## 1 Introduction  
Transportation significantly contributes to air pollution and the emission of harmful gases in the territory of the European Union (EU). According to [1], transportation is responsible for the total emissions of particulate matter PM2.5 (PM smaller than 2.5 \(\upmu\)m) in certain cities, namely Malmo, 39% of overall PM; Brescia, 28%; Parma, 27%; and Angers and Verona, 26%. Maritime transport also contributes to air pollution, especially in the area of coastal cities such as Valletta, 33%; Palermo, 29%; Palma de Mallorca, 26%; Athens, 24%; and Bari, 21%. In the territory of the Republic of Croatia, as much as 95.1% of the population has been exposed to PM10 (PM smaller than 10 \(\upmu\)m) at a concentration higher than EU standards [2]. Air pollution is the main cause of premature death and disease and, as such, represents the greatest health risk related to the environment in the European Union. According to data from the European Environment Agency observed on an annual basis, in 2019 alone, acute exposure to PM caused 307,000 premature deaths in 27 EU member states [3]. The above has significant implications for reduced life expectancy, increased costs of the health care system, and reduced productivity. Therefore, in July 2023, the International Maritime Organization (IMO) revised the strategy to reduce greenhouse gases compared to the ambitions of 2018. Thus, the final goal for reducing GHG emissions in 2050,which was 50% compared to emissions in 2008, was reduced to 0 emissions [4]. In March 2023, the European Commission published the European Green Deal [5], which introduces a zero-emission requirement for ships at berths with the mandatory use of power supply from land or alternative technologies without emissions. The main goal of this agreement is to reduce air pollution in ports, often located near densely populated areas. The Fuel EU maritime initiative [6] is an interim agreement reached in March 2023 that promotes the systematic use of renewable energy sources and low-carbon fuels. However, the forecast for assessing the use of a certain type of fuel in shipping is quite uncertain [7]. Due to technical limitations, the decarbonization of maritime transport will increase total costs by 70% to 110%. According to [8], the gradual introduction of renewable fuels is foreseen, as shown in Figure 1.  
The European Union's current goal is to increase the share of renewable energy sources (RES) in energy consumption by 32% by 2030. In the Republic of Croatia, in 2023, 50% of the total electricity produced was produced by hydroelectric power plants alone [9]. In accordance with the energy needs of ships and the capabilities of the shore electrical system, the design of a battery charging station is proposed. The charging station can be performed in different ways; however, it is most often designed in one of the following configurations:  
* Direct charging from the shore network (AC or DC);
* Combined charging using own diesel generators (DG) and shore network;
* Combined charging using a shore energy storage system (ESS) and power supply from the shore. Direct charging from shore is the most acceptable solution if the energy infrastructure fulfills the needs of the battery charging station. The possibility of the connection is usually feasible only in large seaports with a developed energy infrastructure. The charging station can be connected to low-voltage, medium-voltage, or high-voltage levels. However, in practice, ferry docks are often located in sheltered ports without an available infrastructure that adequately meets the requirements of the charging station. Therefore, simultaneous charging using the ship's generators and a connection from shore is often applied. In this case, when ship generators are used, it is a hybrid system. If the shore connection does not enable sufficient power, an electrical ESS can be used, which is charged when the ship is not connected to the charging station.