Lab-Scale Investigation of the Integrated Backup/Storage System for Wind Turbines Using Alkaline Electrolyzer

Abstract

The depletion of fossil fuel sources has encouraged the authorities to use renewable resources such as wind energy to generate electricity. A backup/storage system can improve the performance of wind turbines, due to fluctuations in power demand. The novelty of this study is to utilize a hybrid system for a wind farm, using the excess electricity generated by the wind turbines to produce hydrogen in an alkaline electrolyzer (AEL). The hydrogen storage tank stores the produced hydrogen and provides hydrogen to the proton-exchange membrane fuel cell (PEMFC) to generate electricity once the power demand is higher than the electricity generated by the wind turbines. The goal of this study is to use the wind profile of a region in Iran, namely the Cohen region, to analyze the performance of the suggested integrated system on a micro scale. The output results of this study can be used as a case study for construction in the future, based on the exact specification of NTK300 wind turbines. The results indicate that, with the minimum power supply of 30 kW from the wind turbines on a lab scale, the generated power by the PEMFC will be 1008 W, while the maximum generated hydrogen will be 304 mL/h.

1. Introduction

The adverse impacts of fossil fuels have directed the decision-makers to use renewable energies such as wind, which has a variable nature as a function of meteorology. The reported data by the International Renewable Energy Agency (IRENA) [1] shows that the world maximum net generating capacity of power plants and other installations that use wind energy to generate electricity has increased from 266,918 MW to 824,874 MW from 2012 to 2021. It is believed that the integration of the energy storage systems with power plants will increase the efficiency of the existing renewable power plant, hence facilitating and improving the usage of renewable resources [2,3,4].

At least one year before constructing a wind farm, it is necessary to record and analyze all the wind meteorological information in the construction region [5]. Despite all the advances in obtaining the required data, the exact intensity and time of the wind cannot be commented on [6]. On the other hand, turbines produce less than half a day at their rated power, even in the best wind profiles [7]. Thus, finding an optimized design for the wind turbine has been widely investigated by active researchers in the field. Although different designs have been suggested to improve the performance of the wind turbines, devising a backup/storage system that can store the excess electricity by the wind turbines at periods of low demand and generate electricity in high power loads is needed [8,9].

Long-term storage of power generated by wind turbines in remote locations has always been a problem [10]. Based on Figure 1, the output power of the wind turbines can be stored for future usages such as balancing, distributed, bulk, residential, commercial, and thermal storage. It should be noted that Figure 1 shows the possibilities for storing the wind energy rather than supplying energy to consumers. Lehtola et al. [11] reviewed wind power supply supported by storage technologies. Using the simultaneous usage of battery storage and vehicle-2-grid (V2G) battery storage, it was concluded that wind energy provides a reliable supply for the power grid. As another result, it was mentioned that the combined system of wind turbines and battery storage meets the demand for 99.9% of hours of load. Kim et al. [12] analyzed the techno-economic aspects of a wind-energy storage system in the far eastern region. Batteries and regenerative hydrogen fuel cells were considered as candidates, and energy and exergy analyses were conducted for the hybrid system. It was concluded that batteries were efficient, but the regenerative fuel cell was economical. Gou and Yousefi [13] provided a conceptual design of an energy system based on solid oxide fuel cells and wind turbines. In their system, the waste heat of the fuel cell was converted to more power in thermionic and thermoelectric generators, the energy produced from the system was stored by a relatively new energy storage system, and a water electrolyzer, coupled with a wind turbine, provided the hydrogen needed by the process. The results showed that the power generation system was capable of generating 533.4 W of electricity (with an output efficiency of 76.6%). Although many studies have proposed different options as a storage system for wind turbines, such as using batteries to directly store the electricity, storing the hydrogen through hydrogen production using an electrolyzer such as an alkaline electrolyzer (AEL) is of high interest. In this regard, hydrogen can be used in many other industries if the hydrogen produced by the AEL is more than the required electricity for the backup power of the wind turbine. The concept will be similar to the unitized regenerative fuel cell (URFC) [14,15], which is a fuel cell capable of electrolyzing water in a regenerative mode in one stack. However, for large-scale applications it is not considered efficient, and the usage of platinum particles inside the catalyst will increase the costs. In this regard, having a separate AEL is suggested, to reduce the costs and the possibility of large-scale applications.

For long-term storage, electrical energy can be converted into hydrogen using an electrolyzer to be used later by the fuel cells [16]. Rostami et al. [17] investigated a solar-driven multi-generation system with electricity storage. In their research, electricity generated from the fuel cell, thermoelectric generator, and organic Rankine cycle was stored by a thermal storage system. The results showed that 22.5 kW of electricity, 140.8 kW of heat, and 97.3 g/h of hydrogen were generated with a system efficiency of 60.3%, while the storage system capacity was 89 m³. Maleki and Pourfayaz [18] focused on modeling, sizing, and cost analysis of a photovoltaic (PV)/wind generator (WG)/diesel hybrid system, considering two storage devices: battery and fuel cell (FC). They proposed PV/WG/diesel/FC systems that combine fuel cells, an electrolyzer, and hydrogen storage tanks as the energy storage system, in comparison with the traditional PV/WG/diesel/battery systems in which battery banks are used as the storage system. Ercan and Kentel [19] assessed the performance of an integrated wind energy co-generation system with a hydrogen fuel cell and PEM electrolyzer. They assessed energy and exergy efficiencies at different wind speeds. Considering the developed research on the AEL in hybrid systems, there is a gap in the integration of the AEL into the proton-exchange membrane fuel cell (PEMFC), which is assumed to be an efficient type of fuel cell at low operating temperatures, as a backup/storage system for the wind turbines.

After many technological advances, proton-exchange membrane fuel cell (PEMFC) technology has now reached the demonstration and commercial phase [20]. Habani et al. [21] defined various polymeric electrolyte membranes (PEMs) for application in fuel cells. They reviewed and compared the utilized membranes in terms of power generation and renewable energy recovery. The results showed the limitations of Nafion in wind energy hybrid systems, while SPEEK membranes lead to better coupling with wind turbines and energy recovery at higher proton conductivity. SPEEK membranes benefit from low cost and acceptable proton conductivity (between 4.2 $\times$ 10⁻³ and 1.3 $\times$ 10⁻² S·cm⁻¹ with a sulfonation degree from 57% to 87%), while having different nanophase separation between hydrophilic and hydrophobic domains compared to Nafion [22]. Although PEMFC has been used widely in different applications, a concentrated effort should be made to adjust the hydrogen input flow rate to the stack to generate the required electricity using the integrated system.

In continuation of the previous works by the authors [23], the aim and the novelty of this study is to experiment with the possibility and the performance of a backup/storage system based on PEMFC and AEL for the wind turbine. The fundamental operation of the system is using the surplus produced electricity as the prime mover for the AEL. Thus, hydrogen will be produced and stored in the hydrogen tanks for future uses by other industrial applications or the devised PEMFC unit, which is supposed to act as a backup system for the wind turbine to provide electricity once the power load is higher than the electricity generated by the wind turbine. The lab-scale experimental results are used as an input database to suggest a prototype hybrid system for one of the regions in Iran, called Cohen, to be constructed in the future. The idea is to provide electricity for 250 households in the Cohen area, where each household consumes an average of 2740 kWh of electricity per year. The results of this study are divided into two categories: laboratory results and modeling results. In the laboratory section, the results are divided into three categories of hydrogen storage, PEMFC, and integrated system test results. In the modeling section, different scenarios are investigated, considering the changes in the effective parameters. At the end of the modeling section, two top operating scenarios are suggested, followed by a technical analysis.

2. Methodology

The hybrid system that will be introduced in this research has four main parts: wind turbine, alkaline electrolyzer (AEL), hydrogen storage, and fuel cell (see Figure 2). The mechanism of this system is such that during low power-load hours, the excess power generated by the wind turbine will be utilized by the electrolyzer unit to produce hydrogen and oxygen, which will be compressed and stored in special tanks in gas form [24]. It should be noted that hydrogen storage can be carried out in three common forms, namely, liquid (extremely low temperature), gas (very high pressure, around 700 bars), and solid (through adsorption or metal hydride) [25]. During peak power-load hours, the stored hydrogen can be used by the fuel cell unit to compensate for the shortage of electricity in the system. To better explain the working performance of the system (Figure 2), the power load that will be used by the consumer will be either provided by the wind turbine farm or by the fuel cell. When there is enough energy from the wind turbines, the power load that will be used by the consumers will be supplied only by the wind farm. When there is a shortage of electricity generated by the wind farm, the fuel cell will provide the remaining required electricity for the consumers (see Figure 2). However, the fuel cell requires hydrogen to operate, and providing the hydrogen may be difficult. In this regard, the required hydrogen for the fuel cell is being produced using an AEL that uses electricity to operate. The electricity needed for the AEL will be provided using the surplus of electricity during the operation of the wind farm. In other words, when the wind farm is producing more than the required electricity for the consumers, the extra electricity will be used by the AEL to produce hydrogen. The produced hydrogen will be later used by the fuel cell when the wind farm fails to provide electricity for the consumers.

In this research, laboratory methods have been used for technical analysis of the system. In other words, a lab-scale prototype of the hybrid system has been developed with a focus on hydrogen production through AEL and its connection to the existing PEMFC. It should also be mentioned that the goal of this study is to analyze the joint configuration of the units for the continuous performance of the wind turbines to provide electricity with a certain amount of power demand. To better evaluate the performance, different operating parameters have been tested. Laboratory results were described for three general tests on the electrolyzer and its hydrogen production, fuel cell, and output power, and finally the composition of the hybrid system. It is noteworthy that a graduated cylinder filled with water that was floated upside down in a water pan was used to calculate and adjust the hydrogen gas outlet flow rate [26].

2.1. Alkaline Electrolyzer (AEL) and Hydrogen Production

First, to determine the hydrogen production capacity of different metals, eighteen experimental tests were developed, using different electrode materials for the AEL (see

Table 1. Generation of hydrogen by different electrodes [29,30,31,32,33,34].

No	Cathode	Anode	Hydrogen Production Status
1	Nickel foam	Nickel foam	Good
2	Aluminum sheet	Aluminum sheet	Low
3	Aluminum sheet	Brass paper	Low
4	Brass paper	Aluminum sheet	Good
5	Nickel foam	Aluminum sheet	Good
6	Aluminum sheet	Nickel foam	-
7	Carbon cloth	Aluminum sheet	Normal
8	Aluminum sheet	Carbon cloth	-
9	Nickel foam	Brass paper	Good
10	Brass paper	Nickel foam	Good
11	Copper mesh	Steel mesh	Good
12	Steel mesh	Copper mesh	Good
13	Copper mesh	Brass paper	Good
14	Brass paper	Copper mesh	Good
15	Nickel foam	Copper mesh	Good
16	Copper mesh	Nickel foam	Good
17	Steel mesh	Nickel foam	Good
18	Zinc sheet	Zinc sheet	Good

) [27,28]. It should be noted that, although titanium electrodes have proved to have good performance, especially in proton-exchange membrane electrolyzers (PEME), they are not considered in this study since they lead to high costs. Furthermore, considering the scarcity of titanium, the usage of them for the electrolyzer is not environmentally friendly, according to the life-cycle assessments. The tests were performed in such a way that, by using the power supply and keeping the amount of potential difference constant, the negative and positive poles were connected to the cathode and anode, which were connected in half-molar sulfuric acid solution, and the amount of hydrogen content was observed. The sulfuric acid is the electrolyte that enables the production of hydrogen at the negative electrode, while the positive electrode is bathed in sulfur dioxide which it oxidizes to sulfuric acid. According to Table 1, one of the situations in which there is adequate hydrogen production is in the use of nickel foam as the anode and copper mesh as the cathode. In this case, using these electrodes, once by adjusting the voltage from 0 to 15 and once by adjusting the input power to the electrolyzer from 0 to 30, the output hydrogen was measured.

2.2. Fuel Cell

The fuel cell used in this experiment was a fuel cell stack with 5 cells and an output power of 2 watts. The electrode membrane of this fuel cell consists of an electrolyte polymer membrane with two layers of catalyst and two layers of gas penetration. To test the fuel cell, the flow rate of hydrogen gas was adjusted to 55 mL/min. The experimental tests were performed under hot ventilation conditions, ambient temperature ventilation, and without ventilation for the PEMFCs. In the present study, there was no increase in the internal temperature of the fuel cell, fuel heating, and humidification. Considering the operating conditions, the relative humidity is equal to 1, while the operating pressure is 2.5 bar at the operating temperature of 353 K. The Pt loading in both the anode and cathode catalyst layer is 0.4 mg/cm², using Nafion as the membrane with a density of 1980 kg/m³, heat specific capacity of 833 J·kg⁻¹·K⁻¹, thermal conductivity of 0.95 W·m⁻¹·K⁻¹, and the equivalent weight of 1.1 kg/mol. The Pt/C ratio is 0.35 in the catalyst layers, followed by a porosity of 0.4 and a permeability of 1.0 × 10⁻¹³ m². The electric conductivity, heat specific capacity, thermal conductivity, and thickness in the catalyst layer are 5000 $\mathrm{\Omega }$⁻¹·m⁻¹, 3300 J·kg⁻¹·K⁻¹, and 1.0 W·m⁻¹·K⁻¹, respectively.

2.3. Powe-Supply Electrolyzer Fuel Cell

The components of the hybrid system including power supply, AEL, and PEMFC are integrated to perform the lab-scale experiments. In this test, the output power load of the turbine is simulated by the power supply. The output power of the power supply enters the AEL, and the produced hydrogen is stored in a tank. Once the stored hydrogen reaches the proper flow rate, it enters the fuel cell and enters the circuit as auxiliary power. The maximum observed output power by the fuel cell was 1465 MW in which the potential difference between the two fuel cells was 2.05 volts and its current was 715 mA. The reason for the sharp drop in output power of the fuel cell in addition to the voltage drop is because of the ohmic drop. In addition, the decrease in the current is a result of the reduction in the input flow rate of the reactants to the fuel cell. The various parameters that can be used to improve the performance of the PEMFC are [35,36]:

• Changing the utilized membrane in the AEL leads to a multiplication of hydrogen production. Additionally, selecting an improved membrane for the PEMFC leads to higher input electricity to the AEL, and hence higher power of the electrolyzer to produce hydrogen, which results in higher hydrogen production.
• Increasing the surface area of the electrodes in the electrolyzer and bringing the plates closer.
• Keeping the operating temperature of the fuel cell between 65 °C and 80 °C.
• Keeping a constant hydrogen mass flow rate from the inlet of the flow channels to the PEMFC’s membrane.

2.4. Wind Turbine Fuel-Cell Electrolyzer Hybrid System

By integrating the components of the system, which are the wind turbine, electrolyzer, and fuel cell, the hybrid system was created, based on the power curve given by Ref. [37] for the wind turbines. The wind turbine has a blade diameter of 2 m and a tower height of 2.5 m. Figure 3 shows the utilized wind turbine power curve (Sabaniro brand).

Table 2. Determining the rotation speed of the wind turbine in varying dimensions.

Round per Minute (RPM)	Rotational Speed (rad/s)	Moment of Inertia (kg/m3)	Blade Length (m)	Mass of Blade (kg)	Blade Number
1007	105	0.009	0.3	0.1	3
755	79	0.016	0.4	0.1	3
604	63	0.025	0.5	0.1	3
503	53	0.036	0.6	0.1	3
712	75	0.018	0.3	0.2	3
534	56	0.032	0.4	0.2	3
427	45	0.05	0.5	0.2	3
356	37	0.072	0.6	0.2	3
581	61	0.027	0.3	0.3	3
436	46	0.048	0.4	0.3	3
349	37	0.075	0.5	0.3	3
291	30	0.108	0.6	0.3	3
503	53	0.036	0.3	0.4	3
377	40	0.064	0.4	0.4	3
302	32	0.1	0.5	0.4	3
252	26	0.144	0.6	0.4	3
450	47	0.045	0.3	0.5	3
338	35	0.08	0.4	0.5	3
270	28	0.125	0.5	0.5	3
225	24	0.18	0.6	0.5	3

also determines the rotational speeds of the turbines with different dimensions. According to Table 2, the minimum required rotational speed was 23.57 radians per second or 225 rpm, which is related to a 3-blade turbine with a blade diameter of 0.6 m and a mass of 0.5 kg.

2.5. Case Study

Table 3. The climatic data for the Cohen area for 3 years.

	2017	2018	2019	The Average for 3 Years
Minimum temperature (°C)	−16	−8	−10.2	−4
Maximum temperature (°C)	40	42.2	37.8	40.1
average temperature (°C)	14.1	13.6	14	13.9
Average relative humidity	53	55	54	54
Annual rainfall (mm)	339	410	326	358.3

represents the weather information of the Cohen region for three different years. As pointed out in the problem hypotheses, the electricity demand is equal to the electricity demand of 250 households in the Cohen area, where each household consumes an average of 2740 kWh of electricity per year, and the peak electricity consumption during the year is in August. The average amount of electricity demand per month, electricity demand per day from different months, and annual profile of electricity consumption at different hours of the day are displayed [38]. The wind turbine considered in this research is a 300 kw NTL turbine with an ABB generator, whose power curve, along with its technical specifications, are mentioned in Ref. [39].

One of the anemometers of the New Energy Organization of Iran (SANA) is located near the site. The anemometer tower is located in the eastern part of the site at a distance of 3.5 km, with coordinates of 49.7100 N and 36.3375 E, at an altitude of 1447 m above sea level. Cup sensors are installed at the three heights of 40, 60, and 80 m above the surface. In addition, there are two windmills at a height of 60 and 78 m, and all sensors are calibrated according to international standards.

The output information from the anemometer tower was recorded for a period of 10 min and the output data from 17 May 2017 to 27 June 2019, were used in this research.

Table 4. Average wind speed at 40-, 60- and 80-meter height.

Sensor Height (m)	Amount of Data Coverage (%)	Average Speed (m/s)
40	94.4	7.31
60	94.8	7.78
80	94.5	8.18

presents a summary of the output report. As can be seen in Table 4, the percentage of information coverage is more than 94%, which is higher than the acceptable level. Based on this information, the highest amount of electricity consumption is achieved in December [40], while the highest wind speed occurs in the summer (July to September). Based on the obtained information, and the technical specifications of the wind turbine used, which are shown in

Table 5. Technical features of wind turbine NTK 300.

Information	Unit	Amount
Nominal power	kW	300
Rotor diameter	m	28
Hub height	m	31
Speed range	m/s	4 to 25
Blade number	-	3

, the wind turbine is selected. In this research, an NTK 300 KW wind turbine with the ABB generator was selected. The power diagram of this turbine is shown in Figure 4. In addition, Table 4 shows the average wind speed at 40, 60, and 80 m heights.

3. Results and Discussion

3.1. Laboratory Results

Figure 3 and Figure 4 show the effect of changes in the velocity of the wind and the output power from the wind turbines on the electrolyzer output. Additionally, the changes in the voltage of the electrolyzer result in the output hydrogen production in this unit. With increasing voltage, the anode plate dissolves in acid, in addition to the reduction in the intensity of electrolyte acidity. One of the situations in which there is adequate hydrogen production is in the use of nickel foam as the anode and copper mesh as the cathode of the AEL. Using these electrodes, once by adjusting the voltage from 0 to 15 and once by adjusting the input power to the electrolyzer from 0 to 30, the output hydrogen gas was measured.

In Figure 5, hydrogen production decreases over time as a result of the reduction in the sulfuric acid due to the corrosion of the anode. Figure 5 also shows that hydrogen production decreases after a specific voltage of 12 volts. Furthermore, Figure 6 and Figure 7 show the changes in hydrogen production in terms of changes in the input power to the AEL and the volume flow of hydrogen, respectively.

Thus, in 60 min, the volumetric flow rate of hydrogen production will be equal to 4.85 mm/min. As a result, the average hydrogen production for this system can be considered as 5.07 mm/min. This means an hour of operation of the current suggested system leads to the production of 3 to 4 mL of hydrogen. There are several approaches to increasing hydrogen production by about 50 mL, such as increasing the level of electrodes. The electrodes used in recent experiments had the highest possible surface area, so that they could be placed in a chamber built into the electrolyzer. Moreover, Figure 8 illustrates the performance of the fuel cell under hot ventilation conditions, ambient temperature ventilation, and without ventilation.

The maximum power output of the fuel cell can be obtained when the air is preheated and enters the fuel cell through the fan. It is also concluded that aeration through the fan has a great effect on the output power of the fuel cell. Note that at this stage only the initial tests were performed on the fuel cell, with the help of dry hydrogen capsules. However, the final tests were performed with the help of a hydrogen-producing electrolyzer. This has also been tested in Figure 9 and Figure 10, in various modes.

As the potential difference between the two ends of the electrodes increases, the amount of hydrogen production increases to a point where the hydrogen output is almost constant and then decreases. The reason for the constant state and then the decrease in hydrogen production can be considered as the increase in resistance due to the fusion between the electrodes. In this regard, a part of the applied voltage must be used to overcome this resistance. The corresponding graph of voltage and current density in terms of power is shown in Figure 11. Figure 12 also shows the amount of hydrogen produced in three hours, which indicates the enhancement in the hydrogen production to about 800 mL.

After three hours of operation and storing the hydrogen in the hydrogen tanks, this system was able to produce 1008 W of power through the PEMFC. It should be noted that the nominal power input to the electrolyzer can be calculated. Thus, the hybrid system must use 90 watts per hour of power from the power supply to generate the required hydrogen for the fuel cells to generate an average of 1008 W of power in 20 min.

It is assumed that the system is constantly generating power with load variation during the day. It is considered that 8 a.m. to 10 p.m. is the high-power load demand and 10 p.m. to 8 a.m. is the low-power load demand. In addition, the power supply will produce at least 30 kW in all cases; hence, during low-power load demand, this can be carried out for 10 h. In this regard, in 10 h of low load, stored hydrogen will be able to produce 3.36 kilowatts of power during peak hours. In these conditions, power generation by the power supply, input power to the electrolyzer, the amount of stored hydrogen, and fuel-cell output power are 720 Wh, 300 Wh, 2800 mL, and 3.36 kW, respectively. Figure 13 shows twenty minutes of operation of the fuel cell.

3.2. Modelling Results

The hybrid system consists of the wind turbine, fuel cell, electrolyzer, hydrogen storage tank, and the DC to AC converter. In this section, after presenting the hypotheses, the modeling of a hybrid system built on a larger scale to supply electricity to 250 households is carried out. The obstacles ahead are examined, and a more complete model is presented. The Cohen region, which is known in Qazvin province as one of the windy regions of Iran along the corridor originating from the Alborz mountains range, was considered as the case study. The model assumptions were as follows:

• The system is intended to supply electricity to 250 households in the Cohen area.
• The average annual electricity consumption of each Iranian household is 2740 kWh.
• In July and August, electricity consumption reaches the highest level.
• Economic analysis is based on energy prices and current capital prices.
• The service life of the system is estimated at 20 years.
• A wind turbine with a horizontal axis and a life of 20 years and a capacity of 300 kW is considered.

In the lab-scale model of the hybrid system, the output power of the electrolyzer was about 50% and the production capacity of the fuel cell in the maximum state was 6.7% of the electrolyzer output. Considering these two values, the output power of the fuel cell is one to thirty, compared to the output power of the wind turbine. Achieving an optimal economic system requires examining different scenarios. Therefore, different capacities were considered for each component of the system and the system was simulated according to them. To simulate the system optimally, 1000 simulations were performed, of which 123 scenarios were able to meet the demands. In addition, the intended capacities for the system components are shown in

Table 6. Capacities taken into account for system components.

Converter (KW)	Hydrogen Tank (kg)	Electrolyzer (KW)	Fuel Cell (KW)	Wind Turbine (Number)
100	1500	200	100	3
200	2000	300	120	4
300	2500	400	150	-
400	3000	500	200	-
500	3500	600	-	-

. In this research, 100 to 500 KW converters with four turbines were used.

4. Conclusions

The suggested hybrid system in this study was evaluated using a lab-scale experimental setup, which was on a micro scale, to calculate the amount of hydrogen produced by the AEL and electricity generated by the PEMFC. According to the experiments performed on the hybrid system, it was found that in the AEL, increasing the distance between the plates enhances the resistance and decreases the AEL’s efficiency. The anode plates are corroded over time and the voltage increases, hence the electrolyte loses its properties, which increases maintenance costs. To increase the output power of the fuel cell, hydrogen and air must be preheated, and the hydrogen flow must be continuous. In addition, the moisture content of the fuel and the incoming air affect the output of the fuel cell. The maximum amount of hydrogen produced by the hybrid system was 304 mL per hour. The built-in hybrid system was able to increase the wind turbine power capacity by 1.8%.

In the hybrid system of the laboratory sample, the output power of the electrolyzer was about 50% and the power produced by the fuel cell in the maximum state was 6.7% of the electrolyzer output. Taking these two values into account, the power output of the fuel cell relative to the output power of the wind turbine was 1 to 30. Therefore, a hybrid system built to generate electricity for 250 households was modeled, and a case study was conducted on the system in the Cohen area. In the scenario of using four wind turbines, a fuel cell with a capacity of 200 KW, a 200 KW electrolyzer, a 3000 kg hydrogen tank, and a convertor with a capacity of 200 KW, the system was able to meet the approximate required demand.

Although this study covered important aspects, the following topics can be considered for future studies:

• The alkaline electrolyzer (AEL) is considered an efficient type in comparison to the proton-exchange membrane electrolyzers (PEME), considering the type of catalyst. In PEME, the catalyst is platinum (Pt) based, which increases the cost. However, AEL uses non Pt-based catalysts, which is why AEL is considered in the suggested integrated system. It can be interesting for the performance of the integrated system to be analyzed using the PEME instead of AEL, since the PEME has been more commercialized in comparison to AEL.
• Although AEL will reduce the overall cost of the suggested system and the electrolysis process, there are still debates on the stability and durability of AELs. In this regard, it can be interesting to dedicate concentrated efforts to analyzing the lifetime of the AELs in the combined systems with wind power stations.
• Devising the wind turbine energy as the main driver of the integrated system is also dependent on nature and its changes, which will result in changes in the wind speed. The unique intermittence and instability of wind power have brought major challenges to the stable operation of the power system, with operational temporal and spatial gaps between the consumption of the energy by the end-users and its availability [41]. In this regard, different energy storage technologies, in addition to the mentioned system, can be utilized to achieve stable and efficient renewable energy.
• Developing efficient membranes for PEMFC applications has been an interesting topic for the researchers in the field. Developing new materials to improve proton conductivity with lower costs will improve the performance of the PEMFC while considering the durability and water/thermal management. Additionally, review articles can be provided to gather together the existing knowledge of this component.