Design Considerations for Fuel Cell Systems Employed in Long-Endurance Autonomous Small-Sized Subsea Robots

Autonomous robots have the potential to significantly decrease operational costs associated with human operations and increase safety through the reduction of human errors. With the advancement in robotics today, many more are considering using autonomous subsea robots in various industries, such as fish farming, subsea oil and gas, ocean renewables and even subsea mineral mining. The ability to have long endurance, i.e., to operate for long periods without refuelling, is crucial to reap the benefits of robot autonomy better. Fuel cells, with their significantly higher energy storage capacity than lithium batteries, offer an attractive option to provide the long endurance required. Fuel cells have been successfully used in various land-based applications, such as cars and trains. However, to date, fuel cells have not been very much employed in underwater vehicles. Several subsea-related challenges arise when fuel cells are employed in subsea robots, which must be addressed. These include (i) underwater storage of hydrogen and oxygen, (ii) subsea-ambient environmental issues such as large hydrostatic pressures and cold ambient underwater conditions, (iii) dynamic manoeuvring actions by the robot that can cause large trim motions and (iv) fuel cell operations in a sealed container and with pure oxygen. This paper will discuss the most important design conditions that can arise when employing fuel cell systems for autonomous small-sized subsea robots with long endurance requirements.