Design of a Fully Electric (Battery/Fuel Cell) Submarine

Abstract

To improve the submerged time of diesel-electric submarines (SSK), air independent power (AIP) systems have been developed in the past. So far only submarines with AIP systemsin combination with one or more diesel generator (DG) sets are designed and built. The increased technological readiness level of modern fuel cells (FC) and the energy density of modern lithium-ion (li-ion) batteries trigger the possibility of a fully electric submarine. This concept of hybrid FC-battery energy storage and generation could eliminate the requirement for DG sets and a snort system to charge the batteries. The operational advantages in terms of improved indiscretion rate, reduced maintenance and smaller crew, silent energy conversion and reduced complexity of the ship systems design could have a great impact on conventional submarine design. In this thesis the design changes due to a switch to a fully AIP plant are described and a submarine concept design is created. The design should have the same submerged displacement and sprint capacity as a set reference design. The selected AIP plant uses a proton exchange membrane fuel cell (PEMFC), lithium iron phosphate (LFP) batteries and hydrogen stored in high pressure bottles. The design is based on a reference design from which the diesel related systems and batteries were removed. Since the new power plant requires less maintenance also the crew size was reduced, which resulted in a smaller accommodation. The removal of systems and the smaller accommodation resulted in a freed up volume for the new power plant. Using a matlab program that systematically generates power plant configurations within the available volume an ideal power plant is selected. The selection criteria is set to maximum
range, while still satifying the speed requirements. Subsequently, this power plant is integrated in the design. Other aspect that are considered during the design are the electric load balance, the heat balance, air quality and the type
of main electric motor. Also the trim and stability are considered. This results in a concept submarine design. Finally, the new concept design is compared with the reference design on the aspects mentioned earlier. For the range and endurance a fully battery powered submarine is also included in the comparison. The results show that the reference design has a three times higher maximum range and endurance than the concept design. However, when the indiscretion rate (IR) was taken into account the full potential of the concept design became clear. The IR of the concept design is 0%, which means it can operated underwater for the entire range and endurance. This is a large improvement over the reference design, which has to snort on regular intervals. When the concept is compared with the fully battery power submarine the maximum range and endurance are approximately doubled. As always, it all depends on the desired operational profile of the user whether the design is the most suitable option; however, it is expected that for most navies the created design is a significant
improvement over the diesel-electric alternatives. Considering all aspects above it can be concluded that the concept design with PEMFC, LFP batteries and compressed hydrogen is capable to perform short to middle long missions, while provided their operating navies with significant operational advantages like 0% IR, lower acoustic signature and smaller crews.