Green shipping: Tomorrow’s zero emission fuels

David Griffiths, Claims Executive of UK P&I Club states that, to enable decarbonisation of shipping by 2050, in alignment with the Paris Agreement temperature goals, zero emission fuels need to make up 5% of international shipping fuels and 15% of domestic shipping fuels by 2030.

What is a zero emission fuel?

The term “zero emissions” has become common parlance to describe zero carbon emitting fuels, carbon being the main source of GHG emissions in the shipping industry. However, other GHGs such as methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3), occur both upstream in energy production and in ship operation must also be considered.

A brief word on the calculation of emissions

It is crucial, when assessing a fuel’s emission credentials, to understand what emissions are included in the calculation. The more complete approach is to consider emissions on a well-to-wake (WtW) basis, as this allows for the accounting of GHG emissions released from extraction or production and distribution to final use onboard the ship.

It is not easy, however, for owners or operators to obtain an accurate figure for the upstream GHG emissions and many of the shipping industry’s regulations are currently based on a tank-to-wake (TtW) basis (for example, EU MRV Regulations, IMO Data Collection System or CII) that do not include upstream GHG emissions.

A WtW approach is important as a fuel’s sustainability ranking may be influenced by several factors and parameters. For example, a fuel produced with renewable energy but transported to its final use point using fossil fuels may have a higher WtW emissions profile than a more GHG-heavy fuel produced and consumed locally.

To achieve decarbonisation in WtW terms, and the aforementioned Paris-aligned goals, it will take far-reaching co-operation from across the industry, including upstream energy and chemical suppliers to authorities and financiers.

Hydrogen (H2)

Once more, when we talk about hydrogen in this article, we are referring to green hydrogen, i.e. hydrogen produced from renewable electricity via electrolysis.

Hydrogen is another promising option in the industry’s push to zero emissions shipping. Scaled-up hydrogen production has the potential to offer clean energy, producing no emissions except water vapour. However, it is not without its challenges, chiefly surrounding safety, infrastructure, technology and scaling up hydrogen fuel production.

Whilst there are currently vessels using hydrogen as a fuel, production is largely fossil fuel based. As such, it comes with the same issues around its WtT emissions profile as described for ammonia, above. This means that although the TtW emissions profile of the ship can boast ‘zero emissions’, the WtW profile would show considerable GHG emissions.

Production and Infrastructure

Hydrogen is the most abundant element on earth but is rarely found in its pure form (H2). Currently, the production of hydrogen emits 830 million metric tons of CO2 globally each year. For context, that’s more than the total CO2 emissions of Germany in 2017.

The large-scale access to renewable electricity is currently a key barrier in attempts to scale up production of green hydrogen, and to keep it financially competitive with traditional fuels. It is unlikely that this will be possible without governmental and supranational support for research and development. Similarly, large-scale investment in bunkering facilities and terminal networks will be needed.


With the use of fuel cells, hydrogen is envisioned to be well-suited for inland navigation vessels and shorter voyages. On larger vessels, it is envisioned for powering auxiliary systems, with more research needed to see if hydrogen can be scaled up to be used in a ship’s primary engine for propulsion.


The main concerns surrounding hydrogen are over its safety as a fuel. It is extremely flammable and explosive, burning with an invisible flame at 2,000°C.

Onboard storage and energy density also present issues. When compared with traditional fuel oils (HSFO – 37.3 MJ/litre, and MGO – 36.6 MJ/litre), hydrogen lags behind, producing a volumetric energy density of only 4.8 MJ/litre for pure hydrogen, or 8.5 to 9.2 MJ/litre when liquefied. This requires significant onboard storage space, at a trade-off with cargo, or very frequent bunkering stops. This low energy density led DNV to rule out pure hydrogen as a fuel for intercontinental shipping in its Maritime Forecast to 2050, instead forecasting that the most likely use will be in shorter sea shipping voyages.


The industry’s choice of zero emission fuel will depend on various factors, including the specific vessel type, operational requirements, availability of port and bunkering infrastructure, regional considerations, and human factors. As set out above, different fuels may be more suitable for specific segments of the maritime industry, such as shorter sea shipping voyages or deep-sea vessels.

It’s important to note that the adoption of zero emission fuels for ships will require significant technological advancements, infrastructure development, supportive policies and industry collaboration.  A further challenge will be to ensure that the maritime industry can recruit and train the people needed to implement and operate these new technologies.  The timeline for the widespread adoption of these fuels by maritime stakeholders will depend on the pace of innovation and the regulatory frameworks implemented to drive their adoption.

Above article has been initially published in UK P&I Club and is reproduced here with authors’ kind permission.

The views presented are only those of the author and do not necessarily reflect those of SAFETY4SEA and are for information sharing and discussion purposes only.

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