Hydrogen infrastructure at a glance
Hydrogen (H2) storage is a key enabling technology for the development & improvement of H2 and fuel cell techs in applications including i) transportation, ii) stationary power generation, and iii) non-energetic use (industrial inputs).
Physical storage, comprised of compressed gaseous H2 (CGH2) and liquefied H2 (LH2), are the established and dominant techs, but chemical storage (ammonia, methanol, LOHC-Liquid Organic Hydrogen Carriers) could offer higher storage performance due to the high densities and compatibility with existing fuel transport infrastructure (though the regeneration of storage material can be problematic). Figure 1 shows some of the H2 storage methods.
Figure 1: Hydrogen storage methods
H2 is moved from production site to final application by trucks/trailers, pipelines, and vessels (ships). Delivered hydrogen gas is often transported in cylinders, tubes, pipes, and liquid tanks.
Trucks haul GCH2 in tube trailers in pressures of 180 bar or higher (up to 500+ bar). Steel tube trailers are most commonly employed, carrying around 380 kg onboard (one truck).
H2 has been transported by pipeline since 1938 (btw the Rhine and Ruhr areas of Germany). Today, there are only about 5,000 km of H2 transmission pipelines around the world, mainly in the U.S., Belgium, Germany, and France, compared with +3 mi km for NG pipelines [Parliament, 2021]. Not surprisingly, about 75% of the proposed European H2 grid is expected to rely on existing gas transmission infrastructure [Goldman Sachs, 2020].
Vessels were developed to provide a means of transporting LH2 at 1/800 of its original gas-state volume, cooled to –253.8 °C. LH2 is stored in super insulated cryogenic tanks, which sizes can range from 1.5 m3 (100 kg) to 75 m3 (5,000 kg).
Compressed H2 can be stored onboard in tanks based on type IV carbon-composite tech, an all-composite construction featuring a polymer, liner (typically a high-density polyethylene) with carbon fiber, or hybrid carbon/glass fiber composite. Pressures used are usually 350 or 700 bar (5,000 or 10,000 psi). Capacities vary between manufacturers, but 5 kg is typical [Fuel Cell Cars, 2022].
LOHC are easily transported chemical compounds that can be reversibly hydrogenated and dehydrogenated. The hydrogenation process involves chemically binding hydrogen to the liquid compound so that it can be transported at atmospheric pressure like many other oil-like substances. At the destination, the H2 is released via an endothermic (heat-requiring) dehydrogenation process, followed by hydrogen purification.
The capital cost for LH2 storage is more than 2x that for the gaseous approach and 4x that for the LOHC approach. Together with other properties such as safety, these factors make LOHCs a possible option for large-scale stationary H2 storage. But, the long-term viability of LOHC in a real-life environment is also yet to be proven, although demonstration projects around the world point in a positive direction [RB, 2022].