# Analysis of a Supercapacitor/Battery Hybrid Power System for a Bulk Carrier
## 1 Introduction  
Although road vehicles currently represent about 70% of total greenhouse gas (GHG) emissions in the transport sector, other forms of transport--including aviation, maritime, and off-road vehicles--are also substantial emissions sources and are expected to see continued growth in the coming years. Specifically, the maritime sector is expected to rise gradually because of its slower improvement efficiency compared to other vehicles; its GHG share is expected to increase from 10% in 2018 to 20% in 2060 among the global transport-related GHG emissions [1]. In this regard, many countries and the international maritime organization (IMO) have been implementing environmental regulations or policies, especially in emission-control areas (ECAs), which are designated areas near ports where ships are required to further reduce emissions. For example, the sulfur limit is currently 0.1% within ECAs; it is 35 times stricter than the outside ECAs. These strict regulations are related to the fact that premature deaths have been increasing each year due to cardiopulmonary disease and lung cancer caused by pollutants emitted from ships at ports [2]. Shipping emissions in East Asia accounted for 16% of global shipping CO\({}_{2}\) in 2013, compared to only 4%-7% in 2002-2005. This increase in emissions resulted in large adverse health impacts, with 14,500-37,500 premature deaths per year [3]. Therefore, ship owners have been making efforts to reduce harmful emissions using exhaust gas treatment systems such as sulfur dioxide (SO\({}_{\times}\)) scrubbers, selective catalyst reactors (SCRs), or changing ship fuels from heavy fuel oil (HFO) to liquefied natural gas (LNG) or marine gas oil (MGO), etc. In addition, major ports have been expanding shore power facilities (or alternative maritime power (AMP)), which can supply electric power for ships from land-based electric power plants while staying at a port. Notably, low voltage AMP facilities have already been installed in many dominant ports worldwide. Additionally, high voltage (3.3 kV, 6.6 kV, 11 kV, etc.) AMP facilities are being installed in major ports for large ships such as in the U.S., Canada, European countries, China, etc., and the European Union (EU) requires European ports to offer shore-based electricity to ships by 2025. In this regard, hybrid systems using an energy storage system (ESS) have gained attention as an alternative solution to solve the environmental issues in the marine industry, and research regarding hybrid systems has already been performed. For example, [PERSON] et al. [4] proposed a hybrid system combined with a photovoltaic (PV) generation system, a diesel generator, and batteries. [PERSON] et al. [5] and [PERSON] et al. [6] each proposed a fuel cell-battery hybrid system for a boat. In addition, [PERSON] et al. proposed a hybrid system with lithium-ion batteries (LIBs) and diesel generators for a bulk carrier [7]. However, there is not much research regarding the supercapacitor (SC) and LIB hybrid system yet, except for some research focused on small ships; [PERSON] et al. chose a SC as the power source for a ferry and proposed a charging strategy [8], and [PERSON] et al. investigated the LIB-SC hybrid system to improve the dynamic response of a boat [9]. On the contrary, many research studies have been conducted to develop the LIB-SC hybrid system for land vehicles, especially in [10; 11; 12; 13; 14]; these are SC-LIB hybrid systems for electric cars. These results show that the hybrid system could improve system performance by overcoming individual limitations (disadvantages) and enabling synergistic effects. In other words, LIBs, which are the most common battery types, have a high energy density; however, their power densities are low compared to that of an SC of the same size. Also, LIBs have a short life cycle compared to an SC, which has an approximately 1000\(\times\) longer life cycle than LIBs (refer to Table 1).