Maritime Shipping: Overcoming the Challenges of the Clean Energy Transition 

Brian McCowan, Zondits staff, 8/8/2023

Zondits has reported extensively on alternative transportation fuels. That reporting has focused on land and air transportation. But with the recognition that almost all internationally traded goods, including fossil fuels such as gasoline, coal, and liquid natural gas, are transported by sea. The United Nations International Maritime Organization (IMO) estimates that maritime shipping has doubled over the last twenty years. Given that nearly all shipping is powered by diesel fuel, transitioning to cleaner fuels is a challenge that must be met if climate goals are to be realized. 

The IMO has taken on that challenge. The IMO’s Greenhouse Gas Strategy maps policy guidelines that promote international regulations affecting fuels, operations, and vessel design. The strategy is being revised this year with alternative fuels being a major focus. 

The Maritime Division of DNV has recently published the Maritime Forecast 2050, which as the title implies, forecasts the anticipated progress to be made in vessel design, including emissions reduction and the transition to cleaner fuels. 

Although the Forecast includes an assessment of the progress with vessel efficiency, including hull design, exhaust gas economizers, and advanced lubrication systems, we expect that alternative fuels hold the most interest for Zondits readers, and offer the highest potential positive impacts. 

The DNV Forecast reports that the transition to alternative fuels has begun. However, for long-distance shipping, the current transition is considered an interim step. This step is primarily a transition to Liquid Natural Gas (LNG). Although an improvement compared with diesel, LNG is not viewed as a long-term solution.  

Hydrogen and ammonia are the two fuels forecast as the future of deep-sea maritime shipping. Nuclear power, which has been used to power military vessels for decades is also gathering interest, although this comes with concerns for protecting the fuel from nefarious misuse. Rechargeable battery power is viewed as practical for short-sea (limited distance) operations, such as ferries and local shipping, where charging stations can be readily accessible. 


DNV forecasts that hydrogen will first play a role in short-sea shipping. Hydrogen’s relatively low energy density requires significant storage space on vessels, limiting its appeal for deep-sea operations. However, the world’s first combustion engine hydrogen-powered cargo ships and tugboats are expected to be introduced within the next few years.  

While some progress is being made in blending hydrogen with other fuels for internal combustion engines, the more promising path appears to be with fuel cells. Norwegian ferry operator Norled has recently conducted sea trials on a commercial ferry powered by two Ballard Power proton-exchange membrane hydrogen fuel cells. The company has received final approvals from the Norwegian Maritime Authority (NMA) and is expecting to place the vessel into service later this year. 

Of course, to be most beneficial to the environment, green hydrogen development must progress. The demand for green hydrogen for land-based uses will help drive that market. 


Ammonia is also considered a promising fuel source for both land and sea operations. Development however is currently at an immature stage. No internal combustion engines (ICEs) burning ammonia fuel are commercially available. But interest in the fuel has driven engine manufacturer research and development efforts which have been termed “promising.”  

According to Sustainable Carbon, ammonia can play a key role, alongside hydrogen, in reducing carbon emissions in heavy industry and transportation. Like hydrogen, it is currently produced by reforming fossil fuels; primarily natural gas. But ammonia can also be produced by chemically combining nitrogen and green hydrogen. It is this latter process that holds the most promise for ammonia as a carbon-free fuel. 

The DNV Forecast claims that ammonia burns free of CO2 emissions and is easier to store onboard than hydrogen, as its energy density is higher and it does not require cryogenic (very low temperature) storage. In order for ammonia fuel to be practical, development must solve nitrous oxide (NOx) pollution that results from ammonia fuel combustion. It is also anticipated that the fertilizer industry will compete for the supply of carbon-free ammonia. 

Early development of ammonia-fueled engines is underway, but like hydrogen, combustion is not the only way that ammonia energy can be harnessed. Solid oxide fuel cells (SOFCs) are able to use a variety of chemistries, including ammonia-based fuels. A demonstration project is currently under development that will retrofit an existing 300-foot Norwegian offshore supply ship with a 2 MW ammonia-driven SOFC system. The project is scheduled to set sail in 2024 for a 12-month test period. 


Methanol, also known as methyl-alcohol or wood alcohol is another fuel that shows promise for marine operations. Some methanol-carrying tankers have successfully been using dual-fuel (diesel and methanol) engines for several years, proving the concept. Now several engine manufacturers are developing both retrofit and new production options for methanol fuel. In addition to cargo ships and tankers, cruise ship companies are expressing interest in the fuel. As with ammonia and hydrogen, methanol can be used as a combustion fuel or as a fuel cell chemistry, but the practical application of methanol fuel cells is anticipated to be further down the road (or the shipping lane in this case) than methanol combustion engine technology. 

For each of these alternative fuels, maritime application development is not happening in a vacuum. Whether it be for combustion or fuel cell chemistry, each of these fuels has a parallel development path for terrestrial applications, mostly for heavy transport, but also for automobiles in some cases. 

Progress with alternative fuels reminds us that electrification is not the only tool in the tool chest to reduce emissions and combat climate change.  

Related – International Maritime Shipping Summit Sets Controversial New Climate Goals 

Delegates of the United Nations International Maritime Organization (IMO) met in London this July in a contentious set of negotiations that updated emissions goals for maritime shipping. With more than 90% of all global trade moving by ship, the impacts will be substantial. 

By the close of the summit, the IMO finalized an agreement to cut total annual emissions of greenhouse gases “by at least 20%, striving for 30% by 2030” and “by at least 70%, striving for 80%, by 2040.” The new goals replace the goals originally set in 2008 that strived to reduce emissions by at least 50% by 2050.  

The IMO termed the summit a success, calling the deal “historic,” adding that it “remains committed to reducing greenhouse gas emissions from international shipping and, as a matter of urgency, aims to phase them out as soon as possible.” Prior to the summit, the IMO was under intense pressure from both proponents of the more aggressive goals and opponents who were skeptical about transitioning away from diesel fuel so quickly. With over 100 delegate nations having a stake in the decisions, there was considerable doubt that aggressive goals could be adopted. 

Heading into the five-day summit, CNBC reported that some of the member nations were seeking 50% reductions by the end of this decade, while others were targeting 50% by 2040. But with many delegate nations urging conservative, or even no, updates to the goals established in 2008, the more aggressive targets were out of reach.  

John Maggs, president of the Clean Shipping Coalition and a senior policy advisor at the Seas at Risk environmental NGO, told CNBC, prior to the summit, that the potential was there for a landmark agreement, but that the shipping sector has been “extremely reluctant” to adopt ambitious climate measures. Aoife O’Leary from Opportunity Green, a non-profit organization and observer at the IMO, told reporters that negotiating interim goals is more difficult than establishing 2050 targets. “Bringing emissions down immediately and quite drastically is what is needed — and that is just much more controversial because then countries see that they have to actually do something.”  

Following the summit, Maggs expressed disappointment in the outcome, stating that far more could have been accomplished and termed the deal a “wish and a prayer agreement. The level of ambition agreed to is far short of what is needed to be sure of keeping global heating below 1.5 Celsius, and the language seemingly contrived to be vague and non-committal.” He contends that Pacific nations were in favor of more ambitious targets but faced opposition from China and other large exporters of goods. 

As the DNV Forecast reports (see previous article) alternative fuels are in development, but all face significant technical challenges, and once those are met, there will remain a lag to retrofit and/or replace ships. Local “short-sea” shipping can take advantage of electrification with port-based charging systems, but deep-sea shipping must rely on onboard fuels. Hydrogen, methanol, and ammonia all hold promise as both combustion fuels and fuel cell chemistries. 

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