Hydrogen has several remarkable properties. It stores enormous amounts of energy, has a boiling point as low as -252.9 °C, and differs significantly from most other fuels and energy carriers in terms of energy density.
In this blog, we review the energy density of gaseous and liquid hydrogen. What makes the energy density of hydrogen so unique? And what does this mean for the application of hydrogen in practical terms? Using various practical examples, we comprehensively answer these questions.
The energy density of hydrogen
As previously explained in our blog on liquid hydrogen, hydrogen is the lightest gas in the universe. Hydrogen gas weighs almost nothing but has an extremely high gravimetric energy density. One kilogram of hydrogen contains a vast amount of energy, making it an efficient and lightweight energy carrier.
In turn, the volumetric energy density of hydrogen is particularly low. Per volume, the energy content of hydrogen is even a lot lower than that of most other fuels and energy carriers. Consequently, storing or using hydrogen at atmospheric pressure and temperature requires a substantial amount of space.
Fortunately, there is a solution to this. By compressing or liquefying hydrogen, it is possible to raise the low volumetric energy density. This makes the storage, transportation, and application of hydrogen considerably easier.
The volumetric energy density of hydrogen in practice
What does the volumetric energy density of hydrogen actually mean in practice? The figures and examples below clearly illustrate the implications:
- The volumetric energy density of gaseous hydrogen at atmospheric pressure is 0.09 kg/m³. Consequently, under normal conditions, much space is required to store gaseous hydrogen. Therefore, hydrogen is virtually not stored or transported in gaseous form at atmospheric pressure because it is simply not efficient.
- At a pressure of 350 bar, the volumetric energy density of gaseous hydrogen is 26,1 kg/m³. This increased pressure makes it possible to store considerably more gaseous hydrogen in the same space. The pressure of 350 bar is used in the tanks of gaseous hydrogen trucks, for example, the ones from Hyzon. A loaded 55-ton truck needs about 50-70 kg of hydrogen to travel 500 to 600 km.
- At a pressure of 700 bar, the volumetric energy density of gaseous hydrogen is 42 kg/m³. This relatively high pressure is used, among others, for gaseous hydrogen passenger cars (such as the Hyundai NEXO as featured in our recent blog ‘What is hydrogen used for?‘). With a 125 liter tank containing 5 kg of hydrogen, a car can drive about 600 km.
- In liquid form and at a temperature of -252.9 °C, hydrogen has a volumetric energy density of 71 kg/m³. Liquid hydrogen is also used as an energy carrier for sustainable trucks and aircraft, which are currently under development.
To drive about 1000 km, a truck needs about 80 kg of liquid hydrogen. This applies, for example, to the liquid hydrogen-powered Daimler GenH2, which we covered in detail in the blog mentioned earlier.
Liquid hydrogen also offers excellent potential for aircraft. Because the energy in liquid hydrogen is so high and hydrogen as a fuel is a lot lighter than kerosene. This is a vast advantage for aircraft.
However, the volume of liquid hydrogen is a lot more than the volume of kerosene. To carry the same amount of total energy on board, you need four times the volume of liquid hydrogen compared to kerosene.
Fortunately, there are ways to use fuel efficiently. For example, fuel cells are more efficient than fuel engines, and superconductivity makes them even more economical. By applying these techniques, it is not always necessary to take a massive amount of hydrogen on board.
The table below shows the energy density of hydrogen compared to some other (liquid) gases, such as biodiesel, diesel, and LNG. The difference here is abundantly clear: the gravimetric and volumetric energy densities of hydrogen are hardly comparable to those of most other gases.
The unique properties concerning energy density make the application of hydrogen different from that of the other fuels and energy carriers and require entirely different infrastructures.
Storing and transporting hydrogen under atmospheric conditions is highly inefficient, so the substance is almost always liquefied or put under high pressure. This brings molecules closer together, increasing the energy per volume and making the gas extra interesting for storage, transportation, and application.
As detailed in our earlier blog on hydrogen pipelines, optimum insulated infrastructures are essential for liquid hydrogen. Liquid hydrogen infrastructures are often equipped with vacuum insulation to prevent energy losses and provide the necessary safety.
Vacuum insulated transfer lines consist of an inner tube and an outer tube, with a high-vacuum environment between them. The vacuum enclosure provides an extremely high insulation value, while the two tubes together provide a double-containment that makes the pipe extra safe.
Demaco has been at the forefront of developing the best liquid hydrogen infrastructures for decades. We experiment with prototypes, work on pioneering projects and demonstrate proof of concept for advanced projects and products. Our vacuum insulated hydrogen infrastructures have lasted for decades within various projects and prove that vacuum technology is the method of choice for safely managing liquid hydrogen.