To fulfil the IMO goals and take the maritime industry to zero-emissions, we need a new generation of fuels. Fuels that result in vessels producing very low or no GHG emissions from well to wake.

In general, this means moving from fossil to non-fossil fuels, produced with renewable or zero carbon energy sources. These fall into roughly three broad categories:

  • ‘Blue’ fuels from reformed natural gas with CCS. 
  • Biofuels from sustainable bioenergy sources (Bio-gas, bio-diesel)
  • Electrofuels from renewable electricity, with non-fossil carbon, or nitrogen (SNG, e-ammonia, e-methanol)

The future fuel supply for shipping will rely on availability and price of these energy sources

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Some of these types of fuels, biogas for example, are already in use, for others primarily non-zero carbon options are in testing or soon to be operational in demonstration projects. The world’s first liquid hydrogen-powered ferry has been delivered. 

Significant investment is needed in coming decades to enable the transition to carbon-neutral shipping.

Current IMO regulations only address onboard tank-to-propeller CO2 emissions from fossil fuels. However, the IMO is working on guidelines to determine lifecycle CO2 and GHG emission factors for all types of fuels, including biofuels and electrofuels.

The transition from fossil fuels to carbon-neutral fuels, will have to coincide with a corresponding development in onboard fuel technology, while onboard CCS technology enabling continued use of fossil fuels may become an alternative for some ships.

Figure: Estimated maturation timelines for energy converters, onboard CCS technologies, and corresponding safety regulations for onboard use.

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The timeline is our best estimate for when the onboard engine and fuel systems can be expected to be available for use on board (actual availability of fuel is not included as a limitation in the shown timeline). 

First demonstration projects (red colour): The technology is ready for demonstration on the ship, and the primary intention will be further development and maturation. Typically, a risk-based approach will address regulatory and safety challenges for the installations. This could require an extensive and costly process of design, approval, and bringing the technology on board.

  Ammonia as ship fuel

Ammonia as ship fuel

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  Hydrogen as ship fuel

Hydrogen as ship fuel

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Benefits and technical considerations by fuel type

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Benefits and technical considerations

Benefits and technical considerations


Green ammonia (produced by electrolysis powered by renewables), or blue ammonia, (produced from byproducts of current fossil fuel production) are promising sources of zero-carbon fuel but will require significant investments in production capacity from renewables and bunkering infrastructure to replace FO.

Benefits of ammonia as fuel:

  • Apart from being a potential zero-carbon fuel, ammonia is cheaper that batteries and easier to store than hydrogen or LNG, and is nearly identical to LPG at low pressure under ambient conditions. 

Technical considerations

  • Ammonia is a toxic and corrosive substance, and emissions from combusted ammonia may contain a high amount of nitrous oxide (N2O), a powerful greenhouse gas. 
  • At present, the technology to clean ammonia exhaust is still being refined and the use of this fuel on existing ships will require engine modifications and the installation of new fuel tanks and safety systems. Such engines are expected to be commercially available in 2024.
  • However, some owners are already building ships that are “ammonia ready”, equipped with stainless steel tanks to manage corrosion and engines that can handle ammonia as a ‘drop in’ fuel. 
  • It should also be noted that ammonia-fuelled engines will require a certain amount conventional pilot fuel. 
  • Moreover, due to the low volumetric energy of ammonia, it may be more practical in many cases to use a combination of ammonia and fuel oil.
Benefits and technical considerations

Benefits and technical considerations


Hydrogen from electrolysis and renewable energy is the basic building block for a range of fuels. Hydrogen can be used directly as compressed or liquefied gas. Other technologies for storing hydrogen are also being developed.

Benefits of hydrogen as fuel:

  • If produced using renewable energy, hydrogen does not result in any CO2 emissions, making it one of the cleanest alternative fuel options. 
  • While fuel cells are considered the key technology for hydrogen, other applications are being studied such as internal combustion engines that have promising marine applications. 

Technical considerations:  

  • Storage of hydrogen requires approximately six to ten times more space than conventional FO, depending on the technology selected. 
  • Liquefied hydrogen is at the lower end of this range, at the expense of very low temperatures (-253oC), which requires appropriate materials. 
  • Cost of the storage systems is another limiting factor, combined with the lack of infrastructure for supplying hydrogen to shipping. 
  • Therefore, in the short- to medium-term future, hydrogen is mainly a viable option for coastal vessels that can secure local fuel supply, especially if supported by government financing.
Benefits and technical considerations

Benefits and technical considerations

Fuel cells

Fuel cells convert the chemical energy contained in a fuel directly into electrical and thermal energy through electrochemical oxidation, enabling efficiencies of up to 60 per cent, depending on the type of fuel cell and fuel used.  


  • Due to the high efficiency of fuel cells, a further reduction of CO2 emissions is possible when using hydrocarbon-based fuels like natural gas or methanol. 
  • Fuel cells minimize vibration and noise emissions, a major drawback of combustion engines, and may require less maintenance than conventional combustion engines and turbines.

Technical considerations

  • The main components of a fuel cell power system are the fuel cells themselves, so it should be noted that the lifetime of fuel cell systems and reformer units has not yet been shown to be satisfactory. 
  • Also, it will be necessary to integrate additional safety and interface components to build a complete ship system that meets regulatory requirements. 
  • Finally, fuel cells perform better under constant loads, so may require supplemental batteries to even out consumption.

    Need more detailed information and guidance?

    Dive in deeper:


    Alternative Fuels Online Conference (November, 2022)

    Watch the video recording – together with a group of experts, we discussed the latest findings on alternative and emerging fuels


    Ammonia as a marine fuel paper

    This paper examines the potential use of ammonia in shipping and other industries and considers what it would take for ammonia to be adopted at scale as a maritime fuel


    Handbook for Hydrogen-fuelled Vessels

    The 1st Edition of the ‘Handbook for Hydrogen-fuelled Vessels’ offers a road map towards safe hydrogen operations using fuel cells


    New DNV Fuel Ready and Gas fuelled ammonia class notations provide maximum flexibility to tackle shipping’s carbon curve

    Read the news (July 2021)


    Five lessons to learn on hydrogen as ship fuel

    Explore the key takeaways of the DNV-led MarHySafe project in our Maritime Impact article (July 2021)


    The future is hybrid – A guide to use of batteries in shipping

    Recent developments in battery technology and ship electrification hold significant promise for a more efficient use of energy, energy recovery and the use of renewables.