Cruise ships often can accommodate thousands of passengers, making them the equivalent of floating towns that present major electricity loads that currently is met most often through diesel generators. Energy efficiency and air emissions issues can result. Those challenges led Swiss-based researcher to propose a fuel cell-based system to reduce the carbon footprint and energy consumption of cruise ships.

“It’s easier to reduce the energy consumption of a merchant ship, because almost all of the energy is used for propulsion, unlike a cruise ship, which has various energy demands,” says Francesco Baldi, a researcher in EPFL’s Industrial Process and Energy Systems Engineering Group. His research, done in collaboration with Aalot University in Finland, focused on cutting CO 2 emissions by optimizing systems and even considering the boat's design to improve efficiency.

As veritable floating hotels accommodating thousands of passengers, cruise ships use a great deal of energy for heating, electricity, air conditioning and other loads. In evaluating the potential of using fuel cells onboard, the researchers examined the special challenges that can come about when sailing for thousands of kilometers at a time.

“You need to store enough energy on board without taking up too much space, Baldi says. He contends that hydrogen fuel cells are not suitable, because storing enough energy to travel long distances would take up a huge amount of space, perhaps as much as one third of the ship’s capacity. "That is not realistic for a cruise ship,” Baldi says.

Instead, solid oxide fuel cells (SOFCs) emerged as a potentially good fit for ships. SOFCs use a solid oxide material as the electrolyte to conduct negative oxygen ions from the cathode to the anode. They operate at very high temperatures, typically between 500 and 1,000 °C. That means they do not require platinum catalyst material, which can be expensive, and are less vulnerable to carbon monoxide catalyst poisoning, although sulfur poisoning can be a problem.

In practice, SOFCs can be used as auxiliary power units. They also can be used as stationary power generation sources with outputs generally from 100 W to 2 MW. Their high operating temperature make them suitable candidates for applications with heat engine energy recovery devices or combined heat and power.

Baldi’s idea, then, was to use a system to transform unused energy generated by the SOFC cells into hydrogen, which could be stored. The resulting fuel cells, customized for ships, could generate either electricity to be consumed on board or hydrogen to be stored for later use.

Baldi says that one advantage of fuel cells is that they only produce CO 2 and water, unlike a diesel engine which also produces other pollutants, such as nitrogen oxides and particulate matter.

Fuel cells also generate power though a chemical reaction. This can make them more environmentally friendly than fossil fuels and also more efficient: fuel cells developed at EPFL reportedly have achieved 75% efficiency. That level is higher than what typically can be achieved for a highly efficient diesel engine.

One downside is that the fuel cells cost on the order of 10 times as much to produce as a traditional engine.

Baldi says that he sees the potential for Europe, where many cruise liners are built, to take on part of the cost in order to incentivize equipping ships with fuel cells. His suggested approach would mirror incentives for renewable energy resources such as solar panels and could help cruise ships cut their pollution in the future.