Electrical design for ef fi ciency: technical and operational measures for optimizing the use of electrical power on ships

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ere is currently a growing concern in the shipping industry about energy consumption and environmental impacts. According to the International Maritime Organization's (IMO) energy e ciency guidelines, today's ships must have an energy e ciency management plan to reduce the CO2 emission and other pollutants. In this article, a bibliographic review of methodologies for the optimization of energy consumption on ships is carried out, starting from the identi cation of sources of energy losses, to the implementation of technical and operational measures that contribute to their improvement, making a qualitative evaluation of the identi ed methodologies. Sources of energy losses associated with equipment and auxiliary systems are analyzed, as well as opportunities for improvement in the use of electrical energy through the implementation of intelligent energy management systems, high e ciency motors, and lighting. e technical and operational energy e ciency measures described above demonstrate the importance of their implementation from the early stages of the ship's electrical design, as well as monitoring energy consumption during its life cycle, to improve energy e ciency on board.
In recent years, the International Maritime Organization (IMO) has implemented several policies to improve energy e ciency in ships and reduce environmental impact during their operation [2]. is paper proposes a methodology based on a literature review. Initially, ship energy e ciency improvement policies issued by IMO are identi ed. Some causes of electrical system e ciency losses in ships and measures to improve electrical systems are described. e causes of electrical e ciency losses described are associated with the operation of the Genset engine outside the established parameters, as well as to e ciency losses in the Genset alternator and power transformers due to losses in the windings and in the core. E ciency improvement measures found in literature include combustion engines with catalytic reduction systems and exhaust gas recirculation, load-dependent transformer e ciency, use of batteries as an additional energy source, implementation of a power management system to avoid overloads in generation, transition of lighting to LED technology, and operation of generators at high capacity Implementing policies, strategies, and technical solutions to reduce greenhouse gas emissions is one of the most signi cant challenges confronting shipowners and operators in the 21st century [1]. To reduce the negative environmental e ects of ships, the International Maritime Organization (IMO) has developed a few tools to monitor emissions. In this context, the Energy E ciency Design Index (EEDI) and the Energy E ciency Operational Indicator (EEOI) are two standardized indicators for energy e ciency assessment. e rst one concerns ship design and commissioning, whereas the second one concerns parameter control while a ship is in service [2].
As with other IMO regulations, the ag state of a ship is ultimately responsible for ensuring compliance with EEDI. A veri cation body issues an International Energy E ciency Certi cate (IEEC) to demonstrate compliance (Maritime Administration or Classi cation Society). e veri cation process is divided into two stages. A preliminary veri cation is performed based on ship design, followed by a nal veri cation test during a sea trial. e shipowner, shipbuilder, and veri er are all involved in the process at every stage of the ship's development [3]. e ship's EEOI is calculated using statistics collected during the voyage and from the ship's operation. ese statistics include parameters such as the equipment's fuel consumption, state of the navigation environment, length of the ship's stay in port, and distance traveled [2].
Given the signi cant changes that ship technologies must undergo, the planned goals are medium-term (by 2030) and long-term (by 2050), with 2008 as the base year. e desired end result is to reduce greenhouse gas emissions from shipping by up to 40% by 2030; 70% in emission intensities; and 50% in total emissions by 2050 [1].
Chemical energy saved in fuels is released as heat through combustion in conventional maritime power systems. e main engines, which are typically diesel engines, convert this heat into work and deliver it to the propellers either directly or via reduction gearboxes. e work is then converted into propulsion thrust by propellers to overcome vessel resistance and accelerate it. Auxiliary diesel engines, on the other hand, convert heat to work, for electrical power, and to power the ship's electrical grid. ese power conversions and transmissions improve components, subsystem, and overall system energy e ciency [4]. Fig. 1 shows the relation between vessel energy e ectiveness, total energy e ciency and in uencing factors.
A logical rst step in discussing how to improve the energy e ciency of a ship's electrical system is to understand the view of power system losses. All elements of an electrical system (transformers,

Introduction
Energy ef ciency in ships Sources of losses in the electrical system Sanabria, Vergara, Mendoza, Salas motors, etc.) provide resistance to current ow and therefore, dissipate some energy to perform their intended function [5]. e losses in power distribution systems can be as follows:

Diesel engine
Diesel engines su er continuous internal wear during their useful life and under normal operating conditions, resulting in a reduction in e ciency. e loss of pieces is proportional to the hours of operation and can be exacerbated by impurities in the fuel or the presence of particles during combustion. It is possible to recover some engine e ciency by following a motor maintenance plan that adheres to the manufacturer's speci cations [6]. e operation of a Genset outside the nominal conditions established by the diesel engine rating can produce several negative e ects. e rst one being that the engine may not reach the temperature and pressure necessary to operate properly, causing a black oily uid to be produced and seep through the exhaust system seals; part of the reason why combustion releases a higher amount of nitrogen oxides into the environment [7]. e second manifests itself when engines are operating at low loads for long periods, causing accumulation of debris in the pistons or cylinders, resulting in loss of power, accelerated wear, and in the worst case, wear of the cylinder liner [7]. Consequently, the motors must be kept operating by the restrictions of their classi cation so as not to reduce their e ciency and service life.

Transformers
Electrical transformers are static electrical machines that deliver electrical power by changing the voltage level from input to output (primarysecondary).
ere are currently three types of transformers, depending on their application: power transformers, voltage transformers and current transformers. e last two are normally used to measure or to sample high voltages and currents in circuits that require low values to operate, while power transformers are used to supply loads at the desired voltage.
All three types of transformers are used on ships, however, for the purpose of this paper, only power transformers will be discussed because of their in uence on the e ciency of the electrical system. Although transformers are static electrical machines, they present the same losses as rotating electrical machines, except for those related to friction due to the lack of movement of the equipment. Fig. 2 shows the losses according to Chapman [8]. total energy ef ciency and in uencing factors [4].

Transformer losses
Losses in windings Core losses • Core losses: hysteresis, core heating due to eddy currents, vibrations, harmonic current, and voltage components. • Losses in the windings: power loss due to the resistance of the windings, these losses are transformed into heat.

Alternator
In electrical groups, the alternator is typically a synchronous generator that supplies the required electrical power to the system. e synchronous generator is classi ed as a rotative electric machine, a category that also includes synchronous motors, inductors, permanent magnet motors, and so on.
Power losses (or e ciency losses) in rotating electrical machines can be broken down into the types of losses in Fig. 3.
Mechanical friction losses are associated with losses due to contact between the bearings and the structures that house them.
Losses in the windings are the result of the energy dissipated by the electrical resistance of the motor windings, including excitation in synchronous generators with this technology.
e losses in the iron core are due to the dispersion of the magnetic eld joining the stator and rotor windings as they pass through the uid, as well as losses in the coupling of the magnetic eld in the motor air gap. In addition, losses caused by the eddy currents induced in the iron by the magnetic elds induced by the windings are included.

High ef ciency motors
Combustion engines: Ships designed for global operation must have main engines that meet the strictest Tier III emission standards. e combustion temperature has the greatest impact on harmful substance emissions because an increase in temperature results in more e cient combustion of the air-fuel mixture in the combustion chamber.
is is associated with lower particulate matter emissions (primarily soot and hydrocarbons) but an unacceptable increase in nitrogen oxide NOx discharge.
e need to solve this conundrum prompted the development of selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) systems [9].

Transformer ef ciency as a function of load
Ships require the transformers be of the dry aircooled type. Transformer e ciency as a function of load has the behavior presented in Fig. 4 for three types of transformers: for a temperature rise of 150°C, 80°C and TP-1 type transformer with higher e ciency.
It can be noted that the maximum e ciency for all transformers occurs at load percentages between 35% and 60%, depending on the temperature rise.
e e ciencies at full load are lower than the maximum transformer e ciencies, which is obtained at partial loads.
Battery compensation e use of batteries enables an additional source of energy that helps to control the power network, allowing on occasions, one or more engines can be shut down to avoid running at low loads and therefore operating with low e ciency. Consequently, fuel consumption, emissions, and noise-vibration-hardness (NVH) level of the generator engines can be reduced. Other battery functions include peak shaving, regeneration of braking energy and standby power. In the event Source: own elaboration on the base of [8].
Measures to improve energy ef ciency in the electricity system of high power demand, battery power can help generators sustain high power demands.

Electrical power management system
Electrical generation equipped with an electrical power management system allows controlling the start-up of the service and emergency generators and the electrical power demand to avoid generator overload and blackout [11]. is system protects the generators and prevents their sequential loss using consumer discrimination, and has the following functionalities: • Automatically reduces the vessel's power demand to keep it within the available generation capacity. • Sectioning the electrical system, opening the main switchgear busbar disconnector in case of generator failure, to isolate the fault. • Requesting automatic start and entry into the system of the standby generators. • e vessel's power demand reduction is performed with the non-vital consumers, according to their classi cation, by opening the load center disconnectors or disconnecting large consumers at the main switchgear. • e management system controls the automatic start-up and entry of the emergency generator in case of failure of the primary generation. • Likewise, the system ensures that the lockedrotor current of the generators is not exceeded by starting electric motors.

Ef cient lighting
Over the course of the last few years there has been a massive transition in lighting technology from conventional lighting to LED technology which is more energy and cost e cient. Research [12] suggests that signi cant energy savings can be achieved by applying LEDs instead of highpressure sodium or metal halide lamps.
Some of the advantages to be highlighted are: • Long life: the average lifetime of a LED luminaire is approximately 35,000 to 50,000 hours, therefore, they also generate an economic bene t from low replacement costs and energy consumption. • Environmentally friendly: LED technology luminaires do not contain toxic chemicals (mercury vapor). • e initial investment is higher than for incandescent bulbs. However, due to the long lifetime and high energy e ciency of LED bulbs, the investment is quickly amortized.

Energy ef ciency potentials of the generator operations
Load sharing practices on ships a ect the performance of generators.
is can indirectly cause di erent amounts of fuel consumption, fuel cost, and emissions for the same amount of onboard electrical power generation.  In [13], the energy e ciency of a number of diesel, chemical, ro-ro and barge vessels was evaluated. e annual fuel consumption and cost, and the potential emissions that may occur from possible load sharing applications of the generator sets on the vessel were estimated. Vessel characteristics, generator speci cation, power demand and time of operation modes were used as input data to assess the potential e ects of load sharing practices on generators. e results showed that running the generators at high capacity instead of low capacity could meet the onboard electrical power demand with less fuel. When generators run at 90% of their capacity instead of 40%, the minimum savings in terms of fuel consumption, fuel cost, CO2 and NOx emissions is about 7% [13]. is ratio should be at least 5% in the case of SOx. At the same time, the savings potential for all parameters was about 17%. Generator load sharing practices can be an important operational measure that does not require any investment among the types of energy saving applications for ships [13].
GEDIN-COTECMAR's design and engineering management have implemented systems/ equipment/solutions with new technologies that contribute to energy e ciency in the design phases, and therefore, to lower fuel consumption. Some of the implementations are:

More ef cient generator technology
In the BDA (Buque de Desembarco An bio) project, generators with more e cient technology were considered to save fuel during the operation periods. Fig. 5 shows the comparison between the DITA Genset technology and the ACERT Genset installed in the BDA.
Some technical and operational measures implemented from the electrical design to optimize the use of electrical energy on ships in COTECMAR.  Source: own elaboration on the base of [8].
Source: own elaboration on the base of [8].

LED lighting
In the PAF-L (Patrullera de Apoyo Fluvial Liviana) project, from the design stage, LED lighting was considered to obtain better lighting levels with less power consumption. Fig. 6 shows the comparison between conventional lighting technology and LED lighting installed in PAF-L.

Renewable microgrids
During the design development of the BALC-L (Buque de Apoyo Logistico y Cabotaje Liviano)

Auxiliary systems efficiency
Air conditioning Evaluation and diagnosis for the energy optimization of the chilled water circulation system: the arrangement of pipes and fittings allows a reduction of the resistance by approx. 40% and an increase of the current pump efficiency by up to 68% (Ref: PAFP-PAFL).

Hydraulic Systems
Application of Pipe Flow expert, in the design and analysis of hydraulic systems, to determine the diameters, pressures, speeds and routing of pipes to achieve the most efficient operation points of the pump, as well as to determine the pressure loss in the system due to the friction with the flow in the pipes, which contributes to have more efficient auxiliary system arrangements.  Renewable microgrids x vessel, deck 02 was extended to provide an available area for the location of the photovoltaic modules, as shown in Fig. 7. e installed peak power is 1.68kW and per year they can produce 1,903 MWh of energy, which will be used to power the lighting loads on deck 01, contributing to the reduction of fuel consumption which per year would represent 137 gallons and a reduction of 2Ton in the carbon footprint per year.
Ef ciency of auxiliary systems Table 1 shows the considerations taken into account for the optimization of the air conditioning and hydraulic systems, which represent one of the most signi cant impacts on electricity consumption.
Technology integration e Table 2 shows the possibilities of integrating technical and operational measures for energy e ciency from the design phase and during the operation of the vessel. e Colombian shipbuilding industry has undeniably strengthened its capabilities in the design phases to implement technical and operational measures to optimize the use of electrical energy in ships, in alignment with the energy e ciency guidelines of the International Maritime Organization (IMO). From the literature ndings, electrical and mechanical losses in motors, transformers, and alternators visibly vary depending on the load and normal operation behavior of these elements. However, the points of view presented on this subject were only from a technical and operational perspective and did not cover considerations on the change of e ciency behavior as a function of time, which is crucial. erefore, this aspect should be addressed in a subsequent study.
From the design phases, measures have been implemented to improve the use of electrical energy in ships, such as the installation of intelligent energy management systems, use of high-e ciency engines, use of LED lighting, and the optimization of air conditioning and hydraulic systems. However, the challenge is providing comprehensive solutions to support the life cycle in terms of the energy e ciency of ships that require maintenance, repair, or warranty care. Nowadays, it is not enough to design and build a good energy performance of the vessel, but also, to make improvements during the operation phase to contribute to energy e ciency and thus, lower fuel consumption.