Efficient, always-on fuel cells could be the centre of an innovative hybrid power arrangement that would be ideal for cruise ships, according to a new study.
The project, by researchers at the École Polytechnique Fédérale de Lausanne, has proposed a hybrid power system centred on solid oxide fuel cells (SOFC) running at a constant load. Batteries would store any excess electricity generated when electricity demand is lower than the SOFC output, while syngas produced by the cells would be processed to hydrogen that could fuel auxiliary proton exchange membrane (PEM) fuel cells at peak power demand.
SOFCs developed by EPFL have achieved 75% efficiency, compare to just over 50% for the most efficient engines, but can take 20 hours to reach full capacity. They can be used to produce a combination of electricity, hydrogen-rich synthesis gas, and high-temperature heat. This heat would be used in a purifying process – consisting of a two-stage water-gas shift reactor and a pressure swing absorption unit - to generate hydrogen. The only by-products would be CO2 and water.
EPFL researcher Francesco Baldi said that the hybrid power system would suit cruise ships because of their diverse power demands, compared to the mainly propulsive power needed for merchant vessels. SOFCs can run on a wide variety of gas and liquid fuels, while PEMs use hydrogen fuel, which would require vast storage space onboard if used as the main power source.
The newly developed fuel cells cost ten times as much to produce as a conventional engine, with total lifecycle cost around 20-30% higher. Mr Baldi noted that the price will drop as demand grows and suggested that Europe – a key cruise shipbuilding market – could incentivise their use.
The study offers an alternative perspective on the future use of fuel cells in shipping. To date, most pilot applications have focused on hydrogen-fuelled PEM fuel cells.