Comprehensive Investigation of Solar-Based Hydrogen and Electricity Production in Iran

Hydrogen is a clean and environmentally friendly energy vector that can play an important role in meeting the world’s future energy needs. Therefore, a comprehensive study of the potential for hydrogen production from solar energy could greatly facilitate the transition to a hydrogen economy. Because by knowing the exact amount of potential for solar hydrogen production, the cost-effectiveness of its production can be compared with other methods of hydrogen production. Considering the above, it can be seen that so far no comprehensive study has been done on finding the exact potential of solar hydrogen production in different stations of Iran and finding the most suitable station. Therefore, in the present work, for the first time, using the HOMER and ArcGIS softwares, the technical-economic study of solar hydrogen production at home-scale was done. The results showed that Jask station with a levelized cost of energy equal to $ 0.172 and annual production of 83.8 kg of hydrogen is the best station and Darab station with a levelized cost of energy equal to $ 0.286 and annual production of 50.4 kg of hydrogen is the worst station. According to the results, other suitable stations were Bushehr and Deyr, and other unsuitable stations were Anzali and Khalkhal. Also, in 102 under study stations, 380MW of solar electricity equivalent to 70.2 tons of hydrogen was produced annually. Based on the geographic information system map, it is clear that the southern half of Iran, especially the coasts of the Persian Gulf and the sea of Oman, is suitable for hydrogen production, and the northern, northeastern, northwestern, and one region in southern of Iran are unsuitable for hydrogen production. The authors of this article hope that the results of the present work will help the energy policymakers to create strategic frameworks and a roadmap for the production of solar hydrogen in Iran.


Introduction
1.1. The Necessity of Using Hydrogen. The continuous growth of the world's population and economy, along with rapid urbanization, has led to a significant increase in energy demand [1][2][3]. Power supply in the traditional form is based on fossil fuels, which have problems such as not being easy to extract, polluting, and being limited to a specific geographical area [4][5][6]. Therefore, the use of renewable energy (RE) is essential for the sustainability of future energy and global security [7][8][9]. Renewable energies, due to the nature of their variability and intermittency, require large energy storage systems to be able to manage supply and demand [10][11][12]. A good idea, which is a cost-effective solution for storing, transporting, and exporting large-scale RE, is to store hydrogen-based energy [13][14][15].
The heat generated by each unit of hydrogen mass is 3 times greater than that of gasoline. In addition, in hydrogen combustion, only water vapor is produced. Therefore, hydrogen energy is a suitable solution for future energy needs due to the environmental problems of fossil fuels [16].
An economic evaluation of renewable hydrogen production is very important for evaluating the durability and feasibility of selecting the type of technology. In this regard, the first step is to examine the potential for renewable hydrogen production at the under study site.

Perspective of Hydrogen
Production. Global hydrogen demand in 2013 was reported to be 255.3 billion m 3 , which in 2020 will reach 342.8 billion m 3 [17]. If the hydrogen economy improves, it should attract about $ 70 billion in investment by 2030. It is also noted that the cost of producing and distributing hydrogen from renewable sources will be reduced by 50% over the next decade [18]. It is also noted that hydrogen can meet up to 10% of the global warming demand of buildings by 2050 [19].
As shown in Figure 1 for the share of RE capacity in Iran's electricity, in April 2020 with 63 power plants, solar energy with 44% has the largest share among all renewable sources in Iran's electricity production [20]. Therefore, the focus of the present study for investigating the prospect of renewable hydrogen production in Iran is solar energy.
1.3. Different Ways of Producing Hydrogen. Today, most of the hydrogen produced (more than 90%) is from fossil fuels such as coal and natural gas, which is considered gray hydrogen and does nothing to reduce CO 2 emissions [21]. Various clean hydrogen production technologies are shown in Figure 2 [21]. As shown, the present study examines the hydrogen produced by the process of electrolysis using solar energy. In other words, the material, method, and energy source used in the present work are marked in yellow in Figure 2.
Water electrolysis is the process of breaking down water into oxygen and hydrogen, which is caused by an electric current. Today, about 4% of the world's hydrogen is produced by electrolysis. Economically, the cost of producing green hydrogen is 1.5-5 times greater than producing hydrogen from natural gas but with a 50% reduction in the price of electrolysis, as well as a reduction in the price of RE, green hydrogen will eventually become economical and be promoted [18]. The price range of hydrogen production technologies based on the energy source is shown in Figure 3 [21]. Based on the results of Figure 3 for hydrogen produced from solar energy, the price per kilogram will be $ 3.41-16.01 [21]. According to studies conducted by the authors of the present work, the reason for this wide range can be the difference in radiation intensity, cloudiness index, air temperature, the wide price range of different solar cell technologies, etc., in different parts of the world. Despite the high price, solar energy is the most abundant and available type of RE, which makes it a very likely option for future hydrogen production [22].
The performance ranking of different sources of hydrogen production is shown in Figure 4 [23]. As can be seen, solar energy has the best performance in terms of social, environmental, and reliability performance among different types of RE. Also, in terms of economic performance, solar energy ranks second after hydro energy. In terms of technical performance, after nuclear and wind energy, solar energy is in third place.

Different Uses of Hydrogen.
Reducing carbon and decarbonizing for use in transportation and electricity generation sectors is one of the goals of hydrogen production from various energy sources [18]. As shown in Figure 5, hydrogen can facilitate the connection between electricity and buildings, transportation, and industry [24]. Hydrogen produced from fossil fuels, which is widely used in several industrial sectors such as refineries, ammonia production, and chemical can be technically replaced by renewable hydrogen. In the home sector, injectable hydrogen into the gas network can reduce natural gas consumption. In addition, excess electricity can be converted to hydrogen and used as heat in winter [24]. In the transportation sector, vehicles based on fuel cells (FCs) that consume hydrogen have been considered because of their low carbon production. The important point is that in this regard, due to the limited capacity of batteries for long distances, the market for FC-based vehicles is very expandable [24].
1.5. Electrolysis Technologies in Iran. Electrolysis technologies are classified based on the electrolyte used in the electrolysis cell [25]. Proton exchange membrane (PEM) electrolysis is more common in Iran and is used in transportation, home generators, and small power plants [26] and has the greatest potential in the Iranian market for portable applications [27]. After PEM-type electrolysis, alkaline electrolysis with liquid electrolyte is widely used in Iran due to its high process efficiency. However, due to the possibility of liquid electrolyte leakage, it is not used for transportation, and its use is limited to military industries and small space applications [28].
1.6. Literature Review. In order to achieve a fully developed hydrogen economy and turn hydrogen into an important element for the energy market, extensive and significant research has been conducted on the potential for renewable hydrogen production in various parts of the world. Table 1 shows the literature review of recent studies in Iran.  Given the important role of hydrogen in the future portfolio of global energy, it is necessary to do comprehensive work to find the potential of all stations in Iran. Also, finding the most suitable solar hydrogen station can help Iranian energy policymakers. In addition, most of the works done are purely potential assessment, and technical-economic optimization has not been done. Therefore, in the present work, for the first time, the potential of hydrogen production from water electrolysis in 102 stations in Iran at home-scale has been evaluated. The cost of renewable electricity produced for water electrolysis is calculated taking into account the up-to-date prices of equipment as well as the actual annual interest rate, and the results are presented in the form of GIS maps for ease of decision-making.

Under Study Stations
A total of 102 stations have been evaluated to assess the potential of solar electricity and hydrogen in Iran. The reason for choosing these stations was the availability of 20-year average climate data on the NASA website. The location of the under study stations on the Iran map and their annual average climate data, i.e., the solar radiation intensity and the air clearness index, are shown in Figures 6(a) and 6(b), respectively. Solar radiation data and air clearness index will be used as input to the HOMER software to perform technical-economic calculations.

Software's and Data Used
The HOMER and ArcGIS softwares are used for the analysis in the present study. The HOMER software is used to find the  3 International Journal of Photoenergy amount of electricity generated by solar cells, and the ArcGIS software is used to display suitable and unsuitable places to use solar energy.
3.1. Solar-Based Electricity Production. The HOMER software uses the following equation for the amount of solar elec-tricity generated [47]: where Y PV is the rated capacity of PV cells in terms of kW, f PV is the derating factor, H T is the solar radiation collides with the surface of the PV under operating conditions in  International Journal of Photoenergy  Figure 6: Climatic data of under study stations in Iran: (a) solar radiation intensity; (b) air clearness index [46]. 6 International Journal of Photoenergy For the solar cells used in the present work, the lifetime is 20 years [48], the derating factor is 90% [49], the angle of the solar cells is equal to the latitude of the under study site [50], the orientation of the solar cells is to the south [51], and the ground reflection coefficient is 20% [52]. The cost of buying and replacing solar cells is $ 3200 and $ 3000 per kW, respectively [53]. Also, the annual operating and maintenance cost of solar cells, which mainly includes cleaning and can be done by the operator itself, are considered zero [54].
The HOMER software calculates the air clearness index (k T ), which is a very important and influential parameter in the performance of solar cells by the following equation [55]: where H is the monthly average daily irradiation on a horizontal plane at the Earth's surface and H oh is the monthly average daily value of extraterrestrial radiation energy falling on a horizontal plane.
H is given to the software as input, and the software calculates the value of H oh using latitude and by the following equations [55]: where H oh is the extraterrestrial radiation in terms of Mj/m 2day, G sc is the solar constant and equal to 0.082 Mj/m 2 -min, d r is the inverse relative distance earth-sun, n is the number of day in the year, ω s is the sunset hour angle in terms of radian, φ is the latitude in terms of radian, and δ is the declination of the sun in terms of radian. Economic calculations in the HOMER software include determining the LCOE parameter performed by the following equation [56]: where C ann,total is the sum of the annual costs and E Load served is the cost of the system's actual electrical load in terms of kWh/year.

Hydrogen-Based Electricity
Production. Water electrolysis requires an external energy carrier to carry out the process of separating oxygen and hydrogen. Among the types of energy carriers, solar energy is one of the main and justifiable    [57]. To calculate the potential of solar hydrogen production in different stations located in eight climates of Iran (cold, very cold, moderate and rainy, semimoderate and rainy, semiarid, hot and dry, very hot and dry, and very hot and humid), the amount of generated solar power (P PV ) was first calculated by the HOMER software (equation (1)). Then, using an analytical analysis according to equation (8), the amount of hydrogen produced per year per kilowatt of solar cells used to generate electricity was estimated [58]. Also, due to the high efficiency, conditions in the Iranian market, and the longer average lifetime [59], the type of technology desired for water electrolysis in the present work is PEM.
In the above relation, η ele is the electrolyzer efficiency in terms of percentage, which is considered 75% in the present work, and HHV H 2 is the high heating value of hydrogen, which is 39.4 kWh/kg.

Assessment of the Areas by GIS Map. GIS technology by
collecting and combining information from a conventional database provides information for map preparation by illustrating and using geographical analyzes. This information is used to make events clearer, to predict results, and to draw maps [60].
The use of spatial relationships between data in interpolation methods increases the accuracy of estimating radiation potential for different regions. In the present paper, the inverse distance weighting (IDW) internalization method is used. Calculations in IDW depend on two factors: select the power of p in formula w = ð1/dÞ p and the position of the adjacent points, or in other words, the position of the neighboring units. The default value for p is considered to be 2, and for this value, the name of the method is the inverse distance squared weighted [61]. As shown in Figure 7, the point weight window includes a list of weights given to each point that are used to predict a value at the target location. In the IDW method, the points closest to the desired location weigh more than the farthest points, and the weight decreases with increasing distance. Table 2 shows the results of the studies. As can be seen, Jask stations with a LCOE of $ 0.172 and Darab with $ 0.286 have the highest and lowest prices per kWh of solar electricity produced, respectively. Bushehr and Deyr stations with 0.178 $ are in the second place of lowest LCOE value, and Anzali station with $ 0.271 is in the second place of largest LCOE value. The average LCOE for the 102 under study stations is $ 0.206.

Results
According to the results of Table 2, the highest and lowest operating hours of solar cells during the year with values of 4399 and 4348 are related to Chabahar and Khash stations, respectively. Also, the average operating hour of solar cells for the under studied stations is 4382. The reason why the maximum and minimum operating hours of solar cells do not correspond to the highest and lowest solar power generation and therefore the highest and lowest LCOE values can be due to factors such as air cloudiness and radiation intensity.
According to the results of Table 2, Jask and Darab stations have the highest and lowest capacity factor with 25.1% and 15.1%, respectively. The capacity factor, which is actually the average output power divided by the nominal capacity of solar cells, is on average 21.21% for all under study stations.
Based on the results, it can be seen that the top 3 stations in the field of solar power generation are Jask, Bushehr, and Deyr stations, which produce 4401, 4267, and 4254 kWh of electricity per year, respectively. Based on the location of renewable power plants in Iran, which are mainly in the central of Iran [62] and given that the top stations generate solar electricity in the southern margins of the country, more attention needs to be paid to Jask, Bushehr, and Deyr stations. The three stations that have produced the least solar electricity are Darab, Anzali, and Khalkhal, which generated 2648, 2792, and 2838 kWh of electricity per year, respectively. The reason for this low production can be climatic factors such as high cloudiness and low radiation intensity. According to the results, the total solar power generated in the 102 stations surveyed will be 380 MWh per year which the average of each station is about 3.7 MWh per year. This result can be very important for decision-makers and policymakers in the field of a distributed generation because so far no comprehensive work has been done to assess the production of solar electricity in Iran.
According to the results, Jask station with an annual production of 83.8 kg of hydrogen was able to obtain the first 10 International Journal of Photoenergy rank in the production of hydrogen on a home scale. The lowest amount of hydrogen production with 50.4 kg per year is related to Darab station. Other top stations in the field of hydrogen production are Bushehr and Deyr, and other unsuitable stations in the field of hydrogen production are Anzali and Khalkhal. According to statistical calculations, the total amount of hydrogen produced in the under studied stations was 7.2 tons per year, with each station producing an average of 70.8 kg of hydrogen per year. In order to better evaluate and understand finding suitable and unsuitable areas for home-scale hydrogen production in Iran, the hydrogen production map in Iran has been drawn using the GIS software in Figure 8. Based on Figure 8, it is clear that the southern half of Iran, especially the coasts of the Persian Gulf and the Gulf of Oman, is suitable for hydrogen production, and the northern, northeastern, northwestern, and one region in southern of Iran are unsuitable for hydrogen production.

Conclusion
Hydrogen can become an important medium for storing RE to become clean electricity if needed. In other words, by using hydrogen, RE can be effectively stored and transferred over long distances and over a long period of time [23]. Therefore, hydrogen is an essential element for becoming 100% RE sys-tems and eliminating the phenomenon of global warming.
Since it is very important for decision-makers and policymakers in the field of distributed generation to know the potential of electricity and hydrogen production on a home scale, in the present work, this issue has been studied for the first time in Iran. Technical-economic investigations have been conducted by the HOMER software on the average 20-year radiation data of 102 stations in Iran. Finally, for better understanding, the ArcGIS software provides a home-scale hydrogen production potential map. The main results are as follows:  Electrolyzer efficiency (%) Hoh: Extraterrestrial radiation (MJ/m 2 -day) φ: Latitude (radian) d r : Inverse relative distance earth-sun n: Number of the day during the year (-) C ann,total : Total annual cost ($) E load served : Real electrical load by the system (kWh/year) δ: Declination of the sun (radian) H: Monthly average daily radiation on a horizontal plane (MJ/m 2 -day) HHV H 2 : Higher heating value of the hydrogen (39.4 kWh/kg).

Data Availability
All data used to support the findings of this study are included within the article.

Conflicts of Interest
The authors declare that they have no conflicts of interest.