The seaport authorities are currently facing a major challenge related to investments supporting the protection of environment and counteracting its pollution. Changes in the Earth’s climate resulting from heavy environmental pollution, caused to a large extent by the activities in the maritime economy, have made international institutions and organizations raise the alarm and introduce numerous restrictions regulated by law. Next to the International Maritime Organization (IMO) Convention for the Prevention of Pollution from Ships (MARPOL) (IMO, 1973), It is worth mentioning primarily the most important ones, i.e., The Directive 2000/59/EC on port reception facilities for ship-generated waste and cargo residues with subsequent additions; Annex VI MARPOL Convention regarding limits on emissions of SOx, NOx and particulate matter from exhaust gases emitted from ships (IMO, 2015), and also a document called “Transforming our world: the 2030 Agenda for Sustainable Development” (General Assembly, 2015). In addition, two other documents developed in recent years, i.e.,: 17 Sustainable Development Goals (SDGS) issued in 2015 by the Organization of United Nations, and the European Green Deal (EC, 2019) issued in 2019 by the European Commission should also be mentioned.

The above-mentioned documents specify, inter alia, the permissible limits for pollutant emissions in maritime transport and when ships are berthed in ports, and pave the way for zero. In the case of seaports, it primarily refers to creating conditions aimed to reduce the level of pollution emitted by ships in ports (Viana et al., 2014) increase the energy efficiency in port facilities and provide it for the operators of ships at berth as well. Seaports are taking various measures in this regard, and among them there is one solution that is lately gaining in popularity, i.e., Onshore Power Supply (OPS). (Vaishnav et al., 2016; Winkel et al., 2016; Innes and Monios, 2018; Chen et al., 2019; OPS Master Plan, 2021; World Port Sustainability Program, 2021). Recently, the area of research as regards OPS has been very popular, but it should be noted that the source literature provides various definitions for OPS, and they are discussed below in the first part of the study.

The above-mentioned issues and many other related to OPS are currently the subject of numerous studies and analyses of scientists from around the world. Therefore, the aim of this paper is to identify the directions of OPS research development and to define the scientific disciplines of research in the field of OPS. The following research questions were formulated: 1) What are the benefits of investments in OPS? 2) In which scientific disciplines is OPS research currently conducted? 3) What are the current trends and areas of research devoted to OPS?

The content of this paper is typical of such scientific papers; it means that the paper consists of five main sections, including an introduction to the subject related to the issues concerning OPS. The second part of this article presents the review of current achievements in the area of studies regarding OPS. The methodology of the systematic literature review applied in the analysis was described in the third part of this article, and the fourth part was devoted to the presentation of the results. The article ends with a discussion and conclusions expressing the recommendations for further research for the potential groups of interests as well as a list of reference literature.

In the article the method of a multi-stage systematic literature review with the use of data mining was applied. The process of selecting the criteria for analysis and the stages of research process are presented in the chapter devoted to methodology. This article may constitute the subject of interest for seaport authorities and cruise ship owners.

The International Association of Ports and Harbours (IAPH) World Port Climate Initiative (WPCI) has developed an important document on Onshore Power Supply, which is a key source of information for all entities interested in investing in and using OPS, showing the benefits of replacing onboard-generated power from diesel auxiliary engines with electricity generated onshore (IAPH, 2010). In addition, the international standards for High-Voltage Shore Connection (HSCV) (ISO/IEC/IEEE 80005-1:2012, 2012) have been developed, describing systems for suppling ships with electrical power from shore.

The website provides information on the environmental benefits of OPS and the associated costs. It highlights the existing installations in ports worldwide and the existing suppliers of the OPS technology and overall provides guidance for OPS implementation. The website is primarily targeted to port authorities, terminal operators and shipping companies who are considering the introduction or expansion of OPS technology.

According to the International Maritime Organization (IMO) Shore Power Supply (OPS) “is considered a measure to improve air quality in ports and port cities, to reduce emissions of air pollutants and noise and, to a lesser extent, to reduce carbon dioxide through ships at berth replacing onboard generated power from diesel auxiliary engines with electricity supplied by the shore” (International Maritime Organization IMO, 2012). At this point, however, it should be noted that in the literature there are several terms defining OPS, i.e.,

• Onshore Power Supply (OPS) (Li and Du, 2020),

Bouman et al. (2017) indicated that Shore Side Electricity (SSE) is an effective CO² reduction measure for ships. Additionally, (Stolz et al., 2021), proved that “shore side electricity can drastically reduce the emissions from fossil fuel-powered auxiliary engines of ships at berth”. They published very interesting research results presenting the “CO² emissions from the production of electricity required for SSE and compared to the emissions of ships at berth”. (Stolz et al., 2021).

Cold-Ironing (CI) is another frequently used term for OPS. For example (Ballini and Bozzo, 2015), wrote that CI is “a fully developed technology that allows vessels at berth to use shore power rather than rely on electricity generated by their Auxiliary Engines (AE)”. Moreover (Bakar et al., 2022), defined cold ironing as “an electrification alternative in the maritime sector used to reduce shipborne emissions by switching from fuel to electricity when a ship docks at a port”. In this paper, the authors presented the method of forecasting ship berthing duration that can contribute to track of the cold ironing consumption. The forecasting method can be used by other seaports in estimating demand.

These various terms used to describe OPS have been applied as keywords in the data mining process among scientific databases.

Various technological solutions for OPS solutions for ships are currently offered on the market, i.e.,: mobile power generator units, compact modular cabling system, or main transformer station with local stations at the berths, and also shore power box and other. It is worth emphasizing that the costs of OPS installations depend on (Bullock et al., 2023):

• types of OPS unit technology (e.g., centralised unit, outlet points, transformer, frequency converter, groundworks etc.);

The average cost of the OPS installation varies between €1 million and €35 million, e.g., a total budget of 36.4 million US dollars was invested in the OPS installation in the Port of Bremen/Bremerhaven (The Port of Bremen, 2023). Moreover, important are also the costs of electricity transportation to the OPS devices, which depend on.

• port location;

Low-power ferries and, for example, small cruise ships with the capacity up to 1000 passengers (Pax) require power only < 3 MW (megawatt), but giant cruise ships with the capacity of 10,000 Pax onboard require power from 6 MVA (megawoltamper) to 20 MVA. The average cost of energy transportation can amount from $300,000 to $4 million per berth. (Bullock et al., 2023; The Port of Bremen, 2023) [6969].

It is also crucial to maintain OPS, and the related costs depend on many factors, i.e.,: costs of maintenance of OPS infrastructure, price of electricity, number of ships mooring into berths (calls), and time of mooring ships into berths (hours).

For more than a decade, scientific research has been conducted in various fields of OPS science by scientists representing technical, engineering, geographical, biological, chemical sciences, as well as social sciences in the field of economics and management (Puig et al., 2022). Maritime transport causes huge environmental pollution. As research shows among global atmospheric pollutants, 2 percent of carbon dioxide (CO₂), 10 to 15 percent of nitrogen oxides (NO_x) and 6 percent of sulfur oxides (SO_x) come from ships. Solutions that will reduce the scale of this phenomenon have been sought (Stolz et al., 2021). OPS is just one of such solution that can bring numerous benefits to the region, local communities, as well as ship owners. The use of OPS in ports provides, among others: lower fuel consumption by ships, reduction of pollution emitted by ships, ship engine noise reduction, removal of vibration caused by ship engines, and easier maintenance of water purity.

Moreover, disconnecting the ships from ship engine power supply and connecting them to the onshore generator also involves savings for the shipowners. However, one more issue needs to be raised, namely, the fact that still few vessels are equipped with devices for connecting the ships to onshore power supply. Despite obvious environmental benefits resulting from using OPS in seaports, many port authorities are still reviewing the economic effectiveness of these solutions. Investments in OPS are highly capital-intensive and their return is spread out over time. The first economic reports indicate that the investments in OPS in ports do not always show satisfactory economic efficiency, but they are certainly ecologically responsible and socially justified (Ballini and Bozzo, 2015).

A review of previous achievements in the field of research on energy system models and onshore power supply systems has showed that this area of research is studied by researchers around the world, i.e.,: in China (Chen et al., 2019), United States, (Bouman et al., 2017; Bullock et al., 2023), Norway (McArthur and Osland 2013), Germany (World Port Sustainability Program, 2021), Spain (OPS Master Plan, 2021). and other European seaports (Winkel et al., 2016). For example, the team (Mattsson et al., 2021) studied, among others: the factors for onshore and offshore wind power, and existing and future hydropower as part of research on the Energy System Model. The authors noted that in order to develop an effective energy system model, cross-sectoral cooperation is necessary and research in this area should also be carried out.

In 2016, (Winkel et al., 2016). raised in their research the economic and environmental aspects of the use of OPS, but they used the term Shore Side Electricity (SSE). Innes and Monios (2018) presented analyses regarding the data on energy demand, and presents a few scenarios for small and medium size ports in the field of cold ironing installation. Qi et al. (2020) showed the results of analysis concerning shore power economic challenges from the perspective of different groups of interests including, i.e., ship owners, port authorities, and state.

Interesting research on policy support on both capital funding and tax reform, and also factors affecting shore power economics for ship and port operators presented by the team of Bullock et al. (2023) based on research in port of Aberdeen in Scotland. The authors raised an important issue with OPS, i.e., “high capital costs for ports, high taxes on land-side electricity and the global lack of taxation on ships’ fuel oils” (Bullock et al., 2023) and pointed to a gap in research on this issue. This work is particularly worthy of deeper analysis, because it contains both economic aspects and feasibility study, including, inter alia, potential shore power demand by ship type and economic viability, and what is crucial environmental and social valuation. Bouman et al. (2017) presented a comprehensive review of CO₂ studies, emissions, reductions, potentials and measures. Many works address the issues of shipping decarbonisation. OPS installations are one of the solutions that is just analyzed by the author.

An important element of research that should also be taken into account is the development of energy facilities in the vicinity of seaports enabling the connection to OPS. Interesting studies on offshore energy hubs were presented by Zhang et al. (2022). The authors presented the model that “can be used to analyse the interaction of an offshore energy system and onshore energy system transition” (Zhang et al., 2022) It should be emphasized that OPS should be powered by renewable energy sources. It is crucial in the decarbonization process.

Current research studies regard the use of new technologies to optimize processes in electrification. The really interesting research in this area has been carried out, among others, by the research team (Wang et al., 2021b) who presented the design principles and techniques used to implement ternary logic gates using memristor-CMOS hybrid chips for use in strategies for optimizing performance indicators, including, e.g., power consumption. A similar line of research was also carried out by Su et al. (2023) presents innovative research presenting ways to monitor the condition of batteries, based on the integration of physical modelling with machine learning techniques. These types of solutions allow for monitoring and evaluation of battery performance and can be used in optimising the performance of batteries and in projects related to the electrification of port devices.

Another interesting field of research concern the safety assurance was carried out by Siu et al. (2022) who presented the use of a multi-agent command authentication system as a solution to increase security and economic reliability in power systems, with particular emphasis on the possibility of emerging cyberattacks.

The important area of research studies in the field of OPS relates process of integration of energy systems with various power sources. An interesting study in this area was carried out by the team of researchers V. Saxena et. al. (2021) (Saxena et al., 2012) who proposed the MPC Based Algorithm and its validation method for a multifunctional grid-integrated photovoltaic system. The results demonstrate the effectiveness of the model-based predictive control (MPC) algorithm for ensuring energy quality and reliability in the integration of renewables into the power grid. Similar studies relating to the management of the integration of renewable energy sources and the operation of microgrids were carried out by the team of N. Kumar et. al. (Kumar et al., 2018). The paper proposes an intelligent control strategy with the use of artificial intelligence to effectively synchronize the microgrid with the main power grid, taking into account the situation of partial shading. Thanks to the proposed solutions, it is possible to ensure energy efficiency and thus reduce economic and environmental costs. On the other hand, research supporting practical solutions for the control and limitations of control techniques for complex systems in various network structures and dynamic conditions was presented by G. Chen (2023) (Chen, 2022). To sum up, it can be seen that onshore power supply is the subject of numerous scientific studies of various nature and range, both geographical and thematic and it seems reasonable to try further in-depth analysis.

The research was a type of qualitative research. In the article, the method of a multi-stage systematic literature review with the use of data mining was applied. The independent variable is Onshore Power Supply (OPS). The literature analysis process consisted of six stages. To achieve the intended objective of the analysis, i.e., to identify the development of OPS research and to organize the terminology devoted to OPS, in the first stage, key phrases and key words related to onshore power supply were defined. In the second stage, three databases were selected to conduct the search, i.e., Science Direct, EBSCO and Web of Science. In the third stage of analysis, selection criteria that narrowed the search to specific areas were defined. The first criterion involved defining the period of search time, which was limited to a decade, i.e., from 2014 to 2023. In addition, the type of publications to be analysed were specified; only research papers and review papers available in the Open Access option were included. Using publications with limited access to conduct the extensive data analysis, as is the case here, is too expensive and often exceeds the researchers’ budgets.

In the next stage of analysis (the fourth), the search was narrowed down to the phrases listed in No_x table in the titles of publications, keywords and abstracts from these publications. As a result, a list of publications for detailed analysis was defined. In the fifth stage, further criteria narrowing the search area were indicated and the collected database was grouped into four subject areas, i.e.,: 1) Engineering analysis (technology, technical, etc.) 2) Socio-economic analysis (financial, fiscal, business, management, etc.), 3) Environmental analysis (protection, pollution, emissions, etc.), 4) Legal analysis (legal standards, law regulations, etc.) (Scheme 1).

The full texts of selected publications were verified, selected and put through detailed substantive analysis, and the results thereof are presented in the next part of this study.

To analyse the data mining of the databases results, the critical and comparative analysis was applied, as well as inductive and deductive reasoning.

A systematic review of databases showed that between 2014 and 2023, assuming the previously described selection criteria, a total of 74,111 scientific publications related to OPS were registered. The EBSCO database included a total of n = 70,424 scientific publications placed in review papers and research papers, which referred directly or indirectly to the issue of OPS, which accounted for as much as 94.98% of all publications in the examined scientific databases. Meanwhile, ScienceDirect database registered a total of 3431 publications (i.e., 4.63% of all publications) during the period under analysis. Unfortunately, in the Web of Science database there are few scientific publications related to OPS, i.e., 279, which accounts only for 0.39% of the total number (Figure 1).

A review of the ScienceDirect, EBSCO and Web of Science scientific databases also indicated that the majority of publications related to OPS, i.e., 63.47% is devoted to issues under the heading of “STSP” and 32.38% of “OPS”. This is valuable information for scientists who will take up the subject of OPS in their future scientific work. The search limited in the literature queries only to the common (as it might seem) terms, i.e.: “OPS” (Onshore Power System) and neglecting “STSP” (Shore To-Ship Power) could significantly distort the scope of analysis. Other terms related to OPS, i.e., CI, SSE, or HVSC are less commonly used in the scientific literature (Figure 2).

By comparing the resources of the three scientific databases above-mentioned, in the area of publications devoted to OPS with the use of criteria described above, we also come to the conclusion that the largest number of publications devoted to “Shore To-Ship Power” and “Onshore Power Supply” was registered in the EBSCO database (94.98%). Similarly, in the ScienceDirect database, the largest number of publications were devoted to “Onshore Power Supply” and “Shore To-Ship Power”. Whereas scientists rather rarely use other terms, i.e.: “Cold ironing”, or “Alternative Maritime Transport” (Figure 3).

As a result of the analysis, a total of 74,135 publications were filtered from all three examined databases where references to OPS were found (3rd Stage). Then, in 4th Stage, in accordance with the planned model of systematic literature review, the search was narrowed only to publications referring directly to specific phrases in the titles of these publications and abstracts and keywords. This resulted in a reduction in the number of publications to 302. The next step in the 5th Stage was to group the publications into individual subject areas. In the last stage of the analysis (6th Stage) the publications were verified and selected. After this stage, only 63 publications were qualified for deeper analysis, which accounted for 20.9% of those selected for analysis, which met the criteria of the 3rd stage (Table 1).

An important element in the considerations, and also the superior objective of the analysis, involves the issue of subject areas of research conducted in the area of OPS (Figure 4). As it was previously mentioned, OPS is the subject of interest to researchers from various fields and disciplines of knowledge. Some areas are excessively analysed in terms of research, while other, not much. Obviously, one can argue that perhaps these are the needs on the market, but one can also argue, quite the opposite, that perhaps these are topics convenient for researchers because they are consistent with their research interests, and not necessarily important for stakeholders.

A review of the scientific achievements to date related to the issue of OPS has shown that this issue is very topical and subject to analysis within different areas of knowledge, which can basically be divided into four main research areas, i.e.,: 1) environmental analysis (protection, pollution, emissions, etc.) 2) engineering analysis (technology, technical, etc.), 3) socio-economic analysis (financial, fiscal, business, management, etc.), and 4) legal analysis (legal standards, law regulations, etc.) (table 2).

The main reason for investing in OPS refers to the environmental benefits that reduce noise, vibrations and emissions of pollution from ships when they are berthed. Hence, in databases there are numerous publications on this subject presenting environmental benefits of using OPS technology (Kizielewicz and Skrzeszewska, 2021; Sciberras et al., 2015; Saxena et al., 2012; Kumar et al., 2018; He et al., 2020; Wang et al., 2021b; Reusser and Pérez, 2021; Chen, 2022; Siu et al., 2022; Su et al., 2023) in particular in the area of CO₂ reduction potential of OPS (Stolz et al., 2021). The research carried out by Reusser and Pérez (2021) (Wang et al., 2021b) is a good example showing “the reduction in the specific fuel consumption of the auxiliary engines, thus reducing emissions in 20% for CO₂, 34% for NO_x and 30% for SO_x” thanks to applying CI power configuration.

These results confirm the expediency of using CI and should constitute an important argument convincing to use these solutions. However, in the area of engineering research, there are numerous scientific works on the development of OPS infrastructure and various technologies in this respect used in seaports, including small and medium ones. Colarossi and Principi (2020) proposed the methodology of evaluation “the energy demand of ships at berth and producing electricity through a highly efficient cogeneration plant”. They also studied the annual trend in electrical energy required by ships at berth and tried to estimate the capital, operational and maintenance costs. They presented the system which consists of a cogeneration plant that produces simultaneously heat to cover utilities in port area and power for ships at berth while (Colarossi and Principi, 2020). Numerous works also refer to the issue of connecting OPS to energy sources, including renewable sources. Interesting research on the use of wave energy extraction and wave energy converters was conducted by Cheng et al. (2022a) (Port Technology International, 2021; Cheng et al., 2022a). They described solutions combing floating breakwaters with wave energy converters and integrating them into a very large floating structure and developed mathematical models confirmed by experimental studies. It would be worth considering the use of offshore wave energy converters in OPS. There is still a gap in this area of research, and only a few experimental works have been done in this area. This could also be an interesting direction for future research.

Bearing in mind different energy supply needs of ships, due to their type and gross tonnage, research is also conducted on the electrical characteristics of OPS (Yang and Chai, 2016; Atallah et al., 2017; Gutierrez-Romero et al., 2019; Badakhshan et al., 2022; Farrukh et al., 2022). Bearing in mind different energy supply needs of ships, due to their type and gross tonnage, research is also conducted on the electrical characteristics of OPS (Bakar et al., 2022; Sciberras et al., 2015) and transient overvoltage protection of OPS System (Haddadian and Haddadian, 2011), and energy efficiency assessment of OPS (Karimi et al., 2022). A serious problem raised in scientific works also refers to the cost of energy transportation to OPS from power sources (Jung and Schindler, 2021), and also energy optimization of OPS systems. (Galkin and Tarnapowicz, 2022; Qiong and Xiao, 2015). Martínez-Lopez et al. (2021) noted that the environmental and economic benefits are only seen when OPS is powered by renewable sources.

The dominant group of works related to OPS also comprises studies in the area of socio-economic analysis, including mainly financial and management analysis of investments in OPS and benefits to local communities from OPS systems. Such analyses are a key element in the investment decision-making process of port authorities. Investments in OPS are highly capital-intensive, as already mentioned above, and many factors determine the success of this type of investment. Martínez-Lopez et al. (2021) presented “a calculation method to estimate a environmental charge in ports to incentivize cold Ironing use”, which takes into account “a pollutant differentiation system by considering kinds of vessel, technical features, port localization and hinterlands populations”. The team led by Najihah (2023) studied the “synergy of the cold ironing and microgrid system on ships” and also presented the “cold ironing cost analysis strategies from ports’ and ships’ points of view” (Najihah et al., 2023). It is one of the few scientific studies of this type containing both technological and economic aspects of CI. Many scientific papers refer to assessing the economic efficiency of investments in OPS including, inter alia, pricing strategy and sale mechanism of OPS (Stolz et al., 2021; Su et al., 2023) and cost-effective optimization analysis of OPS (Hulme, 2006).

The need for financial support for OPS from public funds (Wang et al., 2021a) is also raised, because of the environmental benefits for the region and local communities (Ballini and Bozzo, 2015). Moreover, a valuable source of information for stakeholders includes studies devoted to building strategy for OPS System (Yu et al., 2017) and control strategy for OPS (Ji et al., 2018) presenting also barriers and drivers to the implementation of OPS (Williamsson et al., 2022). Finally, there are also works related to energy management in seaports (Acciaro et al., 2014) including the management of OPS systems and optimization of daily use of OPS (Yu et al., 2022).

However, we can feel certain insufficiency when it comes to scientific studies in the area of managing shipboard energy (Sciberras et al., 2015), and the state of preparing ships to be equipped with devices adapted to connect to OPS system and to ensure ship-to-grid integration (Vlachokostas et al., 2019). Few papers present the results of research on equipping the ships, by segments (cruise ships, ferry vessels, cargo, etc.) with devices enabling the connection to OPS, and future electricity and hydrogen demands for shipping (Ortiz-Imedio et al., 2021; Bakar et al., 2022). This is the area that should become the subject of future research. There is also a shortage of reliable economic analyses for shipowners regarding the benefits of using OPS.

We should also mention the legal and regulatory issues related to OPS systems, issued by the IMO (IMO, 1973) or IAPH (IAPH, 2010) and ISO (ISO/IEC/IEEE 80005-1:2012, 2012) regarding the technical aspects of OPS. These documents provide practical information about OPS, which constitute the subject of analyses and scientific discussions (IAPH, 2010; Yu et al., 2017; Tarnapowicz and German-Galkin, 2018).

Summing up the analysis of databases on previous research on OPS, it should be emphasized that the main streams of research concern the following areas.

• Environmental research area–the use of renewable energy sources to power the operational activities of seaports, including supplying ships with shore energy (OPS). The aim is to reduce greenhouse gas emissions and reduce the emission of harmful substances into the environment.

It should be emphasized that the research conducted so far has focused mainly on the analysis of individual cases of engineering, organizational, technical or architectural solutions in the field of OPS. Stakeholders interested in investing in OPS and their development are looking for comprehensive analyses containing legal, economic, environmental and social analyses, showing a map of the benefits and costs resulting from investments in OPS. This type of interdisciplinary research would be more applicable and could have a greater popularizing value.