What is a hydrogen storage system?

The hydrogen storage system is one of the three major components of a hydrogen refueling station (hydrogen storage system, compressor, and hydrogen refueling machine), but the application of the hydrogen storage system is not limited to hydrogen refueling stations. Therefore, this article will expand the perspective to hydrogen storage nodes in multiple links: storage after hydrogen production, storage after transportation to the hydrogen refueling station, and on-board hydrogen storage. These different nodes also put forward different requirements for hydrogen storage containers.

What is a hydrogen storage system?

According to the definition of the Argonne Laboratory in the United States, the hydrogen storage system can be divided into several major components: hydrogen storage bottles, integrated bottle valves, integrated pressure regulating modules, hydrogen refueling ports, hydrogen storage system controllers, and pressure relief and hydrogen discharge devices for each part.

Hydrogen storage bottle

Hydrogen storage bottles are the most mature field of commercialization of hydrogen storage systems, and a large number of companies have entered the production of hydrogen storage bottles. The technology of hydrogen storage bottles has gone through five generations of iterations. At present, V-type bottles without inner liner and only made of fiber winding are still under research both at home and abroad.

The high-pressure hydrogen storage cylinders put into use are mainly divided into four types: all-metal cylinders (Type I), metal inner liner fiber hoop-wound cylinders (Type II), metal inner liner fiber fully wrapped cylinders (Type III), non-metallic inner liner fiber fully wrapped cylinders (Type IV).

The four generations of hydrogen storage bottles are currently widely used. This is because their Type I and II bottles are suitable as hydrogen storage containers for hydrogen refueling stations due to their characteristics, and type III and IV bottles are more suitable as vehicle-mounted hydrogen storage containers, each with its own uses.

The reason why hydrogen refueling stations and vehicle-mounted hydrogen storage use different hydrogen storage bottles is, first of all, because the transportation field has higher requirements for the weight storage density of hydrogen. Type I and Type II have a large weight-to-volume ratio, which is difficult to meet the hydrogen storage density requirements of hydrogen fuel cell vehicles. Secondly, the self-weight proportion of the hydrogen storage container is very important to the power performance of the vehicle. Type III and Type IV bottles have the advantages of low weight-to-volume ratio and high hydrogen storage density per unit mass due to the fiber full winding structure. They are currently widely used in hydrogen fuel cell vehicles.

The structure of the hydrogen storage bottle from the inside to the outside includes lining material, transition layer, fiber winding layer, outer protective layer, and buffer layer. Take the Type IV hydrogen storage bottle as an example to see its structural composition:

Type IV hydrogen storage bottle and Type IV hydrogen storage bottle liner

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   ● Liner: The total thickness of the bottle wall is about 20~30mm. The innermost layer in direct contact with hydrogen is the gas barrier layer, which is about 2~3mm thick. The material is PA6, PA612, PA11, HDPE, etc., which plays a role in blocking hydrogen.

● Middle layer: A relatively thick pressure-resistant layer, made of CFRP carbon fiber reinforced composite material, composed of carbon fiber and epoxy resin. Under the premise of ensuring the pressure resistance level, the thickness of this layer is minimized to improve the hydrogen storage efficiency.

● Surface layer: The thickness is about 2~3mm, and the material is GFRP glass fiber reinforced composite material, composed of glass fiber and epoxy resin.

The reason why Type IV hydrogen storage bottles are more suitable for on-board hydrogen storage is that they change the metal material of the inner tank, use polymer materials as the inner tank, and use carbon fiber composite materials as the bearing layer. The hydrogen storage mass ratio can reach more than 6%, and the highest can reach 7%, so the cost can be further reduced.

Hydrogen storage system composition

Although the hydrogen storage bottle is the core of the hydrogen storage system, the hydrogen storage system can only be safely put into use with the assistance of a series of auxiliary components.

The hydrogen storage system of the hydrogen refueling station consists of a hydrogen storage bottle, an integrated bottle valve, an integrated pressure regulating module, a hydrogen refueling port, a hydrogen storage system controller, and pressure relief and hydrogen discharge devices of various parts.

Integrated bottle valve

The integrated bottle valve is a key part to ensure the safety of the hydrogen storage bottle and the smooth delivery of hydrogen. It is also composed of multiple parts, namely, a filter, a flow limit valve, a heat & pressure release device, a manual valve, a check valve as the hydrogen refueling inlet, and a series of temperature and pressure sensors.

The integrated pressure control module usually includes an automatic shut-off valve, a manual vent valve (for maintenance), a pressure regulator, an emergency pressure relief valve, and a pressure sensor.

The performance of the hydrogen storage system can be evaluated by several important parameters, including hydrogen storage capacity, system hydrogen storage mass density, system hydrogen storage volume density, hydrogen storage cost per kilowatt-hour, charging and discharging cycle life, and minimum transportation pressure.

On-board hydrogen storage system 

Due to different application scenarios, the composition of the on-board hydrogen storage system is different from that of the hydrogen storage system at the hydrogen filling station. Its structure includes: hydrogen storage bottle with bottle valve, hydrogen supply pipe, hydrogen filling port, high-pressure hydrogen pipeline, pressure sensor, one-way valve, pressure reducer, and hydrogen system truss.

70MPa fuel cell on-board hydrogen storage system

The on-board hydrogen storage system adopts the form of stacking with trusses for fixing. The number of bottles varies according to the power of the vehicle and other indicators. Most commercial vehicles have 6 bottles, and the placement mode is as follows:

In passenger cars, two hydrogen storage bottles are mainly used:

Hydrogen fuel cell vehicles equipped with two type IV hydrogen storage bottles