The great contenders: The case for hydrogen and ammonia as bunker fuels

The debate around the use of hydrogen and ammonia as future marine fuels is growing, but we still need answers to questions on issues such as availability, operational feasibility and cost. Mark Williams takes a closer look.

Theoretically both hydrogen and ammonia can be used as marine fuels. But there are several issues to sort out. Firstly – just how can they be used as fuel either on existing ships or on newbuildings? Secondly, is there enough of each to use as fuel? Thirdly, is there a global infrastructure to use them as fuel? Fourthly, what will they cost?

Can hydrogen be used as a fuel?

Hydrogen has been identified as a key energy source of the future for most applications where electrification is either not viable or too expensive.

Without hydrogen, the EU says it will not achieve its decarbonisation goals on time. As such, says the European Commission, ‘the hydrogen sector is primed to play a key role as an enabler of sector integration and a systemic role in the transition to renewable sources by providing a mechanism to flexibly transfer energy across sectors, time and place.’

Hydrogen could be mixed with LNG (up to a 20/80 Hydrogen / LNG mix) in some current LNG engines. If green hydrogen and bio-LNG were used, a ship using current technology could operate as zero-carbon.  Hydrogen itself is being used in fuel cells in a number of smaller vessels around the world (including ironically some Chinese coal barges) but its use on land as a directly combusted fuel in road vehicles shows that it could be scaled up to be used in ships.

The International Council on Clean Transportation (ICCT) has previously suggested that 99% of trans-Pacific container ship voyages made in 2015 could have been powered by hydrogen and fuel cells. Their study showed that only 5% of cargo space would be lost to fuel storage in 57% of voyages, with 43% of voyages being able to go ahead with no loss of cargo space to fuel storage. Many of the 57% of voyages losing cargo space could add a fuel stop in order to sail with smaller tankers. 

Royal Dutch Shell, a leading proponent of LNG as a marine fuel, has said that hydrogen is ‘Advantaged over other potential zero-emissions fuels for shipping.’   In Norway, where all in-fjord shipping must be emission-free by 2026, Ulstein is working on hydrogen-powered offshore support and wind turbine installation vessels. In Belgium, CMB built its first hydrogen powered shuttle boat in 2017; it is now working as a ferry in Japan.  The Global Maritime Forum mapped out 66 zero-emission shipping projects and found that seven involve the direct combustion of hydrogen as fuel, with another 12 investigating hydrogen carriers like ammonia.

Can ammonia be used as a fuel?

Ammonia can be used as a liquid fuel or in a fuel cell because it is a hydrogen carrier. Fossil fuels work through the oxidisation of carbon, which releases energy and oxides of carbon (CO and CO2).  Hydrogen fuels work through the oxidisation of hydrogen, releasing energy and H2O.  Hydrogen is readily combustible but, being the lightest element in the universe, is hard to isolate, store and distribute. Isolation has traditionally been achieved by reforming natural gas but this fossil fuel source releases CO2.  Hydrogen can be produced by electrolysis of water, and if the electricity is sourced renewably, then the hydrogen can be produced with zero CO2 output.

Ammonia can be used as a hydrogen carrier.  But it can also be combusted as a fuel by itself, making the chemical step of cracking the ammonia into hydrogen and nitrogen redundant.   However, ignition fuels like hydrogen, alcohol or diesel are required to burn ammonia. When ammonia is burned in an engine, its exhaust should be comprised of pure nitrogen and water, both of which can be released into the atmosphere at the point of use quite safely. However, incomplete burning could result in oxides of nitrogen (NOx) being produced.

In May 2020, Doug MacFarlane, a chemist at Monash University who heads the Australian Research Council Centre of Excellence for Electromaterials Science, and colleagues, published ‘A Roadmap to the Ammonia Economy’ which postulated renewably-sourced ammonia replacing fossil fuels in every application by 2050.[i]  MacFarlane and his team write that  ‘For bulk transport by sea, or pipeline, a liquefied form of energy storage is almost certainly the preferred option, and this throws the spotlight onto processes that can generate high energy density liquid fuels from renewables, in a cost-effective and sustainable manner. A breakthrough in this regard would open up a range of very attractive renewable energy futures.’

MacFarlane notes that ammonia has emerged as the ‘increasingly compelling candidate as the renewable energy sourced fuel of the future.’ He also notes the advantage of ammonia over pure hydrogen in the technology of shipping and pipeline transfer of ammonia is well established in the world’s existing energy infrastructure.

‘Possibly the first major market for ammonia as a fuel will be for maritime transportation….We envisage … the production of renewable ammonia for other transportable energy storage applications … will begin to significantly replace fossil fuels in the 2040s.’  The study concludes: ‘ammonia clearly has the potential to become the dominant form of transportable renewable energy in the future, displacing fossil fuels from all but the most demanding of applications. It will sit alongside other forms of chemical energy storage, including hydrogen and renewable carbon-derived fuels….the important distinguishing feature of ammonia is its well-established ease of global transportation by bulk carrier and pipeline.’

Can hydrogen and ammonia engines be retrofitted or is this for newbuildings only?

If these zero carbon fuels can be used in retrofitted engines, shipping will save billions of dollars on building a new fleet of ships.

Ausilio Bauen of e4Tech, a strategy consulting firm working with governments and private sector corporates looking at options to decarbonise says, ‘efficiency won’t get you to net zero unless you go for [carbon] offsets, but is that socially acceptable?’ He says that industries which won’t tackle their own decarbonisation will inevitably face pressure from their investors.  So options like hydrogen and ammonia retrofits look attractive, but, ‘once you get into hydrogen and ammonia, then the ship retrofit cost gets higher, as do infrastructure costs.’  Bauen adds that there is ‘big hype around ammonia at the moment as an energy carrier but big challenges from a toxicity point of view. The containment issues are very important and at the moment slightly overlooked.’

Proponents of ammonia might demur. There is acknowledged anxiety among the general public about the toxicity of ammonia, though the toxicity of fumes from fossil fuel burning generally goes unchallenged. In part that anxiety stems from ignorance; presumably once people get used to ammonia it will go un-noticed.  Proponents of ammonia as a fuel point to its use in road transport Belgium in the 1940s.

At low concentrations of five parts per million (ppm) ammonia is noticeable from its odour. But toxicity levels are more like 25 ppm and ‘immediate danger to life’ begins at 300 ppm.  And unlike gasoline, ammonia is not carcinogenic.  The risks associated with accidental release of ammonia were examined in 2005 by the Danish Riso National Laboratory which put them on a par with LPG, a widely accepted chemical in use around the world.

Still, ship owners and the wider public remain concerned about the effects on the crew and environment of even relatively minor spills. They might take comfort from a 2019 study by Niels de Vries of Delft University. This study investigated 61 modes of failure in ammonia-powered marine transport. It found that, once proper technology and mitigation measures are enacted, unsafe emission risks can be minimised.

In 2019 Maersk reported that its joint research with Lloyd’s Register showed that alcohol, biomethane and ammonia are best-positioned to reach net zero emissions in shipping. LR CEO Alistair Marsh said at the time that ship owners ‘must invest for fuel flexibility…this transition presents more of an operating expenditure than capital expenditure challenge.’

As we have recently reported, Maersk CEO Soren Skou sees the switch to fuels like alcohol and ammonia as a big retrofit opportunity, though Maersk was ‘still working and figuring out what is the best fuel for us and for the future.’  He said ‘it’s not like we’re seeing a huge mountain of CAPEX come up at us because of engine technology if we end up where we think we will end up – with ammonia, with methanol , or something like that as a future fuel.”

Skou is in good company.  Svein Tore Holsether, CEO of Yara International, says that ammonia is the ‘most promising’ non-carbon fuel for shipping. And in the last few months, MAN Energy Solutions unveiled a retrofit package for its ammonia fuelled marine engine. ABS is teaming up with Singapore’s Nanyang Technological University (NTU) and the Ammonia Safety and Training Institute (ASTI) on a study to assess ammonia’s potential for a marine fuel and explore ‘the supply, bunkering, and safety challenges’. The study, entitled ‘Ammonia as a Marine Fuel in Singapore – Supply Chain, Bunker Safety, and Potential Issues’, will look at safety protocols and possible gaps in the supply chain of ammonia as a marine fuel, specifically bunkering for marine vessels. In October 2020, ABS published its white paper on ammonia as a marine fuel. Other class societies have ammonia research programmes and publications.

The momentum is undeniable and goes as far as ammonia powered ships in the dockyards’ orderbooks. Avin International of Greece has converted a newbuilding order into what it says is the first ammonia-ready vessel (a Suezmax oil tanker) in the world classed by ABS while Euronav of Belgium has just ordered two dual-fuel ammonia-capable Suezmax tankers from Daehan in South Korea. Euronav as a public company has investors to answer to, Avin as a private company may be taking more of a gamble with first-user advantage.

OK, but is there enough of either Hydrogen or Ammonia to use as fuel?

Hydrogen production is in the range of 75 million tonnes a year, of which around 38 million tonnes is used in the refining industry (for reformation of gasoline constituents), around 32 million tonnes is used in the manufacture of ammonia and the remainder for a variety of purposes including a small amount used as a fuel. 

Most hydrogen is made by reforming natural gas, and this accounts for around 6% of annual natural gas consumption. Less than 1% of hydrogen is currently produced using renewable methods such as using renewable electricity to electrolyse water, separating the hydrogen and oxygen. According to the IEA, ‘Producing all of today’s dedicated hydrogen output from electricity would result in an electricity demand of 3,600 TWh, more than the total annual electricity generation of the European Union.’ So if we want to build a hydrogen economy including a hydrogen powered oceangoing cargo fleet, then we need first to build up a global infrastructure of renewable energy generation.

This is of course ongoing. Europe leads the way but the US and China have evolving offshore and onshore wind markets, while recent research shows that around one third of the African offshore would be ideal for wind-powered electricity generation. Meanwhile sunshine-rich Saharan nations and Australia are already building up their solar powered hydrogen production and electricity generation. Japan has recently received its first liquefied hydrogen cargo from a joint venture in Victoria, Australia. Floating Power-to-X plants have been well covered elsewhere on

Hydrogen can also be produced biologically by fermentation of biowaste or by the digestive processes of certain algae. Pyrolysis of natural gas in the presence of a catalyst can also cut the GHG emissions of hydrogen production. Many research programmes are active globally to isolate H2 via these various means.

Ammonia has been produced commercially since 1913 when BASF developed German scientist Fritz Haber’s process for combining Nitrogen and Hydrogen over an iron catalyst to the point where 30 tonnes a day of ammonia could be produced.

By the year 2000, global ammonia production was around 130 million tonnes annually. Global production in 2020 was around 175 million tonnes with a market value of between $85 and 100 billion a year.  Counting known ammonia plant investments and announcements suggests that production could exceed 200 million tonnes by 2030.

Nearly 90% of all manufactured ammonia is used in the production of fertiliser with most of the rest used to make formaldehyde and other industrial chemicals. The top producers are China, Russia, India and the US, accounting between them for more than half of global production.  These days most ammonia is produced by the steam reformation of natural gas, though China uses a method of coal-gasification as a source material.

For ammonia to be a carbon-neutral chemical, it has to be produced using renewables. Fortunately, as the costs of producing solar and wind electricity have fallen by 80% and 50% respectively this century, there is now a realistic prospect of making ammonia using electrochemical processes driven by renewable electricity. 

Why not just make hydrogen then?

Because once isolated, hydrogen is also hard to store and distribute. It has to be chilled to -253oC, which is technically feasible but expensive.  Ammonia liquefies at an easier-to-achieve -33oC. And with an established global infrastructure including a fleet of refrigerated LPG tankers that can carry ammonia, there is an infrastructure to build out, rather than to build from scratch as would be required with hydrogen.

Macfarlane again: ‘Entirely electrochemical, renewable-powered Generation 3 ammonia synthesis technology is expected to enter the market at scale toward the end of the [current] decade. There is little doubt that Gen 3 will rapidly become the preferred technology as soon as it…becomes an efficient industrial process.’

And even hydrogen’s most zealous advocates admit there is an infrastructure challenge.  A Hydrogen Europe press release from 16 December 2020 says, ‘The deployment of clean hydrogen at large scale is contingent on the availability of an appropriate infrastructure to transport hydrogen from its point of production to demand centres locally, regionally and internationally.’

There is also the cost element. DNV-GL says that green hydrogen costs around four to eight times the price of VLSFO.  The experience of solar and wind power tells us that electrochemical production costs for hydrogen will fall, but the infrastructure costs for its use as a marine fuel have to be added back on.

For the last five years, global ammonia prices has averaged between $10 and $20 per gigajoule, while green ammonia production has been priced by various studies at between $20 and $35 per gigajoule. It’s not easy to compare the cost of ammonia as a marine fuel with the cost of VLSFO but, as with hydrogen, the cost of green ammonia is going to be higher until much greater renewable electricity infrastructure comes online. And the cost of ammonia as a marine fuel still has to incorporate the bunkering infrastructure changes.

To be continued….

Ammonia and hydrogen probably represent two of the three leading candidates for future liquid marine fuels, along with bio-LNG and perhaps synthetic LNG.  Commercial investment has been rapidly growing to the point where ammonia-capable ships are now on order at shipyards. 

Shipowners considering ammonia or hydrogen as their zero-carbon liquid fuel of choice will have to mull the investment cost for the retrofit or newbuilding, the operational cost including fuel prices, availability and quality, the available bunkering infrastructure, health and safety considerations, climate impacts and – most worryingly – possible upcoming legislation. 

The technical and commercial potentials are condensing into view. What remains is a clear steer from legislators about what marine fuels they will allow, or what other regime they might chose for imposing decarbonisation on the fleet, such as carbon pricing.  For now, there is no conclusion, only the cliff-hanger ending, ‘To be continued….’

[i] MacFarlane et al., A Roadmap to the Ammonia Economy, Joule (2020),

Mark Williams

Mark Williams