures and technologies could also be used here if these energy carriers become established as a storage and transport medium for green hydrogen.Pure hydrogen is currently not transported by ship on a large scale. However, the first dedicated tanker for the transport of liquid hydrogen was built in 2020. After completion of the test operation, hydrogen produced in Australia shall be transported to Japan with the help of this ship. The transport of gaseous hydrogen via ship is not a promising option due to the limited transport volumes and is therefore not expected to play a major role in the future.The world's first ship for transporting liquid hydrogen, built by Kawasaki by HySTRA (2021) (CC BY-SA)
Transportation via pipelinesDue to the relatively low conditioning effort (no energy-intensive liquefaction or bonding to carrier medium), hydrogen transport by pipeline is a particularly attractive option. Already today, pipelines are used to transport (grey) hydrogen between industrial sites. In Germany, there are several smaller hydrogen networks with a total length of just under 400 km. Hydrogen pipelines usually run at operating pressures between 10 and 100 bar. Since the operating pressure must be maintained to ensure gas transport, the compression of the hydrogen plays a central role.Besides the construction of new pipelines, the conversion of existing natural gas pipelines can also be considered for pipeline-based hydrogen transport. With such a rededication, it must be ensured that the hydrogen cannot permeate the wall of the pipeline. In the long term, permeation would lead to the destruction of the pipeline (hydrogen embrittlement). One possible approach to prevent damage to converted pipelines is to apply internal pipe coatings made of hydrogen-impermeable plastic.
