Energy Density

Part one in the series ‘Things to consider when planning your zero-emission future.

Planning for your inevitable zero-emission future tends to be a daunting task. Many of the available options are not yet fully developed and therefore come with a range of uncertainties and risks. Still, you can’t afford to delay preparations for your transition much longer. Deadlines for regulations are closing in and you need to anticipate now in order to sustain your competitive advantage.

We hear you. Here is a series of articles to help you navigate and compare the many aspects that will affect the competitiveness of your future business and make an informed decision based on the many aspects that influence the cost drivers of your operations.

Other publications in this series

Asset reusability
Comparing power solutions based on asset reusability
Energy Efficiency
Comparing power solutions based on Energy Efficiency

Energy density

Hydrogen (H₂), is the lightest element in the universe. Despite its very low weight, it has an extremely high gravimetric energy density (MJ/kg). One kilogram of hydrogen at 20°C and 1 bar contains a vast amount of energy: 142 MJ/kg. This is far more than e.g. ammonia, which holds only 16,9 MJ/kg. At first sight this makes hydrogen an efficient and lightweight energy carrier but there is a second side to energy density which needs to be considered: volumetric energy density (MJ/Liter). Unfortunately, from this perspective the energy density is very low: 0,01 MJ/Liter. In terms of volume, the energy content of hydrogen is much lower than most other fuels and energy carriers. Ammonia for example, contains 11,5 MJ/Liter. When comparing the energy densities of different solutions, it is important to understand the difference between these metrics and to assess how they will impact the operation of your systems. .

Although hydrogen has a very high gravimetric energy density, its volumetric energy density is very low.

In order to really assess the impact of any zero-emission fuel on your operations, you must to look beyond the energy density of the fuel and consider the entire system needed to actually make the fuel power your application. This includes the fuel tanks and how they can be integrated into your application as well as the (re-)conversion systems that turn the fuel into the actual energy that powers your engine. And quite importantly, you also need to make sure you can refuel in a convenient and safe manner. In that respect diesel is a very favourable fuel, as it has a high density both from mass and volume perspective, it is easy to refuel because it’s a liquid, it combusts directly in an engine and the tanks are rather straightforward and easily integrated.

Larger amounts of space are required for storing or using hydrogen at atmospheric pressure and temperature. The required space can be reduced by applying higher pressures (compressed hydrogen at e.g. 350 or 700 bar) or lower temperatures (e.g. liquification at -253°C). Although these approaches increase the energy density in storage and transportation, they require complex storage solutions that are difficult and costly to integrate. Providing sufficient range and autonomy therefore continues to be a challenge with hydrogen as an energy source. A storage method like ammonia evidently has a higher density, but toxicity and the need for pressurized & cooled storage hampers the actual storage capacity in practice.

So, depending on the constraints of your application (i.e. restrictions in terms of weight or volume or both) and which units are compared, hydrogen has either the highest energy density or the lowest. In reality however, context determines how energy density impacts your business. If your business is in trucking or maritime operations, what matters most is the amount of space required to integrate hydrogen as a fuel and still have a sufficient range. Space, safety requirements and range determine if using a substitute is practically and economically viable.

How Voyex LOHC compares

Voyex LOHC carries 60 kg of hydrogen per 1,000 Liter, thus compounding 8500 MJ (almost 2,000 kWh). However, by reusing heat residues from the ICE, releasing the hydrogen from the Voyex LOHC only requires a negligible amount of added energy. This saves up to 10-15% energy!

To make this concept better to grasp, we will explain the concept of energy density in two contexts below.

How energy density impacts construction sites

The current standard approach for powering construction sites is to use tube-trailers that hold approximately (standard) some 350-450 kg of pressurized hydrogen as a storage solution. These tube trailers are typically placed next to refueling stations or on construction sites in a separate, shielded area due to safety requirements. The logistics and safety dynamics accompanied by Voyex LOHC solutions, are noticeably less extensive. 1m³ Voyex LOHC holds 60 kg of hydrogen, so a 4m² footprint is sufficient. This is some 8 times smaller than a tube-trailer. In addition, Voyex LOHC is safer than diesel and can be stored at atmospheric pressure and ambient temperature, which we expect should make the permitting process for Voyex solutions much faster, saving serious time and money. And last but not least, 1m³ one can operate continuously a full day a 100KW generator set.

How energy density impacts transport and storage

Electricity is relatively expensive in (northern)Europe compared to regions such as the gulf region, North-Africa or Australia, This makes it a serious challenge to produce cost-competitive green hydrogen (via electrolysis) in Europe. The general assumption is that the most cost-competitive solution will be to import large quantities of hydrogen to Europe. When looking at volumetric volume densities, ammonia is considered an attractive option for transporting this hydrogen, after which liquified hydrogen comes up and then LOHC. However, energy density is not the only aspect that determines the attractiveness of a transport solution for hydrogen. Safety and handling are equally important, if not more, when shipping massive amounts of fuel. Publications of both IRENA (2022) and IEA (2023) demonstrate that ammonia and LOHC are more suitable options for hydrogen import than liquified hydrogen. Moreover, ammonia and LOHC are expected to be at the same cost level as liquified hydrogen.

However, the LOHC used in these evaluations are NOT based upon the molecule Voyex is using. The voyex LOHC contains 8-10% more hydrogen per cubic meter and requires 10-15% less energy for the conversion back to hydrogen than the LOHC’s used in the above mentioned reports.

As a result, Voyex LOHC should be considered a strong candidate for importing and storing large quantities of hydrogen. Additionally, the Voyex LOHC is safer than diesel, both in terms of safety and toxicity, and allows reusing currently available assets, on terminals as well as ships.

Voyex B.V has developed a Liquid Organic Hydrogen Carrier that will make the transition from diesel to zero-emissions as easy as it gets. We work closely together with many partners in the hydrogen supply chain to help get the zero-emission economy off the ground as fast as possible.