Ecological Hydrogen Production and Water Sterilization: An Innovative Approach to the Trigeneration of Renewable Energy Sources for Water Desalination: A Review

Abstract

In this study, hydrogen production by solar thermal energy has been studied in terms of economics, technology and hydrogen sources. Methane was captured and subjected to solar photovoltaic steam, solar methane cracking, high-temperature water electrolysis and thermochemical cycles. The price of hydrogen production was calculated compared to other methods, and means of using and exploiting hydrogen as an energy carrier were examined in addition to verifying the industrial need for hydrogen, especially in the presence of high solar energy, which improves hydrogen production. The study was carried out in order to generate hydrogen using a solar electrolyzer based on polymeric exchange membrane technology. The study was carried out using two methods. The first was involved the direct connection of the photovoltaic system to the hydrogen analyzer, and the second was a system for a solar electrolysis hydrogen analyzer consisting of a PV array and a maximum power tracker MPPT meant to operate the system at the maximum power of the photovoltaic system at all times uses a DC converter to supply the analyzer. With the necessary current and hydrogen tank, the results showed that the first method was less effective compared to the second method due to the instability of the intensity of solar radiation during the day, and the results show that adding potassium hydroxide, for example, enhances ionization and improves hydrogen supply.

1. Introduction

Hydrogen is being studied as a clean and sustainable energy source to reduce air pollutants, combat global warming, and decrease reliance on finite resources like oil. Renewable energy sources, particularly solar and thermal energy, are being explored for hydrogen production through processes like water electrolysis. The German Aerospace Center has been involved in various projects related to solar thermal processes for hydrogen generation. However, the transportation of hydrogen is expensive and inefficient, leading to economic losses when transporting it over long distances. Despite this, hydrogen remains important for meeting future energy demands and addressing climate and environmental concerns.

Replacing fossil fuels with hydrogen can generate electricity, heat, and mechanical energy, with potential applications in transportation and industrial production. However, challenges exist in establishing infrastructure for hydrogen storage, transportation, and renewable production. The length of the transmission chain reduces energy efficiency and poses a disadvantage. Models and simulations of energy systems have been developed to optimize the cost and utilization of hydrogen. Future projections indicate an increasing demand for hydrogen, particularly in fuel cell vehicle systems.

Solar thermal hydrogen is still under development but holds promise for improving the cost and performance of hydrogen production. It is estimated that hydrogen demand in Europe will reach 3.8% of final energy demand by 2050, with global demand reaching 17 EJ. Nuclear fission techniques are expected to play a role in hydrogen production. In the transportation sector, hydrogen demand is projected to account for about 12 equivalent units globally by 2055. Various concepts and cycles, such as solar thermal chemical cycles and methane separation, are being explored to produce hydrogen efficiently. Concentrated solar radiation is a valuable heat source for solar thermal processes, which involve central receivers and reactors. These processes offer the advantage of low emissions of polluting gases [1,2,3,4,5,6,7,8,9,10,11]. In

Table 1. Hydrogen cost price in 2022 [5].

	Year of Construction of the Station	Production Hydrogen Plant Capacity, Tones/Day	Cost Price, $/kg
1	Commissioned before 2022	607	3.66
2	Put into operation in 2022 with an increase in production efficiency	678	3.51

data on the cost price of hydrogen in 2022 are presented [5].

A case study on the use of 600 MW of electricity from the New Zealand Manapuri power plant for the production of hydrogen by electrolysis of water was carried out in 2022. Three H2 carriers—liquid H2, ammonia, and toluene hydrogenation/methylcyclohexane dehydrogenation—were modeled using Aspen’s HYSYS to estimate the associated energy and annual capital costs. Surprisingly, the total volume of capital investments for all carriers remained unchanged but with clear patterns of distribution between the electrolysis and molding of carriers (Figure 1).

Analysis showed that the energy availability of liquid H2 ranges from 53.9% to 60.7% depending on the energy costs associated with cryogenic liquefaction of H2. For liquid ammonia, the energy reserve was 37.5% after the reverse conversion to H2, increasing to 53.6% when ammonia could be directly used as fuel. The energy availability of toluene/methylcyclohexane was 41.2%.

Total electricity costs and annual capital costs per kilogram of H2 varied depending on the carrier, with ranges from NZ $5.63 to NZ $6.43 for liquid H2, NZ $6.24 to NZ $8.91 for ammonia, and a cost of NZ $7.86 for toluene/methylcyclohexane, taking into account a net electricity cost of NZ $70 per MWh. Our results show that the cost of hydrogen (or energy for the direct use of ammonia) largely depends on the efficiency of energy saving, with electricity costs accounting for about two-thirds of the total costs [8].

2. Materials and Methods

The solar panel data needs to be analyzed. A description of the main characteristics is given in

Table 2. Solar panel specifications [12].

Model type	Bsm 200 m-72
Solar cell type	Mono 125 × 125 cell a grade
Pm 210 W, Vm 38 V, Im 5.5 A	Voc 44.6 V, Isc 5.8 A
Size	1580 × 808 × 35mm
Weight	16.5 kg
Output tolerance	0–4%
Standard test condition	999 W/m2, am 1.6, 25 °C
Operating temperature	−42 °C…+87 °C
Manufacture warranty	11 years
Power performance warranty	>90% after 16 year, >85% after 26 year

.

Charging regulator specifications:

Model: S.C.C-M.P.P. T 650 W;

Input: 35 Vdc-80 Vdc;

Input: 25 A 24 Vdc;

Capacity: 650 W.

Batteries:

Model Type: N.150.(145.G51R);

Capacity: 160 Ah

12 v

Analyzer model:

The analyzer model (Figure 2) consists of a transparent acrylic plastic box with its cover, the electrodes, the aqueous medium, the polymeric exchange membrane, and the copper conductive wires. The analyzer includes two parallel plates with the dimensions of 5.5 cm. Between them is a polymeric exchange membrane, and the distance between the poles can be expressed to become 1.5, 5.0, 7.5, 10 cm [7].

Mediator:

Distilled water solutions containing potassium hydroxide at 5, 10, 20, and 30 gr/L were added to cover the electrodes of the analyte.

Electrode:

Manufactured from 316 stainless steel.

Hydrogen production from the system and direct connection:

Hydrogen productivity was studied according to this method. During daylight hours, the intensity of solar radiation appears as in the following Figure 3, Figure 4, Figure 5, Figure 6 and Figure 7.

2.1. Hydrogen Yield by System

This method depends on feeding the analyzer from the charging battery with a DC–DC converter. The figure shows the relationship between the hourly and cumulative hydrogen gas volumes at the direct connection (vertical axis) according to daylight hours (horizontal axis) and with a distance of 1.5 cm between the electrodes.

Consider the data shown in

Table 3. The need for hydrogen in regions and countries where direct solar radiation is high due to industry (metal oxide TC: solar iron-oxide-based redox pair cycle, SSMR: solar steam methane reforming) [12,14,15,16].

	Hydrogen Demand EJ	Theoretical Number of Plants with 50 MWs SSMR	Theoretical Number of Plants with 50 MWs Metal Oxide TC
Refineries existing	0.44	380	860
Refineries additional	0.8	700	1600
Ammonia production	0.51	440	1003
DRI (pig iron) production	0.12	98	220
Methanol production	0.2	166	–
Total countries	2.07	1784	1683

.

2.2. Thermochemical Solar Cycles

Solar thermochemical cycles have been successfully developed. The redox cycle of iron oxide is a two-stage process of splitting water. The thermal decomposition of water is achieved using a reactor receiving solar heat, supported by a honeycomb ceramic substrate and coated with an active redox reagent containing metal oxide. Oxidation and reduction are activated and oxidized (metal oxide) to produce pure hydrogen with gaseous oxygen from water at a temperature of 820 °C. In the second stage, the oxidizing reagent must be completely regenerated by optimizing the temperature to approximately 1150 °C in an atmosphere with zero oxygen content. Using nitrogen, oxygen is catalyzed to activate adsorption.

Depending on the solar thermal power, the expected efficiency of the process is about 72%. The reduction and oxidation systems were developed in the laboratory by H.Y.D.R.O.O.L. The project focuses on finding optimal reducing agents and oxidants in terms of hydrogen production and regeneration potential. During the process, the appropriate installation and operation strategies are optimized in order to achieve reliability in 500–1000 cycles and thereby increase efficiency.

Consider Figure 8.

The thermochemical cycle of hybrid sulfur and hydrogen sulfide and two processes in which the thermal separation of sulfuric acid at 855 °C in an unidentified recipient reactor at 1250 with or without a catalyst were determined. The hybrid sulfur process uses electrolysis to resume the production of sulfuric acid and pure hydrogen [10].

The sulfur iodization process is based on the Bunsen reaction for the regeneration of used acids and on thermal cleavage (HI) for the production of uncontaminated (pure) hydrogen. Absorption units are used to separate oxygen from the gas stream. Within the framework of the H.Y.T.H.E.C. project, the operational capabilities of various process configurations (heat capacity, catalysts, and temperature) were analyzed. One of the key stages in solar energy is the transfer, optimization and analysis of thermal energy in a reactor using a standard modeling tool.

With reduced heat loss, a maximum efficiency of 36% is required for an industrial plant with a capacity of 50 MW [2]. Developing resistance to concentrated acids at high temperatures is the most difficult task. The integration and design of the main parts, such as the exchanger, absorber and others—which are made of resistant materials (ceramics)—as well as the separation of products are goals for the future. There are some costs associated with coating components and advanced catalytic systems. Research is aimed at optimizing the receiving reactor so as to be suitable for the separation of sulfuric acid. Electrolysis is the second important step for the hybrid. The process of producing sulfur also needs further development in terms of lowering heat loss, lowering overvoltage and achieving high current density; the feedback is low.

2.3. Using Solar Steam to Improve Methane

This process depends on the thermal decomposition of steam and methane mixed at temperatures between 850 and 1100 °C. For the natural gas pretreatment process and the production of pure hydrogen, Syngas must be cleaned. Gas cleaning consists of converting water vapor to carbon dioxide, performing unstable pressure adsorption to remove hydrogen and washing gas with MDEA to separate residual carbon dioxide from recyclable methane.

The hatch is designed to provide the process with the necessary heat from concentrated solar energy and a reformer bowl with a quartz window covering receiver and compact volumetric receiver. A prototype was realized and tested within the S.O.L.A.S.Y.S project. Its operating pressure is 10 bar, and the receiver absorbs 450 kW of heat energy. The project showed the possibility of generating practical heat for operation through the future volumetric reactor. For power generation, the synthesis gas produced in small gas turbines was used and the chemical reaction occurred at around 900 °C. The estimated cost for a commercial plant with a thermal capacity of 50 megawatts and 2.100 full operating hours annually (when direct solarization 2500 kWh/m² general).

The S.O.L.R.E.F project is looking to reach a temperature above 950 °C in order to connect the reactor and process the gas to produce pure (non-polluting) hydrogen and increase process efficiency. Daily start-up and solar power output cause intermittent operation problems, reducing system durability and reliability. Additionally, the catalyst and acceptor materials must be selected to achieve optimum heat, and due to the 85% methane conversion rate, the process requires the recovery/separation of the methane residues. System and operating parameters will be optimized to reach high efficiency, stability, and high recovery rate of carbon dioxide and hydrogen while also working with alternative materials such as biogas [17].

2.4. Solar Methane Separation

The release of solar methane leads to the release of thermal methane, primary carbon and hydrogen in the atmosphere, where the percentage of oxygen is zero when using solar temperatures from 1300 to 2200 °C. Carbon can be separated industrially using a filter and cyclone, and this affects the structure and quality of carbon as well as the cost of processing. One of the most important tasks taken up in this research project is to determine the type of reactor and the layout for optimal technological processing using the results of experimental tests implemented as part of the pilot plant S.O.L.H.Y.C.A.R.B with a thermal capacity of 50 kW [18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36].

The research team aims to convert methane at a rate of more than 85% and research the separation of carbon and hydrogen particles in addition to safety issues. The commercial price of carbon black is the main factor for adjusting the resulting hydrogen costs. For the production of high-quality carbon, a temperature above 1816 °C is required, which leads to problems with the efficiency of the process and the properties of the material.

One possible problem is that the temperature drop is too low, which leads to the formation of polycyclic aromatic hydrocarbons (PAHs), which are by-products. Another problem is that methane cannot absorb solar energy directly, and therefore, methane gas is not heated by solar energy. We will test the receiving tube made of high-temperature material and test the gas flow with particles loaded into it. It is necessary to compare the efficiency of this process with other processes, such as the capture and optimization of solar methane and the storage of carbon particles underground, compared with the release of carbon dioxide.

2.5. Comparison of Hydrogen Getting Methods

After 2030, low-cost wind-based electrolysis will appear as a viable future option for renewable hydrogen production in the market. The gasification method is also a competitive method for low hydrogen production costs. However, the uses of biomass as a fuel for solar thermal power plants and as a transportation biofuel only have limited potential [19]. Methane separation could be competitive with conventional production if gas and coal prices rise further.

The leading method is hydrogen production by relying on methane in direct emissions of multiple gases, including carbon dioxide, and emissions resulting from the distribution, treatment and extraction of gas. Carbon dioxide emissions from methane enhancement with solar steam (not equipped with carbon sequestration technology) can be greater than the emissions from fossil options using CO₂ storage and capture.

In addition to future domestic supply, it is possible to export hydrogen from the producing regions to the consuming and marketed European and American markets, by pipelines or ships, but the energy efficiency decreases and reaches 50% and the costs increase.

Producing clean, carbon-free hydrogen using an unlimited energy source is the main advantage of solar thermal energy, making hydrogen a sustainable and climate-friendly fuel. The efficiency of hydrogen production by electrolysis and photovoltaic means is at or significantly lower than land use and related to solar thermal input, according to Figure 9. Building on process development and future demand for hydrogen and energy, the solar thermal process presents as an alternative a semi-permanent option for transcontinental energy import and an excellent method for hydrogen production renewable for local use.

Other methods of hydrogen production due to solar energy and distillate electrolysis are possible, and they have been presented in various studies.

This study presents the design, modeling, and behavior of a solar distiller using computational fluid dynamics (CFD). The study aimed to measure various parameters, such as changes in internal temperature, coating and volume formed after the solar distillation process, as well as transfer coefficients obtained during the months of operation. The results of the study showed that in May, there was the highest average indoor water temperature—44 °C—and the production of distilled water was the highest—an average of 1000 mL per day. In addition, in the same month, the average amount of falling global radiation per day was 5.8 kWh/m², which is the highest indicator for all months of operation. The Kumar and Tiwari model was applied to study the thermal behavior of a solar distiller. The study also conducted a water quality analysis to determine the suitability of distilled water for drinking, which met the standard NOM-127-SSA1-1994. The study showed that the internal temperature of the coating and water increased as the incident radiation increased. The heat transfer coefficients behaved similarly but also depended on the internal temperature of the glass. The amount of distillate is directly related to the above variables, which indicates that high heat transfer between the various components of the distillation equipment is required to obtain a larger volume of distillate. CFX modeling showed the behavior of distillation equipment during water production and the temperature of glass and water. Differences were found between the experimental method and CFX modeling: the difference in water temperature was 5.8%, and the volume of the distiller was 8.2%. It was found that the efficiency of the equipment is within the parameters reported by other authors. However, it has been observed that climatic conditions can affect the operation of the solar distiller. The key to high efficiency is radiation, but wind speed and ambient temperature can affect system performance. The results in CFD have a slight difference from the results of the experiment, which makes improvements aimed at improving the efficiency of equipment possible, either by adding new components for forced convection, by adding heat to the system, or by improving structural materials. The study concludes that distilled water can be produced in regions with a shortage of drinking water. Overall, the study provides valuable information about the design, modeling, and behavior of a solar distiller using CFD. The results obtained may be useful to researchers and engineers working in the field of solar distillation and may contribute to the development of more efficient systems [37].

This paper presents a mathematical model for the analysis of multi-stage and multi-effect desalination systems. The model takes into account the geometry of the steps, the mechanisms of heat transfer and the physical properties of seawater, including temperature and salinity. Pollution is also taken into account, and its effect on the efficiency of the installation is evaluated. The study shows the relationship between operational and design parameters, including the plant performance coefficient, the specific consumption of recirculating brine, the temperature of the upper brine layer and the specific heat transfer area. The model is applied to a typical operating plant, and the results are compared with data from the Sidi-Krir plant in western Alexandria, which has 17 stages of restoration and three stages of rejection. The calculation results are consistent with the factory data. The model is also used to study various operating conditions, such as partial loading, and the influence of variables such as recirculated flow rate, brine top layer temperature, seawater temperature and pollution coefficient on the efficiency of the installation. With multi-effect desalination using a boiling incident film, the study examines the effect of technological parameters on productivity, including the number of effects and the upper temperature of the brine. The specific heat transfer area and cooling brine consumption are also studied. The study showed that the efficiency depends on the number of effects and slightly depends on the temperature of the upper brine layer [38,39].

This study presents a comparison of the performance of two conventional solar distillers and a heat storage system with a flat plate collector in the city of Shebin el-Kom, Egypt. The experiments were conducted in August, September, November and December 2015. This review examines the technical aspects of heat exchange tubes in thermal desalination plants, which are the main cost item and account for 25–35% of the total cost of the evaporator. The authors seek to identify the technical aspects of the components that could lead to the optimization of the number of materials and improve quality and reliability. The review combines corrosion/material selection aspects and thermodynamic aspects for the analysis and specification of thermal desalination plant pipes. The authors compare the use of different alloys in terms of thermal resistance to heat transfer and resistance to erosion/corrosion and assess the economic consequences associated with the choice of different materials, taking into account the service life of the installation. The technical specifications contain recommendations for future optimization. In general, a comprehensive technical analysis of heat exchange pipes is presented, which is important for reducing costs and improving the efficiency of thermal desalination plants [40].

This study presents the design and production of two single-pitched solar distillers with a heat storage system using a flat plate collector. The system collects solar energy during the day and accumulates it in a heat-insulated tank which is used as a heat source for one of the distillers—a modified distiller. Another distiller, a conventional distiller, uses exclusively solar radiation as a heat source. Experimental measurements were carried out during the day and over four seasons, and a theoretical study was conducted using energy balance equations to predict the performance of system components. The results showed a good agreement between theoretical and experimental data. The use of the recovery system increased the productivity of distillers, especially the modified distiller, which increased from 45% to 106% during the experiment period. The study also showed that productivity gains were lower in the spring and summer seasons compared to the other two seasons. In general, the models used made it possible to accurately predict the performance of a conventional distiller and a thermal storage system [41].

The review presents a study of a seawater distiller that uses the thermal energy of exhaust gases from a portable electric generator using a heat pipe. The distiller is a vertical diffusion unit with a single effect, still consisting of a series of closely spaced parallel partitions in contact with wicks soaked in saline solution. The study shows that 40 to 50% of thermal energy can be transported through a heat pipe and about 35% of thermal energy can be used for distilling salt water. The study also presents experimental results on distillate performance, which are in good agreement with theoretical forecasts. In general, the study represents a promising approach to seawater distillation, which may be useful in remote areas with a shortage of electricity [42].

This study evaluates the performance of a newly developed multi-effect distillation system with a capacity of 3 m 3 per day and a shell-and-tube heat exchanger that has been optimized for solar thermal desalination systems. In the experiment, a corrugated Cu (90%)–NI (10%) tube was used for efficient heat transfer. In the course of the study, the consumption of hot water was studied as a parameter of the effectiveness of multi-effect distillation. The study showed that the development of multi-effect distillation required approximately 40 kW of heat and 35 kW of a cooling source to produce 3 m3 of fresh water per day. The efficiency of the developed multi-effect distillation was approximately 2.0191. In general, the study provides valuable information about the performance of multi-effect distillation systems for solar thermal desalination and can serve as a basis for future research in this area [43].

The review presents a system of natural vacuum desalination of water with an internal condenser, powered by solar energy. This system allows the flowing seawater to absorb a small amount of solar heat to achieve phase-change evaporation. The system is capable of removing accumulated non-condensing gas through the process of filling with water and releasing air. The efficiency of solar-powered distillation was tested in real weather conditions using flat solar collectors with a total area of 18 m². The results of the experiment with a constant temperature show that the output of fresh water and the cycle time increase with an increase in the temperature of hot seawater. Hourly water consumption can reach 12.45 kg/h at a temperature of 60 °C hot seawater and a mass flow rate of 0.1 kg/s seawater. The daily water consumption is 154.14 kg, and the corresponding efficiency is 1.36 in real weather conditions with an average solar illumination of 672 W/m². In general, the review presents an effective system of natural vacuum desalination, which is powered by solar energy and provides high yields of fresh water. The results of the study demonstrate that the system is capable of producing fresh water at a low cost, which makes it an attractive option for increasing the productivity of freshwater [44].

The review presents a mathematical model for the analysis of multi-stage and multi-effect desalination systems. The model takes into account the geometry of the steps, heat transfer mechanisms and physical properties of seawater, environmental pollution is taken into account and its impact on the efficiency of the installation is evaluated. The model is applied to a typical operating plant, and the results are compared with data from the Sidi Crir plant in western Alexandria. The study shows the relationship between operational and design parameters, including the plant’s performance coefficient, the specific flow rate of circulating brine, the temperature of the upper brine layer and the specific heat transfer area. The study showed that the effectiveness depends on the number of impacts and slightly depends on the temperature of the upper brine layer. The review proposes the development of a solar desalination plant using vacuum tubes for water purification, which would provide inexpensive drinking water, especially in remote areas and regions with brackish and seawater. The system is powered by solar energy and does not contain any moving parts, which ensures a long service life of the system with minimal maintenance. The modified plant has an efficiency of about 6.5–7.0%, which is higher than that of conventional solar stills with one tank [45].

This review discusses the growing demand for freshwater due to population growth and industrialization, which leads to the development of desalination technologies using renewable energy sources. Vacuum desalination is presented as a method that involves increasing the pressure of brackish water, creating a vacuum and evaporation using waste heat. The study analyzes a vacuum water desalination system by applying mass, momentum and energy balances and solving control equations using simulation. The simulated performance is confirmed by experimental data from the literature, and the operating parameters, such as the temperature of the evaporator and condenser, flow rate and pressure in the chamber, vary. It is found that the output of freshwater increases with a decrease in the temperature of the condenser and an increase in the temperature of the evaporator, as well as with a decrease in the pressure in the chamber [46].

This scientific article examines the effectiveness of an autonomous solar vacuum membrane distillation (VMD) system for the desalination of seawater. The study evaluates various indicators such as membrane flow rate (MFR), efficiency coefficient (GOR), efficiency coefficient (PR), recovery coefficient (RR) and specific heat consumption (STEC). The results obtained are compared with previous studies of solar-powered membrane distillation systems in order to provide context for the results obtained. The authors also conducted a sensitivity analysis to determine the effect of operating parameters on GOR performance, finding that lower raw material consumption and higher feed temperature yield better GOR results. In addition, increasing the vacuum level and the area of the solar collector can increase the GOR value. Finally, the authors present an economic study to estimate the cost of distilled water production at a VMD solar installation. Overall, this study provides valuable information about the performance of the VMD solar system for seawater desalination, including key factors affecting its efficiency and cost-effectiveness [47].

This scientific review highlights the important role of seawater desalination technology in solving the problems of freshwater scarcity. It presents natural vacuum desalination (NVD) technology, which uses a very low-pressure environment created at the top of a 10 m column of water to facilitate desalination at low temperatures. Unlike other desalination technologies, NVD does not require mechanical pumping, and its simple design means that it can be made of relatively low-quality materials. The review provides an overview of the basic theory and physical model of NVD, summarizes the progress of research on various types of NVD technologies and outlines methods for increasing freshwater production. In addition, the authors discuss the potential future development of NVD technology. In general, this review gives valuable insight into NVD technology, highlights its advantages over other desalination technologies, and discusses how it can help solve the problems of freshwater scarcity [48].

This scientific review discusses the need for new water sources due to the current shortage of clean water on Earth and emphasizes that the desalination of seawater is a viable solution. The review is devoted to a widely used method that involves obtaining clean water by condensing evaporated salt water at low pressure, which is achieved due to natural vacuum and renewable energy using a vacuum pump. The study examines the efficiency of a water desalination system at various low pressures created by a vacuum pump at various condensation temperatures. The volume of desalinated water was measured at different evaporation temperatures, and the efficiency was analyzed for a given volume of desalinated water at reduced temperatures below 0 °C. The results show that salt water can be purified with an average efficiency of 99.6% in each experimental group. However, reducing the condensation temperature to −25 °C turned out to be unnecessary since a similar efficiency could be obtained using less condensation energy at 0 °C. Overall, this study provides valuable information on the effectiveness of low-pressure water desalination methods and highlights the potential for optimizing productivity while reducing energy consumption [49].

This scientific review presents a study on the design of an autonomous desalination plant, the purpose of which is to provide high-quality drinking water to remote coastal areas with weak infrastructure and network connectivity. The system is designed to work exclusively on solar energy, while electric energy is generated by the field of photovoltaic cells, and heating is provided by the field of a selective flat solar collector. The feasibility study led to the selection of 35 collectors located in seven cascades, each of which contains five collectors connected in series. The additional electricity needed to operate the pumps is provided by photovoltaic panels which can generate up to 1.5 kW and store energy using eight batteries. The energy characteristics of the system are improved due to the recovery of latent condensation energy, while a hollow fiber module with a heat exchange area of 4 m² and a plate heat exchanger provides efficient heat transfer. The designed installation is located in the village of orphans in the coastal area of Mares. An experimental study of this system is currently being conducted. The study provides valuable information on the design and performance of an autonomous solar-powered desalination plant, highlighting its potential as a solution for providing clean water to remote areas with limited access to resources [50].

This scientific review presents a methodology for the theoretical prediction of the vacuum load for low-temperature thermal desalination (LTTD) installations and compares it with experimental values for verification, in particular, with an emphasis on the load of non-condensing gas and escaping water vapor. The aim is to determine the accumulated effect of non-condensing gases on the vacuum load of LTTD installations and to propose ways to control these factors during the desalination process. The vacuum system alone accounts for about 31% of the total energy consumption of the LTTD installation, which makes it extremely important to accurately determine the vacuum load. Experimental measurements were carried out at an operating plant with a capacity of 100 m³/day located on Agatti Island, UT Lakshadweep Island Group, India, to measure the contribution of gas mixtures such as escaping water vapor, non-condensing gas and air leakage. The results were compared with published data and predicted values using the proposed methodology, showing good compliance under the same operating conditions. The study showed that the accumulated effect of non-condensing gases on each unit of mass led to the extraction of 1.6 units of mass of steam from the process condenser, which is a relatively low indicator due to the low operating temperature range LTTD and the use of deep cooling water in the condenser pipes. The review also highlights the influence of various parameters, such as operating pressure, pipeline losses and feed water mass flow, on the overall vacuum load of LTTD installations [51].

This scientific review highlights the growing demand for drinking water due to rapid population growth and an increase in living standards. It highlights the need for new, energy-efficient desalination methods to meet this demand, leading to the analysis of vacuum desalination systems. Vacuum desalination involves the use of warm seawater from the ocean surface, which quickly evaporates in an evaporation chamber under vacuum, and then condenses in a shell-and-tube condenser using cold seawater from deeper layers. The review presents a numerical model designed to simulate the operation of a desalination plant and study the effect of operational parameters on system performance. The design of the installation, including a vacuum evaporation chamber, a distillate condenser, a vacuum pumping system and a water pumping system, is also discussed. The control equations are derived based on mass, momentum and energy balances, and modeling is used to assess the influence of key technological variables, such as pressure in the vacuum chamber and the temperature of warm seawater at the inlet, on the operational characteristics of the system in terms of freshwater output. In general, this study provides valuable information about the potential of vacuum desalination systems as an energy-efficient method of drinking water production and the development of numerical models to optimize their performance [52].

3. Results

The circuit operates according to the following explanation: When the solar cell panel is exposed to sunlight during the day, its cells absorb the radiation energy and transform it into thermal electrical energy to conduct the analysis and separate the aqueous solution of oxygen and hydrogen gas. Negative and oxygen for the positive electrode.

$$H_{2}O+(liquid)\to H_2+\frac{1}{2}{O}_2$$

(1)

The release of hydroxide ions simultaneously releases electrons and oxygen is emitted; the reaction of the water molecule is also carried out, releasing hydrogen:

$$2O{H}^{-}\to 2e^{-}+H_{2}O+\frac{1}{2}{O}_2$$

(2)

$$2H_{2}O+2e^{-}\to 2O{H}^{-}+H_2$$

(3)

Solar radiation and its thermal energy are received and exploited to produce green hydrogen according to the circuit diagram. Part of the solar energy is transmitted to the generator connected to the heat exchanger and cooling water condenser, and another part is transmitted to the water sterilizer. The heat exchanger changes the temperature of the liquid by passing it through tubes in another medium. If we want to raise the temperature of the liquid or gas, then the other medium is at a high temperature. We cool the liquid or gas by passing it in tubes in another medium with a low temperature. The condenser is connected to the evaporator via an expansion valve. The valve is connected to a pump with a cooling load through two inlet and outlet paths. The return or exit path is connected to the pump connected to the heat exchanger. An example of such a scheme is shown in Figure 10.

The decomposition of water into hydrogen and oxygen by direct conversion of solar radiation energy can be carried out without high temperatures and electricity. Water molecules absorb solar photons for further decay. In addition, inorganic substances can contribute to the decomposition of water. The electricity generated by solar panels and a steam solar station is used to produce hydrogen, a clean, environmentally friendly fuel, as well as oxygen. The efficiency of the scheme ranges from 5 to 21% [53].

Solar energy is transferred to a vacuum desalination plant. The seawater is pumped by a centrifugal pump through the condenser tubes, where it is heated due to the heat of steam condensation. The heating water heats the walls of the evaporator tubes, where the seawater boils and evaporates. The resulting steam passes through the louver separator and enters the condenser, where it condenses, and the distillate flows by gravity into the collector. The distillate pump takes the distillate from the collector and directs it to electrolysis [53,54,55].

3.1. Installation Calculation

Consider the data shown in the

Table 4. Calculated data [56].

Given	Unit of Measurement	Formula	Option 1	Option 2	Option 3
t’hw	°C	–	68	68	90
tout.w	°C	–	4	4	4
Whw	m3/h	–	80	150	80
dscale	mm	–	0.1	0.1	0.1
hs.	m	–	5	5	5
Calculation	Unit of measurement	Formula	Option 1	Option 2	Option 3
The average temperature of the heating water in the evaporator when cooling the heating water is 6 °C; 8 °C; 10 °C.	°C	$t_1^{\mathrm{av}}=0.5(t_1^{\prime }-t_1^{″})$	65 64 63	65 64 63	87 86 85
The average temperature of the cooling water in the condenser	°C	$t_{out.w}^{av}=0.5(t_{out.w}^{\prime }-t_{out.w}^{″})$	7	7	7
Temperature pressure in the condenser	°C	$\Delta t_c=\frac{t_1^{av}+t_{out.w}^{av}}{1+\sqrt{\frac{K_c}{K_{\mathrm{ev}}}}}$	29.82 29.41 28.99	29.82 29.41 28.99	38.94 38.52 38.11
Secondary steam temperature in the evaporator	°C	$t_2=t_{out.w}^{av}+\Delta t_c$	36.82338 36.40916 35.99495	36.82338 36.40916 35.99495	45.93607 45.52186 45.10765
Secondary steam pressure in the evaporator	kPa	–	6.2162 6.0812 5.946	6.2162 6.0812 5.946	10.04 9.84 9.63
Heat of vaporization of secondary steam	kJ/kg	–	2568 2567 2566.7	2568 2567 2566.7	2392.3 2393.3 2394.3
Heating water density	kg/m3	–	980.4 980.94 981.48	980.4 980.94 981.48	989 990.5 992
Heat load of the evaporator	kJ/h	$Q_1^{\prime }=W_{hw}\cdot {\rho }_{hw}\cdot c_{hw}(t_1^{\prime }-t_1^{″})$	1,971,310 2,629,861 3,289,136	3,696,206 4,930,989 6,167,130	1,988,602 2,655,491 3,324,390
Thermal load of the condenser	kJ/h	$Q_k=Q_1^{\prime }\cdot \eta$	1,892,457 2,524,666 3,157,570	3,548,358 4,733,750 5,920,444	1,909,058 2,549,271 3,191,415
The amount of heating of the cooling water in the condenser	°C	$\delta t_{out.w}=\frac{Q_c}{W_{\mathrm{cool}}\cdot {\rho }_{out.w}\cdot c_{out.w}}$	4.85 6.47 8.08	9.09 12.13 15.16	4.85 6.47 8.08
The temperature of the cooling water at the outlet of the condenser	°C	$t_{out.w}^{″}=t_{out.w}^{\prime }+\delta t_{out.w}$	8.85 10.47 12.08	13.09 16.13 19.16	8.85 10.47 12.08
Salinity of seawater	g/L	–	30	30	30
HEU purge coefficient	–	$\epsilon =\frac{W_b}{W_2}$	3	3	3
Brine salinity	g/L	$S_b=\frac{S_0(1+\epsilon )}{\epsilon }$	40	40	40
Temperature depression	°C	$\delta t_b=\frac{S_b}{80}$	0.5	0.267	0.5
Correction taking into account the average hydrostatic pressure	kPa	$\Delta p_h=\frac{0.5g\cdot x\cdot l_{\mathrm{ev}}\cdot {\rho }_b}{1000}$	1.784	1.784	1.784
Average design pressure of boiling brine	kPa	$p_b=p_2+\Delta p_h$	7.999 7.865 7.729	7.999 7.865 7.729	11.824 11.624 11.414
Temperature difference taking into account the hydrostatic effect	°C	$\delta t_h=t_s^{\prime }+t_2$	4.70 4.77 4.83	4.70 4.77 4.83	3.16 3.28 3.39
Average design temperature of boiling brine	°C	$t_b=t_2+\delta t_b+\delta t_h$	42.025 41.676 41.329	42.025 41.676 41.329	49.6 49.3 49
The area of the living section for the passage of heating water	m2	–	0.0154	0.0154	0.0154
The average speed of heating water in the inter-tube space of the evaporator	m/s	$v_{hw}=\frac{W_{hw}}{3600\cdot F_{se}}$	1.44	1.44	1.44
Kinematic viscosity of heating water	m2/s	–	0.445 0.451 0.458	0.445 0.451 0.458	0.345 0.341 0.345
Reynolds criterion for the flow of heating water	–	$\mathrm{Re}=\frac{v_{hw}\cdot d_{\mathrm{out}}}{\nu }$	45,397.8 44,793.84 44,109.21	85,120.87 83,988.44 82,704.78	58,556.58 59,243.46 58,556.58
The Nusselt Criterion	–	$Nu=0.4{\mathrm{Re}}^{0.6}\cdot {\mathrm{Pr}}^{0.36}{(\frac{{\mathrm{Pr}}_{\mathrm{liquid}}}{{\mathrm{Pr}}_{\mathrm{wall}}})}^{0.25}$	349.339 346.543 343.355	509.387 505.310 500.662	406.979 409.837 406.979
Thermal conductivity of heating water	W/(m·°C)	–	659 658 657	678 677 676	659 658 657
Heat transfer coefficient from the heating water to the evaporator pipes	W/(m·°C)	${\alpha }_1=\frac{Nu\cdot {\lambda }_{hw}}{d_{out}}$	16,443,893 16,287,529 16,113,182	24,668,894 24,435,359 24,174,828	19,157,074 19,262,315 19,098,934
The average wall temperature of the pipes of the heating battery of the evaporator	°C	$t_{\mathrm{wall}}=0.5(t_1^{\mathrm{av}}+t_b)$	53.512 52.838 52.164	53.512 52.838 52.164	68.3 67.65 67
The average temperature difference between the pipe wall and the boiling brine	°C	$\delta t_{\mathrm{ev}}=t_{wall}-t_b$	11.48743 11.1619 10.8355	11.48743 11.1619 10.8355	18.7 18.35 18
Heat transfer coefficient from pipes to boiling brine	W/(m·°C)	${\alpha }_2=25.5{(0.01\cdot p_b)}^{0.58}\cdot \delta t_{ev}^{2.33}$	1740.405 1611.662 1488.931	1740.405 1611.662 1488.931	6794.061 6437.442 6090.232
Pipe wall thickness and scale	m	${\delta }_{wall}=0.5(d_{out}+d_{in})$	0.001	0.001	0.001
Coefficient of thermal conductivity of the pipe wall material	W/(m·°C)	–	28	28	28
Thermal conductivity coefficient of scale	W/(m·°C)	–	0.8	0.8	0.8
Heat transfer coefficient from heating water to brine	W/(m·°C)	$K_{\mathrm{ev}}=\frac{1}{(\frac{1}{{\alpha }_1}+\frac{{\delta }_{wall}}{{\lambda }_{wall}}+\frac{{\delta }_{\mathrm{scale}}}{{\lambda }_{\mathrm{scale}}}+\frac{1}{{\alpha }_2})}$	796.112 795.821 795.498	796.112 795.822 795.498	798.830 798.778 798.722
Temperature pressure in the evaporator heating battery	°C	$\Delta t_{ev}=\frac{(t_1^{\prime }-t_{out.w}^{″})-(t_1^{″}-t_b)}{\ln (\frac{(t_1^{\prime }-t_{out.w}^{″})}{(t_1^{″}-t_b)})}$	36.085 34.268 32.428	34.545 32.240 29.928	54.471 52.692 50.904
Heat load of the evaporator	kJ/h	$Q_1^{″}=3.6K_{ev}\cdot F_{ev}\cdot \Delta t_{ev}$	2,585,560 2,454,476 2,321,748	2,475,208 2,309,198 2,142,746	3,916,221 3,788,064 3,659,278
The calculated value of the heat load of the condenser	kJ/h	$Q_c^e=Q_1^e\cdot \eta$	2,277,000	2,128,500	3,366,000
Evaluation of HEU performance by the amount of evaporated water	m3/h	$W_2=\frac{Q_1^e}{{\rho }_{fw}\left[(1+\epsilon )c_{fw}\cdot (t_b-t_{fw})\right]}$	0.774	0.722	0.786
The speed of cooling water in the condenser pipes	m/s	$v_{out.w}=\frac{4W_{cool}\cdot f_{ev}}{3600\pi \cdot d_{in}^2\cdot z_{ev}}$	1.036	1.036	1.036
Heat transfer coefficient of the condenser	W/(m2·°C)	$K_c=923\sqrt{{\nu }_{out.w}}\cdot \sqrt[4]{t_{out.w}^{av}+17.8}$	2095.952	2091.838	2125.407
Calculated temperature pressure in the condenser	°C	$\Delta t_c^e=\frac{(t_1^{ave}+t_{out.w}^{av})}{(1+\sqrt{\frac{K_c}{K_{ev}}})}$	27.179	27.195	31.243
Secondary steam temperature in the evaporator	°C	$t_2^e=t_{out.w}+\frac{\delta t_{out.w}^e}{2}+\Delta t_c^e$	34.153	33.975	39.639
Secondary steam pressure in the evaporator	kPa	–	5.4	5.29	5.6
Temperature difference of heating water and secondary steam	°C	$\Delta t=(t_1^{ave}+t_2^e)$	30.046	30.224	35.560
Secondary steam pressure	kPa	$p_c=p_2^e+\Delta p$	5.22	5.11	5.42
Distillate temperature	°C	–	33.67	33.28	34.3
Enthalpy of distillate	kJ/kg	–	140.98	139.38	143.52
Enthalpy of secondary steam	kJ/kg	–	2562.2	2561.8	2563.6
Distillate density	kg/m 3	–	993.24	994.6	994
The multiplicity of condenser cooling	–	$M=\frac{W_{cool}}{W_2}$	122.684	131.520	120.790
Specific heat load of the condenser	kJ/(m2 h)	$q_t=\frac{Q_c^e}{F_c}$	87,576.92	81,865.38	129,461.5
Specific steam load of the condenser	kJ/(m2 h)	$q_{st}=W_2\cdot \frac{{\rho }_g}{F_c}$	29.581	27.631	30.067
Heating of the cooling water in the condenser	°C	$\delta t_{out.w}^{\delta }=\frac{W_2\cdot {\rho }_g(h^{″}-h^{\prime })}{W_{cool}\cdot {\rho }_{out.w}\cdot c_{out.w}}$	4.864	4.545	4.941
Intake water pump head	m	$H_{out.w}=\frac{{10}^3(p_{ing}-p_{su})}{{\rho }_{out.w}\cdot g}$	26.767	26.767	26.767
Pump feed	m3/s	$Q_{out.w}=1.2\frac{W_{cool}}{3600}$	0.0316	0.0316	0.0316
Pump power	kW	$N_{out.w}=\frac{g\cdot {\rho }_{out.w}\cdot H_{out.w}\cdot Q_{out.w}}{(1000\cdot {\eta }_m)}$	10.647	10.647	10.647
Power of the drive motor	kW	$N_{e1}=\frac{N_{out.w}}{{\eta }_{em}}$	12.52696	12.52696	12.52696
The suction pressure of the distillate pump	kPa	$p_{su}=-101.3+P_c+(\mathrm{3...5})$	−92.08	−92.19	−91.88
Discharge pressure	kPa	–	264.7	264.7	264.7
Pump head	m	$H_d=\frac{{10}^3(p_{ing}-p_{su})}{{\rho }_g\cdot g}$	36.616	36.577	36.568
Pump feed	m/s	$Q_d=(\mathrm{3.5...4})\frac{W_2}{3600}$	0.00086	0.000803	0.000874
Pump power	kW	$N_d=\frac{g\cdot {\rho }_g\cdot H_d\cdot Q_d}{(1000\cdot {\eta }_m)}$	0.341	0.318	0.346
Power of the drive motor	kW	$N_{e2}=\frac{N_d}{{\eta }_m}$	0.426	0.397	0.432
Electricity consumption for the production of 1 m3 of distillate	kW	$q_e=\frac{(N_{e1}+N_{e2})}{W_2}$	16.728	17.893	16.478

.

The power function in Figure 11 of the dependence of the amount of heating water on the heat load of the evaporator is as follows: at the expense of 80 m³/h: y = 0.000003139581868 × 0.997860639930083; at the expense of 150 m³/h: y = 0.000001676697004 × 0.997860639905449 [56].

The power function in Figure 12 of the dependence of the amount of heating water on the heat load of the evaporator: at the temperature of the heating water 68 °C: y = 0.000003139581868 × 0.997860639930083; at the temperature of the heating water 90 °C: y = 0.000003285180381 × 0.994136417876874 [56].

3.2. Modeling in ANSYS

Standard k-ε(+2E) is a two-parameter RANS model that is computationally efficient and applicable to a wide range of flows. It uses wall-mounted functions and applies only to stationary turbulent flows. However, in this model, there is significant vortex diffusion in many problems. It should be noted that this model can take into account the influence of compressibility and natural convection, which is useful when calculating industrial cooling systems. However, it is not suitable for solving the problem of boiling the refrigerant due to the large error and low convergence of the results at boiling.

The authors concluded that transient flow models should be used (models simulate only the transition from laminar to turbulent flow; the wall function is used).

The transient turbulence model k-kl-ω (+3E) is a widely used turbulence model that combines models k-ε and k−ω together with the Baldwin–Lomax model. This combination of models provides a reliable method for predicting flow behavior in transient regimes, which is especially useful when calculating boiling due to its unstable nature and complexity of forecasting.

The transition model k-kl-ω (+3E) has several advantages over other turbulence models. It can accurately predict the beginning of the transition from laminar to turbulent flow, which is a problem for many turbulence models. In addition, the transition k-kl-ω (+3E) is a three-parameter model and is suitable for solving heat transfer problems in elements that create turbulence, for example, on turbine blades. However, the transition model k-kl-ω (+3E) also has some disadvantages. It is relatively complex and requires significant computing resources to solve. In addition, it is more prone to numerical instability compared to simpler turbulence models, which may make it difficult to use it in some problems. Finally, the model is based on the use of a transition coefficient to another model, which can lead to inaccuracies and errors if the coefficient is set incorrectly.

Boundary conditions:

• The emulsion flow is set from the condition of the appearance of a two-zone liquid flow at the beginning of boiling on the lower surface.
• The temperature of the liquid saturation container is set from the theoretical calculation condition.
• Based on the saturation temperature, the burdened degree of dryness of the vapor-liquid mixture in the transition state is established.

Conditional data of the tank size, water temperature and heating elements were taken for modeling.

Initial data:

Tank dimensions:

length: 0.2 m;

width: 0.2 m;

height: 0.35 m;

Water level: 0.1 m;

Temperature of heating element: 106 °C;

Power of heating element: 3 kW;

Initial water temperature: 80 °C.

A computer simulation was conducted and calculations of liquid evaporation were carried out in which assumptions were made; heating from the heating element is applied to the bottom of the tank and evenly distributed over the area (0.2·× 0.2 = 0.04 m²) in Figure 13.

The calculation was performed in a two-dimensional formulation. Two rectangular surfaces were constructed. The first one is 0.2 × 0.1 m in size, referring to the poured water. The second one is 0.2 × 0.25 m, related to vacuum (Figure 14).

4. Grid

CFD was chosen as the preferred physics, and Fluent is chosen as the solver. The size of the grid structure was set to 0.002 (Figure 15).

During the calculation, the process time was extended twice due to the long boiling period. After the expiration of 4 min, the water temperature rose by 9 °C (Figure 16a). Additionally, when considering the volume fraction of steam, you can see that it boils (Figure 16b). The screenshots above show the estimated time.

Next, 6 min were added in 0.5 s increments followed by another 4 min in 2 s increments. As a result, it was revealed that the water was heated to 100 °C in 13 min. However, at this point, the problem becomes obvious: the water–vacuum interface line turned out to be a solid wall at the set settings, due to which steam was locked in the water area. As a result, before reaching the 15th minute, an explosion occurred, and the solid wall was knocked out due to the high pressure created by steam (Figure 17).

The simulation involves solving the problem of fluid flow in a gravitational field with the formation of vapor bubbles. In order to achieve satisfactory accuracy, a transient turbulence model is used in the non-stationary formulation of problems about the effect of the heating wall on the evaporated liquid k-kl-ω. This three-parameter model, which is part of the RANS group, is suitable for a narrow range of tasks and allows for modeling the transition from laminar to turbulent flow. This model uses wall functions. The main equations solved in the mathematical model are the energy equation, as well as the turbulence and turbulence dissipation model equations.

The lifting force that causes the mixing of the flow occurs due to convection, which is described by the Boussinesq approximation. In this approximation, the system of Navier–Stokes equations and the energy equation are solved using a special dependence of density on temperature only when calculating the volumetric force.

The approximation makes it possible to take into account the gravitational field, that is, the aspiration of the vapor bubbles in the direction opposite to gravity, respectively, and so to take into account the orientation of the tube in space.

5. Discussion

In light of economic and technological developments, studies show the potential of hydrogen demand to be 4% to 10% of global energy demand by 2051. This is consistent with the presence of millions of fuel vehicles in the world. The most promising hydrogen technology is fuel cell vehicles. The development of hydrogen as an energy carrier depends on improved end-use technologies, significant cost reductions, comparison with alternative technologies, and the construction of hydrogen infrastructure.

Consider Figure 18.

In the future, a series of energy-efficient hybrid and electric battery vehicle alternatives will become available with low investment costs. Hydrogen is a supplemental fuel for future hybrid vehicles as well as renewable source of electricity and with limited potential as biofuel. Hydrogen can reduce greenhouse gas emissions within customer segments that cannot be covered by electric vehicle battery and vehicle size combinations. It needs to be analyzed in greater detail in order to clarify concepts for use in the future of hybrid vehicles. The prerequisite for significant environmental benefit is the production of competitive hydrogen through renewable energy sources. A future option in this context is solar thermal hydrogen production.

There are many constraints related to components materials and operating concepts which are defined in order to maintain stable and commercially available solar thermal processes. It is necessary to further improve technical concepts for mass flows and thermal processes. Other problems include spatial temperature gradients and temporal change of load. The main objectives of research are the selection, adoption and rehabilitation of the appropriate resistance for the main components [58]. Commercial stations with a capacity exceeding 120 MW are anticipated for the future. In addition, carbon-free solar thermal processes that produce pure hydrogen are still in the early development stage.

First, it is expected that there will be commercial factories for mass production after 2020. The prototype plant was already implemented a few years ago, and the development of solar energy and the methane improvement process started early. Traditional technology can be added or combined in plants in order to be able to produce at a competitive speculative cost of approx.

It will be cheaper and cheaper to obtain hydrogen using fossil fuels until at least 2030 provided that this process is associated with carbon storage and capture. Commercial competitive options for hydrogen fuel cells are electrolysis, renewable energies and wind energy. Methane can be developed by solar steam. It may compete with conventional gas and hydrogen synthesis in a few years, depending on the evolution of the process and natural gas prices. The long-term costs of carbon-free solar thermal operations are completely autonomous.

The production of components and materials should be researched in addition to research and development work. Hydrogen transport from the solar thermal processes of the continents appears only possible in the long run because of cost and energy losses. However, not only the potential demand for hydrogen for transportation alone is considered a catalyst for the improvement of the solar thermal process. The most important direct reason for improving solar thermal processes and building pilot plants in the future is regions with higher solar radiation due to increased industrial demand for hydrogen.

An estimated 3.5 EJ of hydrogen will be available from future solar thermal plants. The sites of the pilot plants require direct and high solar radiation above 2.200 kW/m² and the availability of electricity, water and gaseous methane. Seawater desalination and cleaning solar heat can be used to supply water demand for hydrogen production.

Despite the challenges, problems, and difficulties of solar thermal processes, it is expected to have great potential for clean, pollutant-free and sustainable hydrogen production, using clean water, solar energy and approximate hydrogen sources without restrictions. Conventional costs of hydrogen production depend on the price and availability of fossil fuels, while the cost of emerging solar energy operations is large and high. Reductions are expected due to further development of design and production techniques for the process and components.

Solar hydrogen markets could improve due to climate and political demand for renewable energy and hydrogen. As a result, it should include industrial and political advertising for hydrogen technologies, a clear strategy to obtain permanent hydrogen in the future and implement renewable energy.

Solar hydrogen was produced using photovoltaic cells based on a polymeric tidy membrane.

The software study was carried out by relying on the direct connection method of the hydrogen analyzer with the photovoltaic system and the second method by designing an integrated system for the electro-hydrogen analyzer [59].

From the results, we find that the first method is less effective and efficient than the second because, during the day, the intensity of solar radiation changes, as the yield of hydrogen production in the second method reached 2.5 per hour, while in the first direct method 1.16 per hour.

The optimum spacing distance is 1.5 cm, and the greater the distance between the electrodes, the lower the hydrogen flow.

Some additives such as KOH can enhance and hydrogen flow and electrolyte ionization.

Consider Figure 19.

Consider Figure 20.

Consider Figure 21.

Consider Figure 22.

The previous figures and circuit modeling indicate that the temperature of the solution, the number of rays falling on the solar panel, the area of the panel and the resulting solar thermal energy are all directly proportional to the amount of hydrogen produced.

Initially, the hydrogen flow will be faster when the solution is cooler and it is not the peak hour in the middle of the day; the hydrogen flow will be greater in the early hours of the day or at the end of the day.

Additionally, the relationship between the volume of hydrogen over time and with the electrical tension is direct, and its production rate reaches about 0.5 milliliters per hour.

6. Conclusions

The production of hydrogen using solar thermal energy has been thoroughly studied from various points of view, including economic, technological and hydrogen sources. Traditional methods such as steam conversion of methane, high-temperature electrolysis of water and thermochemical cycles have been evaluated for their viability in the production of hydrogen using solar energy. A study was also conducted on the generation of hydrogen using a solar electrolyzer based on polymer ion exchange membrane technology.

Two methods of hydrogen generation were considered: a direct connection of the photovoltaic system with a hydrogen analyzer and a solar electrolysis system with maximum power tracking of the photovoltaic system to ensure a constant supply of current voltage to the hydrogen analyzer. The solar electrolysis system proved to be more efficient due to the instability of the intensity of solar radiation during the day. In addition, it was found that the addition of potassium hydroxide increases the ionization of the electrolyte and improves the flow of hydrogen.

Hydrogen has been studied as a means of transferring energy and reducing air pollution and global warming. Renewable energy sources can be used in the electrolysis of water to produce hydrogen, which is an attractive option for future energy systems due to the potential demand for hydrogen in various sectors.

Solar hydrogen markets may improve due to climate change and the demand for renewable energy and hydrogen. It is extremely important to develop clear strategies for obtaining permanent hydrogen in the future and to introduce renewable sources to ensure the safety of energy sources. Despite the difficulties, solar thermal processes have the potential to significantly improve the future use of hydrogen due to cost and performance.

In conclusion, it should be noted that solar thermal processes offer a promising option for the production of clean and environmentally friendly hydrogen. The use of polymer exchange membrane technology in solar electrolyzers has shown promising results that can be improved in the course of further research and development. However, for wider implementation, it is necessary to solve problems such as infrastructure for storing and transporting hydrogen.

The applicability of the scheme is limited to the areas in which the proposed method of producing hydrogen with renewable energy can be used, i.e., the availability of additional equipment, as well as due to restrictions on storage and transportation of the final product.