Onshore Power Supply in Multi-Terminal Maritime Ports

Abstract

Depending on the type of fuels used by ships in maritime port operations, emissions may contribute more or less to the concentration of greenhouse gases in the atmosphere. The maneuvering of ships at maritime ports uses mainly auxiliary engines, resulting in a significant contribution to emissions. It is understandable that the energy transition in this sector brings benefits and is essential to sustainability, considering its economic and strategic importance. Among the measures established to ensure this transition is the onshore power supply and increased electrification in transportation operations. Maritime ports are not yet prepared for these adjustments, as their heterogeneity and contexts require further research, such as studying the impact of depth on energy consumption, terminal type, and others. The purpose of this paper is to quantify the reduction in greenhouse gas emissions achievable through the implementation of an onshore power supply at the Port of Sines, Portugal. Furthermore, it aims to identify the key factors influencing these adoptions to provide practical recommendations that can guide in advancing energy transition, reducing reliance on fuels, and fostering a sustainable future for the port industry.

1. Introduction

The importance of the oceans in regulating the climate [1], providing a carbon sink [2], and contributing to the global and local economy of countries is indisputable [3,4]. Their protection is vital, especially through maritime spatial planning (MSP) resources [5,6], which involves developing practical guidelines and fostering innovative solutions to address the multifaceted impacts of climate change on marine ecosystems and coastal communities [5], including the use of renewable energies within all maritime activities [7].

Ocean activity and the maritime industry are intrinsically linked, as maritime transport is responsible for moving 80% of the world’s trade [8,9], which strengthens the global economy and the cooperation and interdependence between countries. Since 2006, China has been the most integrated country in the world’s maritime transport networks, followed by the Republic of Korea, Singapore, the United States, and Malaysia [10]. By 2024, globally, the world fleet’s carrying capacity reached 2.35 billion dead weight tons (dwt), an increase of 77 million dwt from the previous year [10]. All these integrations and activities pose challenges, which, in turn, have prompted a regulatory framework for reducing the risk of degrading ecosystems, among other aspects.

In terms of controlling emissions and energy consumption, international shipping is subject to an increasingly strict regulatory framework. This is aimed at reducing its environmental impact and contributing to the achievement of the goals proposed in the Paris Agreement [11] and to energy transition [12,13], among other guidelines [14]. This framework began with the signing of the International Convention for the Prevention of Pollution of the Sea by Oil (OILPOL) in 1954 [15]. In 1973, the International Convention for the Prevention of Pollution from Ships (MARPOL) was signed [16], which is the document currently used to regulate the impacts of pollution caused by ships in the maritime industry. This includes regulations aimed at preventing and minimizing pollution in six technical Annexes. In the same year, the Marine Environment Protection Committee (MEPC) was set up as a permanent body of the International Maritime Organization (IMO) with the responsibility of coordinating and supervising policies and measures to protect the marine environment from pollution caused by ships and the maritime industry. This includes the control of discharges into the sea and the atmosphere. Discharges to the atmosphere include emissions of greenhouse gases (GHGs) and other gases, volatile organic compounds (VOCs), and particulate matter (PM) from the use of fossil fuels and chemical compounds throughout the maritime industry.

In 2018, MECP.304 (72) [17] published the Initial IMO Strategy on Reduction of GHG Emissions from Ships with a Roadmap to achieve decarbonization of the maritime industry by 2050. In 2023, the MECP.377 (80) IMO Strategy on Reduction of GHG Emissions from Ships was published [18]. This strategy aims to achieve net-zero GHG emissions for all maritime industry and port activities [18]. Measures include shoreside/onshore power supply from renewable sources, infrastructure to support the supply of zero or near-zero GHG emission fuels and/or energy sources, and further optimization of the logistic chain and its planning, including ports [18]. Onshore power supply (OPS) and offshore power supply are considered measures to reduce emissions from the use of fossil fuels by ships while in berthing or anchoring operations within ports, respectively, if they are integrated from renewable sources [19].

While ships are maneuvering within a port’s jurisdiction area, their main engines (MEs) operate at a lower load factor or are shut down. In this case, the auxiliary engines (AEs) mobilize the ship, where their load percentage varies depending on the type of maneuver. To maintain the functionality and safety of the ship during berthing, AEs provide the necessary power for critical systems. Depending on fuel type and technology, AEs can have even higher emission factors than MEs [20,21].

Depending on the type of fuels for use in marine diesel engines [22], emissions to the atmosphere include CO, CO₂, SO₂, NO_x, PM_2.5, PM₁₀, and total hydrocarbons (THSs) during ship berthing operations [23]. In the short term, these emissions can have an effect on the health of people who work at port terminals or live in nearby cities, even impacting the local economy [24,25]. However, their concentration can vary depending on wind speed and direction, location of the berthing point, use of emission-reducing technologies, and other ship parameters [26]. In the long term, these emissions contribute to the concentration of GHGs in the atmosphere and thus to global warming.

With the increase in cargo per ship worldwide, loading and unloading delays during berthing have increased. As a benefit, this brings a reduction in emissions per unit of cargo [27]. However, the energy consumption for the operation of cargo handling equipment has increased. This equipment has been replaced by electric components, as an additional measure to reduce the use of diesel [28].

OPS is presented as a suitable measure to reduce emissions in seaports and increase their efficiency, especially in those located in urban or coastal areas. This measure is driven by government regulations and incentives, including emission controls established by the IMO [29]. In addition to the term OPS, other terms can be used:

• Shore power (SP) [30];
• Coil ironing (CI) [31,32];
• Alternative maritime power (AMP) [33];
• Shore-to-ship power (SSP) [34];
• Shore-side electricity (SSE) [35];
• High-voltage shore connection (HVSC) [36].

These definitions refer to the supply of power from an onshore network to avoid running diesel engines when the ship is in port. The electrical power supply for the engines can be provided from the public grid, incorporating renewable energy sources (RESs) or energy storage systems (ESSs) [32]. During this maneuver, it requires a continuous and significant supply of electrical power [37].

OPS systems reduce the emissions from the use of fossil fuels in AEs to net-zero GHG emissions. However, the emissions are transferred to the power generation source [38]. Improvements in service continuity and a reduction in failure risks have been obtained by integrating OPS with RESs and microgrids [32].

Figure 1 shows a schematic of the overall electrical system of an OPS consisting of ship-side electrical systems (onboard receiving device), cable management system, shore-side electrical systems, and infrastructure [39,40]. HVSC can be realized at 6.6 or 11 kV [36,41], and low-voltage shore connection (LVSC) is realized at 440~380 V (50/60 Hz) [42].

Some of the benefits of OPS include improvements in air quality and public health; increased efficiency; and reductions in noise, air emissions, fuel consumption, and carbon taxes [43]. Ports with renewable source systems [31,44] or with the use of green hydrogen as a vector [45] have demonstrated the achievement of these objectives. Despite the benefits, their implementation presents some of the challenges shown in Table 1.

As shown in Table 1, several challenges related to OPS must be addressed. These include the following:

• Technical applications concerning energy supply and parameters: a previous case study highlights that the joint coordination between authorities and port operators enhances energy independence, system efficiency, operational reliability, and the profitability of the microgrid [46].
• Installation and retrofitting costs for ships, as well as potential subsidies: there is evidence supporting emission reductions when auxiliary engines are powered by the electrical grid [47].
• Uncertainties regarding investment recovery in decarbonization projects: the cost of electricity is less volatile than that of fuel supply, making OPS a lower-risk alternative [48].
• Finally, despite a variety of publications relating to the use of alternative fuels for emissions decarbonization, current global production cannot meet the necessary demand [49].

Table 1. Challenges of OPS systems [50,51].

Criteria	Sub-Criteria	Description
Technical application	Matching of the port and ship power supply	It is necessary to ensure the matching of voltage and frequencies, and the compatible current phase when using the AMP.
	Direct power supply from the grid	To achieve the direct grid power supply to berth ships, it is necessary to solve technical problems, including high-power electricity frequency conversion, equipment cooling, electromagnetic compatibility, and harmonic wave control.
	Power supply quality	Technical issues of voltage stability and smooth transition between ships and the OPS.
	Technical standard	Technical and standardization issues such as high-power frequency transformation, harmonic control, apparatus refrigeration, and compatibility of electromagnetism.
	Additional power capacity	Not meeting the amount of power required by the ship, and the problem of the consistency of high-voltage and low-voltage interfaces.
	Coordination between the ship and the power supply	Coordination between the port and regional grids, the extent of stakeholder apprehension, and the lack of electricity service rate grades.
Economic	Retrofit costs	Power reception facility installation cost, existing ship renovation cost, ship power monitoring device installation, and repair cost.
	Operating costs	Cost of managing and maintaining human resources, power, and power-using equipment when using OPS.
	Maintenance costs	OPS management measures include establishment and improvement, cable safety maintenance, port cooperation failure prevention cost.
	Lack of economic benefits	No economic benefit in cost–benefit analysis compared to fuel consumption.
Other	Policies and supporting systems	Lack of safety agreements between ships and ports, and OPS implementation plans or guidelines issued by government departments.
	Subsidy/incentive	Lack of policies on port financial subsidies and tax reductions.

Table 1. Challenges of OPS systems [50,51].

Criteria	Sub-Criteria	Description
Technical application	Matching of the port and ship power supply	It is necessary to ensure the matching of voltage and frequencies, and the compatible current phase when using the AMP.
	Direct power supply from the grid	To achieve the direct grid power supply to berth ships, it is necessary to solve technical problems, including high-power electricity frequency conversion, equipment cooling, electromagnetic compatibility, and harmonic wave control.
	Power supply quality	Technical issues of voltage stability and smooth transition between ships and the OPS.
	Technical standard	Technical and standardization issues such as high-power frequency transformation, harmonic control, apparatus refrigeration, and compatibility of electromagnetism.
	Additional power capacity	Not meeting the amount of power required by the ship, and the problem of the consistency of high-voltage and low-voltage interfaces.
	Coordination between the ship and the power supply	Coordination between the port and regional grids, the extent of stakeholder apprehension, and the lack of electricity service rate grades.
Economic	Retrofit costs	Power reception facility installation cost, existing ship renovation cost, ship power monitoring device installation, and repair cost.
	Operating costs	Cost of managing and maintaining human resources, power, and power-using equipment when using OPS.
	Maintenance costs	OPS management measures include establishment and improvement, cable safety maintenance, port cooperation failure prevention cost.
	Lack of economic benefits	No economic benefit in cost–benefit analysis compared to fuel consumption.
Other	Policies and supporting systems	Lack of safety agreements between ships and ports, and OPS implementation plans or guidelines issued by government departments.
	Subsidy/incentive	Lack of policies on port financial subsidies and tax reductions.

Currently, there is scarce research related to the limitations that consider the increased risks that may occur when electrical energy is converted uncontrollably into heat or when uncontrolled flames, glows, or sparks occur [32,52,53], especially when the OPS involves high-voltage equipment [54]. Additionally, the process of ship berthing is considered crucial in the safety of seaports [55].

Notably, 31% of the risks in ship berthing activities in maritime ports are related to oil and its derivatives, chemicals, and natural gas [56]. Due to poor resilience of infrastructure [42] and losses, maritime terminals with the highest vulnerability are those storing chemicals (particularly chlorine, ammonia, methanol, nitrogen, sodium, etc.), liquefied natural gas (LNG), liquid and solid bulk [57], and general cargo [58] (especially roll-on/roll-off), as well as cruise terminals [59,60]. Hazardous events related to accidents during berthing may occur, such as explosions due to loading and unloading operations, and fires on ships/carriers during electrical installations and on cargo carriers during cleaning operations [61].

The purpose of this paper is to quantify the reduction in greenhouse gas emissions achievable through the implementation of an OPS at the Port of Sines, Portugal. Furthermore, it aims to identify the key factors influencing the adoption of OPS in multi-terminal ports and to provide practical recommendations that can guide port authorities in advancing energy transition, reducing reliance on fossil fuels, and fostering a sustainable future for the port industry.

The heterogeneity in port types and contexts implies that further empirical research is needed [62] and that smart approaches associated with efficient and clean energy use for port-to-ship pathways to reach net-zero GHG emissions in the maritime shipping sector need urgent research [63]. Finally, a cascade of challenges is observed, where research on operations can help the planning, making it possible to simulate future scenarios and reduce risk in investments [64].

2. Materials and Methods

The Port of Sines is a maritime infrastructure of vital importance for Portugal and other countries. The maritime area is 147.5 km² (Figure 2), with a maximum depth of 28 m. Presently, this port has five specialized terminals, including a sports and fishing port, with private concessions, which are included in

Table 2. Identification, berths, depth, and cargo type from different terminals of the Port of Sines.

Terminal	Identification	Depth (m)	Cargo Type
Containerized cargo	SCT	17	Container
Liquid bulks	LBT	28	Crude oil, refined oil, liquefied petroleum gas (LPG), methanol, and chemical naphtha.
Liquefied natural gas	NGT	15	LNG
Petrochemical	PCT	12	Propylene, ethylene, butadiene, ethyl tertiary butyl ether, ethanol, methyl tertiary butyl ether, aromatic mixtures, and methanol
General cargo	GCT	18	Dry bulk, general cargo, and ro_ro
Others	Others	--	Sports and fishing port, tugboat service, and other services

.

In this study, we calculated the electrical energy consumption and emissions from the operation of equipment used for the unloading and loading of cargo at the terminals and the maneuvering of ships within the maritime jurisdiction area for the period 2018–2022. Only four terminals (LBT, NGT, SCT, and PCT) were considered, since the GCT started its operations only in August 2022.

The electrical terminal load handling devices are as follows:

• Centrifugal pumps for liquid products of the oil and petrochemical industry in the LBT;
• Centrifugal pumps for petrochemical products of different viscosities and densities in the PCT;
• Cryogenic pumps for natural gas liquids at low temperatures in the NGT;
• Electric rubber-tired gantries (RTGs) and rail-mounted gantries (RMGs) in the SCT.

To calculate the electrical energy consumption of the terminals’ equipment, the measurements of the electrical supply of the network were considered. Monthly records measured at the transformation points (TPs) in the LBT and SCT, managed by port authorities, were used. Additionally, the concessionaires that manage the NGT and PCT provided their energy consumption records for the same period. Emissions were calculated according to Equation (1), where the grid emission factors used are those indicated for each year by the APA [65]. Since 2005, the APA has been publishing annual emission factors used to calculate the emissions associated with Portugal’s energy consumption. These factors are based on measurements and real data and consider the impact of renewable energy penetration. Their purpose is to establish or plan measures to reduce emissions (Lopes, 2023) [66]. These factors were used to estimate emissions from electricity consumption across all terminals.

$$Em=E * EF$$

(1)

where

• Em: emissions due to the activity (tCO₂eq);
• E: energy (MWh);
• EF: emission factor (tCO₂eq/MWh).

Since 2005, the APA [65] has been publishing annual grid emission factors to calculate emissions linked to energy consumption in Portugal. These factors are grounded in actual measurements and data, accounting for the growing penetration of renewable energy sources. Their primary aim is to facilitate the establishment or planning of measures to reduce emissions [66]. Furthermore, these factors were applied to estimate emissions from electricity consumption across all terminals, aligning with methodologies from other studies [67].

The methodology shown in Figure 3 was used to calculate electrical energy consumption and emissions from ship maneuvers within the area of jurisdiction. The methodology involved the use of maritime transport information within the area of jurisdiction, maintained by the port authority.

Regarding the ship movement data until 2019, they were collected using the maritime transport information from the Port Single Window (JUP). After 2020, the data were collected from the Logistics Single Window (JUL) [68] as a technological platform. The JUP and JUL include information on the scales of the ships, cargo, access to facilities, and operations in the terminals. Among the maritime transportation data are the type and times of maneuvers per terminal [69,70], which include the following:

• Passenger locator form (PLF)—entry;
• Anchoring;
• Suspending;
• Berthing;
• PLF—exit;
• Others.

The calculation was carried out based on information about the type of ship, the fuel used, and the time duration of the maneuvers, according to the methodology recommended by the European Environment Agency (EEA) [71,72,73]. This is based on the function of the power and load factors of the ME and AE of the ship and the execution time of each maneuver, the load factor, the proportion of the AE/ME, and the fuel type. In this methodology, the AE power is estimated as a percentage of the ME depending on the type of ship.

In total, 28,785 maneuvers were analyzed over the 5 years of the study; however, only 48% of these data included the power generated by the ME. For data completeness, missing ME power data [74] were assigned numerical values based on linear regression. In the literature, various methods for imputing missing data have been discussed. Among these, the statistical models utilizing direct data input based on dead weight tons (dwt) [75], twenty-foot equivalent unit (TEU) [76], or gross tonnage (GT) [74,77] stand out due to their advantages. These models consider the asymptotic nature of the data, offering moderate accuracy while ensuring high interpretability. Moreover, similar studies, applying empirical rules, have been used for estimating ship emissions in ports.

3. Results and Discussion

Figure 4, Figure 5, Figure 6 and Figure 7 show the bubble chart of the dwt and power of ME by terminal, for the period 2018–2022. The ME power was divided into quartiles as a statistical tool to facilitate comparison and analyze trends in GT by year for each terminal. Given the different types, densities, and quantities of cargo and ships, this representation allowed for characterizing the trends in cargo/ship handling across the various terminals. From this analysis, the following observations emerged:

• In 2022, there was a significant increase in the ME power and GT in the LBT.
• Starting in 2019, the NGT managed ships with ME power in the third quartile (Q3). However, it was not until 2022 that it began to handle ships from this quartile with higher GT.
• Throughout the analyzed years, ships with ME power across all quartiles were observed. The only exception was the PCT, which during the same period, exclusively handled ships from the first quartile (Q1), regardless of GT.

Table 3. Berths from different terminals of the Port of Sines.

Terminal	2018	2019	2020	2021	2022	Total
LBT	564	611	495	187	857	2714
NGT	23	29	20	--	55	127
SCT	649	672	791	540	644	3296
PCT	51	96	55	--	96	298
Total	1287	1408	1361	727	1652	6435

and

Table 4. Average time (hours) of berths from different terminals of the Port of Sines.

Terminal	2018	2019	2020	2021	2022	Average
LBT	16.03	17.54	16.25	10.27	19.06	15.83
NGT	23.52	23.28	23.61	--	22.33	23.19
SCT	16.37	14.80	15.34	19.04	23.36	17.78
PCT	26.15	23.66	24.62	--	24.27	24.68

show the number of berths and time in the terminals for this period.

Figure 8 and Figure 9 show the average power consumption and emissions for each terminal. It is noteworthy that in the NGT, SCT, and PCT, the energy consumption per electrical energy (EE) was higher than the consumption of the AE in berthing operation. Additionally, these emissions were only surpassed by the emissions from the operation of the equipment in the LBT and SCT. The reason for this is multifaceted. One of the factors was that, in these terminals, there was an increase in per ship charge (Figure 4 and Figure 7), berthing time (Table 4), and emissions (

Table 5. Average emission (kCO₂eq) of berths from different terminals of the Port of Sines.

Terminal	2018	2019	2020	2021	2022	Average
LBT	9.59	12.41	11.54	4.00	16.61	10.83
NGT	93.27	98.52	89.46	--	84.29	91.39
SCT	48.22	42.53	46.78	58.34	73.49	53.87
PCT	16.79	14.53	12.33	--	13.09	14.19

).

To change an AE from a combustion to an electric engine, a series of steps must be followed [78,79,80]. This increases its efficiency and reduces losses. However, this improvement was not considered in this work. Figure 10, Figure 11, Figure 12, Figure 13 and Figure 14 show the emissions of terminals in two cases: with an AE (case 1) powered by fossil fuels or electrically with connection to the public grid (case 2) [32].

Figure 13 shows the reduction in emissions if the supply of electrical equipment is connected and, in addition, the SCT, since the latter has lower risks than those found to occur in the other three terminals, with a penetration of 10, 15, and 25% of RESs and an emission factor of 0 tCO₂eq for these types of energy [81].

4. Conclusions

The implementation of onshore power supply (OPS) in multi-terminal seaports is a strategy for decarbonizing maritime transport and improving environmental quality in port areas. This study has shown that it offers environmental benefits despite the limits imposed by the presence of hazardous terminals.

OPS systems need to overcome several challenges. The integration of renewable energy in the supply and the adaptation of existing port infrastructure are critical aspects that demand attention. This work highlights the need to accelerate the implementation of OPS in multi-terminal ports. This is due to an increase in time and emissions due to the presence of ships with larger gross tonnage. Only through a concerted and coordinated effort can we fully reap the benefits of OPS systems and move toward a sustainable and environmentally friendly maritime future.

Given the critical nature of terminal operations, the application of renewable energy sources could be limited to powering ancillary equipment, such as ship loading and unloading systems, where intermittency and variability do not compromise safety. The integration of renewables into the main grid of these terminals may require advanced energy storage and management solutions, as well as reliable backup systems, to mitigate the risks associated with fluctuating renewable generation.

While the integration of renewable energies in the future would further optimize the benefits of OPS, connection to the public grid remains a valuable and affordable strategy. It allows ports and shipping lines to take a concrete step toward sustainability, demonstrating their commitment to reducing the carbon footprint of shipping. The widespread adoption of OPS, even in its most basic form, represents a crucial step toward a cleaner and more responsible maritime sector.