Maritime Energy Efficiency: Emerging Trends and Key Performance Indicators

Recent studies [5] highlight the shipping industry's capacity for adopting sustainable practices by integrating various technological innovations. The technologies discussed in these studies can be categorised into different groups, each targeting specific elements of ship design and operation to enhance energy efficiency and lower CO₂ emissions.

Current trends in energy efficiency within the maritime shipping sector emphasise significant innovations and regulatory responses aimed at reducing fuel consumption and emissions.

The maritime sector is actively implementing various strategies to enhance vessel efficiency and environmental sustainability. These include improvements in design, hydrodynamics, machinery, and the use of alternative energy sources. Enhancements in machinery for better efficiency encompass the adoption of energy-efficient lighting, engine derating and tuning, as well as advanced management of pumps and fans. Innovations like common rail fuel injection, high-efficiency boilers, and diverse power generation technologies, including hybrid and electric propulsion systems, are being investigated to reduce energy consumption and emissions. Additionally, waste heat recovery and improvements in internal combustion engines are other avenues for increased efficiency.

Exploring alternative energy sources such as hydrogen, ammonia, methanol, and liquefied natural gas offers numerous advantages and poses challenges related to emissions, storage, and safety. Renewable energy options like wind propulsion and solar power are also being considered, although they encounter specific challenges in implementation.

Emerging technologies in the maritime industry, such as fuel cells, advanced battery systems, gas turbines that can adapt to alternative fuels, nuclear propulsion, and carbon capture, are at the forefront of maritime innovation. These categories and technologies are outlined later in the text.

Design enhancements such as bulbous bows, extended aft waterlines, and optimised vessel shapes decrease resistance and drag, boosting fuel efficiency. Innovations in propulsion systems, including shaft line configurations and lightweight materials, as well as strategies like reducing vessel speed and designing aerodynamic superstructures, also contribute to energy conservation.

Hydrodynamic improvements continue to advance this efficiency by employing devices that optimise the flow of water around the hull and propeller. Additionally, integrated systems that combine propellers and rudders, along with advanced propulsion technologies like pod drives and thrusters, enhance navigational performance and energy usage.

The maritime industry has devised a series of operational solutions and incentive initiatives aimed at reducing emissions through a combination of technological advancements and improved operational efficiencies.

Strategies such as slow steaming reduce fuel consumption by operating ships below their maximum speed, though this can increase fouling and resistance due to longer travel times. Speed optimisation tailors ship speeds to achieve maximum fuel efficiency and minimum emissions, considering factors like sea-state and route conditions, and requires specific crew training and tools like trim optimisers.

Optimising a ship’s trim and draft can significantly decrease resistance and thus fuel consumption. Similarly, efficient planning of ship movements—including better cargo handling and weather routing, along with optimised port arrivals and departure - minimises unnecessary fuel use. Cold ironing, which involves powering ships via shore-based sources while docked, reduces onboard emissions, provided the shore power is derived from renewable sources.

Digitalisation supports these efforts significantly [6]. Technologies like big data and artificial intelligence optimise routing and manage fuel consumption effectively. Digital twins of ships allow for real-time monitoring and maintenance, while blockchain enhances the transparency and efficiency of cargo movements. Advanced communications technologies such as cloud solutions and 5G networks enable more efficient remote operations and data transfer. Autonomous technologies and the Internet of Things further refine operational decisions, reducing reliance on fossil fuels through improved routing and speed management. Moreover, 3D printing reduces logistical emissions by allowing on-demand production of parts, and environment-sensing devices optimise operations based on real-time data. Together, these innovations mark a significant transformation towards a more efficient, sustainable, and technologically equipped maritime industry.

Market and incentive initiatives in the maritime industry include a variety of market-based measures such as carbon trading schemes and fuel levies. These are designed to encourage the adoption of environmentally friendly technologies and practices [7].

Under the "Poseidon Principles," a framework has been established where banking finance is provided primarily to those shipowners who meet specific emission standards, integrating climate considerations directly into lending decisions. This not only promotes the use of green technologies but also ensures financial backing is aligned with environmental objectives.

Reduced taxation is another strategy being employed. Ships that implement green technology and comply with environmental standards benefit from reduced port dues, which can significantly decrease their operational costs.

The Green Fund, established through carbon credits, motivates further emission reductions. It requires each flag state to show measurable decreases in emissions. Those failing to meet their targets must buy carbon credits from more efficient states, thus fostering a collective push towards global emission reduction [8].

In addition, broader regulatory measures like the evaluation of the Energy Efficiency Design Index (EEDI) and the Carbon Intensity Indicator (CII) are implemented. National and regional policies that include carbon pricing and incentives for adopting green technologies play a crucial role in accelerating the decarbonisation efforts in the maritime sector.

The research across various studies highlights the integration of efficiency evaluation models in promoting sustainable practices within the maritime industry, emphasising the critical interplay between environmental management, technological innovation, and regulatory frameworks.

The research articles provided explore a range of innovative strategies and technologies aimed at advancing the sustainability and efficiency of the maritime industry.

Various studies focus on the environmental and technical viability of zero-carbon fuels like ammonia, hydrogen, and electricity, as well as methanol and LNG [9-11]. These fuels are evaluated for their potential to reduce greenhouse gas emissions in different types of vessels and operational conditions. These studies also address the broader economic and policy frameworks necessary to support the maritime sector's transition to greener practices, including the strategic production of ammonia in response to global shortages and the role of government subsidies in promoting eco-friendly technologies [12].

The transition to cleaner maritime operations is supported by infrastructure development like LNG bunkering stations and the adoption of shore power technology, which reduces [13] emissions from ships while docked but while alternative fuels present environmental benefits, they also introduce challenges such as the high flammability of LNG, requiring new safety assessments and technologies to ensure safe bunkering and operations [14]. Innovations such as improved hull designs, advanced propulsion systems, and the adoption of alternative fuels like LNG and biofuels are crucial. These technological advances are complemented by operational strategies like slow steaming and weather routing to reduce energy use and emissions [15].

Additionally, the role of green port initiatives emphasises the need for technical innovations, operational enhancements, and supportive policies to foster sustainable port operations [16].

Research on hull coatings [17] and modernisation of propulsion systems in ships highlights potential fuel savings and emission reductions [12, 18]. The integration of photovoltaic panels and hybrid electric systems is also explored [19].

Innovative approaches for ship efficiency are discussed [20], and the integration of circular economy principles into maritime operations through data-driven technologies such as Iot and data analytics to optimise ship operations for energy efficiency and emission reduction, indicating potential for reduced environmental impacts and operational costs.

Considering the outcomes drawn by the analysis conducted in the present research, and shown in Table 2, the selected KPIs have been grouped and classified according to three main categories, referring to energy, environmental impact, and traditional/alternative KPIs, respectively. Each of the mentioned categories is described in the following sub-sections.

Table 2. Results of the literature review

4.1 Energy related KPIs

Energy efficiency KPIs in the maritime sector focus on managing and reducing the consumption of fuel and power efficiency. These metrics include the efficiency of propulsion systems, the power demand of ship propulsion systems, and fuel consumption of various systems. Additionally, advanced propulsion technologies, like hybrid propulsion systems and Wind Assisted Ship Propulsion (WASP), aim to enhance operational flexibility and optimise fuel savings under different conditions such as wind speed and wave height, further contributing to energy efficiency in maritime operations.

Another critical aspect is represented by resource management, which involves monitoring the consumption of electric energy, fuel, and water, alongside waste management on ships. Metrics in this category emphasise reducing overall consumption and improving the efficiency of systems that convert fuel into electrical and thermal energy, particularly in cruise ships. For instance, the cogeneration efficiency KPI measures the efficiency of power plants onboard in converting fuel into useful energy forms, which is crucial for optimising onboard energy utilisation.

Operational KPIs also include the use of shore power to reduce fuel consumption at berths and the optimisation of propulsion systems. These strategies not only reduce the environmental impact but also lead to significant cost savings. The use of advanced technologies like shore power enables ships to minimise their reliance on onboard fuel, resulting in decreased emissions and better fuel efficiency. A systematic evaluation of changes in fuel consumption under various operational scenarios can contribute to the understanding of the effectiveness of the applications mentioned technologies in the shipping context.

4.2 Environmental impact KPIs

Environmental impact KPIs in the maritime industry mainly focus on emission and pollution reduction, monitoring, performance evaluation, and assessing broader environmental impacts. Key metrics include the Carbon Intensity Indicator (CII), which measures the efficiency of ships in terms of CO₂ emissions per cargo-carrying capacity and nautical mile, and the Energy Efficiency Existing Ship Index (EEXI), targeting emission reductions through design improvements.

Specific KPIs such as the Energy Efficiency Design Index (EEDI) measure the efficiency of ship designs in reducing CO₂ emissions, while the Energy Efficiency Operational Indicator (EEOI) evaluates the operational performance of ships in terms of GHG emissions per tonne-mile of cargo transported. These KPIs are part of comprehensive strategies to reduce specific pollutants like CO₂ and NO_x and manage overall environmental impacts.

Ports play a significant role in monitoring and managing environmental performance. Environmental management systems (EMS), certified by standards like ISO 14001, are implemented to monitor air and water quality, as well as greenhouse gas emissions. For instance, ports like Rotterdam monitor various environmental parameters, including oxygen and nutrient concentrations in water, as part of their quality initiatives. Such systems provide a framework for evaluating and recording environmental performance, which is crucial for continuous improvement.

Additionally, global environmental impacts are assessed through Life Cycle Assessment (LCA) metrics such as Global Warming Potential (GWP) and Eutrophication Potential (EP). These measures help quantify the broader environmental consequences of maritime activities, providing a basis for developing strategies to mitigate adverse impacts. By incorporating these comprehensive assessment tools, maritime operators can better understand and address the environmental footprint of their operations.

4.3 Traditional/Alternative KPIs

Traditional and alternative KPIs related to maritime energy efficiency encompass economic, managerial, and environmental dimensions. Economic KPIs include macroeconomic indicators like value-added growth rate and contribution to GDP, as well as specific cost categories such as operational expenditure (OPEX), capital expenditure (CAPEX), and fuel costs. Financial metrics like Net Present Value (NPV), Real Option Value (ROV), and Financial Value at Risk (FVaR) are used to evaluate profitability, investment sustainability, and risk. These metrics help in understanding the economic implications of adopting green technologies and optimising operational costs.

Furthermore, environmental KPIs, which include both traditional and innovative measures, emphasise the reduction of emissions and resource consumption. Traditional KPIs like emissions of CO₂ and NO_x and newer measures like the Energy Efficiency Design Index (EEDI) and the Carbon Intensity Indicator (CII) provide a comprehensive view of the environmental impact. Advanced propulsion technologies, such as hybrid systems and WASP, offer alternative solutions for improving energy efficiency and reducing environmental impact. These KPIs collectively guide the maritime industry towards more sustainable and efficient operations.

This research was conducted as part of the project “CENTRO NAZIONALE PER LA MOBILITÀ SOSTENIBILE – CNMS” – CUP I63C22000340001. The authors gratefully acknowledge the financial support provided under the National Recovery and Resilience Plan (Piano Nazionale di Ripresa e Resilienza – PNRR) – Mission 4.