An optimal standalone wind-photovoltaic power plant system for green hydrogen generation: Case study for hydrogen refueling station

Results in Engineering 22 (2024) 102234 Available online 6 May 2024 2590-1230/© 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/bync/4.0/). An optimal standalone wind-photovoltaic power plant system for green hydrogen generation: Case study for hydrogen refueling station Rizk M. Rizk-Allah a , b , Islam A. Hassan c , Vaclav Snasel a , Aboul Ella Hassanien d , e , 1 , * a Faculty of Electrical Engineering and Computer Science, Vˇ SB-Technical University of Ostrava, 70800 Poruba-Ostrava, Czech Republic b Basic Engineering Science Department, Faculty of Engineering, Menoufia University, Shebin El-Kom 32511, Egypt c Mechanical Power Engineering Department, Faculty of Engineering, Zagazig University, Zagazig, 44511, Egypt d College of Business Administration (CBA), Kuwait University, Kuwait e Faculty of Computers and AI, Cairo University, Egypt ARTICLE INFO Keywords: Hydrogen refueling station Renewable energy power Levelized hydrogen cost Optimization Sustainability ABSTRACT Sustainability goals include the utilization of renewable energy resources to supply the energy needs in addition to wastewater treatment to satisfy the water demand. Moreover, hydrogen has become a promising energy carrier and green fuel to decarbonize the industrial and transportation sectors. In this context, this research investigates a wind-photovoltaic power plant to produce green hydrogen for hydrogen refueling station and to operate an electrocoagulation water treatment unit in Ostrava, Czech Republic’s northeast region. The study conducts a techno-economic analysis through HOMER Pro® software for optimal sizing of the power station components and to investigate the economic indices of the plant. The power station employs photovoltaic panels and wind turbines to supply the required electricity for electrolyzers and electrocoagulation reactors. As an offgrid system, lead acid batteries are utilized to store the surplus electricity. Wind speed and solar irradiation are the key role site dependent parameters that determine the cost of hydrogen, electricity, and wastewater treatment. The simulated model considers the capital, operating, and replacement costs for system components. In the proposed system, 240 kg of hydrogen as well as 720 kWh electrical energy are daily required for the hydrogen refueling station and the electrocoagulation unit, respectively. Accordingly, the power station annually generates 6,997,990 kWh of electrical energy in addition to 85595 kg of green hydrogen. Based on the economic analysis, the project’s NPC is determined to be € 5.49 M and the levelized cost of Hydrogen (LCH) is 2.89 € /kg excluding compressor unit costs. This value proves the effectiveness of this power system, which encourages the utilization of green hydrogen for fuel-cell electric vehicles (FCVs). Furthermore, emerging electrocoagulation studies produce hydrogen through wastewater treatment, increasing hydrogen production and lowering LCH. Therefore, this study is able to provide practicable methodology support for optimal sizing of the power station components, which is beneficial for industrialization and economic development as well as transition toward sustainability and autonomous energy systems. Nomenclature Abbreviations Symbols and Subscripts NPC Net Present Cost Bcapacity The battery’s capacity LCH Levelized cost of Hydrogen Cp Coefficient of performance FCVs Fuel-cell electric vehicles Disdep Depth of discharge (continued on next column) (continued) RESs Renewable energy sources Effbat Battery’s efficiency PI Proportional integral Gt Solar irradiation SM Sliding mode Hn Hydrogen produced in the nth year BS Backstepping Hload Hydrogen load FL Fuzzy logic HVH2 Hydrogen’s heating value (in kWh) (continued on next page) * Corresponding author. College of Business Administration (CBA), Kuwait University, Kuwait. E-mail address: [email protected] (A.E. Hassanien). 1 Scientific Research School of Egypt (SRSEG) www.egyptscience-srge.com. Contents lists available at ScienceDirect Results in Engineering journal homepage: www.sciencedirect.com/journal/results-in-engineering https://doi.org/10.1016/j.rineng.2024.102234 Received 9 March 2024; Received in revised form 1 May 2024; Accepted 5 May 2024 Results in Engineering 22 (2024) 102234 2 (continued) ANNC Artificial neural network control HVEP Equivalent heating value of one kWh of electrical energy BSIAC Backstepping and integral action control ˙ mH2 Hydrogen mass flowrate (kg/hr) FCHEVs Fuel cell hybrid electric vehicles PEL Electrolyzer consumed power (in kW) EVs Electric vehicles Ppv Power output of PV HRS Hydrogen refueling stations Pwt Wind turbine power PV Photovoltaic Rwt Radius of the blade EC Electrocoagulation Scapacity Hydrogen tank’s storage capacity EU European Union Sp Total area that the PV panels cover SREP Stand-alone renewable energy power Ta PV panels’ temperature REPP Renewable energy power plant TCn Project’s total expenses per nth year O&M Operational and maintenance costs Vbat Battery’s voltage Vw Wind speed η El Electrolyzer efficiency η p Efficiency of PV panels ρ a Air density 1. Introduction 1.1. Overview of hydrogen technology-based transition trend Concerns such as climate change and the exhaustion of fossil fuels have driven the search for sustainable alternatives to traditional energy sources [1]. Globally, there has been a need for renewable energy sources (RESs) [2]. Hydrogen is regarded to be the cleanest fuel, especially when produced using RESs [3]. Moreover, its production from RESs via electrolysis technologies provides a way to stabilize energy grids and easily integrate into existing infrastructures, in addition to achieving zero greenhouse gas emissions [4]. Hydrogen production from RESs is essential to meet the essential requirements for sustainability and address the energy and environmental challenges in a flawless, competent, convincing, and fair manner. It is anticipated that creative approaches for producing hydrogen would enhance system design, ecological preservation, asset and resource utilization, and efficiency [5,6]. Numerous study groups have worked extensively on scientific investigation, technology innovation, and research on hydrogen production advancement [7,8]. The practicality of both traditional and innovative hydrogen production methods largely depends on new developments that maximize their potential while minimizing their detrimental impacts on the environment. Authors in Ref. [9] examined the microbial methodology for hydrogen production and highlighted operational and technical difficulties. In a different study, authors in Ref. [10] provided an overview of different fermentation approaches that include dark, photo, and integrated fermentative modes of producing hydrogen. Authors in Ref. [11] revealed that catalytic hydrogen production techniques can generate hydrogen from biomass. Recently, authors in Ref. [12] used alkaline water electrolysis created with a handmade alkaline electrolyser to produce a sizable amount of hydrogen. Since the new infrastructure needed to collect, store, and transport hydrogen is so expensive, the development of hydrogen energy technologies has been comparatively slow. Several studies have considered the optimization of components capacity for renewable energy generating system. Furthermore, extensive research has been performed in the field of maximizing and controlling the wind power output utilizing the optimal wind speed via intelligent controller. Chojoa et al. [13] have investigated integral sliding mode and field-oriented controller to manage active and reactive power for grid-connected systems. Chojoa et al. [14] have assessed the utilization of a robust artificial controller to enhance the dynamic performance of the wind turbine system. Throughout the study, an energy management algorithm determined the charging mode and power distribution between the grid and the storage system. Moreover, Chojoa et al. [15] have utilized an artificial neural network-based controller to achieve the same objectives. In Ref. [16], an emerging second-generation CRONE controller has been evaluated for achieving maximum power generation, high stability and favorable dynamic characteristics when applied for a real wind speed variation. In terms of dynamic characteristics, CRONE controller has shown better system performance than other controllers including proportional integral (PI), sliding mode (SM), backstepping (BS), fuzzy logic (FL) controllers. A comparative study [17] has been carried out to determine the best controller for wind turbine system. PI, SM, BS and FL have been compared to artificial neural network control (ANNC). According to the simulation results on MATLAB/Simulink software, ANNC have demonstrated the best performance. Furthermore, a robust nonlinear controller involving backstepping and integral action control (BSIAC) has been assessed as a solution to overcome the catastrophic effects of the network fault [18]. Thanks to BSIAC, the reactive power sustainment has been optimized at higher value than the case of PI controller. 1.2. Necessity for the green transportation sector The emission of CO 2 , SO x , and NO x continues to rise, driven by the increasing number of vehicles in use worldwide [19]. Indeed, the global emission of greenhouse gases attributed to the mobility sector alone accounts for 12 % of its overall quantity [20]. Investments in the green transport industry can play a crucial role in substantially decreasing greenhouse gas emissions. The green mobility industry includes fuel cell hybrid electric vehicles (FCHEVs), and electric vehicles (EVs) are all included in the green mobility sector [21]. The new vehicles’ production and technological advancement have grown significantly during the last decade. Nonetheless, the fuel and power needed to charge green transportation should be generated using green energy sources in order to meet sustainability targets and lower greenhouse gas emissions [22]. Furthermore, there are several benefits of green mobility over traditional fossil-fuel-based transportation. In addition to offering drivers a comfortable environment, green vehicles are also regarded as completely clean and silent vehicles [23]. Electricity is used to charge the EVs while hydrogen gas is used for refueling the FCVs [24]. FCVs have several advantages, including longer traveling distances and shorter refueling periods compared to battery electric vehicles [25]. FCVs utilization is a significant technique for decarbonizing the transportation industry, especially for long-distance purposes. Nonetheless, challenges related to the advancement of hydrogen generation methods, cost containment, and infrastructure development stand in the way of the broad use of FCVs. In this sense, ongoing research and development endeavors aim to improve fuel cell and fuel cell vehicle performance, cost, and accessibility, thereby making a valuable contribution to the future of clean transportation. Due to the shift towards a sustainable and clean energy future, there has been a growing interest in hydrogen as an alternative fuel. In fact, hydrogen is a promising energy carrier that is currently used in chemical industries and could be used in the production of green fuels in the future [26]. Europe accounted for 38 % of the world’s hydrogen refueling stations (HRS) in 2021, with a total of about 550 HRS in operation [27]. More refueling and charging facilities are needed in the clean mobility industry to supply the energy source needed for the new generations of vehicles. The most efficient way to boost system resilience is using hydrogen storage tanks. Furthermore, vehicles equipped with hydrogen tanks reduce system operator hydrogen demand reduction and boost power reliability [28]. According to a study on solar-powered hydrogen refueling stations, a 2 MW photovoltaic (PV) power plant in Tunisia can produce the necessary fuel which is approximately 150 kg of green hydrogen per day [29]. Additionally, it is suggested that wind energy be used to create green hydrogen for Saudi Arabian refueling R.M. Rizk-Allah et al. Results in Engineering 22 (2024) 102234 3 stations [30]. Most of the suggested renewable energy technologies are grid-connected. There is a range of 7.5 € /kg to 9.34 € /kg for the levelized cost of Hydrogen (LCH) [31]. Analytical models and optimization tools were used to size and optimize the green hydrogen refueling stations [32]. According to case studies and analysis, the cost of producing green hydrogen in Argentina is approximately 3.2 € /kg [33]. Having a high specific energy capacity, 132 kWh/m 3 , hydrogen is an excellent medium for storage. Furthermore, water is the product during the process of hydrogen conversion into energy, producing no greenhouse gases. Hydrogen also demonstrates a transformational nature [34]. Electrocoagulation (EC) is a reliable technology for treating wastewater. EC is an electrochemical process in which anodes, often made of aluminum or iron electrodes, undergo corrosion to release active coagulants into the solution. The key advantages of EC compared to conventional techniques like chemical coagulation and adsorption include the "in situ" delivery of reactive agents, the absence of secondary pollution generation, and the compact nature of the equipment [35]. Numerous studies have proven the potential of EC in the treatment of a variety of wastewater [36–39]. On the other hand, HOMER software has been extensively employed to optimize a renewable based energy system to while supplying the required power for water treatment plant. In this context, a technoeconomic study has been performed, using HOMER software, to evaluate the benefits from sewage treatment process utilization to produce biogas [40]. The study has simulated the process using real treatment plant data which demonstrated the great potential of the methodology to provide up to 55 % of the plant’s electricity consumption. Erdal et al. [41] have optimized a hybrid renewable diesel microgrid system to provide the required electricity for a wastewater treatment plant in Turkey using HOMER PRO software. Owing to high renewable fractions, about 770 tons of hazardous gases have been avoided. In Ref. [42], the technical and economic performance of two proposed grid and off-grid renewable based plants have been assessed when employed to supply a drinking water treatment plant in Ecuador in two different operating modes. Throughout the study, HOMER PRO software has been employed to determine the optimum capacity for each component in each scenario to achieve the minimum net present cost. Battery price directs the optimum capacity towards increasing the power generating components rather than increasing the storage system capacity. In Ref. [43], a multi-objective nonlinear dynamic model has been developed for optimal design and performance investigation of grid-connected hybrid renewable system providing a drinking water treatment plant. Moreover, LINGO software has been applied for a case study in China. According to the study, the utilization of onsite hybrid power generating system in water treatment units could enhance energy transformation and reduce greenhouse gases. Notwithstanding the abundant availability of wastewater from various sources, including meat and poultry processors, metal plating facilities, textile manufacturing industries, and steam cleaners [44], the sustainability regarding optimizing hydrogen generation from RESs and water recovery from EC process has not, to the best of our knowledge, been previously examined in literature. By incorporating the EC station with hydrogen production-based stand-alone renewable power station, sustainability and mobility can be improved. 1.3. Literature review Various research studies in the wider domain investigated the most efficient sizes for hydrogen refueling stations that are operated by renewable energy systems. Barhoumi et al. [45] conducted a study on obtaining the most efficient size for a hydrogen refueling station that can dispense 150 kg of hydrogen fuel per day. In this study, the investigation involved the production of hydrogen fuel by an on-site water electrolysis device that was driven by a solar photovoltaic array. The findings indicated that the price of hydrogen amounts to 3.32 € /kg. Mastropasqua et al. [46] assessed the practicality of producing hydrogen fuel with a high temperature electrolysis unit powered by a parabolic solar dish system, while maintaining the same daily dispensing capacity. The cost of hydrogen ranges from 5.9 to 9.1 € /kg. In their study, Gu et al. [47] conducted a comparison of several hydrogen supply routes that were combined with solar energy for a hydrogen refueling station. The station had a daily capacity to dispense 500 kg of hydrogen. This study examined hydrogen production using water electrolysis, and coal gasification, both on-site and off-site. The results indicate that the cost of distributing hydrogen is 13 RMB/kg for gaseous hydrogen refueling stations, whereas it is 14 RMB/kg for liquid hydrogen refueling stations. In all the aforementioned investigations, solar energy was employed to drive the hydrogen production and to power the refueling station. Moreover, wind energy has been employed in several studies for the purpose of supplying electricity to hydrogen refueling stations. Ayodele et al. [48] investigated the most efficient configuration for a hydrogen refueling station that is powered by wind turbines. Hydrogen was generated on-site using the process of water electrolysis, resulting in a minimal cost of 6.34 $/kg of hydrogen. Wang et al. [49] examined the optimum size of a hydrogen refueling station when the generation of green hydrogen was driven by offshore wind turbines. The findings indicated that the price of hydrogen falls within a range of $11.8 to $15 per kilogram. In addition, Siyal et al. [50] assessed the economic aspects of a wind-powered hydrogen refueling station that provides hydrogen fuel to 200 vehicles daily. This study utilizes two distinct wind turbines: the Vestas 112 (V112) and the Vestas 82 (V82). The results indicate that the lowest price of hydrogen is 5.18 $/kg for refueling stations operated by V112 wind turbines, and 6.52 $/kg for stations powered by V82 wind turbines. Hybrid solar/wind systems have been utilized in numerous studies to generate the necessary electricity for hydrogen synthesis in hydrogen fueling stations. Murat and Kale [51] evaluated the technological and economic feasibility of a hydrogen filling station that is powered by an off-grid hybrid renewable energy system, specifically solar and wind energy. The purpose of the station was to supply hydrogen fuel for 25 vehicles daily. The findings indicated that the price of hydrogen is 8.92 $/kg. Viktorsson et al. [52] performed a lifecycle cost analysis for hydrogen refueling stations with a specific focus on those with a daily dispensing capacity of 65 kg. Hydrogen fuel was generated using an alkaline water electrolysis equipment that was powered by a solar/wind system connected to the grid. The findings indicated that the price of hydrogen amounts to 10.3 euros per kilogram. Tang et al. [53] conducted a comparison of the feasibility of hydrogen fuel production for hydrogen refueling stations utilizing a hybrid solar/wind system in both off-grid and on-grid scenarios. The results indicated that the price of hydrogen fuel was comparatively lower in the grid-connected scenarios, ranging from 3.5 to 7.2 € /kg. No study has examined the impact of people’s availability on the desire for refueling. Existing research indicates that the majority of techno-economic studies on renewable powered hydrogen refueling stations have been carried out in Europe. For instance, Bansal et al. [54] assessed the most efficient size of a hydrogen refueling station in Denmark that can dispense 40 kg of hydrogen per day. This project involved the production of hydrogen by an on-site water electrolysis device, utilizing electricity generated by both wind turbines and the electric grid. In a similar manner, Gruger et al. [55] addressed the optimum size of a hydrogen refueling station in Germany that has a dispensing capacity of 53 kg/day. This was achieved by utilizing an on-site water electrolysis plant that is powered by grid-connected wind turbines. The price of hydrogen was 12 € /kg for a fleet consisting of 200 fuel cell electric vehicles. However, in Monforti et al.’s study [56], hydrogen is generated off-site through the process of biomass gasification and water electrolysis. This hydrogen is then used to fuel a refueling station in Italy, which has a dispensing capacity of 65 kg/day. The study found that the cost of hydrogen was 12.71 € /kg for electrolysis and 5.99 € /kg for biomass gasification. Several further investigations were carried out in several European nations, including Italy [56–63], Sweden [50,53], Croatia [64], and Belgium [52]. In addition to Europe, feasibility studies on hydrogen refueling stations R.M. Rizk-Allah et al. Results in Engineering 22 (2024) 102234 4 have been carried out in many countries like China [47,49,65,66], Turkey [51,67,68], USA [46,69], Tunis [45], Canada [70], and Oman [31]. The results of all the aforementioned articles regarding the most efficient size of hydrogen refueling stations are presented in Table 1. The ever-increasing demand for green hydrogen production and demand within the European Union (EU) highlights a significant gap in understanding and addressing the needs of individual member states. Despite the global demand for hydrogen reaching 90 Mt in 2020, key EU nations such as Germany, the Netherlands, Poland, and Spain accounted for a substantial portion of this demand and production capacity. However, this falls short of fully meeting the growing demand within the EU, as demonstrated by the ambitious targets set by countries like Slovakia, Poland, and notably, the Czech Republic, for hydrogen production by 2030. In particular, the Czech Republic aims to produce 101 kt/year of H 2 by 2030, signaling a critical shift towards hydrogen-based energy solutions [71]. Additionally, the current reliance on hydrogen imports to meet electricity demands from RESs in countries like Germany and the Czech Republic underscores the need for comprehensive research and strategic planning to enhance domestic hydrogen production capabilities and ensure sustainable energy security within the Table 1 Overview of recently published studies on hydrogen refueling stations. Authors Ref. Location year Power source Dispensing capacity (kg/ day) Process of producing hydrogen Hydrogen production location LCOH Barhoumi et al. [45] Tunis 2021 Solar 150 Electrolysis On-site 3.32 € /kg Mastropasqua et al. [46] USA 2020 Solar 150 Electrolysis On-site 5.9 to 9.1 € /kg. Gu et al. [47] China 2020 Solar 500 Coal gasification and Electrolysis On-site/Off-site 13 RMB/kg (gaseous) 14 RMB/kg (liquid) Ayodele et al. [48] South Africa 2021 Wind 125 Electrolysis On-site 6.34 $/kg Wang et al. [49] China 2022 Wind 500, 800 and 1000 Electrolysis Off-site 11.8–15.0 Siyal et al. [50] Sweden 2015 Wind 1600 Electrolysis On-site 5.18 $/kg urat and Kale [51] Turkey 2018 Solar/Wind 125 Electrolysis On-site 8.92 $/kg Viktorsson et al. [52] Belgium 2017 Solar/Wind/ Grid 65 Electrolysis On-site 10.3 € /kg Tang et al. [53] Sweden 2022 Solar/Wind/ Grid 125 Electrolysis On-site 6.9 to 14.87 € /kg for off-grid 3.4 to 7 € /kg for on-grid Bansal et al. [54] Denmark 2020 Wind/Grid 40 Electrolysis On-site NA Grüger et al. [55] Germany 2018 Wind/Grid 53 Electrolysis On-site 97 € /kg (fleet of 10 FCEVs) 23 € /kg (fleet of 50 FCEVs) 12 € /kg (fleet of 200 FCEVs) Monforti et al. [56] Italy 2018 Grid 65 Electrolysis and Biomass gasification Off-site 12.71 € /kg for water electrolysis 5.99 € /kg for biomass gasification Minutillo et al. [57] Italy 2021 Solar/Grid 50, 100 and 200 Electrolysis On-site 9.29 € /kg for system with 50 % grid penetration for capacity of 200 kg/day. Fragiacomo and Genovese [58] Three Italian cities: Capo Suvero, Cosenza and Civita. 2020 Solar/Wind/ geothermal/ Grid 287, 180 and 22 Electrolysis On-site 6.9–9.85 € /kg. Perna et al. [59] Italy 2020 NA 200 Ammonia cracking. On-site 7.35 € /kg Di Micco et al. [60] South of Italy 2022 Solar/Grid 450 Electrolysis On-site 10.71 € /kg Perna et al. [61] Italy 2022 Solar/Grid 450 Ammonia cracking, Biogas reforming and water electrolysis. On-site 7.92 € /kg (electrolysis) 7.25 € /kg (Biogas) 6.28 € /kg (ammonia) Silvestri et al. [62] Italy 2022 Solar/Grid 200 Electrolysis On-site 9.02 € /kg and 7.86 € /kg Minutillo et al. [63] Italy 2021 SOFC technology 100 Ammonia On-site 6-10 € /kg Jakov et al. [64] Croatia 2022 Wind 100 to1000 Electrolysis On-site/Off-site 16.58 € /kg for 100 kg/day to 13.51 € /kg for 1000 kg/day Pang et al. [65] China 2022 Solar/Wind 165 Electrolysis On-site Total life cycle cost: $ 23,332,240 for Load A and: $ 25,019,872 for load B. Chen et al. [66] China 2021 Solar/Wind/ Grid 500 Electrolysis On-site/Off-site NA Turkdogan [67] Turkey 2020 Solar/Wind 1 (weekday) 1.5 (weekend day) Electrolysis On-site 6.85 $/kg Murat and Kale [68] Turkey 2018 Solar/Wind 125 Electrolysis On-site 7.52 $/kg Zhao and Brouwer [69] United States of America 2015 Solar/Wind 24 kg/week Electrolysis On-site 9.14 $/kg (solar-powered plant) 6.71$/kg (wind powered) Yaïci and Longo [70] Canada 2022 NA NA Steam methane reformation and Electrolysis On-site/Off-site For 100 % technology integration: 8.3–25.1 CAD$/kg For 10 % technology integration: 12.7–34.1 CAD$/kg Barhoumi et al. [31] Oman 2022 Solar/Grid 160 Electrolysis On-site 5.5 € /kg for on-grid PV. 5.74 € /kg for off-grid PV/ batteries. 7.38 € /kg for off-grid PV/fuel cells. R.M. Rizk-Allah et al. Results in Engineering 22 (2024) 102234 5 region. Motivated by these challenges, this study represents a pioneering effort in assessing the economic aspects of a wind-solar-powered hydrogen refueling station in the Czech Republic, laying the groundwork for future development in this area. To the best of our knowledge, no attempts have assessed the feasibility of renewable powered hydrogen refueling stations in the Czech Republic. 1.4. Shortcomings of grid-connected refueling station United States of America, China, Japan, and several European countries have established grid-connected EV charging stations [72]. However, there are a number of issues and consequences for the electrical grid with grid-connected charging stations [73,74]. The critical points of connection, safety, and power quality are the three key EV charging station [75]. Indeed, the stability of the distribution power networks is impacted by the EVs’ intermittent charging cycles. Additionally, the network’s distribution transformers and protective devices must be redesigned and optimized in order to integrate EV charging stations [75]. Consequently, the distribution power system components must be upgraded in order to include renewable energy power plants for the EV charging station. Furthermore, creating an energy management system for EV charging stations to implement a scheduling plan for EV charging becomes imperative to prevent technical problems [76]. 1.5. Novelty of the paper To produce clean fuel and avoid the negative impacts of charging stations for EVs on the distribution power network, the stand-alone station, denoted as off grid power station, provides a fascinating means of supplying FCVs with green hydrogen [77]. Moreover, to meet the industries’ water demand and make up for the lack of freshwater supplies, EC is incorporated to treat the discharged wastewater, which is environmentally friendly, especially when electricity is produced from RESs. In this regard, this paper presents a stand-alone power station incorporating EC station for generating green hydrogen for refueling FCVs as well as treating wastewater to supply water required for industrial requirements. It is composed of main generation units such as PV panels and/or wind turbines, and energy storage equipment such as batteries and hydrogen storage tanks. The stand-alone renewable energy power (SREP) station is more stable and independent when it comes to supplying green hydrogen for the refueling station and electricity for the EC station. The most efficient SREP is identified through the analysis of Net Present Cost (NPC), and LCH. Achieving the optimal sizes for wind turbines, PV panels, batteries, and electrolyzers improves the power station’s overall effectiveness and economics and extends its operational lifetimes. This study investigates the potential benefits of installing off-grid hydrogen refueling stations and electrocoagulation wastewater treatment units in Ostrava, Czech Republic’s northeast region. The key contribution of this study can be succinctly described as follows. ⁃ Developing a fully islanded green hydrogen production system. ⁃ Coupling large-scale electrocoagulation and hydrogen loads in a novel offering model. ⁃Testing the model using the climatic conditions in one of the industrial cities in the Czech Republic. ⁃ Optimization and sizing assessment of the RESs scheme using HOMER-Pro software. ⁃ Assessing the Czech Republic’s cost-effective potential to generate green hydrogen. The sections of this paper are organized in the following order: Section 2 overviews the renewable energy schemes. Section 3 provides the method and approach of system optimization. Section 4 offers the obtained results and discussions. Section 5 offers the conclusions and perspectives. 2. Overview of the renewable energy schemes 2.1. Renewable energy characteristics The Ostrava of the north-eastern part of the Czech Republic is characterized by mild warm climate with plenty of RESs, e.g., wind and solar. Indeed, Ostrava’s daily average solar radiation is approximately 2.89 kWh/m 2 . In the Ostrava wind farm, the average wind speed is about 5.69 m/s. Moreover, Ostrava represents one of the largest industrial cities in Czech Republic. Therefore, Ostrava city set a target not only to reduce the emission of CO 2 utilizing green transportation system but also to meet the industries’ requirements from the water by means of EC technology. The chosen site is located in the north-eastern of Czech Republic, as illustrated in Fig. 1. The coordinates of the site are 49.83465, 18.28204. The altitude of the site is 260 m [78]. 2.2. Electrocoagulation perspective The EC process offers a simple, trustworthy, and cost-effective approach for treating wastewater without the need of extra chemicals, reducing secondary pollution. It also decreases the amount of sludge that must be disposed of. In the EC technique, a direct current source is used between metal electrodes immersed in polluted water. Metal hydroxides are developed when an adequate current is applied to soluble metal electrodes. Metal hydroxides serve as coagulants, resulting in removing a variety of pollutants. In this sense, the renewable energy power plant (REPP) is established to provide the required power for the EC station while simultaneously producing hydrogen for FCVs. The EC is considered as the electric load in the off-grid system. The electric load profile is illustrated in Fig. 2, providing a fixed load of 30 kW with daily load of 720 kWh. 2.3. Hydrogen load perspective The primary goal of the REPP’s sizing and implementation is to provide green hydrogen for FCV refueling stations whether in this industrial area or to serve the international road of the city. According to a preliminary assessment of the necessary vehicles, hydrogen should be delivered on a regular basis at a rate of 10 kg per hour on average. Vehicle refueling is done with the hydrogen that is generated. The extra green hydrogen is kept in dedicated tanks for vehicles that are not refueled. As a result, 240 kg of hydrogen are needed daily. Using on-site renewable energy sources, the REPP will generate 87,600 kg of green hydrogen annually (Fig. 3). The location has significant wind resources, with a peak average wind speed over 5.69 m/s, while the lowest average wind speed exceeds 4.69 m/s. The wind speed fluctuation illustrated in Fig. 4 indicates that throughout the months from November to March, there are instances of high wind speeds, with some days in February higher than 21 m/s. Throughout the remaining months, the velocity of the wind might reach up to 18 m/s. Overall, the first investigation indicates that the site possesses abundant wind resources with the capacity to generate a substantial amount of green hydrogen. The PV power potential was assessed by analyzing the solar irradiation and temperature at the location, as these factors directly influence the output electricity of PV. The site’s average daily solar irradiation is seen in Fig. 5. The peak average solar irradiation occurs throughout the months of May and August. Fig. 6 displays the average daily temperature, indicating favorable circumstances for generating electrical energy using PV systems. 2.4. System description The presented system for the generation of green hydrogen contains wind turbines and PV panels that represent the electricity generating units. The generated electricity will be used to feed the electrolyzer; R.M. Rizk-Allah et al. Results in Engineering 22 (2024) 102234 6 hence, the hydrogen produced is green. Power electronic converters are incorporated to guarantee the conversion of AC power to DC power. Afterwards, hydrogen is kept inside hydrogen tanks for storage. Since the renewable power batteries are constantly accessible at the hydrogen refueling station site, the system can run in a stand-alone mode. The components of REPP are shown in Fig. 7. 2.4.1. PV source The primary supply of electricity for the REPP is the PV system. The PV system’s electrical power is expressed by Ref. [6]. Ppv =Sp× η p×Gt× (1−0.005 × (Ta−25)) (1) where Ppv represents the power output of PV; η p denotes the efficiency of the employed PV panels; Sp represents the total area that the PV panels cover; Gt defines the solar irradiation and Ta denotes the PV panels’ temperature. 2.4.2. Electrolyzers The electrolyzers are employed to supply the hydrogen needed for refueling FCVs. The amount of produced hydrogen is determined by the electrolyzer’s efficiency ( η El) and the amount of available electricity. Accordingly, the mass of generated hydrogen is given by Ref. [77]: ˙mH2= η El × (PEl ×HVEP) HVH2 (2) Where ˙ mH2, η El, PEl,HVH2,HVEP represent the hydrogen mass flowrate Fig. 1. Location of the site: google map for Ostrava, Czech Republic. Fig. 2. The daily variation in electric electrocoagulation load. Fig. 3. The daily variation in hydrogen load. Fig. 4. Instantaneous changes of the wind speed. Fig. 5. Variation of the solar radiation and clearness score. Fig. 6. The average daily temperature recorded at the location. R.M. Rizk-Allah et al. Results in Engineering 22 (2024) 102234 7 (kg/hr), electrolyzer efficiency, electrolyzer consumed power (in kW), Hydrogen’ heating value (in kWh), and the equivalent heating value of one kWh of electrical energy, respectively. 2.4.3. Hydrogen tank In order to meet safety regulations, hydrogen gas is kept in specially fabricated tanks. The primary factors influencing tank size are hydrogen load requirements, electrical energy availability, produced hydrogen capacity, in addition to economic parameters. Depending on the hydrogen load, the hydrogen tank’s storage capacity is expressed as follows [77]: Scapacity =Hload (3) 2.4.4. Wind turbine The location’s promising potential for wind energy is what makes it special. Wind turbines allow for the conversion of wind energy into electrical energy. The wind turbine generator’s electrical power output is determined by Ref. [77]: Pwt = ρ a×Cp×Vw3× π R2 wt 2(4) where Pwt, ρ a,Rwt,Cp,and Vw represent the wind turbine power, the air density, radius of the blade, coefficient of performance, and wind speed, respectively. 2.4.5. Battery system Batteries are utilized as backup items to supply the necessary electricity in situations where RESs are unavailable. The optimum battery size for a PV-wind standalone system must consider several factors, such as the required load characteristics, the system losses, the intended autonomy, and the economic parameters. The amount of battery capacity needed is expressed in kilowatt-hours (kWh) or ampere-hours (Ah). Depending on how much energy is required for the intended amount of autonomy. Then, the capacity of the battery is given by Ref. [30]: Bcapacity =Energy Consumption Vbat ×Disdep ×Effbat (5) where Bcapacity defines the battery’s capacity, Vbat denotes its voltage; Disdep defines the depth of discharge; Effbat defines its efficiency. 3. Method and approach of system optimization 3.1. Optimization concept and decision making The optimization process of the REPP involves determining the optimal sizes of the necessary components installed in the power station [45]. All of the system’s components have varying capacities, and each one’s capacity is determined by the size of the others, the hydrogen load, and the renewable energy sources that are available. The optimization prospective aims to achieve at the best (minimum) value for the cost of producing green hydrogen. In order to optimize hybrid RESs, specialized software is needed. The HOMER Pro software is implemented for optimizing the NPC regarding the presented RESs [45]. The software employs a patented derivative-free scheme to look for the least-costly scheme by means of solving non-linear least-squares problems. The following defines the renewable energy project’s NPC [77]: NPC =∑ n=25 n=1 TCn (1+i)n(6) The entire costs and the total amount of hydrogen produced determine the LCH [6]: LCH =∑ n=25 n=1 TCn (1+i)n ∑ n=25 n=1 Hn (1+i)n (7) where TCn is the project’s total expenses per year n and the hydrogen produced in the same year is denoted by Hn. The flowchart shown in Fig. 7. Representation of the green hydrogen production unit and electrocoagulation system. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) R.M. Rizk-Allah et al. Results in Engineering 22 (2024) 102234 8 Fig. 8 describes the optimization procedure. 3.2. Optimization and initialization The REPP optimization aims to identify the best configuration that can deliver the necessary hydrogen and electricity at a minimal NPC. In this regard, the initial operating costs and lifetime of various components are integrated by the Homer-Pro software in order to perform optimization. Table 2 lists the designated economic parameters for each installed component in the REPP system. Meanwhile, PV panels require an initial expenditure of 1000 € /kW. On the other hand, a PV system’s yearly operating and cleaning costs are 10 € /kW. An initial investment of 50000 € /kW is required for the wind turbine. Batteries and electrolyzers require an initial expenditure of 150 € /kWh and 500 € /kW, respectively. After that, the software will carry out the computation and identify the best sizing based on the details specified in Table 2, [77,79]. The methodology presented in this study involves analyzing the techno-economic optimization using Homer-Pro. Then, the obtained minimum NPC results and optimal rates for the installed components are identified. Also, the produced electricity and green hydrogen are obtained. Therefore, the components of the analyzed design include electrolyzers, wind turbines, PV panels, power converters, hydrogen load, and EC load, as seen in Fig. 9. Fig. 8. System optimization and decision-making process. Table 2 Specifications of the model component. Component Capital cost/kW O&M cost/ kW Replacement cost/kW Lifespan (years) Wind turbine 50000 € 2500 € /year 50000 € 20 PV panel 1000 € 10 € /year 1000 € 25 Battery 150 € 10 € /year 150 € 15 Electrolyzer 500 € 20 € /year 400 € 15 Hydrogen tank 100 € 1 € /year 100 € 15 Power converter 500 € 1 € /year 500 € 15 Fig. 9. The optimization process of the green hydrogen system. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) R.M. Rizk-Allah et al. Results in Engineering 22 (2024) 102234 9 4. Results and discussion The Homer Pro software aims to figure out the optimal economic and technical specifications for every equipment in the energy system that relies on renewable energy sources. Accordingly, the software determines the required electrolyzer capacity and the desired power converter capacity based on the available electric power provided by the PV panels and wind turbines, where matching between the produced Hydrogen and hydrogen load determine the size of hydrogen tanks. The model’s components have distinct lifespans. In order to compute the LCH over a 25-year period, the model assumes that components with a lifetime of less than 25 years will be sold and replaced with new ones. The NPC of each component is determined by the model. The LCH is then calculated by adding up all the NPC and dividing it by the total amount of hydrogen produced over a 25-year period. The optimization results, as indicated in Table 3, confirm that the power station generates approximately 6,997,990 kWh of electrical energy annually. The PV solar produces 300425 kWh/year, while wind turbine generates 6,697,566 kWh/year. The annual energy consumption of the electrolyzers is around 3,972,059 kWh. As a result, 85595 kg of green hydrogen are produced annually by electrolyzers. The electricity consumed by the electrocoagulation station in the presented power station is 262678 kWh annually, while the achieved LCH is 2.89 € /kg excluding compressor unit costs. Based on the specified costs per unit, the project’s NPC is determined to be 5,490,226 € . The LCH and the NPC are determined by analyzing the technical details and the outcomes of the economic evaluation of the various components. Each component’s necessary rated capacity is ascertained at the first step. Since the project’s total annual electricity production is estimated to be 6,997,990 kWh, electrolyzers with a rated capacity of 1000 kW can be installed to produce 10 kg of hydrogen per hour. Consequently, the highest amount of hydrogen produced in one day is 240 kg, equivalent to 87600 kg of green hydrogen annually. For the preservation of hydrogen, 800-kg hydrogen tanks are required, assuming that green hydrogen is not utilized immediately. The costs for the replacement, investment, operational and maintenance (O&M), and overall costs of each component are computed as specified in Table 3 based on the estimated costs per unit of the various project components. After that, the project’s total cost is determined. The findings displayed in Table 3 demonstrate that wind turbine has a capital cost of 1,100,000 € . On the other hand, the PV panels have a capital cost of 297,673.95 € . The capital cost of the electrolyzer is 500,000 € , and its total cost, including repair and maintenance expenses, is 1,093,503.59 € . The distribution of the power produced by the PV system throughout a complete year is shown in Fig. 10. The PV system produces an average of 823 (kWh) of energy per day while running constantly throughout the year. The PV panels can produce up to 296 kW of power at their utmost. In accordance with its operational schedule, the PV system produces 300425 kWh of electricity per year while running for 4384 h annually. On the other hand, the distribution of the power produced by the wind turbine throughout a complete year is shown in Fig. 11. The wind turbine farm produces an average power of 765 kW. The wind turbine farm can produce up to 2200 kW of power at its utmost. In accordance with its operational schedule, the wind turbine farm produces 6,697,566 kWh of electricity per year while running for 7518 h annually. These striking results demonstrate that the PV system’s and wind farm’s potential to supply an effective renewable energy source for a variety of uses, such as industrial facilities, employment, and commercial and residential properties. The electrical power consumed by the electrolyzers to generate the hydrogen needed by the load is displayed in Fig. 12. All electrolyzers are turned on automatically based on the amount of solar energy available in order to maximize energy utilization. Therefore, 85595 kg of green hydrogen are produced annually by electrolyzers. The total consumed electricity by the electrolyzers is 3,972,059 kWh. The variation in hydrogen tank levels throughout a year is shown in Fig. 13. The hydrogen tank holds 160 kg of hydrogen at the beginning of the year. Nonetheless, this number progressively rises over the course of the year, culminating in a final level of 793 kg by the year’s end. The tank has a capacity to store 800 kg of hydrogen, corresponding Table 3 Optimized system technology and economics. Component Rated capacity Capital cost ( € ) O & M cost ( € ) Replacement cost ( € ) Salvage Total ( € ) Wind turbine 22 kW 1,100,000.00 616,041.74 964,030.82 399,692.29 2,280,380.27 PV panel 298 kW 297,673.95 0.00 52,175.79 $0.00 349,849.74 Battery 600 kWh 90,000.00 58,264.71 105,167.00 14,534.26 238,897.45 Electrolyzer 1000 kW 500,000.00 323,692.84 350,556.66 80,745.92 1,093,503.59 Hydrogen tank 800 Kg 80,000.00 0.00 $70,111.33 0.00 150,111.33 Power converter 997 kW 498,331.27 322,612.53 174,693.35 80,476.43 915,160.72 System – 2,566,005.22 1,320,611.82 2,179057.29 575,448.9 5,490225.44 Fig. 10. Output power of PV system. Fig. 11. Output power of wind turbine system. Fig. 12. Input power of electrolyzer. R.M. Rizk-Allah et al.