SOFCs are fuel-flexible, allowing for use of ammonia, hydrogen, LNG, LPG, methanol, ethanol and more, and use relatively low cost and abundant materials, creating potential for greater cost reduction than PEMFC at high volumes, the report states.

Moreover SOFCs can achieve the highest efficiencies of >80% when recycling heat, due to their high temperature operation of 800C. This results in less ammonia or hydrogen consumption per mile compared to an ammonia combustion engine or PEMFC, respectively.

Long start-up times and poor dynamic response are often cited as SOFC drawbacks, but this is manageable if paired with a battery system and a use-case of long voyages out at sea.

“The main disadvantage is simply that SOFC technology and the green ammonia as fuel is not readily available – few FC suppliers exist, creating a bottleneck and driving costs, and demonstrator projects for green ammonia are in their infancy,” it notes.

The 2MW SOFC system being delivered to the Viking Energy in 2023 will make it the first ammonia SOFC vessel in the world, and it will run on green ammonia from Yara.

Compared with hydrogen, ammonia has a “head start”, since at –33.5C, ammonia is easier and less energy-intensive to liquify and store than LNG and hydrogen at –161C and –253C, respectively.

It shows that while some bunker infrastructure facilities are currently in operation for ammonia, none yet exist for hydrogen.

While hydrogen proton exchange membrane fuel cells (PEMFCs) are the most commercially available and focus of most suppliers, their “achilles heel” is hydrogen, which has a volumetric energy density of 8.5GJ/m3 as a liquid (–253C), with the bar set by diesel at 33GJ/m3 (STP).

Per ship mile, liquid hydrogen, therefore, requires much more storage space, while reaching/ maintaining –253C is both difficult and energy intensive. Nevertheless, maritime PEMFC markets are growing rapidly today, particularly in inland and coastal sectors where ‘opportunity refueling’ has more potential, according to the report.

Overall, batteries and hydrogen and ammonia fuel cells have high potential to create long-term pathways to zero emissions.

“It is easy to envisage a future with broader adoption of hydrogen PEMFC and batteries in the mid-term and ammonia SOFC adoption in the long term. What is clear is that lowering emissions in the maritime sector will continue to rely on tremendous investment, financial support, and policy drivers from both the public and private sectors.”