Proposed Hybrid Power System for Short Route Ferries Prijedlog hibridnog porivnog sustava za trajekte na kraćim rutama

A fractional fuel consumption saving as well as pollution cuts will be a thinking pattern or a key concern in modern ship designs. Recent advances in technology for solar cells and photovoltaic (PV) modules have resulted in solar power being a cost-eff ective fuel reduction alternative for this objective. This paper is intended to provide a hybrid solar diesel power system for short-run ferries. This work proposes and emphasizes the energy effi ciency, cost effi ciency and minimal environmental impact of hybrid-powered ferries with solar diesel. The proposed system has been studied on the example of passenger-car ferry connecting the two banks of the Suez Canal at Port Said city - Egypt. Economic and environmental analyses have been conducted to determine and measure the advantages of the proposed system. The results show an economically viable and environmentally sustainable system if it were treated as a long-term investment. Compared to the equivalent diesel generator system, this system reduces exhaust emissions by about 375 tonnes per year. The fuel cost savings achieved are also signifi cant.


INTRODUCTION / Uvod
Nowadays, reducing exhaust gasses emitted from seagoing ships is actually one of the most important environmental concerns in the marine industry. In addition, the international regulations have become stricter on this issue. Hence, many ship operators have started to rely on alternative energy sources to reduce emissions from ships and therefore work in an environmentally friendly manner. In this regard, especially with the volatility of oil prices, renewable energy sources have become more attractive to ship owners. Since the ocean is exposed to vast quantities of sun rays, solar energy can be considered as one of the most promising energy sources in the maritime sector. It also reduces the use of fossil fuels, with consequent economic and environmental advantages.
The Photovoltaic (PV) solar system has recently been regarded as one of the most important alternative sources of energy. Hence, solar photovoltaic systems are commonly used to provide all or part of the electrical requirements on board marine units. Where many multihull marine units (catamaran and trimaran) are designed to use PV solar system as a hybrid propulsion system together with diesel generators [1]. Palmer and Sembler [2] have proposed a high-effi ciency hybrid system which would generate electrical power onboard a very large crude carrier. The proposed system includes PV solar panels, a solid-oxide fuel cell, a gas turbine, a vapor generator for heat recovery and a steam turbine [2]. The results showed that the proposed system would cover only about 78 percent of the hotel load required in port. Sulaima and Saharuddin [3] tested the feasibility of using solar photovoltaic system as an auxiliary power source for the auxiliary engines of a 16.5 m long diving boat. The results indicated that some economic and environmental benefi ts will be achieved by using the PV solar system to cover boat power requirements [3].
Egypt receives an annual direct solar radiance of between 1950 and 2600 kwh/m 2 /year [4]. In addition, its unique location within the solar belt countries makes it one of the most important countries that can benefi t from applications of solar energy. These advantages have encouraged many Egyptian researchers to conduct more research on the use of solar energy in some inland units. Kotb et al. [5] focused on the exploitation of solar energy on board an inland waterway unit named "Dahabiyya" through experimental study and numerical analysis to simulate temperatures and other parameters of a hybrid photovoltaic thermal system consisting of PV solar modules and thermal units absorbing the heat produced that aff ects the effi ciency of the PV modules. Moustafa and Essam [6] conducted a lifecycle cost analysis to check the feasibility of installing a solar photovoltaic system that generates part of the electrical load required on board the River Nile cruiser navigating between Cairo and Aswan.
There are about eight Passenger-car ferries crossing the Suez Canal during the day and linking the cities of Port Said and Port Fouad which considered the Asian part of Port Said governorate. These ferries and large numbers of seagoing ships passing through Suez Canal constitute a major source of air pollution in that region. Where, this area receives about 8.16 million tons of exhaust gasses released from seagoing ships alone annually [7]. Therefore, the aim of this paper is installing a photovoltaic / diesel hybrid power system on board one of Port Said passenger-car ferries to take advantage of the benefi ts of this system and to leverage the Port Said Governorate's geographical position, which stretches nine miles along the Mediterranean coast.

PORT SAID FERRIES / Trajekti u Port Saidu
Port Said ferries connect the two banks of the Suez Canal at Port Said Governorate and hold both people and cars for free all day long, see Fig. 1. The Suez Canal Authority (SCA) is responsible for the execution of orders and the maintenance & repair processes for these ferries. It doesn't take these ferries more than 10 minutes to travel from one bank to the other Suez Canal bank.  .500 m, -Design Speed = 12 km/h. Unfortunately, there were no clean energy sources used to supply this unit with the electrical charge required. Therefore, in this paper, a photovoltaic (PV) /diesel hybrid power system is installed onboard "Tahia Misr 1" to boost its energy effi ciency, thereby reducing both fuel consumption and exhaust gas emissions.

ROUTE METEOROLOGICAL DATA / Meteorološki podaci rute
In general, the performance of any photovoltaic (PV) system is sensitive to the meteorological and environmental characteristics of the navigation route considered. As Port Said's passenger-car ferries navigation route is fully laid in Port Said, the Egyptian solar radiation atlas is taken as a source for this kind of knowledge. The meteorological details of the navigation route considered in this analysis are shown in Table 1 [4]. Such values are fairly high and promote the installation of a PV solar power system onboard "Tahia Misr 1".

SOLAR HYBRID POWER SYSTEM / Solarni hibridni pogonski sustav
In general, solar hybrid power systems are often combine solar power with another power source. In addition, PV-diesel hybrid system is the most common hybrid power system. In most cases, diesel generators are used to cover the gap between the electric charge required and the power generated by the solar photovoltaic system. The proposed photovoltaic / diesel hybrid power system confi guration is shown in Fig.3. This system fulfi ls the load needed for every hour in the year.
Electricity produced by solar panels and stored in the batteries has priority in supplying the candidate ferry's necessary electrical load. In such a device, the diesel generator would be turned on to act as a temporary source of power when the battery storage capacity reaches its minimum permissible level and the energy provided by solar panels is not suffi cient to supply the necessary load. This mode will continue until the batteries are charged to their full capacity as the bidirectional inverter acts as a rectifi er and allows for battery charging. In addition, in some situations, if the produced energy exceeds the electrical load required and the batteries are completely charged, a dump load will consume the excess energy. Therefore, the decision to charge and discharge the batteries or run the diesel generator is generally based on a comparison between the load needed and the solar panel energy generated available.

PHOTOVOLTAIC (PV) SOLAR SYSTEM / Fotonaponski (PV) solarni sustav
Any solar photovoltaic (PV) system consists mainly of four components (PV solar panels, charging controllers / solar regulators, storage batteries and solar inventers). Every component 's role is set out as follows: -Solar photovoltaic panels: they capture solar rays to generate electricity, -Charge controllers / solar regulators: they are used to regulate the charge fl owing to the batteries and prevent overcharging. They also don't allow the reverse night-time feed of the current into the solar panel, -Storage batteries: they are used to store the excess electricity. Accordingly, they will be used when there is a lack of or no charge from solar panels,  The photovoltaic (PV) solar panel effi ciency is highly susceptible to both cell operating temperature (TC) and solar irradiance (G). Panel output rated power is the electrical output of a PV solar panel measured at a standard test condition (T STC = 25°C and G STC = 1000W/m 2 ). Eq. 1 is used to calculate the electrical output power generated from any photovoltaic (PV) solar panel at a real operating condition [8]. (1) Where, P Out-PV is the output electric power generated at a real operating condition in kW/h, P R-PV is the output rated power of the PV solar panel in kW/h, G is solar irradiance at a real operating condition in W/m 2 , G STC is the solar irradiance at a standard test condition in W/m 2 , α is the temperature coeffi cient for the maximum power at solar irradiance G, T C is the cell operating temperature in °C , T STC is the cell operating temperature at a standard test condition in °C and T amb is the ambient temperature in °C . (3) (4) Also, Eq. 3 and Eq. 4 are used to calculate both the short circuit current (I SC ) and open circuit voltage (V OC ) of a PV solar panel at real operating conditions, respectively [8]. Where, I SC-STC is the short circuit current of a PV solar panel at a standard test condition in Amperes and β is the temperature coeffi cient for the short circuit current at solar irradiance G, V OC-STC is the open circuit voltage of a PV solar panel at a standard test condition in Volts, γ is the temperature coeffi cient for the open circuit voltage at solar irradiance G and δ is the temperature coeffi cient for the irradiance. According to the manufacturer's instructions for 340W mono-crystalline silicon PV solar panels, α, β, γ and δ can be taken -5.5 x 10 -3 , 3.0 x 10 -4 , -3.6 x 10 -3 and 2.596 x 10 -2 , respectively. In the present paper, 76 mono-crystalline PV solar panels are used to cover an area of 148.5 m 2 available on the top deck of Port Said passenger-car ferry "Tahia Misr 1". Table 2 displays selected panel specifi cations in standard test condition [9]. Based on the geographical characteristics of the navigation route of "Tahia Misr 1" and the manufacturing specifi cation of the selected solar panels, Eq. 5 is used to calculate the daily output electrical power of the installed PV solar system (E d ) in kWh [6], see Fig. 4. (5) Where, N P is the number of PV solar panels, T SS is the daily sunshine hours, η B is the effi ciency of the battery and η Inv is the inverter effi ciency. In this paper, η B and η Inv are taken equal to 0.85 and 0.9, respectively [10].

Figure 4 Daily Output Power of the Proposed PV Solar System Slika 4. Izlazna snaga predloženog PV solarnog sustava po danu
The results also show that the proposed PV solar system would generate 41,483.5 kWh of electrical power per annum. In addition, maximum short circuit current (I SC ) and the maximum daily output electrical power (E d ) are equal 7.345 A and 150.934 kWh, respectively. Other components of that system are therefore selected to match those quantities. Charge controllers are typically classifi ed according to the amount of I SC they can receive from the PV solar panels. In addition, a 15% margin can be used to cover the excess that may occur in the PV solar panel output. Thus, 12 charge controllers of 60 A are used in the present paper to handle a short-circuit current of 670 A (7.345 A x 76 panels x 1.2). Table 3 shows the manufacturing specifi cations for the selected charge controller [11]. Solar batteries are usually rated in ampere hours (Ah) that specifi es the amount of current in Amps that the battery can deliver in hours over a specifi ed period of time. In addition, lead acid solar battery is the most common type of battery that is used in the maritime industry. Thus, in the present case, a battery bank consisting of 54 lead acid solar batteries each 12V 300Ah is used to store 150.934 kWh electricity, which is the maximum daily electrical output of the installed PV solar panels. Battery tank size is calculated using a discharge battery depth (DOD) of 80 % [12]. Table 4 shows the manufacturing specifi cations for the selected battery [6].  The battery bank stores low-voltage DC current, typically around 12-24 volts. In addition, most of the onboard ship's existing appliances are powered by AC power source and operate at 220 volts. Any solar PV system must therefore include inverters to convert DC to AC, and vice versa. The inverter 's input rating should never be less than the total appliance capacity. Inverters also need to have the same nominal voltage of the battery chosen. According to the candidate ferry's electric power balance sheet "Tahia Misr 1", the current appliances' total power equals 86.7 kW. In practice, 15-20% oversize of the inverters is recommended. Pure sine wave inverter is also the most commonly used type of inverter in marine applications. Therefore, 20 pure sine wave inverters each 5000W are used for the candidate ferry to handle a power of 99.7 kW (86.7 kW x 1.15). Table 5 shows the manufacturing specifi cations for the selected inverter [6].

ECONOMIC ANALYSIS / Ekonomska analiza
In the present paper, a life cycle cost (LCC) is calculated and annualized to predict the installed PV solar system's average annual cost (AAC), as follows [13]: Where, CR is capital recovery factor, i is interest rate and n is the life span of the installed PV solar system. The cost of the life-cycle of any PV solar system is usually equal to the sum of the present cost values: -PV solar panels, -Charge controllers, -Storage batteries, -Solar inverters, -Installation, -Maintenance & repair.
The life span of all components of this system is presumed to be 20 years except that of the group of solar batteries which is considered to be 10 years. Hence, the group of solar batteries installed must be replaced after 10 years. The present cost value of the second group of batteries shall be determined as follows [6]: Where, C B1PW and C B2PW are the present values of the fi rst and second solar batteries groups, respectively. Also, PW is the single present worth factor, d is infl ation rate and n is the life span of each batteries group. Values of 5% and 10% for infl ation and interest rates, respectively, can be considered. In addition, installation and maintenance costs are taken 10% and 2% of the cost of PV solar panels, respectively [10]. The total present values of the cost of maintenance & repair (C MRPW ) can therefore be calculated as follows [6]: Where, C PV is the cost of PV solar panels and SPW is series uniform present worth factor. Now, as shown in Table 6, present values of the components of the installed PV solar system, LCC and AAC are calculated and summarized. In order to check the economic feasibility of a solar PV system producing 41,483.5 kWh per year, it is necessary to calculate annual cost of the fuel consumed to generate the same amount of electricity by diesel generators. As mentioned earlier, Port Said's new passenger-car ferry "Tahia Misr 1" is equipped with 2 x 48 kW diesel generators. Each diesel generator can cover the electrical load required for such ferry, and consumes 15 litres of fuel per hour. A 48 kW diesel generator would therefore generate 41,483.5 kWh of electricity per year, if it operates 864.24 hours per year (41,483.5 kWh / 48 kW). In addition, 17284.8 litres of diesel fuel would be used during its operating period. If the average price of diesel fuel is $1.0/litre worldwide, the price of the fuel consumed will be $17284.8 per year. Hence, it can be said that this system is economically feasible and can save $11512.94 annually.

ENVIRONMENTAL ANALYSIS / Analiza utjecaja na okoliš
To evaluate the environmental benefi ts of the proposed photovoltaic/diesel hybrid system, an annual decrease in "Tahia Misr 1" released exhaust gases is estimated. These calculations are based on the amount of the fuel consumed to generate 41,483.5 kWh of electricity per annum (17284.8 litres or 14.433 tons of marine diesel fuel) and the exhaust gas emission factors as shown in Table 7 [14].This paper takes into account nitrogen and sulphur oxides, carbon monoxide, carbon dioxide, and particulate matter. Where, they are the main harmful emissions from marine diesel engines.  Table 7 shows that the proposed "Tahia Misr 1" system would reduce the volume of exhaust gasses generated annually by 46.86 tons. Moreover, if that system is generalized to the rest of the passenger-car ferries in Port Said, the annual reduction in exhaust emissions will exceed 375 tonnes.

CONCLUSION / Zaključak
The rapid development of solar cell technology, which combines low prices with improved effi ciencies, makes solar energy the most promising energy source and it can be widely used in the maritime fi eld. Thus a photovoltaic PV / diesel hybrid power system is proposed in this paper to supply the auxiliary power needed for the instrument on board Port Said's "Tahia Misr 1" passenger car ferry. This system would ensure a continuous supply of power if both generators faced a failure or some emergency.
The results showed that if it were handled as a long-term investment, the proposed photovoltaic PV / diesel hybrid power system is economically feasible. Where, this system will produce an annual fuel cost reduction of about $17284.8. Moreover, if it generalized to all Port Said passenger-car ferries, it could also reduce the amount of exhaust gas emitted by more than 375 tons per annum. That sum may be low but if it is considered for a long time, reducing the exhausts gasses produced will also help to save our atmosphere from pollution.