Hybrid backup energy based on PV/Wind system for marine tugboat: A case study of ASD tug of Arzew port in Algeria

Abstract

This study proposes a hybrid Solar PV/Wind backup solution for a marine tugboat. Tugs are an important kind of vessel that should be able to maneuver continuously without any interruption of their electrical energy system. New power management integrating a hybrid solar/wind energy aims to ensure a long period of continuous safe operation in case of a total blackout and also to replace the perturbed power grid of the port for a partial time. These standard tugs built in Holland by DAMEN shipyard and attached to Arzew port in Algeria, are suited to operate for a maximum of 1 hour with a storage battery unit in an emergency situation like a blackout. The two main diesel engines are able to operate normally with 24 V DC voltage control under such situations. During this problem of power failure, the tug can’t reach safely the harbor and hence immediate assistance is needed. To avoid this scenario, the idea is why not extend this period of emergency operation, and also try to supply the vessel inside the port only with clean energy. First, the electrical distribution system is presented and detailed including the power demand study of installed loads. The proposed hybrid energy source is also discussed for its many benefits especially in the case of favorable maritime climatic conditions of the Arzew port area. HOMER software is used to verify if the new power scheme can succeed. The results confirm that the new combined Diesel/PV/Wind solution appears to be very interesting, it reduces CO₂ emissions from diesel generators and annual fuel costs can be saved.

Keywords

Emergency blackout photovoltaic PV wind turbine battery energy storage diesel generator

Introduction

Maritime vessels also called ships are classified into many categories such as cargo ships, passenger ships, tankers, and service vessels like offshore tugs and harbor tugs. This classification is depended on its capacity, power, and type of work which are deployed. Each ship has specific tasks to be accomplished, tanker to carry petrol and gas, passenger to transport the people and cargo ship to carry cargo. We would know that 96% of the world’s trade volume is carried by ship (International Maritime Organization, 2014). Tugs are service vessels that maneuver other vessels by pulling or pushing them through direct contact or by line ships. Tugs typically help ships that are either limited in their ability to navigate on their own, such as ships in the narrow canals or busy harbor. Strongly built, tugs are powerful for their propulsion allowing some sail at ocean sea for offshore works or salvage. There are also other very important stains like firefighting and anti-pollution inside or outside the harbor. Therefore, tugs are also the most common type of vessel in the marine industry, with 18,199 tugs in 2016, or 20.3% of all commercial ships (Equasis Statistics, 2017; Rolls-Royce, 2021).

To perform the above tasks, tugs need a reliable electrical installation starting with the diesel generator as the main source of power on board to the various installations and equipment. The aim of a ship’s electrical distribution system is to safely convey power energy to all items of installed equipment.

Blackout means a total break of electrical energy. It presents a pure problem after the shutdown of the main engine that can paralyze any vessels and expose them to serious danger.

Furthermore, faced with the enormous problem of CO₂ emissions, the international maritime convention for the prevention of pollution MARPOL strictly required that vessels must search for a new strategy of reducing their emissions (MARPOL, n.d.). Very recently with regulatory compliance becoming more and more of the emissions issue, many companies and shipyards are launching a new propulsion system for tugs integrating electric motors for their propulsions. Wartsila HY tug propulsion system (WÄRTSILÄ, 2021) is one of hybrid propulsion technology that uses electric motors and batteries to ensure the propulsion system. Japan shipyard like NIGATA (IHI Power Systems, 2021) also develops a new hybrid tug for Z-PELLER propulsion system that combines conventional shaft drives with the driving force of the electric motor in order to optimize performances in various types of propulsions.

With the contemporary growth of renewable energy like photovoltaic and wind based systems, many technical fields have been benefited from this free and green energy including the maritime domain which begins little by little to exploit this type of energy (Katagi et al., 1996; Weiming, 2011).

In this research, a new idea is studied and developed. A hybrid wind-PV source can be installed on board the tug in order to ensure a maximum continued maneuverability performance in the case of a blackout situation, particularly when the vessel is so far from the harbor or in operating time under critical situations with other ships inside the harbor. The second objective is to feed the tug only with clean energy inside the port when the vessel is not solicited for working (stand-by). The external electrical grid of Arzew port is much perturbed and caused several failures of sensible electronic cards. The tug’s electrical distribution system is referring to a real model of a modern ASD tug built by DAMEN SHIPYARD in Holland and operated in the port of Arzew in Algeria. These tugs have an efficient design and high trust and maneuverability. But as a chief engineer and supervisor during 15 years on these types of tugs, we have remarked a serious problem of maneuverability in the case of a blackout caused by the limited time of maneuvering with the storage battery system. Principally, technical problems of diesel generators or gasoline provision systems are the main reason for this emergency situation. For that, a new electrical circuit design is proposed as a solution using special marine solar panels and wind turbines which are designed to withstand the harsh conditions of the sea. Many companies produce these marine renewable solutions suitable for all vessels ranging from small pleasure craft to big ships. The Japanese company Eco Marine Power is one of the leading companies that market and develop renewable energy based systems for marine vessels (Spagnolo et al., 2011; Straatman and van Sark, 2008).

By using a real model of tug working in Arzew port, one of the major harbors in Algeria, the main purpose is to provide a useful study and analysis using an alternative renewable source in order to ensure a safe operation of the tug under blackout. The present study is organized by two different scenarios. The first scenario is the major issue of total blackout taking into account just a minimum of necessary loads for sailing safely, the second is to be supplied fully by renewable energy instead of the power grid of the port. In this case, we can protect sensible loads, decrease generator emissions, and also economize fuel consumption. In the final section, the new proposed system using diesel/wind/PV based energy generation is evaluated under HOMER software.

Design, specifications, and lay out of the ASD tug 3110

Considered as a modern generation tug, this vessel features a compact deckhouse on the forecastle deck with a top deck placed wheelhouse, a large aft deck, and a spacious foredeck. The deckhouse and below-deck accommodation are designed to accommodate officers and crew for a total of 10 persons. For the engine room space, all installations are placed well. In the following study, we are interested only in electrical installations. Figure 1 represents the external view of the ASD tug and Figure 2 shows with more details the design charts of the engine room with generators disposition. The specification below in Table 1 describes the hull, equipment, and machinery of the studied vessel. Note that the word ASD signifies Azimuthal astern drive (Damen Shipyard in Holland, 2021).

Table 1.

Specification of the Damen standard tug.

Vessel	The Damen ASD Tug 3110 RAS EL MA
Owner	ARZEW port in Algeria
Builder	Damen Shipyard, the Netherlands
Total power	4000 ch (provided by two main diesel engine MaK 8M20)
Diesel generators	2 diesel generators MAN of 113 kVA with air starter motor
Emergency battery	4 batteries of 12 V 200 Ah connected to deliver 24 V 400 Ah
Control room	Placed in the engine room and contains all electrical panels
Electrical ship installation	Gebhard-Electro BV, the Netherlands

Figure 1.

External view of the tugboat (RAS EL MA).

Figure 2.

Diesel generators disposition in the engine room.

Electrical installation design and power management

The most obvious elements of an electrical installation on board the ships are the main generator and switchboards that supply different loads and equipment.

The distribution system of our tugboat is mainly designed according to the following specifications (Damen Shipyard in Holland, 2021):

Two diesel generator sets 113 kVA/400 V/50 Hz with LEROY-SOMER alternator providing three-phases and neutral insulated from earth.

One harbor diesel generator 58 kVA/400 V/50 Hz.

Two 400 V distribution panels for the three-phases loads such as pumps, air compressor, and ventilator.

One 230 V distribution panel for single-phase loads like lighting system and some electronic cards used for controlling engines and generators such as the AVR (automatic voltage regulator) card for exciting current of the alternator LEROY-SOMER and the electronic regulator WOODWARD for the main engine MaK 8M20.

Emergency battery system which consists of four accumulated batteries 12 V/200 Ah each, combined to one battery bank 24 V 400 Ah and installed on a wooden grating in a ventilated battery store on the deck.

Battery charger 24 V 50 A intended for float charging of the batteries with automatic change over to trickle charging.

Cables, circuit-breakers, and measuring instruments.

Electronic cards: SLIO and CAN MAN for controlling vessel (between the wheelhouse and engine room).

Figure 3 shows real pictures of some important equipment installed in the engine room of the tug.

Figure 3.

Diesel generator and principal equipment on board: (a) control room, (b) diesel generator coupled with LEROY-SOMER, and (c) SLIO and CANMAN electronic cards.

As shown in Figure 4, a general scheme of the electrical distribution system according to GEBHARD BV company is presented. Figure 5 depicts with more details the AC and DC bus including the emergency battery storage system. Under a blackout situation, the original electrical grid can feed the tug with four batteries for 1 hour. In this case, the principal feeding loads are the control system of main engines and propellers, radio communication, and DC emergency lighting.

Figure 4.

Electrical distribution scheme.

Figure 5.

Battery storage bank and emergency electrical scheme.

The problematic of blackout on board vessels

The aim of a ship’s electrical installation is to safely convey power to every item of its equipment with a maximum of reliability and efficiency. Among all emergency electrical problems, blackout is a pier catastrophic scenario for ships as its effects are most determined for the security of the vessel. For RAS EL MA tugboat, in order to improve the survivability under such an emergency situation, the initial power system contains four accumulator batteries of 200 Ah which can supply principally (Khan and Iqbal, 2009):

The control system of generators and main diesel engines.

The control system of propellers.

The communication system VHF.

The emergency lighting system.

Power demand analysis

The load power demand of the tug vessel can be easily calculated from its operational status and not from the total load power and equipment operating in specific conditions such as a hydraulic pump for anchoring and some transfer pumps operating rarely for ballast and seawater. For pumps and ventilator, alternating asynchronous motors with squirrel-cage rotors are used (Eco Marine Power Company, 2021; Maclay et al., 2007).

We assume that the tug operates daily for only 6 hours. Table 2 illustrates the principal electric loads necessary for ensuring a continuous operation with an average time of 6 hours per day.

Table 2.

Load demand in an emergency maneuvering operation.

Minimum equipment	Nominal power (kW)	Nominalvoltage (V)	Nominal current (A)	6 hours average operatingtime in the day (kWh)
1 Gas-oil pump	1.5	400	3	6 hours 9
Lighting system	1	230	10	12 hours 12
Electronic cards	0.3	230/24	2	6 hours 0.18
1 Air compressor	3.5	400	8.2	10 minutes each 6 hours 2.1
1 Fresh water pump	0.75	400	2	10 minutes each 1 hour 0.45
1 Fridge and cooker	1	230	10	4 hours each 24 hours 4
2CommunicationVHF	0.1	230/24	1	Full time 0.1
Total	8.15 kW		36.2 A	27.83 kWh

In addition, load characterizations under transient operating conditions especially during the start-up period should be noted. The concerning loads are the air compressor, gas-oil pump, and fresh water pump. These loads have a direct on line starting method with a minimal transient time which cannot affect the steady-state analysis.

With a basic calculation and under emergency operating conditions, it is shown that the alternator rated 113 kVA will be loaded to approximately 7% of its rating.

Diesel engine loading = 100 % . \frac{Load demand}{alternator rating} = \frac{8.15}{113} \approx 7 %

(1)

From these previous results indicated in Table 2, we can conclude that 7% operating load can be delivered by using other alternative energy sources.

Two scenarios will be considered, the first scenario is the blackout situation without heavy loads as the ventilator and air compressor. In this case, 8.15 kW of the load demand suffice to operate the vessel which means:

Load demand under Blackout = Minimum load demand \approx 8 kW

(2)

The second scenario focuses on supplying the tug in partial time when it’s out of service inside the port with only renewable energies. In this case, we have to reduce some hourly loads like the gas-oil pump which is ineffective when all engines are stopped. Generating 8 kW of power can be assured by 10 PV panels of 300 W each and two wind turbines of 5 kW. Consequently, the proposed system can reduce both fuel consumption and CO₂ emissions produced by the generator when the tug is out of service in the port. As shown in Table 3, during the night time (stand-by), the tug can work under strict minimum load without air compressor load as:

Load demand during the night time = Minimum load demand = 6.35 - 3.5 \approx 3 kW

(3)

Table 3.

Load demand when the tug is stand-by inside the harbor.

Minimum equipment	Nominalpower (kW)	Nominalvoltage (V)	Nominalcurrent (A)	12 hours average stand-by time in the day (kWh)
Lighting system	1	230	10	12 hours 12
1 Air compressor	3.5	400	8.2	10 minutes each 6 hours 2.1
1 Fresh water pump	0.75	400	2	10 minutes each 1 hour 0.45
1 Fridge and cooker	1	230	10	4 hours each 24 hours 4
2CommunicationVHF	0.1	230/24	1	Full time 0.1
Total	6.35 kW		31.2 A	18.65 kWh

This strict minimum load demand includes the lighting system, one freshwater pump, and VHF communication instruments.

Renewable source based energy

In the last few years, renewable energies have been considered as a very promising solution in order to decrease the exploitation of fossil energies and cope with CO₂ emissions. Several domains including the maritime sector have integrated this green energy due to its multiple advantages like respect for environment, saving energy, and reducing emissions from ships. In 2007, whole navigation vessels emitted 1.046 million tons of CO₂ which represents 3.3% of the global emission on the earth. This figure may triple by 2050 according to current trends (Yang et al., 2009). It is noted that many specifications are held which the wind turbines and PV panels have to fulfill so that to install on board vessels. These considerations are determined by the special conditions of the marine environment like humidity, wind, and corrosion.

Hybrid PV-wind system

A photovoltaic system is based on the principle of a PV cell that converts the incoming power of lighting photons to an electrical current. In the shipping industry, the PV-powered ship attracts big attention in the maritime worldwide. Unlike the big navigated vessel which is along one navigation route, the energy derived from PV panels to the tug is not regular and depends mainly on the position of the tug, local time, and date. Consequently, more source power is required to ensure the desired objective which consists of maintaining stable feeding energy. The use of wind energy and battery storage systems can considerably help to fulfill the objective of ensuring safe continuity of service. Figure 6 shows the basic scheme of the proposed configuration. In the normal situation, a diesel generator provides the necessary energy to different loads directly on 230 V/400 V voltage AC bus in the control room panels. However, during an emergency blackout, both PV and wind energy systems can help to supply the following main loads:

Three 24 V control panels for generators.

Two 24 V control panels for main diesel engines.

Two 24 V for alarms and fire-fighting panels.

One 24 V panel for emergency lighting system.

24 V for VHF communication instruments.

Three phases voltage 400 V for air compressor needed to start main engine and generator.

Figure 6.

The new topology with a diesel generator and the integrated hybrid energy system.

Modeling of the new proposed system

This project discusses 8 kW PV-Wind hybrid source with system storage capability. The system includes PV panels with 3 kW of power connected to a boost converter DC/DC with MPPT functionality. Additionally, a wind turbine of 5 kW and a battery bank connected to a DC/DC bidirectional converter are used.

With a total load of 3 kW and under the duration of 6 hours, the watt-hours of a PV system can be calculated as:

PV kWh = 3000 * 6 = 18 kWh

(4)

Considering the peak sun hours of 4.6 in the area of Arzew, the wattage output of solar panels can be defined by:

PV kW = \frac{18000}{4.6} = 3.913 kW

(5)

If a panel of 300 W is chosen, hence the number of panels needed for this design is given as:

Number of PV panels = \frac{3913}{300} = 13 panels

(6)

For the charging controller, the current can be calculated directly by:

I = \frac{P}{V} = \frac{300 * 13}{12} = 325 Amps

(7)

Where, V represents the battery voltage.

In order to avoid occupying unnecessary volume and much weight, a battery of 2000 Ah is chosen. In this case:

Number of battery = \frac{18000 * 4}{2000 * 0.8} = 45 batteries

(8)

Where a depth of discharge (DOD) of 80 % is used in this study.

Finally, more than 3 kW of power for a pure sine wave inverter is required. Table 4 indicates the necessary number of PV panels and battery storage for the proposed design.

Table 4.

PV system components under the different period of operation.

Duration (hour)	Number of PV panels	Number of 2000 Ah battery
3	7	23
6	13	45
12	26	90

Figure 7 illustrates the overall scheme of the studied hybrid PV-wind system using both PV panels and wind turbines. The optimal parameters of the new system are the first found with the load demand study. This provides a sort of real model and thus helps to future realizations.

Figure 7.

The overall scheme of the proposed method.

The new integrated system consists of 13 PV panels of 300 W each, two wind turbines of 5 kW each, and converters (DC/DC and DC/AC). Many batteries are also added in order to ensure satisfactory and continued service during less irradiance and/or low wind conditions (Katiraei et al., 2007).

Marine solar panels and frames

In the case of tugboat and unlike on land, the energy derived from PV panels depends on various parameters such as date, time zone, coordinates and position of the tug. In order to increase efficiency and reduce the impact of tug position, PV panels should be installed in the front, port ant starboard side faces.

For use on the tug, PV panels need to be installed correctly. The mounting frame and PV panel kits are fixed in the front and side faces of the tug with a good attachment to withstand the harsh conditions at sea. According to the calculation, 13 panels of 300 W can be easily mounted on the exterior face side of the tug.

Figure 8 shows the proposed marine panel of 300 W manufactured by MSI (Marine Solar Innovation Company). The MSI 300 W panel is characterized by (Marine Solar Innovation Company, 2021; Rehman et al., 2007):

Panel size: 1640 × 992 × 35 mm.

Max power of 300 W.

Maximum Current of 9.15 A.

Maximum System Voltage of 1000 V.

Panel Voltage of 32.8 V.

Figure 8.

MSI PV Panel with 300 W of power.

Proposed DC/DC and DC/AC conversion system

The phoenix range of DC-AC conversion and MPPT charger shown in Figure 9 can be an interesting solution with optimized efficiency. This inverter is well suited to power up difficult loads as electric motors, air compressors, pumps, and similar appliances. To provide maximum power, a sophisticated battery charger with an adaptive charge technique using the maximum power point technology (MPPT) is needed. The MSI-MPPT battery charger is proposed for the system.

Figure 9.

The proposed Victron inverter for DC-AC system and a 100 A Victron MPPT battery charger.

To achieve higher AC output power, 6 units of phoenix sine wave inverters can operate in parallel mode to provide 18 kW (Feng et al., 2010; Victron Energy, 2021).

Horizontal wind turbine system

Since humans started using wind for sailing, wind turbines are considered as an efficient source of power especially with the development of power converters. This powerful energy is great for the environment and entirely renewable. In our case, two 5 kW turbines suffice for providing the necessary energy demand. It can run at speed of 40 m/s under a minimum wind speed of 2 m/s.

With high efficiency, ENAIR type 70 represented in Figure 10 can easily generate 80 kWh/day with a low wind speed. For its features (Abdel-Karim et al., 2011; Koutroulis et al., 2006; ENAIR Company, 2021):

Survival Wind Speed of 60 m/s.

Max power 5500 W.

Remote control system.

Only 1% above ambient noise.

Figure 10.

The proposed 5.5 kW wind turbine (marque ENAIR 70 PRO).

When the battery charge reaches the set point voltage, an intelligent battery brake system is integrated into this wind turbine that allows it to stop. This turbine can even resume charging when the load levels drop. For the installation, this turbine can be placed on the mast of the tug without any problem.

Energy storage system

The secondary power source in the marine tug is the battery bank. This energy storage allows the vessel to operate for a period of time of 1 hour in a blackout. The original system contains four batteries of 12 V 200 Ah each, combined to one battery bank of 24 V 400 Ah to feed small DC loads such as:

Emergency lighting system.

Main engine control system 24 V.

ROLLS-ROYCE Aquamaster propulsion control 24 V.

Fire fitting alarm system.

VHF radio communication.

In the new configuration, the extended capacity storage system can serve during 2 hours of emergency blackout in the sea and also a period of time at night when the tug is off service. Note that the tug can accommodate a large number of batteries by the space available in the engine room.

Favorable environmental factors in Arzew port

Before installing any wind turbine in each area of the world, a study of the site is necessary for knowing the annual average speed and direction of the wind (Windfinder, 2021). As shown in Figure 11, an average speed of almost 10 m/s is measured monthly which favorite for any wind turbine installation in Arzew.

Figure 11.

Monthly average wind speed and direction in Arzew port.

Harbor situation (AOA Algeria/Oman charging post)

We mentioned this special charging post named AOA which is the furthest operating post (more than 1 hour) for tugs. In the event of an emergency situation related to the power supply, the tug can’t reach the harbor and hence the immediate assistant of another tug is needed. However, the new electric installation scheme using renewable energies allows the tug to safely reach the harbor. Figure 12 provides a clear view of the geographic situation of this post (Google, 2021).

Figure 12.

Chart of AOA charging post using Google Earth.

Simulation under HOMER software

As shown in Figure 13, the designed system is simulated under HOMER software. Its specification consists of a diesel generator of 113 kVA, load demand, 3 kW PV array, two 5 kW wind turbines, bidirectional converter, and battery bank. HOMER software can simulate the proposed system with and without a diesel generator and can determine useful information about energy source capacity, excess energy, optimal size of different components, and also costs and emissions.

Figure 13.

The proposed system and load demand under HOMER.

Results discussion

The new power management integrating Wind/PV energy system has been simulated under HOMER software. Using the study shown in Table 2, the system in Figure 13 is consists of AC loads, one diesel generator of 80 kW, one wind turbine of 10 kW, 10 solar panels of 3 kW, and finally a battery bank of 50*1500 Ah. Considering favorable climatic conditions in the area of Arzew, both internet statistics of Figure 11 and HOMER monthly average speed of Figures 14 and 15 indicate a good convergence of results.

Figure 14.

Monthly Wind speed in Arzew port under HOMER.

Figure 15.

Monthly ambient temperature in Arzew port under HOMER.

In this simulation, the new system is supposed to provide almost real values by 31.3 kWh/day (14.04 kW peak) as depicted in Figure 16. Considering in this scenario 2 hours of daily blackout between 13 and 15 hours with 8.15 kW load demand and a partial time of 5 hours at night from 00 to 5 hours with the minimum load of 3 kW as in equation (3). Among these conditions, HOMER software tries to search for an optimum case without a diesel generator which has the minimum cost, maximum renewable energy penetration, and also a minimum of emissions.

Figure 16.

Seasonal load demand under HOMER.

Figures 17 and 18 show the provided energy shares in the new configuration. A maximum power output of renewable energy during the month of Feb/Mar/Apr is shown. This can be explained by the moderate temperature in Arzew and also the good wind speed in this period of the year. For the storage system, HOMER suggests that 50 batteries of 1500 Ah are required as illustrated in Figure 19. Figure 20 shows that in the 4 month of the year (Jan/Feb/Mar/Apr) a good energy excess is produced due to favorable wind speed and ambient temperatures.

Figure 17.

One success case without a diesel generator.

Figure 18.

Monthly average electric production with the proposed hybrid Wind/PV system.

Figure 19.

Total renewable power output.

Figure 20.

Monthly averages of the excess energy production.

Table 5 indicates a cost comparison of the studied system, the first case with a diesel generator and the second using only renewable energy. It can be concluded that the adoption of clean energy is very useful point of view cost. As in Figure 21, with a minimum diesel consumption of 7 L/hour, an annual cost of 17,900$ can be economized for 7 hours of daily operation with renewable energies. If the operating and maintenance cost (O&M) is taken into account, the O&M cost of the wind-PV system is low when compared to the diesel generator maintenance cost. Every year, each diesel generator needs approximately 16,600$ for its O&M including oil consumption and spare parts.

Table 5.

The cost comparison results.

Energy type	Duration (hours/year)	Fuel consumption (L/year)	Fuel cost ($/year)	O&M cost ($/year) by HOMER
Diesel generator	7 × 365	17,900	17,900	16,600
Renewable Wind-PV	7 × 365	0	0	6968

Figure 21.

Fuel consumption of the used diesel generator.

Conclusion

In this paper, challenges for a new design of the electrical grid of a modern tugboat were discussed. Two different scenarios have been studied. Firstly, under blackout, it is observed that the adopted hybrid PV-wind energy system can be useful and significant for the safety of the vessel to reach the harbor without any damages. In the second objective, supplying minimum system loads when the tug is stand-by can be easily realized. It can reduce CO₂ emissions and economize an annual cost related to the fuel consumption and O&M of the diesel generator. This several advanced features and benefits prove that environmentally friendly technologies based on PV and wind systems can be incorporated into the maritime domain especially on board small vessels. Furthermore, due to its favorable environmental factors, it has been shown that Arzew is a suitable area for installing renewable energy sources. Some results are presented using the HOMER simulation program in order to confirm that the proposed scheme can succeed. The obtained outcomes revealed that the integration of green energy appears to be an interesting sustainable alternative and deserves further investigation under real hardware implementation.

Footnotes

Acknowledgements

The author would like to acknowledge the contribution of Arzew Port Company presented by the chief engineer Mr. Bouhouta Ahmed.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Ahmed Bouhouta

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