Design of an Electric Vehicle Charging System Consisting of PV and Fuel Cell for Historical and Tourist Regions

Abstract

One of the most important problems in the widespread use of electric vehicles is the lack of charging infrastructure. Especially in tourist areas where historical buildings are located, the installation of a power grid for the installation of electric vehicle charging stations or generating electrical energy by installing renewable energy production systems such as large-sized PV (photovoltaic) and wind turbines poses a problem because it causes the deterioration of the historical texture. Considering the need for renewable energy sources in the transportation sector, our aim in this study is to model an electric vehicle charging station using PVPS (photovoltaic power system) and FC (fuel cell) power systems by using irradiation and temperature data from historical regions. This designed charging station model performs electric vehicle charging, meeting the energy demand of a house and hydrogen production by feeding the electrolyzer with the surplus energy from producing electrical energy with the PVPS during the daytime. At night, when there is no solar radiation, electric vehicle charging and residential energy demand are met with an FC power system. One of the most important advantages of this system is the use of hydrogen storage instead of a battery system for energy storage and the conversion of hydrogen into electrical energy with an FC. Unlike other studies, in our study, fossil energy sources such as diesel generators are not included for the stable operation of the system. The system in this study may need hydrogen refueling in unfavorable climatic conditions and the energy storage capacity is limited by the hydrogen fuel tank capacity.

1. Introduction

Sustainable development is not possible without environmental protection. Therefore, green technologies are one of the future requirements of industry [1]. Increases in oil prices, depletion of fossil fuel reserves, global warming and harmful gases produced by the combustion of fossil fuels, geopolitical tension and growth as a result of energy demands create an unsustainable and unlivable situation. For this reason, interest in alternative energy sources, renewable energy sources and the efficient use of fossil fuels has reached a higher point than at any other time in history [2,3,4]. One of the most important challenges of this century has been how to deal with climate change [5]. To stabilize global climate change, environmentally harmful gases such as GHGs must be reduced by at least 50% to 80% by 2050. Recently developed energy technologies and system structures can help realize these GHG reduction targets [6]. Growing environmental problems such as the spread of traditional energy sources, the GHG emissions caused by the transportation system [7,8,9,10] and air pollution as a result of CO₂ emissions are cause for increasing concern in society [5,11,12,13]. Due to the harmful effects on the environment of fossil fuels in power generation on a global scale, the development of sustainable energy resources has become a critical issue for societies and governments [8,10,14,15,16,17]. In addition to PV electricity generation, there is a need for alternative and renewable energy sources such as FCs, wind energy, hydroelectricity and biomass [18,19].

Energy consumption and GHG emissions in the transportation sector are one of the biggest problems [9,20,21]. Increasing concerns over climate change and energy resource security have caused the transport sector to shift away from fossil fuels towards long-term sustainable electric vehicle technologies [13,16]. The growing need to reduce fuel consumption and emissions in transportation has accelerated the adoption of emerging electric transportation technologies [21,22,23]. One of the biggest technological advances in the transportation system will be the conversion of internal combustion engines to electric motors [1,24,25]. Electric vehicles have gained global momentum due to their environmentalist image when compared to vehicles with traditional internal combustion engines [7,11,13,25,26,27,28,29]. Electric and hydrogen-fueled vehicles can reduce emissions in the transportation sector with low or no carbon emissions [30,31]. Due to the increasingly stringent emission standards, vehicle manufacturers are trying to increase the efficiency of traditional internal combustion vehicles. The development of electric vehicles such as hybrid electric vehicles (HEVs), pure battery electric vehicles (BEVs), FC electric vehicles (FCEVs) and plug-in hybrid electric vehicles (PHEVs) requires great effort [1,14,16]. This is because, while electric vehicles can convert 60% of electricity to motion energy, this situation is at the level of 20% for the conversion of the energy stored in the fuel into motion energy in vehicles with conventional internal combustion engines [26].

The use of renewable energy sources for charging electric vehicles is one of the most innovative approaches [8]. Electric vehicles meet electricity needs by generating electricity from batteries or high-efficiency fuels such as hydrogen [24]. The charge requirement for electric vehicles is met from the grid [7], which is fed by power plants that produce electricity by burning fossil fuels [14,22,26,32]. Many electric vehicles charged in this way will significantly increase the load on transmission lines and power plants [1,14,26,28]. In addition, the main deficiency of this type of charging system is that it cannot be installed in remote locations where there is no grid [32,33]. Fast, medium and slow charging systems are used in electric vehicle charging. In the study by the authors of [34], the power values for fast, medium and slow charging systems were modeled as 116 kW, 84 kW and 52 kW, respectively. To meet the energy demand of the charging stations, the grid needs to be strengthened by 183% [34]. Electric vehicle charging infrastructure has a significant impact on the grid [35]. The capacity, stability and ability of the electricity grid to meet the increase in load demand should be assessed [10]. In addition, with the increasing plug-in EV charging requirement, another issue to be considered on the grid will be load frequency control. This situation can be stabilized by various economic model forecasting methods. EV charging demand behavior can be regulated by communication infrastructure [36,37].

Hybrid renewable energy systems (RESs) that are a clean, reliable, uninterrupted energy source and reduce GHG emissions are an alternative that will reduce fuel use [18] and carbon emissions [19] in electricity generation [21]. Renewable energy sources have another advantage of reducing costs as well as reducing emissions [38]. Electricity generation with PV and wind power is becoming a very realistic alternative to fossil fuel electricity generation in many parts of the world [5,19]. However, wind and PV, which are considered as the primary sources of hybrid systems, are directly affected by environmental conditions and their electricity generation has dynamic characteristics [19]. They can used for combinations of renewable systems such as PV systems, wind turbines and FCs in these plans [8,9,39,40]. The use of hybrid RESs has the potential to meet load demand in remote or isolated areas and can make a significant contribution to rural or urban life [3]. The use of FC and hydrogen technologies as an alternative energy source is not widespread enough due to the availability of hydrogen and difficulties in transportation and storage [14,26]. There are still many technical and economic problems associated with the utilization of hydrogen. Researchers and industry have explored options that could enable the development of hydrogen sooner [41].

Many renewable energy sources, such as wind and solar, cannot generate electricity continuously as they are tightly dependent on weather conditions such as wind speed and irradiance and have an intermittent nature [2,5,8,15,21,24,25,33,41,42]. Therefore, a flexible electricity system is needed [15,24]. Especially in off-grid systems, energy storage units need to be used together with these energy systems due to changes in wind speed and non-generation of electricity by the PV system after sunset [19,21,43]. An electricity system that can provide demand flexibility can only be realized if it has a structure that stores electrical energy or converts it into fuels and chemicals [2,24,38,44]. Electricity generated from renewable energy sources can be converted into hydrogen and stored under pressure if it exceeds the demand [2,24,38]. The instability of obtaining continuous energy from renewable energy sources reveals the need for storage systems. Storage systems consisting of batteries can meet this need, but batteries are both expensive and have a short lifespan due to continuous charging and discharging during the day [8,32]. They also have other disadvantages such as low energy density, self-discharge and efficiency, and are not considered suitable for long-term storage [2,3,5]. This situation can solved by using an FC instead of a battery [8,32,41,42]. There is also an interest in hydrogen in industry and academia for long-term storage of electricity [5,41]. The FC has a permanent lifespan and is less costly than the battery [32]. FCs are renewable energy sources that do not pollute the environment and convert chemical potential into electrical energy [45]. FCs convert the chemical energy of fuel into electrical energy without combustion [17,33]. At the same time, FCs are characterized by low noise, efficiency and eco-friendliness [17,46]. Hydrogen production from renewable energy sources offers an excellent and complementary solution. The use of renewable energy in hydrogen production offers affordable [42], more flexible, decentralized [33] and environmentally responsible alternatives to traditional energy systems [5,14,47]. If hydrogen is produced from renewable energy sources and used in FCs, only heat and water are released as waste [2,17]. Therefore, FCs are environmentally friendly and can be used for green energy production [33]. Hydrogen as a promising alternative fuel for the transportation system is a transportation technology that has important features that other transportation technologies cannot provide, such as fast refueling, increasing vehicle range and zero emission values in the operation of electric vehicles [27].

Renewable hydrogen produced by the electrolysis of water with electricity obtained from renewable energy sources [12] will eliminate GHG and air pollutant emissions. The electrolyzer is a device that produces hydrogen and oxygen from water. The electrolysis of water can be considered the reverse process of a hydrogen FC. Therefore, this reverse chemical reaction, which converts DC electrical energy into hydrogen, which can provide chemical storage, is carried out by the electrolyzer. The hydrogen production rate is linearly dependent on the current injected into the electrolyzer. From an electrical perspective, an electrolyzer works similarly to a battery in charging mode [48].

Some studies in the literature on electric vehicle charging stations and hydrogen FCs are summarized in Table 1 below.

Regarding EVs to date, it is necessary to assess the potential EV charging infrastructure to support the development of EVs. The lack of adequate charging infrastructure and storage technologies in the field of electric transportation is an important issue that needs to be evaluated at the point of transition of consumers to electric vehicles [28,35,49]. On the other hand, the integration of electric vehicles into the electricity grid will put enormous pressure on the grid [28,35]. Charging of electric vehicles can be carried out on-grid or off-grid [30]. Considering this need for renewable energy sources in the transportation sector, our aim in this study is to model an electric vehicle charging station using PVPS and FC power systems by using irradiation and temperature data from historical regions. This designed charging station model performs electric vehicle charging, meeting the energy demand of a house and hydrogen production by feeding the electrolyzer with the surplus energy from producing electrical energy with the PVPS during the daytime. At night, when there is no solar radiation, electric vehicle charging and residential energy demand are met with an FC power system. One of the most important advantages of this system is the use of hydrogen storage instead of a battery system for energy storage and the conversion of hydrogen into electrical energy with an FC. Some of the most important motivation points for us to plan this study are the negative image that will be created by moving the power lines to remote locations, the high cost that will be incurred if the power lines are passed underground and the fact that it is not always possible to excavate underground to lay cables in historical and tourist spots. With the proposed electric vehicle charging system, there will be no additional load on the grid and no additional infrastructure costs will be required. Unlike other studies, in our study, fossil energy sources such as diesel generators are not included for the stable operation of the system. Since the system consists entirely of renewable energy sources, an environmentally friendly electric vehicle charging station system has been designed and tested. The system in this study may need hydrogen refueling in unfavorable climatic conditions and the energy storage capacity is limited by the hydrogen fuel tank capacity.

In this study, the design and modeling of an electric vehicle charging system consisting of PV and fuel cell (FC) power system were carried out for a tourist region with historical buildings. The charging system power demand problem faced by electric vehicles can be met with renewable energy sources to ensure zero greenhouse gas (GHG) emission transportation with the design of this electric vehicle charging system. The designed system generates electricity by the photovoltaic power system (PVPS) during daylight hours, and when generating electricity that exceeds the demand, surplus power is used to produce hydrogen. When there is no PV power generation, the FC is activated and produces the electrical energy to meet residential and charging demands with the produced and added hydrogen. The electrical energy generated in the system is stored as hydrogen with the electrolyzer and the elimination of the need for batteries provides a great advantage in terms of both system cost and system lifetime. The system consists of a 100 kW PVPS, a 25 kW FC power system, a residential load with a power demand ranging from 1 kW to 7 kW, electric vehicle charging sockets capable of providing one 7.4 kW, two 25 kW and one 50 kW power charges and an electrolyzer. In the simulations, if the load demand exceeds 80 kW, which is the maximum PV power generation value according to irradiance and temperature data, the FC is activated and generates 25 kW power. If the load is low and PV power generation is at maximum value, the residual energy after the electric vehicle load is met can produce hydrogen in an exceeding amount of 1 kg. If the irradiance and load demand are low, the load demand can be met by the PV and FC hybrid system. The simulation study demonstrates that the designed system, based on the irradiation and temperature data specific to historical and tourist regions, can effectively operate in these areas.

The main contributions of the proposed system can be listed as follows. In this study, a solution to electric vehicle charging station problems using real meteorological data is presented. It has been shown that charging station and residential load demands can be met with renewable energy sources without the need for infrastructure installation in areas that are far from the grid and have historical and touristic features. The applicability of the system and hydrogen production simulation were carried out by operating the modeled system for different seasons and load conditions. The duration of the system’s operation under unfavorable climatic conditions depends on the hydrogen storage capacity.

The rest of this paper is organized as follows: Section 2 presents the components of electric vehicle charging stations. Section 3 explains the simulation procedure and analysis. Section 4 discusses the analyses and results of the proposed system. Finally, conclusions are drawn in Section 5.

2. Electric Vehicle Charging Station Components

2.1. PV Power System

PV panels convert solar radiation into electrical energy [21]. A PVPS consists of series and parallel connections of PV panels. PV panels have a nonlinear characteristic. Equation (1) shows that the current generated by the PV panel depends on the irradiance and temperature values. $I_{pv}$ is the current generated by the PV panel, $K_I$ is the open-circuit current coefficient, $G$ is the irradiance on the panel surface, $G_n$ is the nominal irradiance (25 °C ve 1000 W/m²), $I_{pv,n}$ is the current generated by the PV panel at the nominal irradiance. The temperature values are in kelvin where $T$ is the actual temperature, $T_n$ is the nominal temperature and ${∆}_T$ is the temperature difference (${∆}_T=T-T_n$). The nominal saturation current is obtained from Equations (2) and (3) below [50].

$$I_{pv}=\left(I_{pv,n}+K_I{∆}_T\right)\frac{G}{G_n}$$

(1)

$$V_t=\frac{N_{s}kT}{q}$$

(2)

$$I_0=\frac{I_{sc,n}+K_I{∆}_T}{\mathit{exp}\left(\frac{V_{oc,n}+K_V{∆}_T}{{aV}_t}\right)-1}$$

(3)

where $N_s$ is the number of series cells, $k$ is the Boltzmann constant (1.38 × 10⁻²³ J/K), q is the electron charge (1.602 × 10⁻¹⁹ C), $K_V$ is the open-circuit voltage coefficient, $I_{sc,n}$ is the nominal short-circuit current, $V_{oc,n}$ is the nominal open-circuit voltage, $V_t$ is the series cell voltage, $I_0$ is the reverse saturation or leakage current. The current to be taken from the PV panel output is obtained by Equation (4) [50].

$$I=I_{pv}-I_0\left[\mathit{exp}\left(\frac{V}{V_{t}a}\right)-1\right]$$

(4)

where a diode ideality constant is generally selected between 1 and 1.5. $I$ is the current value taken from the PV panel output [50].

$$I=I_{pv}-I_0\left[\mathit{exp}\left(\frac{q\left(V+I{R}_S\right)}{kT}\right)-1\right]-\frac{1}{R_{sh}}(V+I{R}_S)$$

(5)

Equation (5) expresses the current for the PV equivalent circuit including both series and parallel resistors. The PV equivalent circuit is shown in Figure 1. Figure 1 shows the circuit model used to model PV systems, from which the most basic equations are derived. Due to its simple structure, it is frequently used in the modeling of PVPSs. Figure 2 shows the current–voltage and power–voltage graphs of the PVPS. Figure 2 shows the maximum power point that enables maximum power to be generated in PVPSs. Although power can be obtained from the PV power system at every point, maximum power can only be provided at and around a point. Figure 1 and Figure 2 also show the decrease in the generated power with increasing temperature.

2.2. FC Model

FCs are electrochemical energy conversion devices that convert the chemical energy of fuel into electrical energy. Depending on the electrolyte type, FCs are named and developed as proton exchange membrane (PEM) FC, alkaline FC, molten carbonate FC and solid oxide FC. FCs are an alternative source for transport and power generation from a fixed point [3]. The FC electrical equivalent circuit model is shown in Figure 3 [3,51]. FC internal voltage is expressed as the thermodynamic potential in the open-circuit state. It is calculated by the Nernst equation using hydrogen and oxygen pressure and cell temperature [51].

The FC terminal voltage is lower due to subtracting the activation voltage, ohmic voltage and concentration voltage from the generated voltage in the FC. The activation voltage is required to initiate chemical reactions to accelerate the slowed-down electrode kinetics. Ohmic losses are caused by the resistance to the flow of ions in the electrolyte, electrons in the external circuit and contact resistances. At high current densities, the reduction in reactants to provide high currents causes a further drop in voltage, known as concentration polarization. Two opposite charge layers are formed along the boundary between the electrode and the electrolyte. These opposed layers act as capacitors and tend to store charge. The capacitor is presented in parallel with the activation and concentration voltage drops. The FC output voltage can be given by Equation (6). In this equation, E represents the voltage on the FC, $V_{act}$ is the activation voltage drop due to temperature, ${\mathrm{V}}_{\mathrm{C}}$ is the voltage drop across the capacitor and $V_{ohm}$ is the ohmic losses due to resistance.

$$V_{out}=E_{cell}-V_{act}-V_C-V_{ohm}$$

(6)

The calculation of the voltage value E with the Nernst equation is shown in Equation (7) below.

$$E=E_0+\frac{RT}{2F}\ln (\frac{P_{H_2}{P_{O_2}}^{\frac{1}{2}}}{P_{H_{2}O}})$$

(7)

where $E_0$ is the standard voltage of the hydrogen/oxygen reaction (about 1.229 V), $R$ is the universal gas constant, $F$ is Faraday’s constant and $T$ is the gas temperature. $P_{H_2}$ is the partial pressure of hydrogen available at the anode, $P_{H_{2}O}$ and $P_{O_2}$ are the partial pressure of water and oxygen available at the cathode, respectively.

$${\mathrm{V}}_{\mathrm{a}\mathrm{c}\mathrm{t}1}={\mathsf{\eta }}_0+(\mathrm{T}-298)\mathrm{a}$$

(8)

In Equation (8), ${\mathsf{\eta }}_0$ and $\mathrm{a}$ are experimental constants.

$${\mathrm{V}}_{\mathrm{C}}=\left(\mathrm{I}-\mathrm{C}\frac{{\mathrm{d}\mathrm{V}}_{\mathrm{C}}}{\mathrm{d}\mathrm{t}}\right)({\mathrm{R}}_{\mathrm{a}\mathrm{c}\mathrm{t}}+{\mathrm{R}}_{\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{c}})$$

(9)

In Equation (9), $\mathrm{I}$ is the load current, $\mathrm{C}$ is the internal capacity value, ${\mathrm{R}}_{\mathrm{a}\mathrm{c}\mathrm{t}}$ and ${\mathrm{R}}_{\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{c}}$ are the activation and concentration voltage drops, respectively.

$$V_{ohm}=I{R}_{ohm}$$

(10)

In Equation (10), $V_{ohm}$ is the ohmic voltage drop at FC [3].

2.3. Electric Vehicle Charging Model

Although many types of batteries are used in electric vehicles, Li-ion batteries are the most suitable for electric vehicles. Li-ion batteries are the most suitable battery type because they have high energy density, low maintenance requirements and long service life [52]. Electrical equivalent circuit models used to describe the electrical behavior of batteries consist of circuit elements such as voltage source, resistor and capacitor [52,53]. Simple battery models with a voltage source and a series resistor may not accurately represent the true characteristics of electric vehicle batteries. Among the battery-equivalent circuit models, one RC equivalent circuit model, two RC equivalent circuit models and three RC equivalent circuit models are widely accepted circuit models [52]. Two or more parallel RC circuits are added to best reflect the characteristics of a battery. While the addition of many more parallel RC circuits provides high estimation accuracy, estimating parameters is much more difficult [54]. In the equivalent circuit in Figure 4, the voltage source represents the open-circuit voltage of the battery. Resistance $R_0$ is used to account for the contact resistance between parts such as electrolyte material, diaphragm resistance and electrolyte. The parallel RC circuit structure expresses the polarization internal resistance and capacity and reflects the dynamic characteristic of the diffusion and polarization effect of the battery [53].

$$V_{bat}=V_{oc}-I{R}_0-\frac{1}{C_1}\int \left(I-I_{R_1}\right)dt-\frac{1}{C_2}\int \left(I-I_{R_2}\right)dt-\frac{1}{C_3}\int \left(I-I_{R_3}\right)dt$$

(11)

In Equation (11), $V_{bat}$ is the battery cell output terminal voltage, $V_{oc}$ is the battery cell open terminal voltage, $R_0$ is the cell ohmic resistance, $R_1$, $R_2$, $R_3$ and $C_1$, $C_2$, $C_3$ are the internal resistance and capacitance values [55,56].

3. Simulation Procedure and Analysis

The coordinate values of the historical city and its location, where the simulation study was carried out by taking the irradiance and temperature values, are shown in Figure 5. In this historical city, it is not appropriate to extend electric vehicle charging stations to every location due to its historical structure. In addition, the installation of PVPSs using large areas or the installation of high wind turbines is not suitable for the natural structure of the historical city. The irradiance and temperature data used in this study in Figure 6 and Figure 7 are published in reference [57] as measured values with 15 min periods. For these reasons, the irradiation and temperature data of August and January given in Figure 6 and Figure 7 are used in the modeling of the power generation of the PV panels. Thus, this study aimed to create system models where a significant portion of the electric vehicle charging load can be met from the PVPS.

In reference [1], using hourly changing irradiance data, the use of a PV power system in a microgrid to meet the load demand and hydrogen production was realized. Electric vehicles are considered as a load- or power-generating source. Unlike that study, in the model developed in this paper, the system that can be located far from the grid, generates power with PVPS, stores it as hydrogen and uses it in energy production with an FC has been tested for different climate and load conditions. In reference [1], while cost optimization was performed, the operating cost was zero in the proposed system. Unlike the off-grid system realized with a PV panel, an FC, an electrolyzer and a diesel generator in reference [12], the proposed system does not include a diesel generator. Unlike this study, the proposed system was tested for different load conditions and climatic conditions by using the irradiance and temperature data of a region and the power management algorithm was realized according to the energy supply and demand with charge control. In reference [20], for EV and FCEV, an on-grid charging station where hydrogen produced by PV and electrolyzer were stored and an energy management system were presented. In reference [58], the optimization of the energy management system of an on-grid charging station for EV and FCEV, including electrolyzer, FC, hydrogen tank and PV power system, was performed. Unlike these two studies, in the proposed system, the energy management system and design of an EV charging station ensure that it has a PVPS as the main energy generation source, does not need grid connection, can meet the load demand of electric vehicles and residences, can be installed in remote locations and has been tested for different climatic conditions. One of the most important differences of the proposed system is that most of the energy produced in the system is used in electric vehicle charging. Thus, losses occurring during energy conversions are significantly reduced. In reference [31], a charging demand prediction method for EV and HV was investigated by collecting information from different sources. In this study, the estimation of the optimal charging location in terms of time and cost is performed for a charging station consisting of a wind turbine, PVPS, on-grid connection, electrolyzer, FC and hydrogen tank. With the proposed system, an electric vehicle charging system can be installed in many locations including historical and tourist regions, has a cost advantage, can eliminate the electric vehicle charging queue, has no infrastructure installation requirements, and can meet the simple residential load. In addition, the proposed system has been tested for irradiance and temperature data taken under different seasonal conditions. In reference [8], an off-grid EV and HV charging station energy management algorithm consisting of a PV system, diesel generator, electrolyzer and hydrogen tank is presented. Unlike this study, in the proposed system, an electric vehicle charging system that does not include a diesel generator, is off-grid, fed by a PV power system, stores the hydrogen produced by the electrolyzer, meets the residential demand and electric vehicle charging in periods when there is no sunlight and has no infrastructure requirement is proposed and tested for different climatic conditions with the energy management algorithm.

Modeling and simulation of the electric vehicle charging system are carried out with Matlab R2022b Software. The system consists of a 100 kW PVPS, a 25 kW FC power system, a residential load with a power demand ranging from 1 kW to 7 kW, electric vehicle charging sockets capable of providing one 7.4 kW, two 25 kW and one 50 kW power charges and a 75 kW electrolyzer. Moreover, 100 kW PVPS covers an area of approximately 600 m². Irradiance and temperature values that changed according to the seasons were entered into the system with signal builder blocks. When PV power generation, which can perform fast charging with DC/DC power electronics converters, is realized, the DC bus voltage operates at 800 V DC voltage level. The simulation was run for 24 s for 24 h. With the energy management block, PV output power and load demand are monitored, and power management for when the FC will be activated or when the increased energy will be converted into hydrogen is carried out. Since DC/DC converters have an efficiency of over 99% [59], losses are negligible. The electrolyzer operates with 67.2% efficiency. FC efficiency is 60% [30]. This system is simulated with the assumption of charging six vehicles per day for the summer months and four vehicles per day for the winter months because the region is a tourist region for the winter and summer months. It is possible for the proposed system to be installed at many points. The residential load is assumed at the same power value in summer and winter. Although the electric vehicle battery capacity varies according to the vehicle types in the market, the average value is accepted as 60 kW and this value is used in the proposed system.

The power management algorithm of the proposed system is shown in Figure 8. Power management is based on meeting electric vehicle charging by generating electricity with the PVPS. The surplus PV power is converted into hydrogen and stored. During the hours of no or low solar radiation, the stored hydrogen is converted into electrical energy by FC and meets electric vehicle charging and residential load demand. The power management system first checks whether there is solar irradiation. If there is no or a very low level of irradiation, the FC will be activated and feed the system with a maximum power value of 25 kW. If PV power generation is available and there is surplus PV power after meeting the entire load demand, it is converted into hydrogen and stored. If PV power generation cannot meet the load demand, it is checked whether there is PV power generation greater than 25 kW. If the PV power generation is greater than 25 kW, fast charging with 50 kW is supported; if it is smaller, normal charging is carried out from the charging sockets. With the proposed system, this study aims to design a simple and stable power management algorithm using renewable energy sources, so that electric vehicle charging can be easily adapted to a building or an enterprise located in a protected area or on a historical site that does not need the electricity grid. The recommended charging system design is shown in Figure 9.

To enable electric vehicle charging, DC charging sockets which charge at 800 V DC voltage with 50 kW and 25 kW power values and an AC charging socket with 7.4 kW power are planned. As a load profile, the residential load demand and electric vehicle load demand scenarios were applied as shown in Figure 10. An electric vehicle battery assumed an average capacity of 60 kWh. The production of electricity from solar energy, which exceeds the load demand is evaluated for hydrogen production. In the applied scenario, the residential load demand reaches a peak value between 15 and 19 h and the electric vehicle charging demand reaches a peak value between 14 and 15 h in summer and a peak value between 9 and 18 h in winter. In the case of exceeding load demands for PV power generation or at night when there is no PV power generation, the FC is activated and meets the power demand. The 25 kW and 50 kW charging sockets are available for use during daylight hours when PV power generation is active. The 7.4 kW charging socket provides all-day electric vehicle charging. The residential load demand can be met in full during the day and night.

4. Results and Discussion

The peak power demand of 105 kW is seen to meet with the modeled electric vehicle charging station. The FC activates in the event of a decrease in PV power generation and meets the electrical energy demand of the charging system. The installed power value in this designed system is 125 kW. Due to the instability of renewable energy sources, electrical energy production may not always be provided at the installed power value. The changes in irradiation and temperature values cause changes in the electrical energy produced by the PVPS. For this reason, instead of battery systems that have many disadvantages, electric vehicle charging systems that feed the load with renewable energy sources during high production hours and store hydrogen fuel during low consumption hours are a promising charging system approach.

In the proposed system, the energy management algorithm was tested with three different scenarios. With three different load types and two different irradiance and temperature values for summer and winter, the system was simulated and the results were obtained. The simulation was carried out using August data with high irradiation and temperature values for summer months with high electric vehicle power demand in Scenario 1. The temperature and irradiance values used in Scenario 1 are shown in Figure 11. The simulation was performed by applying residential load demand and electric vehicle load demand in the summer months. In Scenario 1, during the daytime hours when the load demand is high, the PVPS meets the majority of the demand and transfers power to the system. The changes in the power graphs for this case are shown in Figure 12. Due to the high load, the surplus PV power generation will be lower than in Scenario 2; for this reason, the hydrogen production also remains at a lower value. When PV power generation is not sufficient, the FC is activated to support the PVPS. In the system, fast charging was constantly activated due to high irradiance values.

As shown in Figure 13, in Scenario 2, the test of the system for the low load demand case was carried out by simulation using the high irradiance values of August in the historical and tourist regions. Residential load demand and electric vehicle load demand, which can be generally faced in winter months, have been applied to the power system. In this scenario, due to the low load demand and high PV generation in the system, most of the produced PV power is used for hydrogen production. According to the maximum hydrogen production values obtained in Figure 14, a hydrogen tank with a capacity of 20 kg will be sufficient to store hydrogen. There was no need for the FC to operate during daylight hours. During the hours when the irradiance is very low or absent, the FC is activated to meet the electrical energy required by the system. In addition, the high irradiation level and low load demand ensured that the fast charging was continuously activated during daytime hours.

As shown in Figure 15, Scenario 3 is the scenario where the most challenging conditions for the system are tested. In Scenario 3, with low irradiance and low EV load demand, fluctuations occur in the power supplied from the PV and FC power systems. The fluctuation of irradiance in winter months causes fluctuations in the power transferred to the system by PV. In this case, the FC is activated and works to ensure power balance in the system. The charging voltage remains above 800 V DC voltage even at low irradiance hours, and continues to charge the electric vehicle. Thus, the continuity of high-efficiency electric vehicle charging is ensured with low current value at high voltage levels. Keeping the current level at a low value, inefficiency caused by heating in the system ensures that it remains at the lowest level. In the system, fast charging is disabled due to low irradiance. However, the system ensures uninterrupted EV charging and meets the residential load demand. Because the irradiance values in the region during January are very low and fluctuate, as shown in Figure 16, they are only sufficient to meet the power demand, resulting in very low hydrogen production. Additional load demands to be encountered at this point will be met with approximately 33.6 kW electrical energy to be obtained from 1 kg hydrogen with a hydrogen tank capacity of 20 kg. In this worst-case scenario, with a full hydrogen tank, the FC will be able to provide uninterrupted energy to the system for approximately two days.

Scenario 1 is the scenario with the highest load demand and PVPS power generation, Scenario 2 is the scenario with low load demand and high PVPS power generation and Scenario 3 is the scenario with low load demand and low PVPS power generation. In Scenario 2, where the irradiance is high and the EV load is low, the best performance is demonstrated by stably producing hydrogen with the surplus energy after the EV load is met. In Scenario 1, due to high irradiance and high EV load demand, hourly fluctuations occurred in hydrogen production with surplus energy after the load demand was met. However, the system has shown stable operation. In Scenario 3, where irradiance and EV load were low, hydrogen production could be realized during the hours when PVPS generation was higher than the EV load. When the electric vehicle load exceeded the PVPS power generation, the FC was activated to meet the energy demand. The 100 kW PVPS used in all scenarios covers an area of approximately 600 m² and is suitable for installation in almost all buildings in the region. Considering the covered area and vehicle battery values, it is seen that the installation of a PV power system with a power value of 100 kW is appropriate with the performed simulations. All scenarios show stable behavior in meeting the energy demand, and the EV charging system is able to meet the load demand in different climates and load demand values.

5. Conclusions

This study evaluated the modeling and simulation using real irradiation and temperature data from historical and tourist regions. It demonstrated that the deficiency of electric vehicle charging systems, which will be a significant issue in future, can be addressed by using renewable energy sources in this region. The electrical energy generated by the PVPS was observed to be quite sufficient for electric vehicle charging systems.

The primary purpose of this study is to reduce the costs of obtaining hydrogen which is a clean and renewable energy source. As electric vehicles become increasingly widespread, it is important to develop hybrid systems that can meet both residential electricity needs and electric vehicle charging demand. In addition, this system is suitable for operation in remote locations from the grid. A concept that electrical energy is produced with 100% renewable energy which does not have any harmful effects on the environment, and charging and residential electricity usage is possible at a point where there is no grid was presented. One of the important advantages of the system is that it does not contain a battery. Another advantage provided by this study is to show that the installation and operation of electric vehicle charging stations in old settlements where there are many historical and cultural assets can be realized with renewable energy sources without damaging cultural assets and disrupting the historical texture.

Three different models with the highest load demand and PVPS power generation, low load demand and high PVPS power generation, and low load demand and low PVPS power generation were tested for their performance according to the climate of the region.

Hydrogen production was realized in all scenarios, being highest in the scenario where irradiance was high and EV load was low. Hydrogen production exceeds 1.5 kg in Scenario 1. In the scenarios, the peak power demand of 105 kW could be met by the modeled system. In all scenarios, the electric vehicle charging system has shown stable performance in meeting the energy demand, and it has been observed that the energy demand can be met in different seasons and load demand values.