Adapted from ‘The Myth of Hydrogen for Export’ by Paul Martin, Chemical Engineer and Process Development Expert.
Hoping to spearhead the development of a global market, high-profile deals such as the Japan-Australia Hydrogen Energy Supply Chain (HESC) Project aim to use ships to transport hydrogen across continents.
Despite a long list of such project announcements, no hydrogen trade industry exists anywhere in the world in 2024. Import deals lag far behind the scale of planned exports, and globally, almost all hydrogen continues to be produced and used in the same place.
This isn’t because transporting hydrogen is impossible. It’s because faced with the challenges of moving hydrogen long distances, there is almost always a better energy transition solution – making hydrogen transport a last resort.
We’ll examine the feasibility of hydrogen transport via pipeline in a future article, but here we look at the feasibility of shipping hydrogen or its derivatives across transoceanic distances.
Shipping pure hydrogen
Pure hydrogen is extremely challenging to transport. Taking up so much space at normal temperatures due to its extremely low energy density, the only way to move it long distances is to compress or liquefy it.
Shipping hydrogen as a compressed gas in large quantities is a non-starter. At a pressure of 150 bar, 15 ships of compressed hydrogen would be needed to carry the same amount of energy as one typical liquid natural gas (LNG) tanker [1].
Shipping hydrogen at this pressure is unlikely to ever be attempted in the real world, as such ships would be of immense weight due to heavy storage tanks required to resist the high pressure, and any reduction in pressure would result in an even greater number of ships.
Shipping liquefied hydrogen is almost as impractical, and rife with technical difficulties. It has been attempted in the real world just once to date as part of the Japan-Australia HESC Project, resulting in a brief fire onboard the carrier ship.
One of the greatest technical challenges here is that hydrogen becomes a liquid at atmospheric pressure at minus 253 degrees Celsius – just above absolute zero, the lowest temperature possible.
Even at this temperature, it is still not very dense – fitting about 71 kilograms of hydrogen per cubic metre, which is less than half the energy density of LNG [2].
To put this in perspective, 2.4 ships of liquefied hydrogen would be needed to carry the same amount of energy as one typical LNG tanker.
While this may sound more reasonable than shipping compressed hydrogen, it is just the first of many challenges when it comes to shipping liquefied hydrogen.
Energy losses and leaks
Liquefying hydrogen is a highly energy-intensive process that outright consumes about a third of its energy, compared to about 10% to liquefy natural gas [3].
More hydrogen will be lost daily during transport as some of it boils – known as boil-off – as keeping heat out of a liquid that boils at -253 C is very difficult.
While the most optimal large, land-based storage tanks report an excellent performance of just 0.2% boil-off of hydrogen per day, at least 1% boil-off per day can be expected at the size of tank possible to put on a truck to transport the hydrogen to and from a ship.
Recapture and re-condensation of hydrogen boil-off is not possible during transit – which is not only inefficient, but presents a climate problem as hydrogen has a global warming potential 35 times that of carbon dioxide (CO2) in the first 20 years after its release into the atmosphere [4].
Hydrogen is a small molecule, and is far more prone to leak from pipes and storage tanks than natural gas. Even the lowest-emission form of green hydrogen, made from renewable electricity, risks releasing significant fugitive emissions during transport as a result.
If electricity is used to make renewable hydrogen, which is then liquefied, shipped overseas and used to make electricity at its end destination, less than one third of its original energy input will remain by the end in a best-case scenario – without even accounting for boil-off or the energy used to power the ship for its transport [5].
This means shipping liquefied hydrogen will deliver an energy loss of around 70% – making it a complex, costly and inefficient vehicle for the export of renewable electricity.
Converting hydrogen into other molecules
Faced with the difficulties of transporting pure hydrogen via ship, it is often proposed to convert hydrogen into another molecule with more favourable transport properties.
These export options each have their own challenges as hydrogen transport vehicles, with one theme in common: converting renewable hydrogen into another molecule is typically so energy-intensive that a costly amount of energy will be lost in the process, with significant capital and other operating costs further resulting in expensive energy at destination.
Most frequently considered are ammonia and methanol, which we examine below.
Ammonia
Ammonia is made by reacting nitrogen with hydrogen at high temperature and pressure over a catalyst. As the atmosphere is 79% nitrogen, there is nitrogen everywhere that hydrogen might be produced, making ammonia production appealing.
Ammonia is easier to ship and store than hydrogen, and around 8-10% of annual global production is already transported by sea today – most of it made from emissions-intensive fossil fuel hydrogen.
Cycle energy efficiencies for processes involving renewable ammonia, from electricity to hydrogen to ammonia and back, are around 11 to 19% when re-converting it into hydrogen at its destination – meaning at least 80% of the original energy input will be lost [6].
In a best-case scenario, cycle efficiency could rise to 23% if ammonia is burned in a power plant at destination, without being re-converted or “cracked” back into hydrogen – meaning 77% of the original energy input will still be lost.
Ultimately, for every 5-9 kilowatt-hours (kWh) of wind energy input into an electricity-hydrogen-ammonia-electricity shipping cycle, just 1 kWh of electricity will be fed into a grid overseas by its end.
Safety is furthermore a heightened challenge when it comes to shipping ammonia. While both it and LNG are hazardous flammable liquefied gases, ammonia is also extremely toxic and very corrosive, requiring far more intensive safety precautions.
An ammonia spill risks devastating aquatic environments, and when burned, such as in an engine or power plant, it generates high levels of polluting nitrogen oxides (NOx). Ammonia is a regulated pollutant itself, meaning its unburned emissions must be carefully avoided.
Methanol
Methanol can be made from hydrogen, and either carbon monoxide or carbon dioxide, in an energy-intensive process that produces water and heat as a byproduct.
Almost all the world’s methanol is currently made from synthesis gas mixtures of hydrogen and carbon monoxide, both produced from fossil fuels.
To make renewable methanol, hydrogen must instead come from renewable electricity, while carbon dioxide must come from biogenic sources or be collected from the atmosphere. Finding locations suitable for both of these inputs is a production challenge.
Once made, methanol is considerably more favourable as an energy transport medium than hydrogen or ammonia. It is a liquid at room temperature, meaning its cost of storage is very low per unit of energy, and its energy density is higher than that of hydrogen or ammonia – though still lower than that of gasoline or diesel. It is toxic, but far less so than ammonia.
Despite the advantages of methanol’s liquid state and high energy density, the process of producing it, and of later returning it to hydrogen and carbon dioxide, is so energy-intensive that it makes little sense to use it as a vector for hydrogen transport.
The cycle energy efficiency of processes involving renewable methanol, from electricity to hydrogen to methanol, and finally its burning in a large ship’s engine or power plant at destination, is about 25% – meaning around 75% of the original energy will be lost.
This efficiency is even lower if the methanol is re-converted back to hydrogen at its end destination [7].
Note: e-Methane or e-LNG can be made by further chemically reducing methanol to methane – requiring more hydrogen, producing more water and heat waste, and creating this familiar gas that loses 8% of its energy content when turned into a liquid for transport. This is an extremely weak economic and energy-efficiency case for its use to export hydrogen.
Our final take
The export of hydrogen via ship, either as hydrogen itself or hydrogen-derived molecules, is technically possible but difficult to make viable from a practical, economic and energy efficiency standpoint.
Losses from energy transformations, along with high capital and other operating costs, make hydrogen a complex and expensive vehicle for the transoceanic transport of energy, and it should only be used as a very last resort where no alternative exists.
Countries that make themselves dependent on importing energy in the form of hydrogen or its derivatives will ultimately see their economic competitors use energy that, without a lossy middleman, costs just a fraction as much per joule.
Alternative solutions
We advise to prioritise direct electrification, energy efficiency and – if necessary – locally-produced renewable hydrogen before relying on hydrogen imports to advance the energy transition.
It is always more efficient to use renewable electricity directly wherever possible – for example, heating buildings with boilers using renewable hydrogen takes 5.5 times more electricity than electric-powered heat pumps, while powering a hydrogen fuel cell vehicle with renewable hydrogen uses three times more electricity than one running on a battery.
Places with large amounts of renewable electricity with a high capacity factor – meaning electricity is being produced almost all of the time – and thus the ability to economically produce renewable hydrogen, can take advantage of this by becoming production hubs for green, energy-intensive materials and chemicals that are currently made from fossil fuel hydrogen and needed in a decarbonised future.
These include ammonia for use as fertiliser, methanol for use as a chemical feedstock, and iron for steel-making.
Products produced locally using renewable hydrogen as a raw material, and then exported – such as steel – are also a better option than directly exporting hydrogen or its derivatives.
Above all, it is vital that countries deploy currently scarce renewable hydrogen to decarbonise their own existing fossil hydrogen industries, for uses needed in a net-zero future, before considering hydrogen exports.
Transport simply serves to amplify the energy efficiency challenges of renewable hydrogen, which, even if used directly where it is produced, has a cycle efficiency from production to end use of just 37%.
Footnotes
[1] A QMax LNG tanker contains 266,000 m3 of liquid natural gas (LNG), equivalent to 162,000,000 m3 of natural gas, with an energy content of about 6,500,000,000 MJ of heat energy. That much heat energy in the form of hydrogen would require 46,000 tonnes of hydrogen, which would have a volume about 15 times larger than the Q-Max tanker at 150 bar and room temperature.
[2] LNG, which is mostly liquid methane, has a raw heat energy density (joules of higher heating value per unit volume) over 2.4 times higher than liquefied hydrogen.
[3] Worse still for energy efficiency, it consumes this energy in the form of electricity rather than heat.
[4] While there is some potential for hydrogen boil-off to be used as a ship’s engine fuel while it is moving, this does not address the issue of boil-off during loading, unloading, and while the ship is sitting in port.
[5] This best-case calculation assumes a cycle efficiency of 29%, based on: electrolysis 70% lower heating value (LHV) efficiency x liquefaction 70% efficiency (30% loss) x powerplant/fuelcell best case 60% LHV efficiency = 29%.
[6] Ammonia can be “cracked” back into nitrogen and hydrogen again, but this requires the input of the same amount of energy, in the form of high temperature heat, to reverse the process used to make the ammonia. This heat must be made either by burning some of the ammonia or the hydrogen product, which further reduces its efficiency.
[7] Methanol, like ammonia, can be broken down by heating it over a catalyst to produce carbon monoxide and hydrogen again. Carbon monoxide can be reacted with water to produce more hydrogen and carbon dioxide. Like with ammonia, high temperature heat (derived by burning methanol or hydrogen) is required to supply the process, making the energy cycle efficiency even lower if hydrogen rather than heat is the desired output.
