1. Introduction
Inland navigation is, together with road and rail transport, one of the three mainland transport modes and can be considered as the most cost-effective and safest mode of transport [
1]. Freight and passengers are transported by vessels via inland waterways, such as canals, rivers, and lakes, between inland ports and wharfs [
2]. Design requirements for inland waterway vessels and seagoing vessels are fundamentally different, and therefore inland waterway vessels are generally not allowed to navigate at sea [
3]. Xing et al. [
4] compared the operational energy efficiency of inland waterway vessels with seagoing vessels and concluded that the presence of a river current leads to a reduction of energy efficiency for vessels engaged in inland waterway transportation.
Research into emissions from shipping and their impact on air quality has mainly been directed to seagoing vessels, such as in the studies by Ančić et al. [
5], Lindstad et al. [
6], Miola and Ciuffo [
7], Ammar and Seddiek [
8], and Chen et al. [
9], and has focused less on inland waterway vessels. However, it is important to mention that inland navigation regularly takes place within highly populated areas, and its effect is therefore even more pronounced [
10,
11]. This particularly refers to emissions that have a strongly local character, although carbon dioxide (CO
2) emissions should not be ignored either.
The exhaust gases produced by the combustion of fuel oil in marine engines contain different harmful substances, such as sulphur oxides (SO
X), nitrogen oxides (NO
X), carbon monoxide (CO), particulate matter (PM), and greenhouse gas (GHG) emissions, which particularly refer to the emissions of CO
2, methane (CH
4), and nitrous oxide (N
2O). In order to control these emissions, the International Maritime Organization (IMO) has set different standards related to the Energy Efficiency Design Index (EEDI) and Ship Energy Efficiency Management Plan (SEEMP) [
12]. Furthermore, by establishing several Emission Control Areas (ECAs), IMO has ensured emission control in specific areas where emission requirements are stricter than outside these areas [
13]. SO
X emission control is performed by limiting the sulphur content in fuel, while NO
X emissions are limited depending on the engine maximum operating speed. Both the SO
X and NO
X regulation standards differ depending on the navigation area (global or ECA) [
14]. Besides their environmental impact, exhaust gases negatively affect human health [
15]. This is more pronounced when ships spend more time in ports and near inhabited areas [
16], which is typical for ships engaged in short-sea shipping and inland navigation.
The most attractive research topic in the field of shipping emissions is decarbonization, i.e., reduction of GHG emissions. Generally, decarbonization of the shipping industry can be achieved by increasing ship energy efficiency, leading to a reduction in fuel oil consumption and ultimately to a reduction in GHG emissions [
17]. Bouman et al. [
18] discussed technical and operational decarbonization measures that can be implemented in the shipping sector. Since most of the measures are based on the reduction of fuel consumption, besides GHGs, other emissions (NO
X, SO
X, PM, etc.) are reduced as well. Among different operational measures, voluntary speed reduction represents the most effective operational measure for CO
2 reduction, as investigated by Corbett et al. [
19] and Lindstad et al. [
20]. Furthermore, the most promising technical measure to reduce the negative effects of shipping emissions includes replacing conventional marine fuel oil with alternative fuels (such as biodiesel, hydrogen, electricity, natural gas, methanol, dimethyl ether, ammonia, etc.) as indicated in the study of Perčić et al. [
21] and replacing the conventional propulsion system (a diesel-engine-powered ship) with a hybrid propulsion system (HPS) or an integrated propulsion system (IPS) [
22]. Psaraftis et al. [
23] investigated the inclusion of carbon allowance policy in the shipping sector as a market-based measure that could lead to decarbonization, where the CO
2 cost impact represents an incentive to implement technical or operational measures that result in lower CO
2, preferably a zero-carbon emission solution, such as full electrification of ships. Such a ferry was presented by Gagatsi et al. [
24]. The great advantage of such vessels is that they do not release exhaust gases during navigation, although they do have some limitations regarding battery capacity, power source degradation, price, weight, and charging, as well as sailing distance [
25]. A comprehensive review of promising technologies and practices that are applicable to onboard energy systems of all-electric ships, including sensitivity analysis of the energy efficiency of all-electric ships with respect to different applications, was recently done by Nuchturee et al. [
26].
The implementation of renewable power sources onboard leads to a reduction of emitted GHGs, as indicated in many studies. Geertsma et al. [
27] presented a review of developments in the field of design and control of HPSs for smart ships analyzing their trends, challenges, and opportunities and finally claiming that a combination of torque, angle of attack, and relevant control strategy could improve their fuel consumption and consequently environmental footprint. In the design and operation of ships with HPS, optimal sizing of power generation units plays a key role, where regularly minimum investment and operating costs are set as objectives [
28]. However, most often, expenses related to emission allowance are not taken into account. Ghenai et al. [
29] presented an HPS for a cruise ship, where the total power is generated by photovoltaic (PV) cells, fuel cells, and a diesel generator, which also resulted in reduced emissions. The inclusion of a battery system for a diesel mechanical short sea ship was investigated by Ritari et al. [
30], who claimed that the battery system can result in significant fuel savings, which become more important with the increase in fuel price. By investigating a PV cell diesel. engine-powered ship, Yuan et al. [
31] showed that its operation leads to a reduction in both diesel consumption and GHG emissions. Wu et al. studied cost-effective energy management strategies considering hybrid fuel cell and battery propulsion systems for coastal ships, providing a novel so-called reinforcement learning approach for their optimal use [
32]. Energy management itself represents an important research topic for both hybrid and all-electric vessels, as can be seen in [
32,
33]. HPSs are presented for different ship types differing in their purposes and operative performances, as for instance tankers [
28], cruise ships [
29], passenger ferries [
32], offshore platform supply vessels [
34], etc., but in most cases, investment costs represent a key issue in their wider application. However, life-cycle assessment (LCA) of a new-build HPS for a ro-ro cargo ship performed by Ling-Chin and Roskilly, ref. [
35], by means of GaBi software, resulted in a rather high impact on the environment, human beings, and natural reserves. Furthermore, as reported by Lindstad et al. [
36], a combination of battery and internal combustion engines on an existing ship resulted in reduced emissions, but the main obstacle for this retrofit was the price of the battery. One way to evaluate the profitability of a retrofit is to consider the total life-cycle costs (LCCs) by performing a life-cycle cost assessment (LCCA). Wang et al. [
37] investigated the implementation of a solar panel array onboard a ferry where the LCCA results showed that the investment payback period is only three years, which makes a solar panel array not only an environmentally friendly technology but also an economical one. It is necessary to mention that these findings are generally applicable but strongly dependent on a set of assumptions and considered operative conditions.
Based on the above extensive literature review, an evident literature gap can be seen. Even though the utilization of renewable energy sources onboard shows a reduction in shipping emissions, none of these studies was oriented towards inland waterway vessels. Due to the many special features inherent in inland waterway transport, the results of the above-mentioned studies cannot be directly used, especially regarding cost assessments. So, it is not clear which option would have the lowest environmental impact and would be the most profitable for inland waterway vessels. Moreover, the operation of inland waterway vessels is highly dependent on the location, since waterway conditions regularly differ greatly from one area to another, and the application of relevant measures to improve ship energy efficiency should be assessed on a case-by-case basis. Therefore, the aim of this paper is to set a model for investigation of the applicability of different power system configurations both from the environmental and economic point of view for the retrofit of three different vessel types. The procedure is illustrated for the Croatian inland waterway fleet, which is rather aged and requires a significant increase in its energy efficiency and reductions in fuel oil consumption to meet emerging environmental requirements. However, it is applicable to any other inland waterway sector, if a set of input data is known. It should be mentioned that the bounds of the analysis are set at the single ship level, while this paper did not address the cooperation and optimal operation of onboard energy systems and on-land shore power. This should be considered further in order to obtain cost savings from the perspective of a shipping company, where approaches from [
38,
39] could be adopted.
The original contribution of this study is summarized as follows: (a) the development of models to assess the GHG, NO
X, SO
X, and PM10 emissions of different power system configurations for three inland waterway vessels; (b) the identification of the most cost-effective powering option for the observed ships; and (c) an estimation of the policy impact on the profitability of each option. In order to achieve a fair comparison between different power system configurations, an approach by Jeong et al. [
40] is adopted, where all incomparable values are converted into monetary values, and the proper solution is selected in a straightforward manner.
This paper is structured into six sections. In the next section, the methodology is described. A model for alternative power configuration selection that takes into account lifetime emissions and costs is elaborated. The LCA and LCCA procedures are described in detail. The third section is dedicated to the analysis of the Croatian inland waterway fleet, with the aim of identifying typical vessels according to their purpose and operative profile and to calculate their energy needs as a prerogative for LCA and LCCA. The results are listed in the fourth section, while a discussion of the procedure and the obtained results are presented in the fifth section. Finally, concluding remarks are drawn in the sixth section.
3. Case Study—The Croatian Inland Waterway Vessels
The Croatian inland waterway network consists of the natural streams of the Danube River (137.5 km), Sava River (446 km), Drava River (198.6 km), and Kupa River (5 km),
Figure 7. This network’s geographical position in the center of Europe represents a significant potential. However, due to different navigation conditions, technical obsolescence, and low capacity, the Croatian inland navigation is underutilized [
62]. In 2017, inland navigation accounted for 24% of the total Croatian shipping sector according to the data on goods carried [
63]. Apart from rivers, some Croatian inland waterway vessels operate on lakes, which are located in protected areas of nature and serve primarily touristic purposes.
The Croatian inland waterway fleet is comprised of several types of ships: dredgers, tugboats (tugs and pushers), passenger ships, and cargo ships, so the general model presented in
Figure 1 is adapted and shown in
Figure 8.
The exploitation characteristics of a ship determine the ship’s economic output and depend primarily on the ship type, as shown in
Table 1. A dredger’s primary task is to reshape the riverbed, while tugboats are ships tasked with pushing and/or tugging ships, barges, or other vessels. Passenger ships are used to transport passengers and most of them sail in protected areas of nature, while cargo ships are used to transport different types of cargo. All vessels use high-speed four-stroke diesel engines connected via a gearbox to the propeller (diesel-mechanical propulsion) [
64]. The average age of ships in the fleet is around 40 years, implying that they will soon need to be replaced by new ships, or at least retrofitted with new power systems. Since the profitability of this sector is relatively low, the latter option seems to be more realistic. This represents an opportunity to introduce new energy-efficient and greener technologies, which is very important bearing in mind the overall European goals to shift a significant portion of road transportation to inland waterways where possible.
The economic output of dredgers and tugboats is expressed in the specific task they should accomplish during their operation. The economic output of passenger ships is expressed in the number of passengers transported over a certain distance, while for cargo ships, it is similarly expressed in the cargo carried over a certain distance. The selected representatives are shown in
Figure 9.
Considering the exploitation characteristics of each representative, the average and annual energy consumption is calculated. The representatives’ particulars are presented in
Table 2, as obtained from [
64]. Additional data on their exploitation were gathered from the shipowners.
The representative of cargo ships is the tanker named “Opatovac”. It is mostly used to transport oil between two Croatian refineries, covering a distance of about 223 km. On average, it performs 20 round trips annually. The ship speed depends on the river environment. The average speed of a cargo ship of this size is 14.4 km/h, with an average main engine load of 75% of the maximum continuous rating [
68]. With an average speed of the Sava River of 1 m/s [
69], the estimated average duration of the trip is 20.5 h for upstream and 12.5 h for downstream navigation. The average load of the auxiliary engines is estimated at 50% of the maximum continuous rating. The average ship power is determined by Equation (1). After calculating
Pave, the ship energy consumption per distance travelled is calculated according to Equation (4). Since the observed tanker sails on rivers, its annual energy consumption is calculated according to Equatipn (5), while its
FOC for both for the upstream and for the downstream journey is calculated according to Equation (6).
The representative of passenger ships is the ship named “Trošenj”, which operates in Krka National Park. The river speed is very low on this 5-km route, so it is not taken into account, i.e., the power for both upstream and downstream sailing is considered to be equal. It takes around 20 min for a one-way trip, with an average speed of 15 km/h. On an annual basis, the ship sails around 2190 round trips, depending on the weather [
58]. It is assumed that the ship operates at 70% of the total installed power. In a similar way as for the cargo ship, the annual energy consumption of the passenger ship is calculated according to Equation (7).
The representative of working ships is the dredger named “Papuk”. Since this kind of vessel belongs to stationary units, a modified approach, explained in the previous section, is applied. The annual fuel oil consumption of this ship equals 63,023 L as reported by the shipowner. With the assumption that the average load of the ship power system is 50% of the rated load, the time that the dredger spends in operation is approximately determined according to Equation (8). Therefore, the annual energy consumption of the dredger is calculated according to Equation (9).
After estimating the energy consumption of each representative, it is possible to define different power configurations. In this paper, three power configurations are analyzed and compared. As a conventional power configuration, a diesel-powered ship is selected. Furthermore, the diesel-powered configuration is compared to two alternatives, a battery-powered ship and a PV cell battery-powered ship. The environmental impact of each power configuration is assessed by the LCA method and the LCCA method is applied for estimating all relevant costs during the operation time.
3.1. LCA of the Croatian Waterway Fleet
As shown in the previous section, the current Croatian fleet should be retrofitted, so the applicability of different power system configurations for retrofitting three different ships is investigated. Since the emphasis is on a comparison of different retrofitting options, only emissions related to power system configurations are taken into account.
3.1.1. LCA of Diesel Engine-Powered Ships
The first option considered in this paper is to retrofit the selected ships with new diesel engines. MAN high-speed four-stroke heavy-duty diesel engines are considered with the corresponding power outputs based on the manufacturer’s data [
70], as shown in
Table 3.
The environmental impact of diesel engines was assessed by observing the manufacturing process and considering the weight ratios of material contents in the engine as proposed by Jeong et al. [
71]. In order to calculate the weights of the engine materials, these ratios were multiplied by the weight of the engine. The materials’ manufacturing process parameters were obtained from the GREET 2020 database.
The Croatian inland waterway fleet uses “Eurodiesel Blue” as fuel oil. This fuel oil is diesel colored with blue dye according to the Regulation on the Implementation of Excise Duty Act [
72]. According to viscosity, it corresponds to Conventional Diesel from the GREET 2020 database, from which the parameters are obtained to describe the process of diesel refining and the process of crude oil recovery. Crude oil used for the production of “Eurodiesel Blue” in Croatia is primarily imported from the Middle East since domestic crude oil production is not sufficient for the Croatian needs. It is considered that crude oil is transported via tankers and pipelines from the Middle East to Croatia. For reasons of simplicity, it is assumed that the diesel is produced only in the Rijeka refinery [
73]. After the diesel is produced, tank trucks transport it to the gas stations. This distance is different for each considered ship because it depends on where the ship is refueling. Therefore, the distance for the cargo ship is 200 km (from Rijeka to Sisak); for the passenger ship, it is 300 km (from Rijeka to Šibenik); and for the dredger, it is 450 km (from Rijeka to Osijek). Tailpipe emissions released during the vessel operation are calculated according to Equation (10).
3.1.2. LCA of Battery-Powered Ships
The battery-powered ship configuration has a simpler life-cycle. As explained in the previous sections, a fully electric ship has zero PTW emissions and the manufacturing emissions depend on the type of battery that is being implemented.
As one of the issues, the battery capacity was mentioned. In this case study, three different types of ships are studied. It is assumed that the capacity of the battery should be sufficient for the cargo ship to sail one-way upstream without recharging, with an average speed over ground of 10.9 km/h, i.e., an average speed over water of 14.4 km/h. As for the passenger ship, it is assumed that the battery is charged after a round trip, while for the dredger, the battery should have enough capacity to allow it to operate for 8 h without recharging. The calculations are carried out according to Equation (13). The next step is to calculate the weight of the batteries with the assumed power density of 0.25 kWh/kg. The battery manufacturing process parameters are obtained from the GREET 2020 database.
The WTP of electricity is the main emission contributor in a battery-powered configuration. As said in the previous section, it depends on the electricity generation process in the country where it is being implemented. The main energy sources for the Croatian electricity generation are shown in
Figure 10, except for nuclear energy, which is not produced in Croatia [
74]. In order to describe the electricity generation process in GREET 2020, data on the Non-distributed U.S. Mix are used, where the shares of electricity generation sources are replaced with the shares characteristic of Croatia.
3.1.3. LCA of PV Cell Battery-Powered Ships
As described in previous sections, besides the battery, the manufacturing process of PV cells has a large role in the total lifetime emissions. In this assessment, crystalline silicon (c-Si) cells are used due to their low cost, high density, efficiency, and suitability for use on horizontal surfaces [
75]. Their efficiency ranges from 12% to 19% [
76]. They consist of glass for the panel surface (76%), polymer (10%), aluminum for the frame (8%), silicon for the PV cells (5%), and copper for the interconnectors (1%) [
77]. According to some commercial c-Si PV panels, the module of 1.64 m
2 weighs 19.5 kg, which is used to calculate the weight of PV module materials (glass, aluminum, silicon, and copper) [
78]. Their manufacturing process parameters are obtained from the GREET 2020 database.
Another factor that affects the efficiency of the system is the average annual solar irradiance. Data for the case of Croatia are obtained from the Climate Atlas of Croatia [
79].
3.2. LCCA of the Croatian Waterway Fleet
LCCAs of different power system configurations implemented on the Croatian inland waterway vessels are performed. It is assumed that the lifetime of each retrofitted vessel is 20 years. Therefore, the results of the LCCA refer to the total costs during that time.
3.2.1. LCCA of Diesel Engine-Powered Ships
A major part of the investment cost is the engine procurement and installation, but in this case study, the purchasing costs that will be presented consider only the engine purchase. Due to this, they are increased by 40% to take into account additional equipment connected to the engine, the installation cost, and the gearbox cost. The annual maintenance cost is assumed to be 7.5% of the total installation cost.
In terms of operational characteristics, the Croatian fleet uses the “Eurodiesel Blue” with the price of €0.66/l, taking into account the reduction in the excise duty [
80]. Considering the operational characteristics of each ship, the annual fuel oil consumption cost in € can be calculated. For the cargo and passenger ship, Equation (14) considers the characteristics of the routes, while the calculation of the dredger, Equation (15), is determined with the annual operating time.
3.2.2. LCCA of Battery-Powered Ships
The investment costs include all costs connected to the replacement of a diesel-powered system with a battery-powered system. This includes the battery procurement and, in this case, the battery price is assumed to be €200/kWh [
61]. Another major factor in the cost assessment is the electric power price. For the Croatian industrial sector, the electric power price equals €78/MWh [
80] and, according to Equation (18), the annual electric power cost for different vessels can be calculated. Considering that the assumed lifetime of a vessel is 20 years and a lifetime of a Li-ion battery is assumed to be 10 years [
81], the battery replacement is also included in the LCCA as a significant maintenance cost.
3.2.3. LCCA of PV Cell Battery-Powered Ships
Similar to the calculations of a battery-powered ship, the total costs of a PV cell battery-powered ship include the investment and maintenance cost of a battery-powered configuration and the addition in costs of a PV system. The annual electric power cost is calculated according to Equation (22) and it includes the electric power price as indicated in the previous section.
In this paper, it is assumed that the PV system price equals €165/m
2. This price is obtained according to the World Energy Outlook 2018 for the European Union [
59], taking into account the average electric power which c-Si PV cells can convert from solar energy per 1 m
2 [
76]. The annual maintenance cost is assumed to be 5% of investment costs, which is calculated according to Equation (23). Manufacturers of PV cells provide a 20-year warranty for PV systems, which is the expected lifetime of the considered ships. Hence, the replacement cost for PV cells is not taken into account. In order to determine the maintenance cost for the entire PV cell battery-powered ship, both the maintenance cost of the PV cells and the replacement of the battery cost should be considered.
5. Discussion
Based on the LCA results presented in the previous section, it can be observed that diesel engine-powered ships make the highest contribution to GHGs, PM10, and NO
X emissions. With the application of alternative power system configurations, the environmental impact can be significantly reduced. However, the alternatives implemented on the cargo ships and the dredger result in higher SO
X emissions than the existing diesel engine-powered ship. The main reason for this is the required large capacity of the battery, whose manufacturing process releases a great amount of SO
X emissions into the atmosphere. Since the passenger ship requires a battery of small capacity, among the considered different power systems onboard, the main contributor to SO
X emissions is the diesel engine power system configuration. Regarding all considered emissions, the PV-BAT configuration results in the lowest lifetime emissions among the different considered power system configurations. It can be noticed in
Figure 11 that the impact of the installation of PV cells is less pronounced for the passenger ship due to the relatively small area that can be covered by PV cells. In addition, due to the high battery capacity required for a cargo ship and dredger, the impact of the battery manufacturing process is also relatively high, especially when compared with the diesel engine.
According to the LCCA, it is evident that the diesel engine options for both the cargo ship and the dredger have the lowest LCCs compared to the alternative power system configurations. The greatest difference in the LCCs between the different configurations is shown for the cargo ship, where the LCCs of the PV cell battery-powered ship is equal to €12.9 million, while for the diesel engine-powered ship, the LCCs is €2.1 million (in the NT scenario). The primary reason for this discrepancy is the high cost of the battery. A reduction in the battery capacity would lead to a reduction in the investment cost. This could be achieved by reducing the required sailing distance (which is defined by market needs and is unlikely to be reduced) or by reducing the speed. The upstream speed over water for which energy consumption is the lowest can be calculated by minimizing the ratio of the required power output and the sailing time, and equals 150% of the river speed, i.e., 1.5 m/s. This would significantly reduce the power output to around 40 kW but also extend the trip duration six times to roughly five days. In this extreme scenario, the battery capacity could be reduced by almost 70%, resulting in an LCC of a battery-powered cargo ship of around €4 million. This is still higher than the diesel engine option, but at least it opens the possibility for the use of the battery in the future, providing the battery price decreases or some environmentally oriented policies are introduced. An example of such a policy is shown in the analysis of carbon credit, as shown in
Figure 6. Even though its impact is not crucial, it still makes alternative options a little more appealing.
On the other hand, the most cost-effective option for the passenger ship is the PV cell battery-powered ship. Due to its smaller size and relatively low requirements regarding autonomy, the battery capacity is quite low and the installation area for PV cells is smaller. Hence, both the investment and maintenance costs are low. It should also be mentioned that currently, there are several passenger ships in operation in Krka national park. They are used depending on the number of tourists (varying both during the season and during the week) as well as the maintenance schedule. Since the PV cell battery-powered ship seems to be more cost-effective if used more often, it can be aimed at the transportation of tourists. If, occasionally, additional vessels are required, the currently used vessels with diesel engines could be employed. It is also worth mentioning that the noise and vibrations emitted from PV cell battery-powered ships are significantly lower, thus increasing the level of comfort for both passengers and crew on board.
Another reason why the PV cell battery option seems feasible only for passenger ships is battery utilization. The observed passenger ship sails around 1500 h annually, while the dredger is used for less than 400 h annually. Additionally, the passenger ship needs autonomy for a round trip (roughly 1 h), while the dredger requires autonomy of at least 8 h. Hence, the battery capacity for the dredger is around 50 times higher, while the total annual energy consumption is in fact even higher for the passenger ship, as can be observed in
Table 7. This increase in capacity leads both to an increase in weight (which is not crucial for marine application) and to an increase in the investment cost, which makes the battery option unfeasible both for the cargo ship and the dredger.
A possible option to reduce the lifetime emissions and the LCCs of the dredger is to use shore-side electricity to satisfy its power needs. This requires an appropriate power grid, which can sustain such power surges and obviously limits the area of dredging operations. Therefore, a solution can be found in the implementation of an HPS. Such an HPS should be designed by applying proper bi-objective optimization procedures, considering not only fuel consumption but also lifetime emissions [
82]. When the ship operates in populated areas (where electricity is available), it could use shore power, while to operate in other areas, it can be powered by a diesel engine. Such a solution would increase the investment costs compared to the diesel engine-powered option since the ship would have both diesel engines and a battery (although of lower capacity) with the appropriate electrical equipment. The advantage can be seen from the environmental point of view since this option would not pollute the environment in highly populated areas. Such advantages should be recognized by national authorities in adopting appropriate policies leading to sustainable development.
However, Croatia, like many other EU states, currently implements policies that encourage the application of diesel in the shipping sector. The last available data for 2016 [
80] estimated fossil fuel subsidies in the EU at around €55 billion (an amount that is not declining). The EU has called for these subsidies to be removed as they hamper the implementation of innovative energy-efficient technologies. As described before, the inland fleet in Croatia uses the same fuel as road vehicles. However, the price of this fuel for road vehicles is almost twice as high when compared with marine applications. Additionally, Croatia has offered state aid to cover up to 40% of the purchase price of electric vehicles on several occasions. Such opportunities have never been presented to shipowners. In short, the current Croatian policy stimulates electric vehicles and diesel-powered vessels.
If the policy were changed, i.e., if the fuel oil price for marine application was the same as for road vehicles (€1.18) [
80], and if the subsidies covering 40% of the investment costs for battery and PV systems were introduced, the LCCs would change significantly. The estimates are presented in
Table 9.
As can be observed, with the application of state aid, the electrification of the passenger ship becomes more attractive, since now the LCCs of the electrification options are around four times lower than the LCCs of the diesel engine-powered passenger ship. The differences between the LCCs of a diesel engine power system configuration and the LCCs of alternative power configurations implemented on the cargo ship and dredger are lower, especially for the dredger whose LCCs of alternative power system configurations are around 30% higher than the LCCs of the diesel engine-powered dredger. As for the cargo ship, the LCCs are not low enough for shipowners to willingly implement these solutions to reduce the lifetime emissions.
6. Conclusions
This paper assessed the applicability of different power system configurations for the electrification of three different ships engaged in the Croatian inland waterway sector. Consideration was given to retrofitting three ship types: a cargo ship, a passenger ship, and a dredger, based on three different power system configurations, namely diesel engines, a battery, and a PV system. While the most ecological solution was established by LCA, through LCCA, the most economical solution for retrofitting these ships was highlighted. The main findings of this study can be summarized as follows:
The most environmentally friendly solution is the PV cell battery-powered ship for each considered ship;
Electrification of inland vessels results in a GHG reduction of up to 64% and NOX emission reduction of up to 99%;
The diesel engine option is still by far the most economical solution both for the cargo ship and the dredger;
For the passenger ship, the PV cell battery option seems to be the most cost-effective solution;
Currently, in Croatia, given that diesel fuel for inland waterways shipping is free of excise duty and there are no incentives to introduce green technologies, the national policy actually encourages shipowners to use diesel engines.
The main difference between the passenger ship on the one hand and the cargo ship and the dredger on the other lies in the required autonomy. The passenger ship sails on shorter routes and has the option of recharging more often, resulting in a required autonomy of around one hour. Hence, its battery capacity is lower, resulting in lower capital, as well as lower maintenance costs. Additionally, greater use is made of the passenger ship, confirming that high investments are justified only if high savings can be achieved. For the dredger, which operates less than 400 h annually and would require a battery of very high capacity, this is simply not a feasible option. It would perhaps be more appropriate to retrofit it with an HPS, although this option should be further analyzed. It might also be beneficial to adapt national policies in order to promote green technologies, instead of encouraging the use of fossil fuels, as is currently the case in Croatia. Finally, the presented model can be applied to analyze the viability of electrification of any other inland waterway fleet, if a relevant set of input parameters is known.