Ships are regularly required to take in fuels for their propulsion. This process is called bunkering. Bunkering takes place in ports either from on-site facilities to the ship, from ship to ship (via bunkering vessels) or from truck to ship. Low greenhouse gas (GHG) emission fuels, or alternative fuels, are transport fuels or energy vectors with a low well-to-wheel GHG emission balance compared to traditional fuels. As various ports have bunker facilities for traditional fuels, a transition to alternative fuels requires additional bunkering facilities or the conversion of existing facilities.

Legislation is already in place in the European Union to enable the transition to alternative fuels bunkering and drive the demand. The EU Renewable Energy Directive III revision requires fuel suppliers to provide alternative fuels, while the Alternative Fuels Infrastructure Regulation revision requires ports to make relevant bunkering infrastructure in ports available. The FuelEU Maritime regulation proposed by the European Commission (EC) will require ships to progressively switch to alternative fuels to meet increasingly stringent fuel-GHG-intensity targets. Any green fuel supplies in ports will need to be accompanied by mandates on ships to use those green fuels on the journeys.

Some bunkering infrastructure can be converted for alternative fuels:

• Biofuels: All biofuels, including hydrotreated vegetable oils and fatty acid methyl esters, those produced through hydrothermal liquefaction (HTL) or pyrolysis, bio-liquified natural gases (LNG) and bio-liquefied petroleum gas (LPG), can be bunkered via current dedicated infrastructure.  Equipment upgrades are required for certain biofuels, such as acid-proofing for HTL and pyrolysis fuel oils. Dual bunkering, i.e. the use of separate tanks for traditional oil on one side and biofuels on the other, can be an efficient solution to enable the start of the transition towards alternative fuels (Dispert and Chase, 2021).
• Bio-methanol and bio-ethanol: Though methanol (produced today from natural gas or coal) is one of the top five chemical commodities shipped every year around the world, dedicated bunkering infrastructure for usage as a fuel is still very limited. Ship-to-ship bunkering can be performed via the same vessels as for hydrofluoroolefins and marine gas oils or by trucks and pumps built-in containers, which are easy to build (Methanol Institute, 2015; Bureau Veritas, 2021).
• Ammonia: Transfer and storage facilities for ammonia already exist in maritime ports, as ammonia is already transported for the fertiliser industry (Environmental Defense Fund, 2019). Bunkering infrastructure for ships is not yet in place, but transfers can be made by infrastructure similar to that used for LPG (Dispert and Chase, 2021).

A seeming contradiction, hydrogen requires higher storage volumes than oil fuels due to its low density. Storing hydrogen gas (GH2) requires high-pressure tanks, while storing liquid hydrogen (LH2) requires cryogenic temperatures in order to attain the boiling point of −252.9°C (Ryste and Wold, 2019). GH2 should be transferred to ships by direct compression or pressure differential, while LH2 should be bunkered using cryogenic pumps similar to those used for LNG bunkering. The direct exchange of container racks can be an alternative for hydrogen bunkering. None of these infrastructures has been developed yet (Dispert and Chase, 2021).

In order to select the priority positions for appropriate bunkering infrastructure, several factors should be considered:

• Prioritise large port infrastructure for important investments: Larger ports are more likely to provide adapted large bunkering infrastructure and to become international hubs for production and refuelling for alternative fuels.
• Design maritime routes of refuelling points adapted to vessels’ endurance range, i.e. the frequency needed for a vessel to bunker energy. A ship’s endurance depends on fuel density and storage systems. If a ship can attain weeks on LPG, methanol and liquid ammonia, it is reduced to days with liquid hydrogen and to hours for compressed hydrogen (Ryste and Wold, 2019).
• Encourage bunkering of local green energy production: On-site transformation systems need to be built to transform energy in an environmentally friendly way. Preference should be given to local facilities and resources, and the bunkering systems should be adapted to the local energy production infrastructure. However, renewable fuel supplies are unlikely to meet the rising global demand; the annual energy demand of just one large container ship can equal the demand of  100 000 gasoline-fuelled cars.
• Implement risk mitigation measures for secured transfer systems: European standards for methanol bunkering infrastructure have existed since June 2020. However, regulation does not exist yet for hydrogen and ammonia bunkering. (Dispert and Chase, 2021) A strong focus on security is crucial at every step of the transfer process. Hydrogen extensive inflammability and the high toxicity of ammonia require important investments in secure on-site infrastructure and vessels and risk-mitigating measures. (Ryste and Wold, 2019)

Action plans for port development and bunkering infrastructure need to include measures that support the Sustainable Development Goals. The UNESCAP has developed a summary of actions needed to attain each Goal, taking into consideration the users’ wellbeing and biodiversity preservation (UNESCAP, 2020). Another TCAD measure on “Support on-shore power and electric charging facilities in ports” advocates for connecting vessels to electricity supply from the shore in order to reduce mainland GHG emissions and improve users’ wellbeing.