Fotios D. Kanellos, George J. Tsekouras, Vassilis C. Nikolaidis, John M. Prousalidis
©Shutterstock.Com/Elnur
As maritime transport rapidly grows, seaports are becoming larger, more complex, and energy intensive. Seaports are facing the challenges of increasing their energy efficiency, adopting and producing technological innovations, limiting their carbon footprint, and complying with legislation that aims to reduce the environmental impact of marine industry activities. To this end, they aim to resynthesize their master plan, according to which they are transformed into smart energy hubs where extensive electrification plays a key role. The electric power consumption of seaports is continuously increasing because of operational, regulatory, and environmental factors, making intelligent energy networks a very promising solution.
Seaports include several flexible loads, such as refrigerated containers (reefers), shore-to-ship power supplies, electric vehicles, energy storage systems (ESSs), lighting, cranes, and so on. Reefers form an ideal solution for distributed cooling energy storage, while shore-to-ship electrical connection, known as “cold ironing,” turns ships at berth into very flexible power producers–consumers and reduces their carbon footprint. Moreover, seaports usually have very good potential to produce energy from renewable energy sources (RESs).
Smart power management has become a crucial factor for seaports in their endeavor to increase their efficiency, flexibility, and environmental friendliness. Moreover, the transformation of seaport energy hubs into flexible energy prosumers will allow seaports to become significant electricity market players. This will also be beneficial for the electricity networks, as the future seaport prosumers will be able to support them with ancillary services, such as frequency support, load shifting, voltage support, “virtual spinning reserves,” and so on.
Cranes are electromechanical machines that are used for the handling of cargo containers. They can be classified as quay cranes that are used to load and unload containers from ships at berth and gantry cranes that are used to load and unload containers from/to yard trailers and stack them at the yard. Gantry cranes can be further classified to rail-mounted and rubber-tired gantry cranes. The intermediate facility between quay and gantry cranes is the yard trailer. It is used for the autonomous transportation of containers on a specific path or guided platform between the terminal and yard area.
The electric system of the cranes includes electrical motors for cargo lifting and the rotation of the crane itself. Several other electrical motors are used to drive pumps for ventilation systems and air conditioning. The major electric power consumption of a crane occurs during hoisting, while energy is regenerated during cargo lowering. This energy can be injected back into the seaport electrical network and stored in batteries.
A reefer is an intermodal container capable of refrigerating its cargo, using an integrated refrigeration unit. When reefers are being transported, they can be powered from diesel-powered generators attached to them. Some reefers that are stored in closed spaces without adequate ventilation to remove the produced heat are equipped with a water-cooling system. Reefers can maintain the temperature in their interior in a range from −65 up to 40 °C, and they can be generally classified as 20- and 40-ft containers according to their size. Reefers constitute a large portion of commercial seaports’ electric power consumption, and they can be a substantial factor of load flexibility.
Shore-to-ship power supply, widely known as cold ironing, is a newly developed technology allowing the connection of the electric power systems of vessels moored at quays to the seaport electric network. This can result in significant reductions of ship emissions, as ship auxiliary diesel engines can be shut down. In addition to the benefits resulting from emission reduction, cold ironing increases the reliability of ship power system operation, as ship loads can be supplied by the shore-to-ship power supply system, by ship auxiliary generators, and jointly by ship auxiliary generators and the shore-to-ship power supply system. Another feature of shore-to-ship power supply systems is their capability to allow ship generators to provide power to the port electrical network and thus supply part of the seaport load if necessary.
The integrated shore-to-ship power supply system includes a set of standardized components, such as high-voltage shore connection systems, step-down transformers, power converters to interface the 50- or 60-Hz power system frequency with that of the ship, cables, a switchboard on the shore side to direct and measure electrical energy and a respective switchboard on the vessel side, grounding, and equipment for the communication of ship and shore systems.
Voltage levels may differ at different seaports and in ships. In that case, the respective equipment should be optimally designed and standardized to bridge incompatibilities. Moreover, the different subsystems and technologies included in shore-to-ship power supply installations should be harmonized following specific standards and technical requirements. In this way, globalization and safety standards will be ensured.
In addition to ship emissions abatement, shore-to-ship power supply systems reduce noise and vibration in seaport areas, directly benefiting ship passengers, crews, port workers, and the inhabitants of adjacent areas. Hence, shore-to-ship power supplies will greatly contribute to the improvement of port operation conditions and living quality in seaport surrounding areas.
Warehouses; technical, industrial, and administration buildings; and passenger stations are hosted in seaport areas. Seaport buildings are usually intense electric power consumers. The variety of the operation characteristics of their loads may lead to interesting power consumption profiles that could pave the way for power management applications exploiting their inherent flexibility in power and time.
Lighting systems are found in seaport parking lots, roads, railway sidings, industrial shipbuilding yards, container storage areas, cranes, buildings, and so on. The replacement of lighting devices with new ones using LEDs has been investigated, as LEDs are able to provide equal luminance with that of incandescent lamps, with significantly smaller power consumption. In that case, energy savings can reach up to 40%. However, it should be noted that most LED technology lamps produce light of 4,000 K that is white and not appropriate for seaports with foggy weather conditions.
The replacement of conventional vehicles by electric ones and the development of electric vehicle parking lots and charging stations seems to be imposed by seaport needs to reduce emissions. Hence, this will render electric vehicles a substantial electrical load of future seaports and a significant distributed energy storage facility at the same time.
Flywheels are large rotating masses (usually in the form of discs), which are used to store kinetic energy. During the charging (respectively, discharging) period, the connected electric machine acts as a motor accelerating (respectively, decelerating) the flywheel. In the steady state, the disk must remain spinning until energy is requested. By using vacuum pumps, air is removed from the flywheel container, and the disk rotates with the lowest possible resistance. In addition, cooling pumps are used to keep the temperature of the magnetic bearings low, which also helps keep the rotation resistance as small as possible. Figure 1 illustrates a simplified schematic of a flywheel connected to the ac grid via a variable-frequency drive.
Figure 1. A simplified flywheel.
A battery cell contains an electrolyte and two electrodes, i.e., the anode and cathode. In practical applications, several battery cells are connected in series and/or in parallel to make up the desired voltage level and capacity. A battery ESS (BESS) is a more complex construction, where several battery packs are used and controlled by individual battery management systems (BMSs). A converter interfaces the BESS with the external grid. The most mature technology uses lead–acid batteries; however, nickel–cadmium and lithium-ion batteries have become cost-effective options for higher-power applications. Figure 2 presents a simplified schematic of a BESS connected to the ac grid via a power converter.
Figure 2. A simplified BESS.
Supercapacitors store energy in the electric field between two conducting plates, i.e., the anode and cathode, which are separated by an insulating material (separator). Due to the very low equivalent series resistance, they are adequate to supply power efficiently. A converter is used to interface a supercapacitor with the external grid. Figure 3 provides a simplified schematic of a supercapacitor connected to the ac grid via a power converter.
Figure 3. A simplified supercapacitor.
Hydrogen can be produced by exploiting RESs from respective generating units located close to a port. The produced hydrogen can be supplied to fuel cells to produce electric energy. The operation principle of a fuel cell is described in Figure 4. In fact, hydrogen is supplied to the anode, and oxygen to the cathode, of the cell. The two electrodes are separated by the electrolyte. The hydrogen molecules first adhere to the electrode material and then separate into atoms, each subsequently releasing an electron to form a positively charged ion. At the cathode, oxygen atoms also adhere to the electrode surface and dissociate, each leaving two oxygen atoms. When wiring the two electrodes, the electrons can pass through the connecting wire to the oxygen atoms, where they create oxygen ions. The latter coalesce with the ions traveling through the electrolyte from the anode to create water molecules.
Figure 4. A simplified fuel cell.
Several fuel cell types can be found in a variety of marine applications (see Xing et al. 2021). In general, due to their low power capacity, fuel cells cannot supply large loads, but base loads and/or ship–shore connections at seaports can be properly served. Alternatively, fuel cells can be used to slowly recharge a ship’s onboard ESS overnight.
When it comes to fuel cell applications for ships, onboard hydrogen storage systems are also an important aspect. The four main storage technologies encountered are compressed, liquid, and solid-state storage systems and alternative carriers.
Thermoelectric ESSs can be used to store thermal energy. In particular, by charging an ohmic heater within a thermal storage tank containing magnesium oxide bricks or molten salt, high temperatures on the order of around 500 °C are generated. When needed, this thermal energy is used to produce steam, which drives a turbine that rotates a generator feeding power into the electricity grid of a port. Figure 5 illustrates a thermal storage unit.
Figure 5. A simplified thermal storage unit.
Reefers could also constitute a distributed thermal storage facility for seaports. For instance, they could consume electric power to cool their cargo down to the lower bound of the acceptable conservation temperature when the electricity price is low and overproduction of power from seaport-hosted RESs takes place.
The exploitation of seaport thermal storage facilities and district heating transmission systems to supply shore heat to a ship at berth could be an option for some seaports. Usually, it is preferable to provide heat to ships in the form of steam. Hence, if hot water from the district heating network is going to be used, then a conversion system to steam should be used on the shore.
There are many pieces of terminal equipment operating at a seaport, everything from yard trucks and forklifts to excavators and cranes. By replacing diesel engines with electric motors in this equipment while also considering the increasing number of electric vehicles visiting a port complex daily, a big opportunity arises to exploit this equipment as a distributed ESS. Indeed, this equipment could be able not only to charge but also return some power back to the grid while connected to a charger. The ability to charge back stored energy to the port power grid depends on the built-in power electronic converters.
Flywheels have a very high cycle and long lifetime. Their power density is high, providing high power peaks for a short time in a repeatable manner. Flywheels also have a fast charge capability. Typically, they are fully charged within a period of 30 min. Their energy density is low, and therefore, they cannot be used in long-term energy storage applications. Moreover, they have a very high self-discharge rate. To minimize losses, a complex installation is required, providing a vacuum operating environment for a flywheel. However, the latter is related to relatively high maintenance costs (higher than supercapacitors). The preceding characteristics make flywheels a good solution for the peak shaving of cranes’ consumption, the smoothening of reefers’ consumption, and so on.
Lithium-ion batteries provide the highest energy density among commercially available batteries. In addition, due to their high cycle life, they are considered one of the most appropriate technologies for BESS applications to seaports and ships. For instance, they could be used to alleviate the possible intermittences occurred in RES power production and reefers’ power consumption. However, their cost is high, and they are potentially dangerous because of the flammable materials (electrolyte) they include. The energy density of lithium-ion batteries is relatively low, making them appropriate for short-term energy storage applications.
Compared to batteries, supercapacitors have higher power density and efficiency as well as a longer lifetime. Moreover, they can instantly adapt to system requirements. For instance, they can charge almost instantly. Batteries require hours to be fully charged. In addition, supercapacitors are maintenance-free. However, supercapacitors have lower energy densities than batteries, and they require a very strictly regulated input voltage to charge, unlike batteries, which is associated with the cost of an additional converter.
Fuel cells are mostly used in maritime storage applications in combination with batteries and supercapacitors. This is mainly due to the low power density of fuel cells and their inability to dynamically adapt to rapid load changes. The latter is due to the possibility of a fuel cell failing if high temperatures and cycling effects occur due to load changes. Having in mind that the transient response time of the fastest fuel cell is on the order of 10 s, batteries and supercapacitors are required to offset sudden changes of external loads within this period. Moreover, maintaining steady-state operation is important to obtain prolonged durability of fuel cells. Finally, the overall financial and nonfinancial cost of hydrogen production is considerable.
As described, ports include a wide variety of flexible loads, and they are able to host local power generation sources and integrate different energy storage technologies. This increases the potential for smart and efficient operation but also poses technical challenges due to the resulting increased complexity. Port power management refers mainly to the optimal real-time power dispatch applied to flexible port loads and local power generation, while energy management refers to the optimal scheduling of operation. The existence of port loads with a degree of flexibility will be a vital benchmark on the road map to efficient and green harbors.
Together with the development of power and energy management algorithms, real-time monitoring and data acquisition systems, including smart meters and sensors, communication lines, and remote-control devices, should be deployed. Some information about the optimal operation of the most critical port power system components, their integration to control systems, and the respective optimization targets, is provided in the following.
Reefers are very flexible loads in time and power, and they are expected to be a major component of future port energy and power management systems. Reefers can preserve the cargo temperature inside a typical temperature window for approximately 24 h without consuming power, while they require approximately 2 h to maintain their internal temperature within the permissible window during refrigeration. This proves that reefers could be a very promising solution for distributed thermal energy storage with high power density and relatively low energy density. For the optimal exploitation of reefers’ flexibility at the port operation level, they should be organized in clusters and aggregators. Due to the increased number of controlled reefers and resulting complexity of the controlled system, hierarchical multiagent systems and distributed control methods could be used.
Electric cranes could provide some load flexibility to port operation. Their energy consumption peaks during hoisting and may cause significant power quality problems in the local power grid. Crane-integrated batteries and bigger ESSs assigned to a group of cranes, e.g., flywheels, can be used to eliminate these peaks, store regeneration power during crane braking, and reduce failure risk and operation cost. The operation of cranes can be further optimized if they are jointly scheduled and optimized, increasing the efficiency of the controlled system and possibly reducing the size of the required ESS. For instance, their operation can be regulated in a such way that the regenerative power from a group of cranes is supplied to other cranes during hoisting.
Electric vehicles hosted in ports will be a great source of power and energy flexibility if their batteries are optimally operated. Plug-in electric vehicles are able not only to absorb but also inject power to the grid [the vehicle-to-grid (V2G) mode of operation] when it is needed. For instance, they can charge their batteries when the electricity price and network loading are low and discharge their batteries by injecting power back to the network when the electricity price and network loading are high. However, the batteries of plug-in electric vehicles are subject to more operational constraints than conventional batteries, as their time being plugged into the network is limited, and they should achieve a specific state of charge when being unplugged. The number of constraints increases for V2G operation, as battery early aging should be also considered. The benefits and obtained flexibility increase when plug-in electric vehicles are organized as aggregators and treated as an equivalent large battery with time-varying parameters and limits.
Other port loads, such as building loads and lighting, could also be exploited by port power and energy management systems. For instance, buildings include sensitive loads that cannot be regulated; loads, e.g., lighting, cooling, and heating, that can be optimally adjusted according to optimization targets; and loads that can be shifted in time, e.g., specific industrial operations. There are also loads that can be shed without causing any problem for the operation of the system. For instance, motion-sensitive lighting can be used in ports. The exploitation of load flexibility and energy storage facilities can provide great solutions to future seaports to accomplish their efforts to reduce their operation cost and carbon footprint and increase their efficiency at the same time.
Energy storage could significantly lower seaport operation cost, improve operation, and, at the same time, provide ancillary services to the host electric network. The main benefits of integrating ESSs into seaports are as follows:
Another interesting exploitation of energy storage is energy bunkering for all-electric ships (AESs) at berth. It could be performed via
Shore-to-ship power supply systems will constitute a large electric power consumption of future seaports. A general configuration of a shore-to-ship power supply system is shown in Figure 6. If the power provided to ships is generated from RESs located in a seaport area or owned by a seaport, then RESs will be among the most effective tools for green and efficient seaport operation. Moreover, sometimes, it will be dictated to shore-to-ship power supplies to operate in parallel with ship auxiliary generators. In that case, ships could be treated as flexible loads and generators, i.e., prosumers. This could happen if the electricity grid hosting the seaport electrical network is experiencing overloading, the seaport system has been organized as a microgrid that should operate autonomously, frequency and voltage support should be provided to the electric power system, and so on. However, emission limitations at the ship and seaport level should be applied to the operation of ship auxiliary generators. Another interesting idea to exploit the capabilities of shore-to-ship power supplies in islands is to operate them as local generators during peak load periods in summer, when the local electric power generation system is under extreme stress or suffering from a shortage of power generation. Sometimes, the operation of ship auxiliary generators could be more economical compared to the use of local power units. To optimize the operation of the system of shore-to-ship power supplies, optimal power dispatch and operation scheduling techniques should be applied. If ESSs are combined with shore-to-ship power supplies, then their operation could be further optimized and their benefits maximized.
Figure 6. A typical shore-to-ship power supply configuration.
Seaports can exploit their capabilities to provide ancillary services to the electrical network and generally improve its operation in terms of cost, reliability, and security aspects. More specifically, seaport operators and electric power system operators can specify predefined procedures that will harmonize their operations and provide mutual ancillary services. Future seaports with significant potential for local power generation and load flexibility will be ideal big prosumers that will be able to exchange power (absorb and inject) with the host electrical network in a fully controllable manner. Hence, seaports could support the electrical network in overloading periods by reducing their power demand and producing excessive power and increasing their power demand and lowering their power generation in low-load periods.
Many seaport electric power system components, e.g., RESs, energy storage units, and so on, will be interfaced with the electric network via power converters. Hence, they will be capable of regulating not only their active but also their reactive power and support the voltage within a seaport network and, to some extent, the voltage level of the hosting electrical network. Moreover, seaports could provide primary, secondary, and even tertiary frequency support by suitably exploiting their local power generation capacity and load flexibility.
In the era of smart grids and microgrids, seaport electric networks and surrounding electrical networks will able to apply optimal reconfiguration algorithms to optimize power flows, power losses, and the reliability and security of the supply. This will be especially useful in cases of reverse power flows due to massive local power generation. However, protection coordination, fault location, short-circuit-level assessment, and so on will be become more complicated and, in some cases, require a total redesign.
It is noted that logistics are a key factor of seaport operation. However, logistics are not jointly optimized with seaport power system operation, so far. Berth allocation, quay crane allocation to ships, and, generally, other energy-consuming activities associated with seaport logistics are expected to add further degrees of freedom to seaport power management systems and, broadly, the operation of seaport area electric networks.
Seaports include a wide variety of loads and can exploit, if necessary, auxiliary generators of ships at birth. They also consist of local control centers, power and energy management systems, and supervisory control and data acquisition systems, which are expected to be significantly modernized and upgraded in the future to address the ambitious targets for greener, smarter, and more efficient operation. These features will allow seaport power systems to be operated as microgrids, as they will be able to optimally schedule and control the operation of their components either in grid-connected or autonomous operation.
The design and deployment of associated seaport power and energy management systems will be a rather challenging and complex task, as the supervised and controlled components are numerous, their individual objectives usually antagonistic, and their operational behavior heterogeneous. Moreover, the optimization targets at the seaport level may be more than one at the same time. To this end, clustering and aggregation approaches together with hierarchically organized control and scheduling processes are usually adopted to address such challenges. Multiagent systems have been proved effective for systems with similar characteristics and complexity. A possible organization of a seaport power system in a hierarchical multiagent system for optimal operation scheduling and real-time control is given in Figure 7.
Figure 7. The smart port as a microgrid and port power management organization in a multiagent system.
Informatics and communication systems are key elements of smart seaports. They should gather, transmit, and process large amounts of heterogeneous data for a variety of control, scheduling, and monitoring tasks of complex seaport power subsystems, logistics, and other seaport-based operations. A variety of different technologies, such as wireless communications and power line carriers, central and distributed control architectures, big data analytics, machine learning, and so on, could be used.
In general, seaport information communications technology infrastructure includes the following components:
Ship gas emissions include sulfur dioxide (SO2), nitrogen oxides (NOx), carbon dioxide (CO2), and particulate matter with a diameter less than 10 μm. SO2 emissions affect human health and the environment. Concentrations of SO2 in the air form sulfur oxides (SOx) that can react with other compounds to form small particles. Small particulate matter may penetrate the lungs and cause health problems. SOx contribute to acid rain, which can harm sensitive ecosystems. NOx contribute to acid deposition and the eutrophication of soil and water.
According to the United Nations, the maritime sector accounts for about 2.2% of all global greenhouse gas emissions. To date, no adequate measures are in place; however, a strategy to this end has been set up, including the monitoring, reporting, and verification of ship CO2 emissions in ports, greenhouse gas reduction targets for the maritime transport sector, and other market-based measures.
It is noted that seaport authorities should adopt extensive electrification policies to comply with environmental legislation. The development of onshore ship power supply systems will drastically contribute to in-port CO2, SO2, and NOx emissions reduction. The benefits will be further amplified if ships are supplied with green energy. However, few seaports have implemented such systems, so far.
Another key seaport operation with significant environmental impact is the collection and treatment of waste produced by seaport-based activities. Waste is produced by land-based seaport activities and onboard ships. In some cases, it could be used for power production. Ballast water management is also another process critical to the health of the seaport environment. Ballast water includes several marine species that may cause ecological, economic, and health problems if they are allowed to invade the seaport environment, as they reproduce in large numbers, eliminating other antagonistic native species.
Seaport areas usually feature good potential for the production of electric power from RESs. Wind, solar, wave, tidal, osmotic, and ocean thermal energy could be harvested to supply local loads and even for sale to the electricity grid. The most significant RES power generation units in seaport areas are wind turbines and solar photovoltaic systems, due to their mature technology. Although the potential for RES exploitation is usually significant in seaport areas, space limitations pose obstacles. Hence, while the seaports are power-intensive consumers, they feature low electric power density for renewable energy production. Electric power generation from RESs is characterized by high stochasticity, intermittency, and prediction difficulty. The resulting volatility and unpredictability may cause operation and power quality problems for a seaport electric system and the electrical network it is interconnected to. However, well-established solutions can be provided using ESSs, seaport load flexibility, and sophisticated optimization and control techniques.
ESSs can be coordinated with in-port RESs to cancel fast variations of their production by using suitable control and short-term RES production forecasting techniques. In this way, power quality indices affected by the volatility of RES power production will be greatly improved. To this end, ESSs with adequate power density and relatively fast response should be used. This type of ESS can also be used to enable RESs to provide short-term ancillary services to the grid.
In a similar way, slower variations of RES production can be suitably managed by the respective ESS. This could enable seaports to minimize the cost of the energy they exchange with the grid and even to provide ancillary services, such as RES production time shifting, to shave the peaks and fill the valleys of the local distribution network load. Moreover, RESs and ESSs can be optimally coordinated to minimize local network power losses according to real-time set points received by the network operator. The preceding justifies the importance of ESSs in RES integration, as the technologies will practically transform ports into flexible prosumers that will even be able to provide technically demanding ancillary services to the network. Finally, it is noted that the suitable selection of energy storage technologies and RES type diversification will help seaports obtain the best possible technical and economical outcome.
Seaports are continuously being transformed and adopting technological innovations to become more efficient, limit their carbon footprint, and comply with legislation. Seaport electrification is expected to play a key role to this end. It will provide significant potential for local power generation, energy storage, and demand response, as future seaports will include several flexible loads, such as reefers, shore-to-ship power supplies, electric vehicles, ESSs, cranes, and so on.
The application of smart power and energy management systems will transform seaports into smart energy hubs that will be able to optimize their operation in terms of cost and efficiency while also being able to provide ancillary services to the power grid, such as frequency support, load shifting, voltage support, “virtual spinning reserves,” and so on.
The adoption of concepts such as microgrids, smart grids, distributed control, and so on will provide reliable solutions to operation problems resulting from the increased complexity of the future seaport electric power system. Seaport transformation into smart energy hubs is still at the beginning; however, it is expected to accelerate in the near future, due to its very promising prospects and the multidimensional operational capabilities and flexibility it will provide to seaport operators.
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Fotios D. Kanellos (fkanellos@tuc.gr) is with the School of Electrical and Computer Engineering, Technical University of Crete, Chania 73100 Greece.
George J. Tsekouras (gtsekouras@uniwa.gr) is with the Department of Electrical and Electronics Engineering, Faculty of Engineering, University of West Attica, Egaleo 12241 Greece.
Vassilis C. Nikolaidis (vnikolai@ee.duth.gr) is with the Department of Electrical and Computer Engineering, Democritus University of Thrace, Xanthi 67100 Greece.
John M. Prousalidis (jprousal@naval.ntua.gr) is with the School of Naval Architecture and Marine Engineering, National Technical University of Athens, Athens 15780 Greece.
Digital Object Identifier 10.1109/MELE.2022.3232980
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