It can absorb fluctuations and, like a buffer, ensure a demand-based energy supply. However, hydrogen is not easy to transport. The hydrogen storing process using iron oxide is an already tried-and-tested process that can overcome many of these hurdles.
H2 storage and transport
H2 is currently primarily stored in two ways: by means of pressurised H2 in compressed gas cylinders, and in tanks or in underground caverns. H2 under pressure is not only space-consuming, it is also a hazardous material. Extensive safety measures are required, and permitting procedures are extensive, time-consuming and costly. The safety aspect will also have a negative impact on public acceptance. Conversion losses from electricity to hydrogen to electricity are also so large that only a third of the original electrical energy is ultimately available for use. Caverns are certainly a suitable option for the long-term storage of large quantities of H2, however, their low availability and the need to install separate H2 grid connections for users and producers limits widespread applications.
The unsolved H2 transport challenge
Transporting pressurised hydrogen in tanks is costly, risky and inefficient. The same applies to liquefied H2, where the energy balance is further worsened by the necessary cooling to -253°C and boil-off losses. In both cases, infrastructure must be adapted accordingly, resulting in lengthy permitting procedures, high investment costs and construction delays. Liquid organic H2 carriers (LOHCs) can be transported using existing infrastructure, have a high energy density, and are not dangerous. However, disadvantages include the complex conversion to H2, the use of non-sustainable materials, and their unsatisfactory efficiency. Transporting hydrogen derivatives such as ammonia and methanol is always the best option if they are ultimately used as a material. Converting them back to H2, on the other hand, makes less sense. The additional energy conversion losses and the extensive, costly safety measures and authorisation procedures required are just some of the disadvantages of this. In the case of ammonia, there is also the residual risk due to its toxicity.
The limits of an H2 grid
Many countries are planning to set up a hydrogen distribution network – in some cases using existing infrastructure. However, it will still take a lot of time and money before these networks are available. In addition, not all hydrogen consumers can be connected, at least for the foreseeable future. There are also limits to the construction and operation of hydrogen networks, both in terms of geographical coverage and topography, and in terms of cost-effectiveness.
What about the alternatives?
In response to these challenges, companies and scientific institutions around the world are addressing this issue. On one hand, work is ongoing to optimise existing solutions, particularly in terms of efficiency and costs, and on the other hand, the process of developing alternative solutions has also begun. One approach is adsorption storage, where the H2 is physically bound to the surface of highly porous storage materials, such as metal-organic frameworks (MOFs). Another is metal hydride storage, where the H2 molecules are stored in the metal lattice. Although the metal lattice has a good volumetric storage capacity, it is expensive and heavy. The use is therefore currently limited to special applications, such as in submarines. One solution that has already been proven on an industrial scale for approximately two years is the use of iron oxide as a storage material.
Written by Matthias Rudloff and Ines Bilas, AMBARtec, Germany,
This article was originally published in the Autumn 2024 issue of Global Hydrogen Review magazine. To read the full article, simply follow this link.