This paper presents a design method of the ship power system containing optimal configuration and assessment. A multi-factor and multi-level A.J.Klee-based method was established considering the system reliability, fuel consumption, emissions, and cost during the ship voyage, after which the optimal comparison of different types of prime movers including diesel /dual fuel engines and their capacities was conducted and analyzed. The case study shows that by using the DF engines and ESS, the CO2 emissions can be reduced by up to 56.6%, and the fuel consumption reduction and carbon tax due to the load shifting of ESS enables the return within the life cycle.
With the growth of demand to meet the requirements of emissions in the shipping industry, the optimization of power systems has become the most feasible way. Especially, considering the working features of large cruise ships, more concern was attracted to their potential to achieve clear shipping and transportation in the areas of ports and near the lands. To reduce the emissions of power systems during the voyages, various measures were presented including ship speed management, system configuration optimization as well as renewable energies. In particular, the studies on ship power systems are mainly focused on hybrid systems and green-fueled engines. The energy storage systems and LNG engines have been used widely in marine applications and showed great potential to improve energy efficiency and lower CO2 emissions.
The conventional power systems of cruise ships are consisted of main engines and shafts to drive the propeller directly. With the growing concern on the improvement of ship energy efficiency, the all-electric ships were proposed as shown in Fig.1 (Nuchturee and Li, 2018). A large cruise propulsion system usually uses an integrated electric propulsion system, mainly consisting of internal combustion engines, inverter, transformer, power distribution systems, propeller, motor, and control system. The internal combustion engines are used to serve as generators to produce power for propulsion and daily life on ships. Differ from driving a propeller via a gearbox, internal combustion engines operating as auxiliary engines will be able to offset the power demand fluctuations caused by transient waves and winds during the propulsion. All power can be integrated and distributed based on the advanced power management strategies to provide advantages on prime mover efficiency, general arrangement flexibility, reliability, and feasibility to facilitate alternative energies integration. On the contrary, due to the introduction of huge amounts of electric components, the loss of power conversion still can be observed, which leads to a negative effect on system energy efficiency(Fan and Xiao, 2019). With the strict legislation of emissions, hybrid power systems including internal combustion engines and batteries as well as PV solar has been issued in medium-sized ships which sail in inland waters and on short voyages. In addition, in merchant marine applications, dual fuel engines have been used to replace diesel engines to reduce greenhouse gases.