Hydrogen Tank
There are many ways in which energy can be stored for use at a later time. Common methods include electrical batteries and fuel cells. Another well-known example can be seen in the rather humble hydrogen tank. Let’s take a look at this technology in slightly more detail. We can then address some practical questions before moving on to discuss how these storage methods are continuing to evolve.
What is a Hydrogen Tank?
A hydrogen tank is defined as any type of vessel that is used to store compressed hydrogen gas. Note that a hydrogen tank may also be referred to as a "vessel" or a "canister". The presence of a hydrogen storage tank can often be seen in hybrid and/or all-electric vehicles.
The first tanks were introduced surprisingly recently (in 2001) and a handful of improvements have been made since this time. For instance, it is now possible to obtain smaller vessels for consumer use. These can also be replaced much easier when compared to their decidedly bulky counterparts.[1]
What is the Main Purpose of Hydrogen Tanks?
The primary intention of any hydrogen fuel tank is to store this gas in a safe manner while still allowing it to be accessed when required (such as within an electric vehicle or when employed as a back-up power supply.
A high pressure hydrogen tank also provides a convenient means to transport this gas from one location to another. For instance, a large hydrogen tank may be employed to deliver this fuel to a distribution centre. It can then pump the hydrogen into smaller units (for storage or immediate consumption).
Having said this, hydrogen tank safety is also a key concern. This primarily results from the fact that hydrogen is an extremely flammable gas. It is also colourless, odourless and tasteless. Thus, it can be difficult to detect a leak. If exposed to an external source of combustion, hydrogen can easily ignite. This is why any hydrogen tank must be engineered to the highest of standards (we will examine the design of these tanks in a later section).[2]
The Different Types of Storage Vessels
A hydrogen tank can be constructed in four unique configurations[3]:
- All-metal (Type I)
- Metal-wrapped composite hydrogen tank cylinders (Type II)
- Composite hydrogen tank cylinders with metal linings (Type III)
- Fully composite cylinders with non-metallic (normally polymer-based) linings (Type IV)
As can be imagined, regulations will often come into play when choosing which type of hydrogen tank is the most appropriate. It should also be mentioned that hydrogen tank materials can impact the amount of gas that can be stored at any given time. For example, all-metal containers are quite heavy. This often renders them impractical for use within vehicles.
Composite hydrogen tank alternatives offer two important benefits. Firstly, their lightweight nature makes them easy to transport. These are often preferred within the EV sector. Secondly, a hydrogen tank comprised of non-conductive materials poses much less of a danger in regard to combustion (such as an accidental static discharge when filling).
Liquid or Gas? Which Type of Hydrogen Tank Configuration is More Efficient?
Note that hydrogen can be stored in either a gaseous or a liquid state. A gaseous hydrogen container will store this element under a significant amount of pressure (known as "compressed hydrogen"). However, it is also possible to keep hydrogen in its liquid state. A liquid hydrogen tank utilises cryogenic technology in order to ensure that the fuel does not begin to vaporise.[4]
So, which is the most common method? Studies have found that liquid hydrogen can sometimes be used for small-scale projects. Furthermore, liquid tanks are frequently used for the distribution of pure hydrogen. There is nonetheless an important drawback to mention. The cryogenic fluid required to keep the hydrogen tank below -252.8ºC will need to be replenished on a regular basis. This makes liquid hydrogen storage tank design impractical for average consumer use.[3]
This is why liquid hydrogen storage tanks are generally not used within electric vehicles and everyday power supplies. Compressed technology is preferred for vehicular use as well as household applications.
Safety Issues with Hydrogen Tank Technology
Although hydrogen tank technology has come a long way, there are still many safety variables that need to be addressed by manufacturers and consumers alike. We touched upon the notion of flammability earlier in this article. Perhaps the most well-known example of the dangers associated with hydrogen tank fuel storage can be seen in the famous Hindenburg disaster of 1937. In this case, it is thought that a static electric discharge from a mooring cable causes the gas to ignite; leading to the deaths of 35 people.[5]
So, it is clear that safety protocols must be in place at all times. There are several ways in which this can be achieved. Some of these include[6]:
- A hydrogen tank (cylinder) must always be stored in the upright position.
- The presence of protective valve caps during transport.
- The use of a hydrogen tank pressure relief system.
- In some cases, the presence of a flammable gas detection system within close proximity of the hydrogen tank.
However, hydrogen fuel cell hydrogen tank technology has addressed many of these concerns thanks to the use of robust canister materials alongside redundant safety systems. This is why a growing number of vehicles have already begun to adopt hydrogen tank systems as a means of propulsion.
Conclusion – Future Hydrogen Tank Technological Innovations
Since the first viable hydrogen tank was introduced in 2001, many advancements have been made. Some of these involve the use of composite materials during their construction. Hydrogen tank storage systems likewise enable these units to offer a reliable source of on-demand power (such as a back-up supply for standalone security and surveillance solutions).
Traffic technologies are likewise beginning to leverage hydrogen tank technology, as hydrogen can be used as an additional source of power in the event that mains electricity is not available.
It is now clear to see that the humble hydrogen tank serves many purposes within today’s society. The good news is that this technology is continuing to advance at a frenetic pace. Not only can a hydrogen tank provide a reliable source of power for electric vehicles, but this "clean" technology is considered safe for the environment (when compared to alternatives such as fossil fuels). We should therefore expect to witness even more hydrogen tank advancements in the near future.
