1 INTRODUCTION

For centuries, maritime transport has been an

important exchange link between nations, regions and

continents. It is currently a vital sector for the world

economy and an essential support for the

international market for exports, imports and

distribution of goods. Likewise, in recent decades, the

transport of goods across the seas has increased

considerably, and jointly, emissions, polluting gases

and the pollution generated by this sector have also

risen notably [1].

That is why the International Maritime

Organization (IMO) forecasts a notable increase in

emissions within the maritime sector, between 50%

and 250% by the year 2050, if limiting measures are

not applied [1-2]. For this reason, the IMO has

established a series of objectives for maritime

transport to reduce greenhouse gas emissions from

ships [2-4]. Specifically, one of the objectives is to

reduce CO2 emissions generated by ships by 50%

compared to 2008 levels. As part of this strategy, the

aim is also to reduce the intensity of CO2 emissions

from the sector by at least 40% by 2030 compared to

2008 levels [1]. In addition, one of the most recognized

shipping companies worldwide, Maersk, has

announced the purpose of achieving carbon neutrality

by 2050, considering that ships that do not generate

harmful emissions can be commercially viable, and

that in such a way they can be incorporated to the

fleet of companies operating in the maritime transport

sector [1-4].

One of the ways to achieve these objectives is to

implement regulations at the international level in

which increasingly restrictive limits are established on

the emissions generated by ships. Halff A. et al.

analyses the implications of these IMO regulations in

the maritime transport [5]. Psaraftis H. N. makes a

wide study of the relation with the market with

respect the implementation of these regulation to cope

this problem [6]. In legislative terms, the IMO,

through regulations such as MARPOL, is focusing its

efforts on reducing emissions of polluting gases and

particles such as sulfur oxide (SOx), nitrogen oxide

The Future of Energy in Ships and Harbors

G.N

. Marichal

, D. Ávila Prats

, A. Conesa

, J.A. Rodríguez

& G. Iglesias

2,3

University of La Laguna, Santa Cruz de Tenerife, Spain

University College Cork, Cork, Ireland

University of Plymouth, Plymouth, United Kingdom

ABSTRACT: In recent decades, maritime transport, hand in hand with the International Maritime Organization

(OMI), has promoted a change in the energetic model in ships and harbors. The main goal of this paper is to

show the most useful advances in technologies with respect to reducing gas and particle emissions, and the

implementation of technologies based on renewable energies for the propulsion of ships and the energy supply

in harbors. Furthermore, new hybrid renewable energy-desalination water technologies which could change the

shape of water supply to the ships from near shore zones will be shown. To carry out this study, exhaustive

bibliographic research was conducted, including scientific and technical papers.

http://www.tr

ansnav.eu

the

International Journal

on Marine Navigation

and Safety of Sea Transporta

tion

Volume 18

Number 1

March 2024

DOI: 10.12716/1001.18.01.

(NOx) and airborne solid particles (PM) and reduce

the level of greenhouse gases in the atmosphere, such

as carbon dioxide (CO2) and methane (CH4). This

agreement was applied to the maritime transport

sector to prevent pollution generated by maritime

transport, and mainly assigns limitations and controls

to the levels of atmospheric pollutants produced by

exhaust gases in ships, especially gases such as sulfur

oxide (SOx ) and nitrogen oxide (NOx), as well as

restricting the emissions of substances that affect the

ozone layer and also delimiting special areas where

emissions are controlled (ECA). Initial efforts have

been done by considering lower speeds in the

shipping transport [7-8]. However, within the

maritime transport sector, shipping companies are

expected to begin to consider cleaner fuel and energy

options, thus including the use of renewables [9-11].

Within said regulation, one of the most important

elements is Annex VI of the MARPOL agreement,

which was adopted in 1997 and entered into force in

2005. In it, the different emission levels were set by a

series of standards known as Tier I, Tier II and Tier III.

The Tier I model is defined in the 1997 version of

MARPOL Annex VI, while the Tier II and Tier III

standards were introduced in the MARPOL Annex VI

amendments adopted in 2008 [1,4].

Given the need to set more restrictive emission

levels, on January 1, 2020, a revision was

implemented in Annex VI of MARPOL, which

requires that the sulfur content in fuel oil for ships be

reduced from 3, 5% mass/mass, which was the

required requirement since 2012, to 0.5% mass/mass

[12-13]. Likewise, the limits of SOx and other

polluting particles were reduced in emission control

zones (ECA) to 0.10% in 2015 [1-4].

As the requirements for the sulfur content of any

fuel used on board ships have changed over the years,

with these limits becoming more and more

demanding in an effort to achieve the objectives. The

IMO suggests a series of changes and measures to

have a positive impact on the emissions generated by

the sector. Like, for example, making use of

compatible fuel oils with low sulfur content (<0.50%

mass/mass) [12-13]. And if the sulfur content is

exceeded, use a cleaning method, for example, a

sulfur scrubber in the exhaust gases. In addition, it

seeks to replace the use of fuels with a high sulfur

content for alternative fuels such as Liquid Natural

Gas (LNG), methanol and others.

Wu Pei-Chi and Lin Cherng-Yuan [13] carried out

a comparison between these two approaches to

reduce emissions, where the choice of fuel with low

sulfur content is a more adequate strategy for longer

periods. In addition to the application of these

strategies, it is important to remark that the energy

supply provided on land during docking periods

helps to save fuel burning and reduce greenhouse gas

emissions. That is, the electrification of the ports and

cold ironing are a key issue in the reduction of

greenhouse gas emissions, as discussed in Section 4.

In this way, the IMO, through different

regulations, has stipulated mandatory technical and

operational measures, which require an efficient use

of energy and simultaneously an exhaustive control of

emissions. New indicators have been introduced as

Energy Efficiency Existing Ship Index (EEXI) or the

carbon intensity indicator (CII) with the purpose of

measuring and improving the energy efficiency [1,14].

In this line, the IMO Marine Environment Protection

Committee has adopted some amendments. These

amendments are expected to be established on 1

November 2022, whereas the EEXI and CII

certification will take effect from 1 January 2023 [1].

Therefore, shipping companies must take into

account the correct choice of cleaner fuels and

energies, such as the use of renewables. In addition,

rising fossil fuel prices in a highly volatile global

market provide an additional reason for shipping to

drive alternatives based on renewable sources and

technologies. Hence the need to introduce more

efficient propulsion systems that are increasingly less

dependent on fossil energy sources. Moreover, in

recent years new proposals of energy and emission

management systems (EEMS) have been devised in

the ships [15-16]. These systems contribute to

minimize the consumption of fuel, minimize and

manage all kind of emissions, minimize all kind of

losses into other ways of optimization. Special

mention inside the EEMS should be made to the

power management systems (PMS) which manage

different enery sources or the battery management

system (BMS) focused on an adequate use of the

batteries [17-18]. All these systems, all acting in a

global way, allows optimizing at a high level the

available energy of the ship. In fact, new proposals

have been put forward by several researchers to

optimize the consumption of the different systems in

a vessel as desalination plants, seawater cooling

systems between others [19-21]. Moreover, these

management systems are essential in the new recent

projects related with autonomous ships with zero-

emissions [16, 22-26].

2 HYBRID PROPULSION SYSTEMS (DIESEL-

ELECTRIC)

A viable alternative for the purpose of improving

efficiency and reducing emissions is hybrid

propulsion, more specifically, diesel-electric. This

combination of mechanical power, provided by diesel

engines, with electrical power, supplied by electric

generators, provides the necessary propulsion power,

thus ensuring a wide operational capacity in ships

and a precise supply of power to the propeller [27].

Thus, for ships that sail most of the time at a

practically constant speed, such as container ships, it

would not be as effective to replace a mechanical

diesel engine with a hybrid propulsion system, while

for tugboats and barges, which require a high degree

of maneuverability, the installation of a hybrid system

in their propulsion plant would be more appropriate

and lead to more efficient results. Notwithstanding, it

is also true that the installation of a set of batteries will

generally be beneficial for any boat, due to the

additional energy that it can provide [28-30].

As an example of the installation of this

technology, the MS Color Hybrid ship [31-32] has a

plug-in diesel-electric hybrid propulsion system and

is therefore considered the largest ship with this type

of technology. An attractive feature is that the vessel

can be powered for a limited time range purely

electrically by a series of additional batteries installed

on the vessel.

The battery bank of the ship has a charging

capacity of around 5 Megawatt-hours (MWh), weighs

a total of 65 tons and can be fully recharged in just one

hour via a fast-charging station at Sandefjord pier.

The battery system can provide enough energy for

about 60 minutes of electric-only navigation at a

speed of 12 knots. This electric autonomy is focused

on port entry and exit maneuvers. Another essential

feature of the electric propulsion system is the

reduction in noise and vibration levels in the ship [33].

Similarly, there is also the cruise ship MS Roald

Amundsen, which has the option of operating for

limited periods of time only with the electrical energy

supplied by the batteries, which means that at those

moments the ship stops consuming fuel [34].

The diesel-electric hybrid system is an option that

is gaining ground because fuel consumption levels are

significantly reduced and, therefore, CO2, NOx, SOx

and other volatile particle emission levels are also

reduced during navigation. Assuming navigation

based only on electric power from the batteries, the

fuel consumption and emissions during this period

will be zero. Furthermore, this system manages to

reduce the noise and vibrations of the propulsion

system as a whole. Another positive aspect is that the

battery operation system is a technology that is

developing rapidly. Therefore, it can be applied and

offer great potential and enormous benefits to the

merchant fleet and the cost of this type of system will

be increasingly cheaper. In addition, the diesel-electric

hybrid system is also applicable to large ships, which

is very attractive for the merchant fleet. Although

currently, a purely electric propulsion is a technology

unfeasible for large vessels, therefore, this technology

will be developed in smaller vessels first.

Like any other powertrain, the diesel-electric

hybrid has some drawbacks. One of them is that this

system requires large spaces in the ships to house the

set of batteries. Additionally, the set of batteries of this

type of system must be replaced when its useful life

ends, which is determined by the total number of

charge and discharge cycles. It should be noted that it

is a system in which a fossil fuel such as diesel is used,

although it is true that a decrease in polluting

emissions is generated, this problem cannot be

completely alleviated. For this reason, it is rather a

system that serves as a transition to a mode of

transport that is increasingly cleaner and more

respectful of the natural environment.

3 RENEWABLE AND CLEAN ENERGIES

The contribution of renewable energy to the shipping

sector is currently somewhat modest. However,

shipping companies are increasingly improving the

design of ships with the application of new

technologies, where significant savings are shown in

relation to fuel consumption and therefore the

reduction of emissions.

These solutions range from aspects related to the

design of the ship to the use of certain marine

technologies, navigation routes or various operational

and maintenance factors. Although it is true that there

is a wide range of possibilities aimed at minimizing

emissions and high fuel consumption in ships, special

attention will be paid to new technologies and

propulsion systems based on renewable and clean

energies [35] that have been applied in the maritime

world. Propulsion systems known as hybrids, systems

based on wind energy: such as rigid sails, kites, wind

turbines or Flettner rotors; systems based on solar

energy through photovoltaic panels; and fuels based

on hydrogen cells, are some of these alternatives that

are beginning to be implemented in the maritime

transport sector.

3.1 Hydrogen propulsion systems

Putting an emphasis on hydrogen fuel, this is an

element that can be harnessed as energy to power

propulsion systems. In addition, it offers great

potential, is a clean energy and could play a

fundamental role in making the transition to an

emission-free maritime transport sector a reality.

However, hydrogen is generally found in nature in

combination with other elements, hence the need to

extract hydrogen from certain substances. Currently,

most of its production is made from natural gas since

it is the most economically profitable option.

There are two ways to harness the energy of

hydrogen. On the one hand, this element is suitable

for generating energy through batteries or fuel cells.

This is converted through the aforementioned fuel

cells into electricity by a chemical process, to later

provide energy to electric motors. On the other hand,

hydrogen fuel can be used directly to power internal

combustion engines or together with other

conventional marine fuels to power dual engines [35-

39].

The process of converting hydrogen energy to

electrical energy through hydrogen fuel cells is highly

efficient and occurs without the emission of carbon

dioxide and sulfur oxide into the atmosphere, and

only negligible amounts of nitrogen dioxide. On the

other hand, burning hydrogen in internal combustion

engines, which is the other way to take advantage of

this energy, is generally somewhat less efficient, and

also somewhat more polluting because exhaust gases

can be generated, being the most common in this

aspect nitrogen oxide (NOx) [35-39].

The MV Viking Lady was one of the first merchant

ships to be fitted with a hybrid propulsion system

using hydrogen fuel cell technology [40-41]. This ship

has a battery system that offers a maximum power of

about 500 Kilowatt-hours (kWh) and was built in

2009. The ship currently has a hybrid propulsion plant

installed with a dual liquefied natural gas/diesel

engine and a set of hydrogen fuel cell batteries that

generate electrical power. The vessel also has the

option of being reconfigured to operate on methanol

fuel. This propulsion system has the capacity to

reduce emissions by 100% in SOx levels, by 25% in

NOx levels and by 30% in greenhouse gases [41]. In

addition, fuel savings 10–15% reduction in fuel are

achieved [43].

Another example is the New York Hornblower

Hybrid ship, which is a passenger vessel that operates

with energy extracted from hydrogen in New York

City, making tourist routes to the Statue of Liberty

and Ellis Island. Additionally, this ship uses solar

energy through photovoltaic panels and wind energy

through wind turbines that supply extra energy to the

propulsion and auxiliary system of the ship [44]. As a

result of the combination of hydrogen, solar energy

and wind energy in this boat, it is possible to

minimize both the environmental impact of its

operations and the savings in fuel consumption,

which means a benefit in efficiency and at the same

time economic.

This type of propulsion system offers certain

advantages. One of them is that hydrogen as a fuel is

clean, depending on the extraction method, and

efficient. Likewise, with these systems it is possible to

significantly reduce the levels of emissions and the

consumption of fossil fuels. In addition, no CO2 or

SOx emissions are generated into the atmosphere. In

addition, hydrogen can be used in different types of

propulsion systems, both in fuel cells, as well as for

internal combustion engines. Additionally, another

positive aspect is that it is possible to reduce noise and

vibration levels inside the ships.

However, there are certain disadvantages to this

type of propulsion system. One of the main ones is

that it is a system that has been scarcely applied in the

maritime industry. Likewise, based on its physical-

chemical characteristics, hydrogen can generate

certain safety problems for the crew. In addition,

almost all hydrogen production is generated from

fossil hydrocarbons, the most common in this regard

being liquefied natural gas, which is not the most

efficient way to produce said fuel for the purposes of

emissions and environmental care [10].

3.2 Wind-powered propulsion systems

Another very effective energy is that produced by the

wind. Wind energy is a renewable energy with great

potential. Taking advantage of the wind to generate

propulsion in ships is something that has been done

since the beginning of navigation, although it is true

that currently the merchant fleet is not giving it

practically any use. However, introducing wind

systems generates certain very attractive advantages.

It is a technology that produces energy without

generating polluting emissions and is applicable to

practically the entire merchant maritime fleet.

Likewise, wind power can be generated from a wide

variety of systems and technologies with different

characteristics. In addition, they provide additional

energy in the propulsion systems of ships, which

means significant savings in fuel consumption.

Like other technologies, wind propulsion systems

have some drawbacks. Among them, the production

of energy through these systems depends on the wind

conditions to be effective, such as the intensity or

direction of the wind. In addition, another aspect to

take into account is that these technologies usually

require an adequate control system, and in some cases

a crew trained for this type of technology is required.

Likewise, normally wind propulsion technologies are

focused only on providing partial benefits to the set of

propulsion systems [44].

Currently there are three different technologies by

which wind energy can be harnessed for ship

propulsion purposes, these are kites, Flettner rotors

and different types of sails.

In the early 1920s, as an alternative to conventional

sails, Anton Flettner invented a propulsion system

known as the Flettner rotor, which is a smooth,

vertically constructed cylinder. It must be taken into

account that Flettner rotors take up space on the deck

of ships and will most likely increase the total height

of the ship and can generate heeling forces on the

ships. Due to such characteristics, possible

impediments may arise for installation in certain

types of ships or complications may arise for the

respective function or operational profile that certain

ships are going to perform. In this way, it is observed

that all these nuances must be taken into

consideration when implementing these systems. A

large number of ships belonging to the merchant fleet

could introduce Flettner rotor technology to their

propulsion systems. However, not all ships are

suitable for this technology, due to a series of

requirements that fall mainly on the practical and

operational profile, and on the space required on

deck.

The installation of Flettner rotors is more

appropriate for general cargo ships than for container

ships, which, unfortunately for this system, require

practically all the space on deck and loading and

unloading operations that make their installation

difficult. Another special feature is that this

technology is more suitable for ships that navigate

mainly at a constant speed than for ships with a

highly maneuverable operating profile, such as

tugboats or supply ships [45].

An example of the application of this technology is

that of the E-Ship 1 cargo ship belonging to the

German company Enercon GmbH dedicated to the

wind turbine factory that has used Flettner rotors as

an additional propulsion system [45-46]. Said rotors

provide the ship with fuel savings between 30% and

40% for a speed of 16 knots with optimal wind

conditions. In addition, this also represents a

reduction in emissions generated into the atmosphere.

So the Flettner rotor manages to generate

emission-free renewable energy. Likewise, it is a very

efficient wind propulsion system, it is approximately

10 times more effective than a traditional sail [45],

achieving a reduction in fuel consumption and

consequently the reduction of emissions generated by

the vessel that makes use of this technology. In

addition, it is a very efficient system as a way of

producing additional propulsion.

However, this technology requires specific wind

meteorological conditions to achieve optimal thrust in

ships. Also, Flettner rotors have limited

maneuverability and take up deck space. In addition,

they can affect the stability of boats.

Like the Flettner rotors, the application of kites in

ships provides benefits in terms of fuel consumption

and reduces harmful emissions. Another positive

aspect of the kites is that they can be actively

controlled from the bridge of the ship in order to

optimize their flying conditions and thus increase the

pulling force. In addition, this technology has an

automatic control system, which facilitates handling.

Also, kites fly at high altitudes where the wind

generally blows with greater intensity, thus achieving

greater traction. In addition, this system does not take

up too much space on deck, hardly causes heeling

forces on vessels and is applicable to practically any

type of vessel.

However, kites have certain disadvantages to take

into account. This system cannot be used in low

intensity winds because it is not effective. Also, kites

should not be used in areas with heavy marine traffic

for safety reasons and cannot be used when sailing

against the direction of the wind.

Continuing with wind-related technology,

different types of sails can be applied as additional

propulsion systems in ships, thus providing a

complementary thrust with other propulsion systems

and generating fuel savings and a decrease in

emissions. Another positive aspect of the sails is that

they can be used in different conditions, in both low

and high intensity winds - they are versatile, and

there are varieties with different characteristics.

Furthermore, most sail systems are controlled by a

computer from the bridge and, in some cases the

controls are fully automated.

Although it is true, there are some negative aspects

about sails that should be highlighted. This type of

system normally requires high maintenance by the

crew. Likewise, the sails must be adapted for each

wind condition if they do not have an automated

control. Like other wind propulsion systems, they

depend on wind conditions to be efficient. In addition,

it is a system that requires areas on deck for its

installation and operation.

Next, several projects present or in the

development phase of wind propulsion systems

specialized in sails are presented.

The Neoliner 1360 vessel is a pilot project in the

development phase [46]. It will be a ro-ro ship of 136

meters in length and a beam of 24.2 meters. It will be

powered primarily by a sail rig system that will have

an aerial draft of around 67 meters, and will

additionally be equipped with a 4,000kW diesel-

electric hybrid propulsion system, for when wind

conditions do not offer the necessary potential. The

Wind Surf is a cruise ship that harnesses the energy

from the wind through a sail system [47]. It is one of

the largest sailing cruises in the world. Rigid sails

were installed on several Japanese ships in 1980 with

the aim of achieving a reduction in fuel consumption.

As a result, these Japanese vessels reported great

savings in fuel consumption, reaching a savings rate

of 30% [48-49].

Bound4Blue is a Spanish company founded in 2006

that has designed and patented a wind propulsion

system that serves as an additional complement to the

propulsion system as a whole. It is a system of rigid

sails capable of offering additional thrust to ships by

making optimal use of wind energy. In this way, this

technology manages to reduce fuel consumption and

cost and, consequently, polluting gas emissions are

also reduced [50].

The Bound4Blue system is a rigid sail system that

operates 100% autonomously, therefore requiring no

additional crew training. The design and structure of

this type of sail is light and low in weight, thus

avoiding stability problems and minimizing possible

heeling of the ship. Likewise, it is a system that

requires little maintenance, and its folding sails

guarantee greater safety and optimize performance in

adverse or unfavorable weather conditions. An

attractive aspect of this system is that it can be

installed on existing ships or on newly built ships [51].

Dyna-Rig type sails are also a wind propulsion

system. They are square sails, of large dimensions

with independent and rotating masts. By turning the

mast, the sail can be adjusted to the wind direction

and when the sails cannot be used, they are furled

inside the mast. Also, the sails can be managed

electronically through automated controls. This

system was developed in the 1960s by the German

engineer Wilhelm Prölss. The Maltese Falcon is a

luxury yacht that uses Dyna-Rig type sail technology

in its propulsion system. The sophisticated automated

control system contained in the yacht allows the

detection of parameters and wind conditions

automatically and displays data and key information

for trimming the sails.

As an example of application, the WASP (Ecoliner)

is a design prototype of a ship that is still in the

development phase. In the design, the Dyna-Rig type

sail system has a meteorological routing program

with the purpose of optimizing the navigation route

and the use of the engine to the maximum. The

reduction in fuel consumption would be around 25%

and 40% depending on weather conditions and routes

[51-52].

The objective of these technologies are aimed at

achieving savings or reduction in fuel consumption

and therefore a decrease in emissions [53].

3.3 Solar power propulsion systems

Similarly, solar energy brings great potential for a

cleaner mode of transport. This is an important source

of renewable energy and has been used by humans

since ancient times through a series of technological

systems that have evolved. As a technology, solar

panels can be installed flat on the deck or in another

way they can be arranged vertically coupled to certain

types of sails. The main limitations for this system are

mainly the lack of spaces for the deployment of

sufficient photovoltaic panels and the lack of spaces

for the storage of energy generated by those panels.

However, over the last few years, solar energy

storage technologies have been developed that offer

greater potential and a better perspective for applying

this type of technology to ship propulsion systems.

Propulsion based exclusively on solar energy is being

directed mainly to develop in relatively small boats,

while for larger boats, solar propulsion will serve to

offer additional power or supply the energy demand

of auxiliary systems [54]. Due to the physical and

technical limitations of this system for large ships,

solar energy is aimed at supplying auxiliary

components, powering the ship in certain port

operations or for use on short-term trips.

The Auriga Leader was the first merchant ship to

be partially powered by solar energy. It is equipped

with a plant of about 328 photovoltaic panels that

generate up to 40 kilowatts of electricity, which

represents 0.05% for the propulsion power and 1% for

the generator systems. On the other hand, when it is

moored in port, solar energy reaches up to 10% of

what the ship requires. The Emerald Ace propulsion

system consists of diesel engines and additionally has

a photovoltaic panel plant on the upper deck of the

ship. The plant has 768 solar panels that generate a

power of 160 kilowatts each one. And by means of a

series of a set of lithium batteries, the solar energy

captured by the photovoltaic cells is stored [53]. Once

the ship docks in port or is anchored, the solar panel

system and the set of batteries take over the power

supply without the need for the operation of diesel

generators, in such a way that this prototype

completely reduces the emission of polluting gases

during the stay in port or at the anchoring points [55-

56].

Solar power can supply some additional power for

propulsion systems, but primarily supplies power to

the auxiliary systems of the ship.

There are certain advantages to employing solar

propulsion systems on ships. This energy does not

generate emissions and is a renewable energy, which

implies that the system will always be supplied. Also,

with the application of this technology it is possible to

reduce fuel consumption and thus pollutants. Another

interesting aspect is that solar technology can be

applied in conjunction with wind or other systems.

However, there are certain disadvantages

regarding solar technology. And it is that the

efficiency of this technology depends on

meteorological parameters as it happens with wind

systems. In addition, the percentage levels of energy

that they generate for the propulsion systems are

usually low, so these systems are aimed at supplying

energy to the auxiliary systems. And it is currently an

economically expensive technology, although it is true

that over the years, with the development and

research of this technology, it has become more

commercially viable. Besides, an aspect to take into

account with these systems is that extensive spaces

are required on the main deck of ships; for this reason,

they are not applicable to any type of ship.

As an example of these technologies based on

renewable energies, it is worth mentioning the Energy

Observer vessel, a French experimental vessel which

has been the first in the world to achieve completely

emission-free hydrogen production on board. [56-57].

Also, the recently built ship MV Yara Birkeland

[58-61] is a totally autonomous and electric freighter

dedicated to the transport of containers, which does

not generate emissions. Its propulsion system consists

of fully electric motors and a set of batteries with a

capacity of 7 to 9 MWh that will provide the energy

supply to said motors.

Likewise, the ZeroCat 120 ship [62-63] is a totally

electric ferry of about 80.8 meters in length, about 20.8

meters in beam and has a capacity for 120 vehicles

and 360 passengers. Its propulsion system consists of

two electric motors of about 450 kilowatts of power,

whose energy is supplied through two lithium-ion

batteries with a capacity of 1,000 kilowatt-hours that

are recharged during the two stops on its route. In this

way, the ferry does not use any type of fossil fuel in

its operations. And consequently, it does not emit any

type of polluting gases or particles into the

atmosphere.

4 ENERGY SUPPLY IN THE PORT

The power required by the machinery operating while

the ship is berthed (e.g, loading cranes, pumps) is

often provided by auxiliary engines running on any

type of fossil fuel, which typically has a large content

of particulate matter. The greenhouse gas and,

importantly, particulate emissions from these

auxiliary engines are an important source of pollution.

A situation that is arguably the result of the absence of

emissions controls for merchant vessels.

In recent years, the emphasis on emissions

reduction has promoted alternative ways of providing

energy to the machinery of ships, most notably cold

ironing.

Cold ironing [18], known also as shore connection

or shore to ship power, effectively reduces emissions

from auxiliary engines, given these engines are not

working at port. Moreover, it allows to incorporate

renewable energies generated or received at port

directly into the energy supply of the ship. Overall,

this is a wide field of research, which can

accommodate, in addition to conventional renewable

energy sources (hydropower, wind), new marine

renewables (offshore wind, wave, tidal energy) [64-

65].

The prospects for emissions reductions through

cold ironing have been investigated by Zis [22], and

case studies considering the integration of renewable

energy into cold ironing have been published for a

number of ports, including Barcelona [23], Aalborg

[66] and Aberdeen [67]. The application of tidal

stream energy from the Shannon Estuary (Ireland) to

serve the needs of the Shannon Foynes Port, among

other uses, was recently proposed by Fouz et al. [68].

The four above-mentioned ports are very different in

size, which corroborates the applicability of

renewable energy sources to supply ships at berth in

both small and large ports. On the other side, it is

worth mentioning the combination of a hydrogen-

based hybrid energy system and cold ironing, which

has been recently investigated by Sifakis et al. [69]

Finally, new ways of obtaining energy near shore

based on temperature gradient of the water column

and the wave energy [70-75] have emerged in recent

years. Because of the increasing industrial activity of

the ports, along with the necessity to support

electrical energy to the ships the ports show a higher

potential energy demand. This fact is promoting the

search of new ways of energy supply based on

renewable energies. In particular, a great emphasis

has been put in the marine energies given the

nearness of the sea to the ports. However, all marine

energies are not adequate for the ports. Offshore wind

needs of wind farms which is not appropriate for a

port. Tidal energy is not possible for a port, given

high differences are necessary in the tides. Because of

that, wave energy is being paid attention in recent

years [73]. Different Wave Energy Converter projects

are being executed as MAtchUP European project in

Valencia port or many others [64,73].

These new approaches can provide additionally

desalinated water [71-72] and refrigeration near the

coast, i.e., ships could be supplied with energy and

water, and refrigerated by these systems. Different

initiatives as the prototypes tested by Wave Piston

[72] or the prototype Gaia tested by Ocean Oasis [76]

are examples of these new wave energy devices

focused on the production of desalinated water.

5 CONCLUSIONS

In this paper a global vision of the normative, applied

by several organisms with respect to the energy

consumed by the ships have been shown. These

directives are aimed at reducing contamination and

achieving an optimal use of energy in the maritime

sector. Different options to provide energy to the

ships are shown, and their advantages and drawbacks

are discussed. In conclusion detailed knowledge of

all these alternatives is necessary in order to choose

the best option in each case. In general, a combination

of alternatives is the best option in most cases.

Moreover, new ways of providing energy from ports

have been shown. In this vein, a number of recent

studies were reviewed which deal with options to

provide energy, water and refrigeration to the ships

from renewable natural resources.

FUNDING

This research has been co-funded by FEDER funds,

INTERREGMAC 2014–2020 Programme of the European

Union, within the E5DES project (MAC2/1.1a/309).

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