Techno-Economic and Environmental Assessment of a Photovoltaic-Based Fast-Charging Station for Public Utility Vehicles

Abstract

The characterization of electric vehicles as environmentally friendly means of transportation hinges, on the one hand, upon the manner in which the energy for their charging is generated and, on the other hand, on the recyclability of the materials composing them, with primary emphasis on the recycling of batteries. Given that we are still in the early stages of electrification in road transportation, it can be argued that at least a decade is required for the development of a sustainable battery recycling industry. Conversely, the progressively increasing number of electric vehicles makes the necessity of charging them with clean, green energy imperative. In this context, this study examines the energy and economic aspects of replacing 50% of the public passenger vehicle fleet, which currently relies on internal combustion engines, with electric vehicles on the island of Zakynthos, Greece. Specifically, it calculates the energy needs of these vehicles and proposes methods for environmentally friendly electricity generation to meet the electrical demand. To assess the benefits for the owners of the charging stations and the electric vehicles, the Life-Cycle Cost Analysis (LCCA) method is employed for various scenarios regarding (a) the pricing of the supplied electrical energy for electric vehicle charging and (b) the evolution of fossil fuel prices. The study concludes by highlighting the environmental advantages of such an investment.

1. Introduction

Climate change has been expedited by human activities in the post-World War II era. Since then, dangerous changes have been triggered, including increased global temperatures, droughts, wildfires, alterations in the duration and timing of rainfall and rising sea levels. For these reasons, mitigating the effects of climate change and addressing its consequences have become imperative for humanity.

Undoubtedly, a significant contributing factor to the climate change issue is the increase in CO₂ emissions due to population growth and the reliance on fossil fuels. It is worth noting that, from the year 1997 (the year the Kyoto Protocol was adopted) to 2022, the human population increased by 33% [1], while CO₂ emissions rose by 51% [2,3]. Today, the primary sources of CO₂ emissions worldwide are the Electricity, Industry, Transportation and Building Sectors [3]. In this context, the Paris Agreement serves as a global tool aimed at mitigating the consequences of climate change by focusing on reducing greenhouse gas (GHG) emissions [4].

The Electricity Sector, the primary source of CO₂ emissions, is gradually integrating Renewable Energy Sources (RES). However, similar progress is not as evident in other sectors [4]. Specifically, in 2020 and 2021, the share of RES in global electricity production reached 28.5%, nearly half of the 2030 target, with wind and photovoltaic (PV) stations accounting for over 10% of global electricity [5]. In the next 2 years, the installed capacity of RES is expected to increase by more than 8%, with PVs representing around 60% of the total RES capacity. Additionally, offshore wind system installations are estimated to double compared with 2020, while the added capacity of onshore wind parks is projected to decrease [4,5].

As for the Transportation Sector, which is the primary focus of the present work, there has been limited progress despite the 5 years that have passed since the ratification of the Paris Agreement [4]. Indeed, transports have the lowest use of RES, even though they represent one-third of the global energy demand. It is also worth mentioning that the Transportation Sector relies on fossil fuels for 91% of its final energy use, with only a minimum reduction of 3.5% since 1970 [6]. The mandatory use of biofuels in conventional vehicles with internal combustion engines (ICEs) can be considered the most significant step forward [7,8].

Figure 1 depicts the cumulative CO₂ emissions of the primary sub-sectors within the European transportation industry [9]. By studying this figure, it becomes evident that road transportation is responsible for approximately 72% of the CO₂ emissions due to the EU Transportation Sector. Consequently, many EU countries have already implemented policies such as tax incentives, subsidies and tax reductions to increase the number of pure battery EVs (BEVs) and plug-in hybrid EVs (PHEVs). Hereafter, in cases where there is no need to emphasize BEVs or HPEVs, the aforementioned vehicles will be collectively referred to as electric vehicles (EVs).

To address the potential insufficiency of the available charging infrastructure, the European Union (EU) has formulated directives and regulations with the goal of expanding electric vehicle charging networks. Specifically, on 28 March 2023, the European Parliament and the Council of the European Union revised the EU Alternative Fuel Infrastructure Regulation (EU-AFIR) of 2014 to offer more extensive support for electromobility at the European level. Significantly, the updated regulation now requires Member States to ensure that publicly accessible recharging stations provide a cumulative minimum power output of 1.3 kW for each light BEV and 0.8 kW for every PHEV registered within their territorial jurisdiction. Additionally, there is a mandating provision for Member States to establish a network of fast-charging stations situated every 60 km in both travel directions along the core Trans-European Transport Network (TEN-T) by 2025; this commitment extends to the comprehensive TEN-T by 2030. Regarding trucks and buses, the EU-AFIR introduces a distance-based target along the TEN-T. Specifically, the revised regulation requires that 15% of the entire TEN-T (both core and comprehensive) must be equipped with fast-charging stations for trucks positioned no more than 120 km apart. This requirement is set to increase to 50% by 2027 and eventually reach 100% by 2030 [10,11].

Unfortunately, until recently, EV charging stations have been based mainly on the utility grid, that is, on carbon-based fossil fuels; this practice causes huge environmental problems, and it is definitely unsustainable. Thus, it is apparent that RES-based charging infrastructure is a key to the mass adoption of EVs. Significant research on the minimization of EV charging stations’ carbon footprint is currently being performed in academia and the industry. Modern concepts, such as the optimal incorporation of both RES and energy storage, alternative energy sources such as hydrogen fuel cells and biomass, the smart charging idea with grid energy transactions and provision of ancillary services, as well as sophisticated energy management schemes, are currently being investigated.

Various recent works, i.e., [12,13,14,15,16,17,18,19,20,21], focus exclusively on RES and energy storage integration into EV charging stations and the impact of such infrastructure on the utility grid. The provision of ancillary services (e.g., peak shaving) is of paramount importance, whilst several works propose the use of incentives for EV users, such as time-of-use tariffs, to encourage them to charge their EVs during off-peak hours, where extra energy from RES exists [22]. This tariff directs users to charge their EVs efficiently, in an environmentally friendly manner, during the hours that RES production is high. The aforementioned technique is considered to be one of the three main types of smart charging, according to [23]. The second type is the unidirectional managed charging, which is a control strategy that takes into account the charging time, rate and duration based on electricity prices and power system needs. Finally, the third type of smart charging is the Vehicle-to-Grid (V2G) operation [13,24,25], which assists in the reduction of the environmental footprint of the Transportation Sector and in the sustainability of the utility grid.

Moreover, energy management schemes play a dominant role in RES-based EV charging infrastructure, whereas modern, sophisticated concepts include optimization models, stochastic models and machine learning algorithms to predict EV charging demands and compensate for the intermittent nature of renewables [14,17,18,26,27]. Finally, a significant issue to overcome when greater RES-based energy amounts are produced is the need for larger energy storage capacity. Nowadays, notable research effort is devoted to innovative technologies for electrochemical energy storage, leading to several new types and concepts for both lead-acid and lithium-ion batteries [21,26,27,28,29].

Building upon the aforementioned works, this study investigates the feasibility of replacing 50% of the fleet of public utility vehicles (PUVs) with exclusively public utility electric vehicles (EPUVs) at Zakynthos Island, Greece. Furthermore, it investigates the installation of a PV-fast charging EV station to facilitate their electric supply. It is worth noting that Zakynthos serves as a representative case study of the operation of a weak island electrical grid, the reliability of which is scrutinized during the summer (touristic) period due to a significant seasonal increase in electrical demand. A similar seasonal load profile and weak grid conditions prevail in all Greek islands and Mediterranean touristic destinations in general. Therefore, the findings of this case study can be extrapolated to this broader geographical area, thereby augmenting the significance of this work’s contribution.

In the following sections, the sustainability of this study is assessed from energy, techno-economic and environmental standpoints. Notably, unlike owners of EV charging stations along national highways, where the frequency of facility usage is uncertain (resulting in high costs for electric vehicle charging), the green charging station for EPUVs is characterized by predetermined facility usage, enabling the establishment of more affordable charging prices. Consequently, a pricing strategy is pursued to mutually benefit both the owners of the green charging stations (ensuring amortization in terms of private market dynamics and fast payback) and the owners of EPUVs. With regards to EPUV owners, the procurement cost of green electrical energy is anticipated to yield reduced usage expenses compared to a conventional public utility vehicle with a Euro 6 diesel engine. To address the above issues, a Life-Cycle Cost Analysis (LCCA) method is employed, considering various scenarios related to the pricing of the supplied electrical energy for electric vehicle charging and the evolution of fossil fuel prices.

Additionally, in determining the optimal installed capacity of the PV station for the green refueling of EPUVs, factors considered include limitations arising from tourist exploitation of island areas (restricted land use for non-touristic purposes), electrical constraints resulting from the seasonal variation in electrical demand in Mediterranean island regions and any available energy programs that promote the development of Renewable Energy Sources.

In conclusion, it is crucial to highlight that the techno-economic assessment, along with the energy planning and management methodology employed in this study, may pave the path toward a swift transition to greener transportations allowing for a compensated social impact. In addition to the case examined in the present study, the owners of petrol or gas stations could be considered as potential owners/investors of green electric vehicle charging stations. In lieu of PUV owners, potential stakeholders might include rental car companies, tourist mini-bus associations, or, on a broader scale, owners of electric marine taxis.

2. The Electromobility at a National Level

Considering that EVs are more energy-efficient compared with conventional vehicles, the continuous increase in their sales can contribute to a CO₂ reduction [30]. This is underscored by recent research outcomes at a European level, which have estimated that electric vehicles are poised to capture a market share between 30% and 40% of annual sales over the next 10 years. In a similar vein, hybrid vehicles are expected to secure a share of 15% to 25% of the market.

Regarding the penetration rate of electric vehicles at the national level,

Table 1. Annual registrations of BEVs and PHEVs as a function of the total number of passenger vehicles’ registrations from 2019 to 2022.

Year	New Registrations of Passenger Vehicles	Annual Variation of Passenger Vehicles’ Sales	Pure BEVs and PHEVs
			Cumulative Number of BEVs and PHEVs	Number of New BEVs and PHEVs	Share of New BEVs and PHEVs Out of New Passenger Vehicles’ Registrations
2019	114,018	-	996	479	0.42%
2020	81,780	−28.3%	3135	2139	2.64%
2021	101,111	23.6%	10,103	7007	6.93%
2022	105,412	4.3%	18,575	8317	7.89%

provides information about EV sales in Greece from 2019 to 2022. These data show that the number of EVs in Greece has been significantly increased during the last 4 years [31]; this can be attributed to various factors, such as economic incentives and the consumers’ environmental sensitization. Moreover, in 2020, the annual number of classified vehicles had been reduced due to the COVID-19 pandemic and the related mobility restrictions. However, the trend was reversed the following year as travel restrictions were lifted and people returned to their daily activities.

Despite the significant increase in the number of EVs within the past 3 years, they still represent a small portion of the total passenger transport fleet in Greece. Indeed, in 2022, gasoline or diesel vehicles accounted for nearly 95.58% of the total transport fleet, while 4.42% corresponded to alternative fuel vehicles. The latter category included 0.11% of the total transport fleet for BEVs and 0.22% for PHEVs. The majority of alternative fuel vehicles (4.09%) used liquified natural gas (LNG) and compressed natural gas (CNG) [31].

Figure 2 provides some information about the share of BEVs and PHEVs out of the total amount of EVs in Greece [31]. These data show that the sales of BEVs do not exceed 40% of the total EV sales, which differs from the situation in the EU, where BEVs and PHEVs are sold in a balanced manner. However, a shift toward BEVs in the European market occurred in 2022. Specifically, in that year, BEV sales surpassed PHEV sales, representing 56% of new EV sales. This shift towards pure BEVs can be attributed to the increased energy autonomy and a reduction in the ownership cost for new BEVs. Nevertheless, PHEVs remain popular among consumers who prioritize flexibility and ease in their daily routes.

Today, Greece boasts numerous EV charging stations, a result of the increased presence of both private and public EV charging facilities, as well as the efforts made by municipalities to develop EV charging infrastructure plans. The technical guidelines for EV charging infrastructure plans are referred to the Government Gazette B’ 4380/2020. The estimation of the number of EVs expected to be on Greek roads by 2030 is detailed in the National Energy and Climate Plan (NECP) [32]. For the Transportation Sector, the NECP analyzes two scenarios for the penetration of EVs on Greek roads with the goal of reducing GHG emissions, particularly CO₂ emissions. The first scenario is a more moderate approach, projecting that EVs will constitute 24.1% of new registrations in 2030. The second scenario is more optimistic, estimating that EVs will make up around 30% of new registrations by 2030.

At this point, it is worth mentioning that the Ministry of Infrastructure and Transport recognizes the contribution of public utility vehicles (PUVs, Taxis) to the atmospheric pollution in the urban centers of Greece. To address this issue, they are developing a subsidy program for the acquisition of pure battery electric PUVs (EPUVs) under the National Recovery and Resilience Plan “Greece 2.0” [33]. This subsidy covers 40% of the pre-tax retail price (VAT not included), and there is also a EUR 500 subsidy for the purchase of a “smart” charger. In total, the subsidy amounts to 50% of the PUV’s retail price. Eligible beneficiaries of the program will all be owners of Euro 5 or older-category PUVs.

Although EVs are undoubtedly characterized by higher efficiency than conventional vehicles, their “green” character in their operational phase depends on the source of the used electrical energy [34]. Figure 3 illustrates the CO₂ emissions from gasoline ICE vehicles and BEVs throughout their life cycle in Europe. The assessment of CO₂ emissions is conducted under two distinct scenarios: (a) vehicles that were registered in Europe in the year 2021, taking into account the electricity mix of that year, and (b) vehicles that will be registered in the year 2030, with considerations made for the envisioned electricity mix of that future period. Moreover, CO₂ emissions throughout a vehicle’s life cycle are classified into subcategories, encompassing manufacturing and maintenance, as well as fuel or electricity production and fuel emissions. Notably, the manufacturing and maintenance subcategory also incorporates battery manufacturing in the context of BEVs. The data pertain to medium-sized vehicles covering a distance of approximately 243,000 km during their life cycle [34].

According to Figure 3, it can be inferred that the life-cycle emissions of BEVs registered in Europe in 2021 were lower by approximately 66% compared with gasoline cars. Looking ahead to 2030, the life-cycle emissions gap between BEVs and gasoline vehicles is expected to reach 77% [34]. However, achieving this improvement necessitates the fulfillment of the objectives outlined in the Paris Agreement. This, in turn, implies that the share of RES in Europe’s gross final energy consumption should be heightened, and consequently, the electricity used for charging EVs will predominantly originate from Renewable Energy Sources.

The present study is oriented in this direction, seeking a sustainable model from both the perspective of EPUV owners and that of the proprietors of electric vehicle charging stations, with a focus on replacing a significant percentage of PUVs with EPUVs. Furthermore, the study explores the supply of green energy to support these vehicles, particularly in regions with weak electrical grids, such as the islands of Greece and, more generally, the Mediterranean tourist destinations.

3. Replacement of 50% of the Conventional PUVs with EVs in Zakynthos

Zakynthos, also known as Zante, is a Greek island located in the Ionian Sea, off the western coast of mainland Greece. It is part of the Ionian Island group, and it is situated to the west of the Peloponnese peninsula. The island of Zakynthos hosts a substantial number of tourists each year, particularly during the summer period (June to September). According to formal data from the FRAPORT company for the national airport of “Dionisios Solomos” in Zakynthos, the total number of visitors in 2023 (from June to September) reached 1,717,961 [35]. Considering also visitors arriving through the coastal connections between Kyllini and Zakynthos, as well as those arriving by private ships, the total number of visitors exceeds 2,000,000. Tourists typically visit various attractions, accommodations and other areas using PUVs. From June to September, these vehicles operate numerous routes daily, covering approximately 40,000 km over 122 days (an average of 330 km per day), despite the fact that the island’s coastline is only 123 km long.

The total number of PUV licenses in Zakynthos amounts to 100. This number of Taxis operates only between June and September, while the rest of the year, the number of PUVs on the roads does not exceed 30. Although PUVs are diesel vehicles and do not contribute to an increase in CO₂ emissions, their engines emit significant amounts of carbon monoxide, nitrogen oxides and hydrocarbons. These emissions are exacerbated in the case of outdated technology vehicles, which use engines older than those in the Euro 6 category (these outdated PUVs constitute the majority of Taxis on the island of Zakynthos).

It is worth noting that similar circumstances exist in all Greek islands and Mediterranean tourist places in general. Hence, our case study and its outcomes can be projected to this wide area, increasing the value of this work’s contribution.

Next, the replacement of 50% of the conventional PUVs with EPUVs on the island off Zakynthos is examined from both economic and energy-environmental perspectives. Additionally, renewable electricity production and demand–response strategies are proposed to address the technical limitations of the island’s electricity network during the summer period when PUV usage is at its peak.

3.1. The Electricity Network of Zakynthos

Although Zakynthos is connected to the mainland’s electricity grid through high-voltage (150 kV) submarine cables, it faces energy limitations due to its restricted capacity. Specifically, the interconnection between Killini (mainland port) and Zakynthos was initially established in the early 1980s with the installation of a 150 kV AC submarine cable. Additionally, Zakynthos is linked to the island of Kefalonia via a submarine cable of a lower nominal capacity. The total capacity of the Zakynthos distribution grid is constrained within the range of 120 to 150 MVA. This capacity is comprised of three 150/20 kV distribution transformers, each with a capacity of 40/50 MVA [36,37]. In Figure 4, the submarine interconnections of Zakynthos with the electrical transmission system of the mainland (Killini) and Kefalonia island are distinguished. Furthermore, the map depicts both existing connections (indicated by solid lines) and planned connections (indicated by dashed lines) between the mainland and the other Greek island complexes [36].

Considering the above, it is evident that the electricity network of Zakynthos encounters limitations in its power supply capabilities, primarily determined by the constraints of the submarine interconnection lines and the capacity of the distribution transformers. These limitations are particularly pronounced during the summer period when there is a significant seasonal increase in electrical demand. Given that the charging of EVs contributes to this seasonal electric load, the only viable approach to ensure the reliability of this service while maintaining the smooth operation of the island’s electricity grid is the installation of local renewable energy production in conjunction with energy storage. This combination serves to balance energy transactions between EV charging stations and the distribution electricity grid.

3.2. Pure Battery Electric PUV Selection

To facilitate the selection of EPUVs as a replacement for the conventional ones, several technical parameters should be considered, such as EV battery capacity, electrical consumption and energy autonomy. Additionally, factors such as the capability to support fast charging and the volume of the cargo space were taken into account as well.

Typically, EV manufacturers provide consumption and autonomy figures in terms of the Worldwide Harmonized Light Vehicles Test Procedure (WLTP). Based on data from 25 EV manufacturers, the average battery capacity is 60.8 kWh, the average energy autonomy is 363.7 km and the average electricity consumption is 157.2 Wh/km [38]. However, a slight increase in the average speed of the moving car, as well as the use of the air conditioning and the infotainment systems, may lead to a 20% increase in the vehicle’s energy consumption, resulting in a reduction in energy autonomy.

Considering that, at present, most drivers charge their EVs in a manner similar to the refueling of their former conventional vehicles, it can be easily deduced that in cases of vehicles that do not support fast charging, drivers may have to wait for a significant amount of time to complete a full charge. This situation may cause discomfort for the driver, whereas it results in economic losses for professional drivers. The waiting time depends on the availability of charging stations and their electricity power. For instance, taking into account the average capacity of the aforementioned EV manufacturers (i.e., 60.8 kWh), the required time for a battery to charge from an initial State of Charge (SOC) of 20% to 90% (i.e., 42.6 kWh) for the three widely adopted charging modes (i.e., Mode I—3.7 kWAC, Mode II—22 kWAC, and Mode III—50 kWDC) will range from 11 h and 30 min down to 51 min [25].

Using the information provided in [38] and some additional data sourced from Electric Vehicle manufacturers, the Mercedes EQE 350 4MATIC [39] has been identified as an appealing model to replace conventional PUVs.

Table 2. Technical specifications of the Mercedes EQE 350 4MATIC [39].

Mercedes EQE 350 4MATIC
Battery nominal capacity [kWh]	100	Cargo space [lt]	450
Electric autonomy [km]	507	Weight [kg]	2310
Energy consumption [kWh/100 km]	17.9	Fast charging in power (up to)	170 kW

summarizes the technical specifications of the proposed EV. Despite the nominal battery capacity being 100 kWh, a decision was made to limit the discharge to 90 kWh to preserve the battery lifespan. Additionally, a 20% increase in the EVs energy consumption was considered due to the use of the air conditioning system during the summer period, resulting in an energy consumption of 21.5 kWh/100 km. Consequently, the energy autonomy of the selected EV is estimated to be 420 km (for the specific case study), which is 27% higher than the average daily route of 330 km that is covered by each PUV during the summer period. Consequently, only one full charge is necessary per day.

Additionally, taking into account that the PUVs under study cover routes of 40,000 km from June to September, with an energy consumption of 21.5 kWh/100 km, the cumulative energy consumption for 50 EPUVs is estimated to be 430 MWh for the summer period. Lastly, the installation of 10 fast-charging direct current stations, each with a nominal power of 150 kW, is proposed for charging the 50 EPUVs. In this scenario, it would take less than 40 min to charge the EV battery to 90 kWh (full charge).

3.3. RES Selection for the EV Charging

As has been previously mentioned, to classify pure battery PUVs as environmentally friendly and maximize the associated environmental benefits, it is imperative that the required energy be renewable. Zakynthos is an island with considerable solar potential. Considering the optimal tilt and orientation of PV modules, based on meteorological data from the Photovoltaic Geographical Information System (PVGIS) of the Institute for Energy and Transport at the Joint Research Centre (JRC), the estimated annual energy production in Zakynthos is 1551 kWh/kWp [40].

Consequently, to generate the required electricity (430 MWh) between June and September, a 660 kWp PV system must be installed. While such a PV system would generate the required amount of energy during the mentioned time period, it poses a challenge as it would also produce a substantial amount of energy (613 MWh) during periods of low EV charging demand (October to May). Additionally, the installation of a 660 kWp PV system necessitates a considerable land commitment, a fact that may not be well-received by the local community. This is particularly noteworthy due to the limited geographical expanse of the island and the essential need to maintain its landscape aesthetics for touristic purposes. The above factors pose challenges to achieving a favorable investment payback period. Therefore, within the scope of this project, it is advisable to install a smaller PV system capable of producing 430 MWh annually. This would entail the use of the annual PV production on an accounting basis, particularly during the period from June to September, through net-metering for self-producers.

The net metering for the self-producers’ regime was delineated in the Ministerial Decision APEEIL/A/F1/econ.24461 (Government Gazette B’ 3583/31.12.2014). According to this arrangement, the synchronization of energy production with consumption is not obligatory. Specifically, the electricity generated by the PV system is used to power electrical loads, such as the EV charging station in the case under study. Any surplus energy produced by the PV system is fed back to the grid, particularly during the period from October to May in our case. The self-producer receives credit for this excess energy, which can be used to offset the cost of electricity obtained from the grid during periods when the PV system does not generate sufficient power to meet the demand of the charging station.

In an effort to avoid committing available land for the PV station installation, the use of the roofs of Zakynthos Central Interurban Bus Station (ZCIBS) was considered. Consequently, the slope angle of the PV modules was chosen to be 6° (considerably less than the optimal value of 31° for the Zakynthos region). This decision facilitates the installation of PV panels on the Central Interurban Bus Station roofs, enabling maximum energy production during the summer months while ensuring esthetically acceptable results. The selection of installation locations for the charging station points was conducted in accordance with the relevant EV Charging Infrastructure Plans outlined in Government Gazette B’ 4390/2020.

With the assistance of the PVGIS, it was calculated that a 1 kWp PV system in the specified area with a 6° slope angle and optimal Azimuth angle of −2° produces 1437 kWh/kWp annually. The proposed solution leads to reduced energy production compared with developing a PV park at an optimal tilt of 7.35%. Nevertheless, considering the multiple uses of this specific space, the proposed site seems to be the optimal choice. Taking into account the reduced annual energy production of 1437 kWh/kWp, it is estimated that the installed capacity of the PV system (capable of generating 430 MWh annually) amounts to 300 kWp.

The monthly energy production of the PV system of 300 kWp is depicted in Figure 5. Considering the results of Figure 5, it is proved that the proposed PV system produces around 198 MWh during the June–September period, i.e., 46% of the required energy, while over the remaining 8 months, the PV production is equal to 232 MWh, offsetting the demand on an accounting basis within the period of high EV charging load demand.

Assuming that the PV canopy will be constructed with bifacial PV panels with a nominal power of 600 W, its total surface area amounts to 1300 m². Additionally, considering the bifacial gain (which represents the ability to absorb light from the rear side of a PV to produce electricity), it is concluded that the PV system energy yield can be increased between 3% and 8% compared with common white backsheet PV modules of the same power level (depending on the ground reflectivity and the albedo value) [41,42]. Therefore, an additional quantity of 13–34 electric MWh can be generated and used by the 30 EPUVs that remain in operation for the rest of the year, ensuring additional electric energy for 2000–5300 km per EPUV.

Figure 6 illustrates the average hourly output power of the 300 kWp photovoltaic system for the typical day of each month, covering the period from June to September. By examining this figure, it becomes evident that, between 10:00 and 15:00, the output power of the PV system surpasses 150 kW from June to August, while for September, this value is achieved between 11:00 and 14:00. Therefore, these time intervals represent the time frames during which the output power of the PV system can fully support the required power for charging an EPUV. However, such an approach would result in poor use of the generated photovoltaic energy.

In order to maximize the use of the generated green energy, the following paragraph presents a generalized charging plan for 50 EPUVs on a daily basis. This plan not only maximizes the use of the generated green electrical power but it also minimizes the occurrence of high peaks in electrical demand from the island distribution grid.

4. Results

4.1. Comprehensive Schedule for Charging 50 EPUVs during a Typical Day in Each Month

Table 3. Charging schedule for 50 EPUVs during a typical day in each month.

Time	Number of Charges	Time	Number of Charges	Time	Number of Charges
03:00	0	10:00	4	17:00	3
04:00	0	11:00	4	18:00	2
05:00	2	12:00	4	19:00	2
06:00	2	13:00	4	20:00	1
07:00	2	14:00	4	21:00	1
08:00	3	15:00	4	22:00	1
09:00	3	16:00	3	23:00	1

presents the charging schedule for 50 EPUVs during a typical day in each month, while Figure 7a–c illustrate the hourly energy production allocation within the typical day in each month. As previously mentioned, the objective of scheduling daily charges is to maximize the use of generated solar energy and limit peaks in electrical power demand from the local electrical grid. The scheduling is based on the assumptions outlined in Section 3.2. Specifically, each EPUV requires roughly 70.95 kWh for its daily charging (on average, each vehicle covers 330 km on a daily basis with an energy consumption of 21.5 kWh/100 km).

It is worth noting that the meteorological conditions during the aforementioned months are relatively stable. As a result, the daily photovoltaic production profile exhibits relatively limited fluctuations compared with that of the corresponding monthly typical day. However, any deviation, such as a cloudy or rainy day, will impact the photovoltaic system’s production profile.

The analysis of the aforementioned figures leads to the conclusion that there is full use of photovoltaic production. Specifically, in accordance with the suggested schedule for EPUV charging, the self-consumption index for each month reaches 100%, while the self-sufficiency indices for the months spanning from June to September are 49.82%, 52.35%, 46.80% and 35.88%, respectively. Additionally, it is apparent that, in any case, the average hourly power drawn from the electrical grid for the charging of the 50 Electric Plug-in Utility Vehicles (EPUVs) does not exceed 150 kW.

4.2. Life-Cycle Cost Analysis of the Proposed PV-EPUV Charging Station

In this section, the Life-Cycle Cost Analysis (LCCA) of the proposed PV- EPUV charging station is conducted. In accordance with the operational principles of the net metering for the self-producers’ regime, the owner of the EPUV charging facilities will not receive invoices for energy supply and regulated charges (including Distribution Network and Transmission System charges, as well as the Special Duty of Greenhouse Gas Emissions charges) when using energy that is locally generated and consumed directly. Furthermore, the energy generated by the PV station between October and May, which is injected into the grid, will be used within the framework of net metering for self-producers during the period from June to September. For these amounts of energy, the owner of the charging facilities will be only billed for regulated charges, amounting to EUR 0.05/kWh.

Given that the proposed canopy for the installation of the PV system is owned by ZCIBS, it is advisable for the latter to act as the investor, which is responsible for the development of the green charging infrastructure for EPUVs. The owners of ZCIBS will come into a Power Purchase Agreement (PPA) with the owners of EPUVs, facilitating the direct sale/purchase of energy between the renewable energy producer (ZCIBS) and the electricity consumer (EPUVs). EPUV drivers will charge their vehicles within the premises of ZCIBS. In the following paragraphs, the focus is on determining the selling price of the green electrical energy generated by the owners of ZCIBS to the drivers of EPUVs. This pricing strategy aims to be mutually beneficial for both the owners of the green charging stations (ensuring amortization in terms of private market dynamics and fast payback) and the owners of EPUVs. Specifically, with regard to the owners of EPUVs, the purchasing price of green electrical energy should result in reduced usage costs compared with a conventional PUV with a Euro 6 diesel engine.

The techno-economic analysis is based on the economic and time parameters presented in

Table 4. Economic and time parameters for the LCCA procedure.

LCCA Parameters
Economic parameters
Discount rate	0.25%
Inflation rate	0.3%
Escalation of energy costs	0.5%
Borrowing rate	0%
Rate of investment subsidy	0%, 25%, 50%
Time parameters
Starting year	2024
Period analysis	25 years

. The detailed equations of the LCCA methodology used in the present work are presented in Appendix A.

According to the previous analysis, the under-study PV-EPUV charging station consists of a 300 kWp PV system and 10 150 kW DC fast-charging stations.

Table 5. Costs of the PV fast-charging station.

PV Fast-Charging Station Costs
Initial cost of the PV fast-charging station (EUR)	750,000
PV system cost (EUR/kW)	1000
Fast-charger costs (EUR/unit)	45,000
Annual maintenance and insurance cost (EUR)	4500
Annual earnings from the EPUV charging procedure	It depends on the charging procedure price cost

presents the costs of the installed equipment, as well as the annual maintenance and operational costs of the proposed PV fast-charging station.

In contrast to the proprietors of electric vehicle charging stations situated along national highways, where the frequency of facility use is uncertain, the green charging station for EPUVs ensures predetermined usage of its facilities. This enables the establishment of more competitive charging prices. The aim of investigating the charging price of the provided green energy is to find a low charging fee that would be mutually beneficial for both the charging station owner and the owners of the EPUVs. It is emphasized at this point that the investor/owner of the charging facilities is the owner of ZCIBS, while the owners/users of the EPUVs are the drivers of the former conventional PUVs. Next, three scenarios of electricity energy price costs are examined for the EPUVs’ charging: (i) EUR 0.30/kWh, (ii) EUR 0.40/kWh and (iii) EUR 0.45/kWh. It is noted that the electricity price costs for EV charging that are used in the present work are significantly lower than the current prices in the existing highway EV charging infrastructure (EUR 0.50–0.65/kWh) [43].

Next, in Figure 8, Figure 9 and Figure 10, the LCCA results of the PV-EPUV fast-charging station are presented, considering the three scenarios of charging price costs mentioned above and for three scenarios of investment subsidy as well (i.e., 0%, 25% and 50%).

In

Table 6. Annual earnings and payback period of the proposed PV-EPUV fast-charging station for each electricity price cost and rate of investment subsidy scenario.

Electricity Price Cost for EV Charging	Rate of Investment Subsidy	Annual Earnings (EUR)	Payback Period (years)
EUR 0.30/kWh	0%	115,000	6
	25%		5
	50%		3
EUR 0.40/kWh	0%	158,000	4
	25%		3
	50%		2
EUR 0.45/kWh	0%	179,500	4
	25%		3
	50%		2

, the annual earnings and the payback period of the proposed EPUV charging station are summarized.

Based on the abovementioned results, it is proved that in case of no investment subsidy, the payback period of the proposed PV fast-charging station is achieved within 4 to 6 years, depending on the electricity price cost for EV charging. Conversely, in the case of 25% and 50% rate subsidy scenarios and for the considered charging costs, the payback period is reduced considerably, within a period of 2 to 5 years.

4.3. Life-Cycle Cost Analysis Results for the EPUVs

In this section, the sustainability of the EPUVs that charge their batteries from the proposed PV fast-charging station is examined compared to Euro 6 diesel PUVs. It is recalled here that this study examines the replacement of outdated PUV technology, which uses engines older than those of the Euro 6 category. These outdated public utility vehicles (PUVs) constitute the majority of taxis on the island of Zakynthos. The considered replacement options are either electric or diesel Euro 6 PUVs. It is noted that, according to European legislation, both electric and diesel Euro 6 PUVs are considered valid options for the replacement of vehicles with outdated technology. The analysis is conducted over a short-term period, i.e., 7 years, due to the uncertainty in the long-term prediction of fossil fuel prices. The comparison is conducted for the three electricity price cost scenarios (i.e., EUR 0.30/kWh, EUR 0.40/kWh and EUR 0.45/kWh) and for the three scenarios of diesel supply price. More specifically, the following diesel price cost scenarios are used: (i) constant diesel supply price (EUR 0.16/lt), (ii) 5% annual increase in diesel supply price and (iii) 5% annual decrease in diesel supply price. In the last two scenarios, the first-year diesel price is EUR 0.16/lt. In the case that the owners of outdated technology PUVs choose to replace their vehicles with new diesel Euro 6 PUVs rather than opting for new electric vehicles, an initial purchase value of EUR 40,000 is considered.

Table 7. Techno-economic specifications of Euro 6 diesel and electric PUVs.

Techno-Economic Specifications of PUVs
Euro 6 diesel PUV
Initial value of the diesel Euro 6 PUV (EUR)	40,000
Maintenance cost of the diesel Euro 6 PUV (EUR/year)	800
Total Route (June–September) (km)	40,000
Average Fuel consumption (lt/100 km)	6.0
Total fuel consumption (tn)	2.4
Operational costs of the diesel Euro 6 PUV (EUR)	It depends on the diesel supply price (EUR/lt)
EPUV
Initial value of the EPUV (EUR)	87,000
Maintenance cost of the EPUV (EUR/year)	400
Rate of subsidy for EPUV purchase (EUR)	50%
Total Route (June–September) (km)	40,000
Electrical consumption (kWh/100 km)	21.5
Total electrical consumption (ΜWh)	8.6
Operational costs of the EPUV (EUR)	It depends on the electricity price cost

presents the techno-economical parameters and operational specifications of conventional Euro 6 PUVs and EPUVs.

In Figure 11, Figure 12 and Figure 13, the LCCA results for the 7 years period analysis of a diesel Euro 6 PUV and an EPUV are presented for three scenarios of electricity sales and three scenarios of fluctuations in the fuel price.

Based on Figure 11, Figure 12 and Figure 13, it is concluded that over the 7 year period, the total acquisition, operation and maintenance costs of an EPUV are lower than in the case of diesel Euro 6 PUV for every scenario combination, despite the fact that the market price of the EPUV is higher by EUR 3500 (considering the subsidy that the market for electric EVs benefits from under the National Recovery and Resilience Plan “Greece 2.0”). However, the only exceptions are the cases of the EUR 0.40 and 0.45/kWh electricity price costs and the 5% annual decrease in the diesel supply price.

Last, in

Table 8. Operational costs of the electric and diesel Euro 6 PUVs (7-year period analysis).

Year	PUV’s Operational Cost
	Diesel Euro 6 PUV	Pure Battery Electric PUV
	Diesel Supply Cost (EUR)	Electricity Cost (EUR)
	5% annual decrease	EUR 0.30/kWh
1st year	3830	2299
2nd year	7280	4600
3rd year	10,376	6901
4th year	13,146	9204
5th year	15,615	11,508
6th year	17,806	13,813
7th year	19,739	16,119
	5% annual increase	EUR 0.40/kWh
1st year	3830	3159
2nd year	8046	6321
3rd year	12,675	9483
4th year	17,750	12,648
5th year	23,303	15,813
6th year	29,369	18,980
7th year	35,986	22,150
	Constant price: EUR 0.16/lt	EUR 0.45/kWh
1st year	3830	3590
2nd year	7663	7181
3rd year	11,497	10,774
4th year	15,333	14,369
5th year	19,171	17,966
6th year	23,011	21,565
7th year	26,853	25,165

, the acquisition and operational costs of the electric and diesel Euro 6 PUVs are presented over the 7 year period, while in

Table 9. Energy savings of electric and diesel Euro 6 drivers (7 year period analysis).

Diesel Supply Cost	Electricity Cost
	EUR 0.30/kWh	EUR 0.40/kWh	EUR 0.45/kWh
5% annual decrease	3620	−2411	−5426
5% annual increase	19,867	13,836	10,821
Constant price: EUR 0.16/lt	10,734	4703	1688

, the corresponding energy savings are summarized. The positive sign indicates energy savings, while the negative sign indicates that the use of EPUVs is more expensive. To sum up, it is worth noting that considering the EU policies after the war between Ukraine and Russia (that led to fossil fuel price increase), it is estimated that the two scenarios in which the use of EPUVs is shown to be more expensive than using conventional PUVs are particularly unlikely to occur.

Considering the abovementioned results, the case of EUR 0.30/kWh is considered to be the optimal scenario, leading to a payback period of 6 years for the PV fast-charging station investment (even in the case of no investment subsidy), while the EPUV operational costs are lower than in the diesel Euro 6 PUV case, considering the three scenarios of diesel supply cost examined in the present work. Actually, even in the case of no diesel supply increase within the next 7 years, the energy savings estimations for the EPUV drivers are higher than EUR 10,000.

5. Discussion of the Environmental Benefits

In the above part of the present study, the replacement of the Euro 3 old-technology PUVs with electric or diesel Euro 6 PUVs was examined. In this section, the environmental benefits of the replacement of 50 conventional PUVs with BEVs are analyzed. In these calculations, the following parameters are used: the average fuel consumption of the diesel Euro 6 PUVs is 6 lt/100 km, and the average route that each PUV operates during the summer period is 40,000 km. Lastly, the emission specifications of Euro 6 diesel engines are presented in

Table 10. Emissions from the operation of diesel Euro 6 PUVs.

Emissions Released from Euro 6 Diesel Engine PUVs	1 PUV
CO	500 mgr/km
NOx	80 mgr/km
HC	17 mgr/km
PM2.5	4.5 mgr/km

[44].

Based on the data presented in Table 10,

Table 11. Environmental benefits from the mass replacement of 50 conventional PUVs with electric PUVs.

Emissions Released from Euro 6 Diesel Engine PUVs	1 PUV	50 PUVs
CO	20 kg	1000 kg
NOx	3.2 kg	160 kg
HC	0.68 kg	34 kg
PM2.5	0.18 kg	9 kg

summarizes the reduction in emissions in the atmosphere thanks to the use of EPUVs. Lastly, it is noted that another significant benefit is the avoidance of transferring 120 tn of diesel fuel in the island of Zakynthos during the tourist season.

6. Conclusions

In the present work, the replacement of 50% of the total conventional PUV fleet with EPUVs on the island of Zakynthos was examined from both energy, techno-economic and environmental aspects. Specifically, the optimal electricity price cost for charging in a short time was estimated based on criteria such as the payback period of the PV-fast charging EV station (even in the case of no investment subsidy) and the operational cost of EPUVs in comparison with the operational costs of diesel Euro 6 PUVs. The investment of the proposed PV-fast charging EV station is sustainable through the expected 25 years of operation, considering that the payback period is achieved within the first 6 operating years. Moreover, the energy needs of PUVs were calculated, proposing a scheme of electricity generation from renewable sources and serving the electrical demand without occupying land and without causing significant disruptions to the island’s electricity grid. As for the vehicle owners, the amount of energy savings for EPUV drivers may approximately account for EUR 3000–20,000, depending on the given scenario. Furthermore, the amounts of hazardous pollutant emissions that are avoided from being released into the atmosphere by choosing EPUVs were calculated, leading to the conclusion that thanks to the mass use of EPUVs, the total amount of pollutant emissions released is reduced by 1.2 tons.

Finally, the environmental and economic benefits presented in this study highlight the role of other social groups that may potentially lose their economic activities during the transition of existing societies to green societies and economies. For instance, undertaking the role of investors in green charging infrastructure, the owners of petrol or gas stations may become crucial players in green transportation. Additionally, in considering the role of PUV owners, potential stakeholders are rental car companies, tourist mini-bus associations, or, on a broader scale, owners of electric marine taxis.