Journal Archive

Global energy demand continues its upward trajectory, with a substantial 81.3% of the global energy supply being dependent on fossil fuels, notably oil, as of 2018. Notably, the maritime sector plays a significant role, contributing 6.8% to the overall energy consumption (Bilgili[2023]). Consequently, in 2018, the greenhouse gas (GHG) emissions resulting from maritime activities amounted to 1,076 million tons of carbon dioxide equivalent (CO₂ eq.), reflecting a 9.3% increase compared to the levels observed in 2012. Ships are also accountable for 2.89% of the total anthropogenic emissions globally (International Maritime Organization[2020]).

In the shipping sector, the International Maritime Organization (IMO) has a responsibility for addressing these critical environmental challenges. The IMO is presently implementing rigorous regulations to pave the way for a more environmentally sustainable future in shipping, as indicated by recent research conducted within the framework of the International Convention for the Prevention of Pollution from Ships (MARPOL) (Gilbert et al.[2018]).

Illustratively, two notable amendments to MARPOL ANNEX VI include the Energy Efficiency Design Index (EEDI) and the Ship Energy Efficiency Management Plan (SEEMP). These regulations are designed to enhance the efficiency of ships and facilitate comparisons in terms of energy efficiency. Key indicators such as EEDI and Energy Efficiency Operating Indicator (EEOI) employ multivariate equations to evaluate a ship’s CO₂ emissions during both the design phase and operational phases (Livanos et al.[2014]). Of particular significance is the introduction of supplementary tools by the IMO during the 76th MEPC meeting in June 2021. These tools, including the Energy Efficient Existing Ships Index (EEXI) and the Carbon Intensity Index (CII), are aimed at further improving energy efficiency (DNV[2021]; DNV GL[2020]).

Numerous strategies have been proposed to adhere to the regulations established by the IMO and mitigate emissions from ships. Within this array of solutions, electric propulsion and solar photovoltaic (PV) systems have emerged as viable alternatives, gaining prominence in the market (Symington et al.[2016]). Subsequently, a concerted research effort also has been spotlighted to advance sustainable maritime transportation by integrating renewable energy systems, notably solar power with fuel cells. These efforts have resulted in an increased adoption of renewable energy systems, resulting in reduced greenhouse gas emissions when compared to conventional dieselonly systems (Ghenai et al.[2019b]).

In contrast to alternative energy sources, solar panels, which utilise sunlight to produce electrical energy, typically exhibit a low range of efficiency. Continuous scholarly inquiry and developmental endeavours encompass a multitude of facets aimed at enhancing the operational effectiveness of PV panel systems and mitigating associated challenges. These encompass a diverse array of solar PV system configurations and control systems such as Maximum Power Point Tracking (MPPT), demonstrating the interdisciplinary nature of the ongoing research in this field (Pakkiraiah and Sukumar[2016]).

To address this research gap, scholars embarked on a comprehensive investigation and comparative analysis of various electric propulsion systems actively employed in commercial maritime vessels. The overarching objective was to discern the most suitable power management techniques that could augment the efficiency of solar power systems. Multiple research studies have been undertaken in pursuit of this objective. In order to bolster the efficiency of the solar power system itself, investigations have concentrated on the design and control methodologies of solar PV systems that integrate solar power modular multi-level inverters (MMI) or multi-level inverters (MLI) tailored for marine applications. This approach has been rigorously substantiated to not only contribute to the amelioration of system efficiency but also to markedly curtail energy losses (Gnanavel et al.[2021]; Shi and Luo[2018]).

Furthermore, through an investigation involving the implementation of a hybrid solar/fuel cell power system on a ferry vessel, the hybrid power arrangement, encompassing a fuel cell, solar panel, and diesel generator, successfully harnessed a substantial proportion of renewable energy, constituting 20% of the total power output. Simultaneously, a notable reduction in greenhouse gas emissions was observed in comparison to conventional diesel engines (Ghenai et al.[2019]). An analogous examination was also conducted, assessing the feasibility of installing a solar array configuration on a roll-on/roll-off (Ro-Ro) vessel operating between Pendik, Turkey, and Trieste, Italy. The solar PV system, in this context, achieved an impressive energy efficiency rating of 7.76%. Importantly, this implementation led to a significant decrease in emissions of sulfur oxides (SO_x), nitrogen oxides (NO_x), carbon dioxide (CO₂), and particulate matter (PM) (Karatuğ and Durmuşoğlu[2020]).

As global research endeavours intensify to advance electric propulsion ships integrated with solar PV systems in regions such as Europe, the United States, and China, a notable research deficiency exists concerning ships operating within the maritime confines of South Korea. This inadequacy has emerged as a fundamental question of whether there will be environmental benefits if ships based in South Korea operate based on the electric propulsion system with/without solar PV system.

Amidst the ongoing research efforts focused on electric propulsion ships integrated with solar PV technology, there exists a need to definitively establish the environmental effectiveness of such vessels. The existing body of scholarly work consistently emphasises the environmentally beneficial characteristics of ships equipped with solar PV systems (Karatuğ and Durmuşoğlu[2020]; Yuan et al.[2021]). These vessels are demonstrated to have the capability to significantly reduce CO₂ emissions and generate noteworthy cost savings when juxtaposed with their diesel-powered counterparts. Moreover, with the rapid advancements in battery and solar PV technologies, it is anticipated that the development of solar-powered ships will play a pivotal role in significantly mitigating greenhouse gas emissions (Leung and Cheng[2017]). The findings from these investigations demonstrate that maritime operations incorporating not only solar power generation but also wind and wave energy sources manifest reduced fuel consumption, thereby fostering more eco-conscious and sustainable sea transportation practices (Rutkowski[2016]). In a parallel vein, research has unveiled that the deployment of hybrid PV, wind, and fuel cell energy systems on tankers can lead to noteworthy reductions in CO₂ emissions alongside tangible economic advantages (Huang et al.[2021]).

Nevertheless, research indicates that electric energy may not consistently align with environmental friendliness when considering the complete life cycle (Jeong et al.[2022]). As clearly shown in Fig. 1, the level of emissions associated with electrical energy varies significantly depending on the source of energy used for electricity generation (National Renewable Energy Lab.[2021]).

Fig. 1. 
GHG emissions by energy sources when producing electricity.

Hence, it is imperative to move beyond the conventional, narrow assessment focused on emission reduction in the usage phase and conduct a more comprehensive scrutinise of technologies such as electric propulsion systems and solar power generation from a holistic life cycle perspective.

Amid increasingly stringent environmental regulations, the Carbon Intensity Index (CII) has emerged as a compelling regulatory framework. However, even this rigorous regulation has clear limitations in contributing to realising substantive environmental improvements when compared to the Life Cycle Assessment (LCA) framework. As illustrated in Fig. 2, the scope of CII is relatively limited as only focuses on CO₂ excluding other emissions, and mainly addresses the fuel consumption phase ignoring the preceding phases of fuel production. As a result, it is difficult to determine actual environmental friendliness based on current environmental regulations.

Fig. 2. 
Necessity of LCA and the scope of each assessment.

Given the insufficient comprehensive environmental assessment that encompasses the importance of electric propulsion systems and solar PV systems with MPPT control algorithms within the entire process, this study holds great significance. It is also urgently required to guide various stakeholders in determining the direction of future research, projects, and policies. Furthermore, research focused on ships operating in South Korea that integrate electric propulsion systems and Solar PV systems should be conducted to provide more detailed observations and assess their feasibility. Currently, there is a lack of in-depth environmental impact studies concerning such types of ships in the Korean maritime area. Therefore, this research is expected to play a pivotal role in explaining the potential environmental impacts associated with the adoption of electric propulsion ships in Korean maritime areas.

The outcomes of this research carry profound implications, as they hold the potential to advance the overarching objective of attaining net-zero emissions within the maritime sector. Moreover, this study is poised to furnish invaluable guidance to policymakers, industry stakeholders, and advocates for environmental sustainability. In so doing, it equips them with essential insights and pragmatic solutions necessary for charting a responsible course toward the future of environmentally conscious maritime transportation.

Excessive reliance on existing data has, thus far, posed a significant obstacle to achieving accurate and situational environmental impact assessments in LCA. This is particularly challenging in processes like maritime shipping, which sail under continuously varying conditions, environments, and operations. Shipping produces constantly changing data, therefore collecting/securing the data is essential to determine the environmental impact. However, acquiring all such data has practical limitations. Consequently, the absence of input data has led to results derived through assumptions and estimations, undermining both the credibility and applicability of these outcomes in diverse scenarios.

To address this challenge, the introduction of the Live-LCA methodology is proposed and implemented as a suitable remedy. Live-LCA relies on data generation through modelling/simulation or experimentation to obtain data that is presently unavailable. Therefore, it greatly enhances the ability to derive context-specific environmental impacts compared to conventional LCA. This enhancement significantly improves the reliability and applicability of research findings.

Notably, the maritime industry has been adopting various fuels and systems to protect the environment. On the other hand, for those kinds of new technology, not only data for vessels equipped with electric propulsion systems and Solar PV systems is, for the most part, not enough, but actual operational records are also quite limited. Additionally, the environmental impact of converting existing vessels to electric propulsion and operating them on the same routes is heavily reliant on databases filled with numerous assumptions and estimations, which compromise the accuracy and reliability of results. Live-LCA effectively addresses these issues, enabling extensive data collection and appropriate assessments through simulations of various scenarios.

In essence, this methodology offers substantial significance by extending the applicability of LCA techniques, traditionally suitable for static conditions, to dynamic situations.

The steps of Live-LCA have been designed to follow the framework specified in ISO 14040, and they also adhere to the requirements outlined in ISO 14044. Consequently, the following steps are executed in accordance: Step 1. Goal and Scope; Step 2. Life Cycle Inventory Analysis (LCI); Step 3. Life Cycle Impact Assessment (LCIA); Step 4. Interpretation.

In the first step, “Goal and Scope”, the research objectives are defined, and why this environmental impact assessment is being conducted and how the results will be utilised are clearly explained. Additionally, the scope of the study is established and the system boundaries are delineated between what is included and excluded from the study. During this process, it is needed to make decisions regarding the functional unit, quantifying the evaluation criteria into measurable units. In this stage, there is no distinction between traditional LCA and Live-LCA; both follow the same process.

In the second stage, known as “LCI,” significant differences between conventional LCA and Live-LCA emerge. This stage involves identifying and quantifying inputs such as materials and energy resources and outputs like environmental emissions and waste generated in the product/system/process. Ultimately, the reliability of the database secured in this stage plays a crucial role in determining the success of the entire research. Conventional LCA heavily relies on existing data to construct its database. However, Live-LCA takes a different approach, striving to eliminate assumptions and estimations wherever possible. This is achieved through modelling, simulation, or experimentation to continuously produce context-specific data for database flexibility. Therefore, Live-LCA can contribute to deriving successful and appropriate research results by building a more accurate and reliable database.

The LCIA step uses the database established during the LCI stage to assess potential environmental impacts by converting them into specific impact indicators. LCIA includes essential sub-stages, such as Classification, which assigns the environmental load to selected impact categories, and Characterisation, which is for estimating results for category indicators. Additionally, optional sub-stages like Normalisation for providing references for consistency, and Weighting, which aggregates scores based on derived weights, can be applied.

Finally, in the step of Interpretation, information collected, classified and characterised in the LCI and LCIA stages is identified, verified, and evaluated. Essentially, this stage determines the accuracy of the outcomes generated in previous stages and, ultimately, whether the results align with the objectives set in the “Goal and Scope” step. Continuous interaction with other stages and various methods to validate the data used are of utmost importance. Ultimately, this stage is responsible for drawing research conclusions and providing insights into limitations and practical recommendations.

The goal of this research is to assess the environmental viability of ships equipped with the electric propulsion system and Solar PV system controlled by MPPT algorithm in South Korea in comparison to conventional fossil fuel-based ships. To achieve this goal, the research scope involves selecting a conventional fossil fuel-based case ship and collecting its operational profile data. Based on this data, energy usage and resulting environmental impact comparison will be conducted for the same case ship navigating with electric propulsion and with the application of the electric propulsion system and Solar PV system. According to this plan, three cases will be considered in this research as follows and Fig. 6;

Fig. 6. 
Three cases of energy supply scenarios for the case ship.

· Case 1: Fossil fuel-based mechanical propulsion system

· Case 2: Electric propulsion system powered by batteries

· Case 3: Electric propulsion system powered by batteries with Solar PV system controlled by MPPT

Case 2 and Case 3 are not from the actual existing ship but scenarios assumed for the purpose of verifying their feasibility in terms of the environment. Accordingly, reliable data for these scenarios needs to be obtained through appropriate modelling based on actual data. In Case 2, unlike Case 1, electric propulsion motors are installed instead of the main engine. The energy source for propulsion is electricity rather than MGO, and this electricity is obtained from South Korea’s national power grid during the ship berth, stored in the ship’s batteries, and used during navigation. The overall concept of Case 3 is similar to Case 2. However, in Case 3, the propulsion energy is not solely supplied by the stored electricity from the national power grid but is also supplemented by the electricity generated by the Solar PV system, which is stored in the batteries and used in conjunction with the grid electricity. In this case, the Solar PV system is continuously controlled to maximise power production through MPPT.

Based on the research and findings from these three cases, the ultimate goal is to ascertain whether electric propulsion ships and, furthermore, vehicles equipped with electric propulsion systems in South Korea indeed bring environmental advantages. Additionally, this research aims to provide insights into the current state of electricity production in South Korea by comparing environmental impact results when ships operating in South Korea use electricity produced domestically versus electricity produced in other countries with the same energy consumption. The final objective of this study is to offer direction for regulations and policies regarding the energy sector.

In this case study, the focus will be on GHG emissions for the three cases of the case ship, and the environmental impact will be assessed using the Global Warming Potential (GWP, kg CO₂ equivalent) as the default functional unit. Furthermore, the scope of the study does not include ship equipment and devices. From a holistic perspective of the Well-to-Wake (WtW) scope, encompassing viewpoints from production to consumption and disposal, the research concentrates on the fuels responsible for over 90% of emissions generated by ships, as they are central to understanding the environmental impact.

Based on the data collected in Task 1-3, the environmental assessment of the fuels and energy used in the three cases considered for the case ship was conducted. Among various environmental impact assessment methods, this research employed the CML 2001 method as the reference. The assessment was carried out with a focus on GWP, following the boundaries established in the Goal and Scope step. Consequently, the daily GHG emissions values for each case of the case ship are presented in Table 6.

When estimating the ship’s lifespan as 30 years, configuring the case ship’s systems according to each case scenario and operating them based on the current navigation route and operational profile, the total GWP that could occur over the lifespan of the case ship is depicted in Fig. 11.

Fig. 11. 
Total GWP of the case ship during lifespan depending on each case.

The research findings indicate that when transitioning a conventional fishing boat using MGO to an electric propulsion system, as in Case 2, only 55% of GHG emissions are generated. Furthermore, when incorporating an MPPT-applied Solar PV system as in Case 3, an additional GHG emission reduction of approximately 2% can be achieved for the case ship.

First and foremost, the most significant novelty of this research lies in its methodology. In conventional LCA, the scope of the study has been strongly affected by the availability of data. Even when aiming to delve deeper into environmental impacts, data limitations constrained the study's boundaries, limiting its scalability and becoming a clear factor in reducing the reliability, accuracy, and precision of research outcomes. However, the Live-LCA introduced in this study not only collects existing data in a conventional way but also relies on accumulating data obtainable through data generation and extracts/utilises the desired and necessary data through appropriate means. This audaciously overcomes the limitations of conventional LCA and allows for an infinitely expandable boundary. Consequently, it eliminates constraints on the scope of the study and significantly enhances the reliability, accuracy, and applicability of research results.

Furthermore, in this study, modelling enabled the integration of the electrical propulsion system into the case ship along with the Solar PV system instead of the conventional MGO-fuelled mechanical propulsion system. This provides environmental insights into scenarios where approximately 52,460 fishing boats of similar types and sizes are converted into electric propulsion ships or ships with integrated Solar PV systems. These research findings can serve as valuable foundational information for stakeholders involved in future shipbuilding and design decisions. They not only offer guidance to policymakers and rulemakers but also provide substantiated evidence for future directions.

Lastly, this research enables a detailed evaluation and consideration of the electric propulsion system, which is spotlighted not only in maritime transport but also in inland vehicle, by incorporating an evaluation of the South Korean national power grid. Given that the environmental efficiency of electric propulsion systems is significantly influenced by the environmental footprint of the electricity they consume, this study generates meaningful results that can further encourage sustainable practices and greening policies.

This study involved the modelling of the electric propulsion system and MPPT-applied Solar PV system based on the operational profile, engine load, route, etc. of a real fishing boat. In essence, it verified the suitability of the modelling by implementing systems that do not exist and ensuring that simulation results aligned with the actual ship's operational data. However, certain aspects, such as battery weight, installation area, and battery degradation, were not included within the scope of this research. Consequently, future research is to encompass an extended scope that considers these factors. It aims to plan and execute evaluations regarding additional emissions resulting from appropriate modelling that accounts for variations in power demand based on the ship's weight and degradation of sources.

Furthermore, recent research has considered and studied fuel cell systems linked to various fuels, in electric propulsion systems. Reflecting this industrial trend, it is crucial to conduct robust research on electric propulsion systems that include fuel cell systems and investigate how these systems can be appropriately integrated and controlled in conjunction with solar PV systems and battery systems.

Lastly, environmental impact is not the sole focus moving forward. Sustainability is increasingly emphasised, necessitating exploration of systems that can be used continuously over extended periods. To achieve this, comprehensive research addressing not only the environment but also the societal (safety) and economic (cost) aspects, integral components of sustainability, is imperative. In other words, there is a need for research that evaluates the safety and cost of electric propulsion systems, in line with this study. In particular, with regard to installing a solar PV system on small ships, advanced research is needed to determine the effectiveness of the emission reduction effect compared to the cost. Moreover, it is essential to assess whether these systems can indeed be sustainably utilised, providing outcomes that can contribute to stakeholders.