Alkaline electrolysis is already a proven technology on land, with a high maturity level and good economic performance. However, at sea, little is known about its economic performance toward hydrogen production. Alkaline electrolysis units operate with purified water to split its molecules into hydrogen and oxygen. Purified water, and especially that sourced from the sea, has a variable cost that ultimately depends on its quality. However, the impurities present in that purified water have a deleterious effect on the electrolyte of alkaline electrolysis units that cause them to drop their energy efficiency. This, in turn, implies a source of economic losses resulting from the cost of electricity. In addition, at sea, there are various options regarding the electrolyte management, of which the cost depends on various factors. All these factors ultimately impact on the levelized cost of the produced hydrogen. This article aims to shed some light on the economic performance of alkaline electrolysis units operating under sea conditions, highlighting the knowledge gaps in the literature and initiating a debate in the field.

Due to the more stringent regulations on pollutant and greenhouse gas emissions in the maritime transport sector, solutions are being sought to reduce or avoid the emissions generated during the operation of ships. The onboard installation of hydrogen-fuelled fuel cells is a solution respectful with the environment and the marine ecosystem through which ships navigate. In this work, the design of a wellboat and its power plant based on fuel cells fed with hydrogen and hybridised with batteries is conducted, making it a zero-emissions ship that can navigate Emission Control Areas (ECAs). The fuel cells used are polymer electrolyte membrane fuel cells (PEMFCs), and the hydrogen they consume is stored in tanks pressurised at 35 MPa, grouping these tanks into three standard containers (Twenty-Foot Equivalent Units) installed on an exposed deck. The electrical and propulsion needs of the ship are covered by the installed power plant, providing an average power of 1266 kW and a peak power of 2624 kW, making it possible to avoid the emission of 10.8 t of CO₂, 195 kg of NO_x and 9 kg of SO_x per 14 h mission.