A hydrogen tank is a canister used to store compressed hydrogen. Type IV hydrogen tanks are an integral part of hydrogen-powered vehicles. Such vehicles can be refueled at hydrogen stations. Compressed hydrogen is being used as an alternative fuel source to oil and other fossil fuels. This has made gas storage an important part of the technology’s development.
Hydrogen can be stored in gaseous and liquid form. Scientists hope to use liquid hydrogen as a fuel source for space exploration. The problem with storing liquid hydrogen is that it has a boiling point of -423.188 degrees Fahrenheit (-252.882 degrees Celsius). In order to keep it liquid, hydrogen needs to be stored in extremely cold conditions. This requires cryogenics, uses large amounts of energy and is expensive to produce.
Storing gaseous hydrogen is much easier. A hydrogen tank works by storing compressed hydrogen under pressure. A vehicle requires hydrogen to be compressed at 350 and 700 bar or 5,000 and 10,000 psi. Bar is a metric measure of pressure based on the standard atmospheric pressure found at sea level. PSI is short for pound per square inch and is an imperial measure based on the amount of pressure exerted by one pound in weight on one square inch.
There are four basic types of hydrogen tank. They differ in terms of what they are made of and what pressures they can cope with. They tend to use metals such as magnesium hydride or sodium aluminum hydride. Several types are mixed with composites or, in the case of the IV model, are all composite in build.
The type I hydrogen tank is a metal tank. The aluminum variety has a working pressure of 175 bar, or 2,538 psi. The steel variety works at 200 bar, or 2,900 psi.
Type II tanks are made with metal surrounded by a filament cylinder. The aluminum-glass tank works at 263 bar, or 3,814 psi. The steel-carbon tank has a working pressure of 299 bar, or 4,336 psi.
Composite materials surrounding a metal liner compose type III. The composites are made from materials such as aramid and fiberglass. The fiberglass model has a normal pressure of 305 bar, or 4,423 psi, while the aramid version works at 438 bar, or 6,352 psi.
A type IV hydrogen tank is a rotary-molded tank made out of composite materials such as carbon fiber with a polymer liner. They have a working pressure of 661 bar, or 9,586 psi. The type IV is most commonly found in vehicles such as automobiles and hydrogen storage trucks.
All hydrogen tanks require extensive testing to ensure they are safe for use. The hydrogen tank is tested in four ways. The bust test uses twice the normal working pressure to see when the tank will break open, while the proof pressure test will examine how the tank copes with 1.5 times the normal pressure. The tank is tested long term for fatigue and leaks as well.