Currently, the energy transition is a topic for discussion and many organizations are taking measures to reduce the effects of climate change. Armed forces are exempt of these new regulations on the grounds of national security, but some have already started taking steps to reduce the amount of harmful emissions. Due to the high efficiency and advantages that fuel cells present, the aim of this master's thesis is to study their feasibility on board of a naval surface vessel, testing it in a concept design.
This report consists of two main parts. The first part tries to find the most suitable combination of naval surface vessel, type of fuel cell, and type of hydrogen carrier. It is concluded that the types of naval surface vessels that could benefit the most from the use of fuel cells are frigates and mine warfare vessels, in order to reduce their acoustic signatures; and offshore patrol vessels (OPVs), due to their constant base load, because it is a type of ship that is mostly cruising or patrolling.
Solid oxide fuel cells (SOFCs) are here considered to be the most promising type of fuel cells for naval surface vessels. This is not only because of their high efficiency, but also due to their ability to internally reform hydrogen carriers, making them more versatile. Other fuels than pure hydrogen can therefore be selected, which leads to the choice of ethanol and methanol as best candidates. The latter has already shown good performance when combined with SOFCs and is largely available worldwide.
Next, in the second part of this report, the concept design of an OPV using SOFCs fuelled by methanol is tested. On a systems level, the integration of SOFCs adds multiple elements and complexity to the power plant of the concept design. Moreover, since the SOFCs are only used to generate the base load needed to reach cruising speed and its auxiliary power, a peak power source is needed to reach higher speeds. After having considered batteries, diesel engines, and methanol engines, it was concluded that methanol engines provide the highest operational flexibility, on top of being the lightest combination.
When comparing the concept design to the reference design, they both score similarly in terms of redundancy and they both fulfil the same design requirements. In terms of operational capabilities, the concept design can sprint for less time due to the difference in efficiency of the power source used to cruise (fuel cells) and to sprint (methanol engines) and does not have the ability to extend its range above the design requirement, opposite to what the reference design can.
The use of a SOFC-based power plant shows a reduction in CO2 emissions between 13-23% depending on the type of mission, a 100% reduction of SOx and PM due to the use of methanol as a fuel, and a reduction of at least 68% in NOx emissions.