Hydrogen production probability distributions for a PV-electrolyser system

In this study, we comprehensively analyze the probability distribution of the hydrogen production for PV assisted PEM electrolyser system. A case study is conducted using the experimental data taken from a recently installed system in Balikesir University, Turkey. A novel computational tool is developed in Matlab-Simulink for analyzing the data. The concept of probability density frequency is successfully applied in the analyses of the wind speed and the solar energy in literature. This study presents a method of applying this knowledge to solar energy assisted hydrogen production. The change in the probability distribution of the hydrogen production with the solar irradiation throughout a year is studied and illustrated. It is found that the maximum amount of hydrogen production occurs at between 600 and 650 W/m² of solar radiation. Annual hydrogen production is determined as 2.97 kg for per m² of PV system. Average hydrogen production efficiency of the studied PEM electrolyser is found to be 60.5% with 0.48 A/cm² of current density. The presented results of this study are expected to be valuable for the researchers working on renewable hydrogen production systems.     

Performance assessment study of photo-electro-chemical water-splitting reactor designs for hydrogen production

Solar water splitting is considered a greatly promising technique for producing clean hydrogen fuel. However, limited studies have paid attention to the designs of photo-electrochemical (PEC) reactors. In this regard, two different designs of PEC reactor are proposed and studied numerically in the present paper. The effects of important design parameters on the system performance are also investigated. The PEC governing equations of transport phenomena related to water splitting reactor are developed and numerically solved. According to the current results, the rate of the hydrogen volume production and the solar - to - hydrogen conversion efficiency increase as an applied solar incident flux increases for both proposed designs. The solar - to - hydrogen conversion efficiencies are calculated to be 12.65% for design 1 and 12.48% for design 2. The hydrogen volume production rate is performed to achieve 78.3 L/m² h by design 1, and 74.8 L/m² h by design 2.     

Oxide particles as combined heat storage medium and sulphur trioxide decomposition catalysts for solar hydrogen production through sulphur cycles

Within the general framework of investigating novel routes for solar hydrogen production, the idea of combining a solar centrifugal particle receiver with sulphur thermochemical cycles, involving SO₃ dissociation to SO₂ and O₂ as key step, is pursued. In this perspective, the present work concerns the synthesis, development, evaluation and characterisation of particles suitable to operate as media for direct solar irradiation absorption, transfer and storage as well as catalysts for the SO₃ dissociation reaction. Commercial bauxite-based proppants were modified to incorporate raw materials with elements known for their catalytic activity with respect to the SO₃ dissociation, namely iron, copper, manganese and their combinations. The catalytic activity of such modified proppants was tested in fixed bed reactor test rigs at 850 °C and ambient pressure with concentrated liquid sulphuric acid as feedstock. Extensive screening tests complemented by physicochemical properties measurements before and after catalytic testing, identified systems that at 850 °C, 1 atm and Gas Hourly Space Velocity of 11,800 h⁻¹ could achieve high SO₃ conversions (60%, corresponding to 68% of equilibrium value) for over 125 h of continuous operation. This performance was achieved without degradation of their mechanical strength which, in fact exhibited a slight increase from 53 N in the fresh state to 55 N after long-term exposure to reaction conditions. However such systems were susceptible to colour alteration, affecting adversely their absorptance in the 1000–2500 nm wavelength range. Compositions with the best combination of properties are scheduled for large-scale synthesis and on-site testing in a pilot-scale solar receiver.     

Photo-electro-chemical chlorination of cuprous chloride with hydrochloric acid for hydrogen production

In this paper, a new photochemical cell is developed and analyzed for copper disproportionation within the Cu–Cl water splitting cycle. In the disproportionation step, cuprous chloride reacts with hydrochloric acid to generate cupric chloride and hydrogen gas. In past literature, it has been demonstrated that this reaction can be conducted electrochemically at 24 bars and 100 °C. This reaction is attractive because it generates compressed hydrogen. Consequently, the work required to compress hydrogen from standard pressure – to 350 bars for example – reduces approximately by 95%. To conduct this reaction electrochemically, the process requires electricity input. Rather than using an external supply, the method proposed in this paper drives the reaction 2CuCl(aq) + 2HCl(aq) → 2CuCl₂(aq) + H₂(g) with photonic energy derived from solar radiation. The photochemical cell comprises one photochemical and one electrochemical reactor separated by a proton conducting membrane. The electrochemical reactor is a half electrolysis cell where CuCl liquid is disproportionated with hydrochloric acid by releasing protons, according to 2CuCl(aq) + 2HCl(g) → 2CuCl₂(aq) + 2H⁺ + 2e⁻. The electrons are transferred to the second reactor by an electron-conducting media, consisting of electrodes and an external circuit. In the photochemical reactor, there are supramolecular complexes dissolved in dimethylformamide that generate multi-electrons at active sites under the influence of solar radiation and catalyze water reduction according to 2H₂O + 2e⁻ → H₂(g) + 2OH⁻. Gaseous hydrogen is collected from above the second reactor, while hydroxyl ions combine with the protons that cross the PEM to supply water according to 2OH⁻ + 2H⁺ → 2H₂O. The overall process is assisted electrically by a dye sensitized solar cell. An optical system including solar concentration, spectral splitting and an optical fibre is developed for enhanced solar energy absorption to supply thermally and electrically the Cu–Cl cycle with energy input. This paper examines the feasibility and expected efficiency of the photochemical disproportionation cell and describes the potential benefits of the thermo-photochemical water splitting process, in contrast to conventional thermochemical water splitting.     

Experimental investigation of hydrogen production integrated methanol steam reforming with middle-temperature solar thermal energy

Developing a hydrogen production method that utilizes solar thermal energy in an effective manner is a great challenge. In this paper we propose a new approach to solar hydrogen production with the integration of methanol steam reforming and middle-temperature solar thermal energy. An experiment on hydrogen production is conducted using a 5-kW solar reactor at 150−300 °C under atmosphere pressure. The 5-kW solar receiver/reactor is fabricated and positioned along the focal line of one-tracking parabolic trough concentrator. As a result, the chemical conversion of methanol can reach levels higher than 90%, and the volumetric concentration of hydrogen in the gas products can account for 66−74% above the solar flux of 580 W/m². The obtained maximum hydrogen yield per mole of methanol is 2.65−2.90 mol, approaching the theoretical maximum value, and the experimentally obtained thermochemical efficiency of solar thermal energy converted into chemical energy is in the range of 30−50%, which is competitive with other high-temperature solar thermochemical processes. A kinetic model of solar-driven methanol steam reforming related to solar flux is also derived based on the experimental data. The promising results demonstrate that this solar-driven hydrogen production method can be feasible in practical applications.     

Thermoeconomic analysis and artificial neural network based genetic algorithm optimization of geothermal and solar energy assisted hydrogen and power generation

The study aims to optimize the geothermal and solar-assisted sustainable energy and hydrogen production system by considering the genetic algorithm. The study will be useful by integrating hydrogen as an energy storage unit to bring sustainability to smart grid systems. Using the Artificial Neural Network (ANN) based Genetic Algorithm (GA) optimization technique in the study will ensure that the system is constantly studied in the most suitable under different climatic and operating conditions, including unit product cost and the plant's power output. The water temperature of the Afyon Geothermal Power Plant varies between 70 and 130 °C, and its mass flow rate varies between 70 and 150 kg/s. In addition, the solar radiation varies between 300 and 1000 W/m² for different periods. The net power generated from the region's geothermal and solar energy-supported system is calculated as 2900 kW. If all of this produced power is used for hydrogen production in the electrolysis unit, 0.0185 kg/s hydrogen can be produced. The results indicated that the overall energy and exergy efficiencies of the integrated system are 4.97% and 16.0%, respectively. The cost of electricity generated in the combined geothermal and solar power plant is 0.027 $/kWh if the electricity is directly supplied to the grid and used. The optimized cost of hydrogen produced using the electricity produced in geothermal and solar power plants in the electrolysis unit is calculated as 1.576 $/kg H₂. The optimized unit cost of electricity produced due to hydrogen in the fuel cell is calculated as 0.091 $/kWh.     

Hydrogen production from methane using vanadium-based catalytic membrane reactors

The application of vanadium-based membranes as the hydrogen separation membrane for a catalytic membrane reactor system was investigated for the direct production of hydrogen from methane. The methane conversion and hydrogen production rates of the catalytic membrane reactor system with Pd-coated 100 μm-thick vanadium-based membranes were comparable with the reactor using 50 μm-thick Pd–Ag alloy membrane at all temperatures examined. The methane conversion rates of the catalytic membrane reactor with the Pd-coated vanadium-based membranes were approximately 35% and 62% at 623 K and 773 K, respectively. The hydrogen production rates were around 660  μmol min⁻¹ at 623 K, and reached over 1710  μmol min⁻¹ at 773 K. The relationship between the methane conversion rates and hydrogen permeation fluxes of the catalytic membrane reactor confirmed that the removal of hydrogen from the reaction site enhances the methane decomposition reaction. Further, the vanadium based membrane exhibited good stability against Fe in a hydrogen containing atmosphere.     

Experimental validation of a pilot membrane reactor for hydrogen production by solar steam reforming of methane at maximum 550 °C using molten salts as heat transfer fluid

An innovative steam reformer for hydrogen production at temperatures lower than 550 °C has been developed in the EU project CoMETHy (Compact Multifuel-Energy To Hydrogen converter). The steam reforming process has been specifically tailored and re-designed to be combined with Concentrating Solar plants using “solar salts”: a low-temperature steam reforming reactor was developed, operating at temperatures up to 550 °C, much lower than the traditional process (usually > 850 °C). This result was obtained after extensive research, going from the development of basic components (catalysts and membranes) to their integration in an innovative membrane reformer heated with molten salts, where both hydrogen production and purification occur in a single stage. The reduction of process temperatures is achieved by applying advanced catalyst systems and hydrogen selective Pd-based membranes. Process heat is supplied by using a low-cost and environmentally friendly binary NaNO₃/KNO₃ liquid mixture (60/40 w/w) as heat transfer fluid; such mixture is commonly used for the same purpose in the concentrating solar industry, so that the process can easily be coupled with concentrating solar power (CSP) plants for the supply of renewable process heat. This paper deals with the successful operation and validation of a pilot scale reactor with a nominal capacity of 2 Nm³/h of pure hydrogen from methane. The plant was operated with molten salt circulation for about 700 h, while continuous operation of the reactor was achieved for about 150 h with several switches of operating conditions such as molten salts inlet temperature, sweep steam flow rate and steam-to-carbon feed ratio. The results obtained show that the membrane reformer allows to achieve twice as high a conversion compared to a conventional reformer operating at thermodynamic equilibrium under the same conditions considered in this paper. A highly pure hydrogen permeate stream was obtained (>99.8%), while the outlet retentate stream had low CO concentration (<2%). No macroscopic signs of reactor performance loss were observed over the experimental operation period.     

Integrated design of hydrogen production and thermal energy storage functions of Al-Bi-Cu composite powders

In recent years, the hydrolysis of Al-based composite powders to produce hydrogen has become a hot topic in the field of hydrogen energy research. However, the hydrogen generation products of Al-based alloys have not been reasonably utilized. For this purpose, this study proposed a novel research idea to achieve the integrated design of hydrogen production and thermal energy storage functions of Al-based composite powders. Specifically, Al-Bi-Cu composite powders with stable hydrogen production were taken as research objects. The hydrogen was obtained by the reaction of Al-Bi-Cu alloy powders with H₂O for different reaction times, and then the hydrogen generation products were directly sintered at high temperature to obtain Al-Cu alloy based composite phase change thermal energy storage materials. The results indicated that at 50 °C, the hydrogen yield of Al-Bi-Cu alloy powders in 100min, 200min and 400min are 319.9 mL/g, 428.5 mL/g and 665.8 mL/g, respectively. Importantly, the Al-Cu alloy based composite phase change thermal energy storage materials prepared by the hydrogen generation products exhibited an adjustable phase change temperature (577.3 °C ∼ 598.2 °C), high thermal energy storage density (44.1J/g ∼ 153.5J/g), good thermal cycling stability and structural stability.     

Modeling of a direct solar receiver reactor for decomposition of sulfuric acid in thermochemical hydrogen production cycles

Hydrogen production thermochemical cycles, based on the recirculation of sulfur-based compounds, are among the best suited processes to produce hydrogen using concentrated solar power. The sulfuric acid decomposition section is common to each sulfur-based cycle and represents one of the fundamental steps. A novel direct solar receiver-reactor concept is conceived, conceptually designed and simulated. A detailed transport phenomena model, including mass, energy and momentum balance expressions as well as suitable decomposition kinetics, is described adopting a finite volume approach. A single unit reactor is simulated with an inlet flow rate of 0.28 kg/s (corresponding to a production of approximately 11 kg_H2/h in a Hybrid Sulfur process) and a direct solar irradiation at a constant power of 143 kW/m². Results, obtained for the high temperature catalytic decomposition of SO₃ into SO₂ and O₂, demonstrate the effectiveness of the proposed concept, operating at pressures of 14 bar. A maximum temperature of 879 °C is achieved in the reactor body, with a corresponding average SO₂ mass fraction of 27.8%. The overall pressure drop value is 1.7 bar. The reactor allows the SO₃ decomposition into SO₂ and O₂ to be realized effectively, requiring an external high temperature solar power input of 123.6 kJ/molSO2 (i.e. 123.6 kJ/mol_H2).     

Oxidation reaction kinetics for the steam-iron process in support of hydrogen production

A hydrogen generation research program is focused on solar-driven hydrogen production by means of reactive metal water splitting. In order to dissociate water molecules at significantly reduced thermal energies as well as providing a practical means for efficient hydrogen and oxygen separation, an intermediary reactive material is introduced to realize water splitting in the form of an oxidation reaction. Elemental iron is used as the reactive material in the process commonly referred to as the steam-iron process. In order to exploit the unique characteristics of highly reactive materials and ultimately achieve the potential efficiency gains at the solar reactor scale, a monolithic laboratory-scale reactor has been designed to explore the fundamental kinetic rates during the iron oxidation reaction at temperatures ranging from about 650 to 900 K. Results show hydrogen production rates on the order of 1E-8 g/cm² s. Micro-Raman spectroscopy is used to access information on the exact iron oxide phase produced, and high resolution SEM and electron dispersion spectroscopy (EDS) are used to assess the oxide morphology and further quantify the oxide state, including spatial distributions.     

Application of aspen plus to renewable hydrogen production from glycerol by steam reforming

Steam reforming is the most favored method for the production of hydrogen. Hydrogen is mostly manufactured by using steam reforming of natural gas. Due to the negative environmental impact and energy politics, alternative hydrogen production methods are being explored. Glycerol is one of the bio-based alternative feedstock for hydrogen production. This study is aimed to simulate hydrogen production from glycerol by using Aspen Plus. First of all, the convenient reactor type was determined. RPlug reactor exhibited the highest performance for the hydrogen production. A thermodynamic model was determined according to the formation of byproduct. The reaction temperature, water/glycerol molar feed ratio as reaction parameters and reactor pressure were investigated on the conversion of glycerol and yield of hydrogen. Optimum reaction parameters are determined as 500 °C of reaction temperature, 9:1 of water to glycerol ratio and 1 atm of pressure. Reactor design was also examined. Optimum reactor diameter and reactor length values were determined as 5 m and 50 m, respectively. Hydrogen purification was studied and 99.9% purity of H₂was obtained at 25 bar and 40 °C. The obtained results were shown that Aspen Plus has been successfully applied to investigate the effects of reaction parameters and reactor sizing for hydrogen production from glycerol steam reforming.     

Investigation of hydrogen production potential from different natural water sources in Turkey

Hydrogen production from the electrolysis of water by sea or lake waters used as electrolyte plays a crucial role in providing sustainable hydrogen production. Production of hydrogen from these natural sources is highly utilized from small scale to complex applications due to water resources' inconsumable potential. In this study, the hydrogen production potential of Turkey's different regions such as the Black Sea, Aegean Sea, Marmara Sea, Mediterranean Sea, Lake Van, Ağcaşar Dam, Yeşilırmak, and Kızılırmak rivers are investigated. Solar energy potential values are used as the current sources for simulating their renewable energy hydrogen production values. According to the results, higher hydrogen production rates are obtained from the Marmara and Lake Van regions. It is concluded that the hydrogen production potential is highly dependent on the pH values of the water source and the salinity rate of seawater that is descending from the Mediterranean Sea to the Black Sea region. Besides, solar radiation, sunshine duration, and water temperature are the other essential factors. Moreover, Mediterranean Sea water (Içel-Anamur) has about 23% higher hydrogen production than Lake Van and has the most increased hydrogen production by 80 L m^-2 in May and June.     

Development and test of a solar reactor for decomposition of sulphuric acid in thermochemical hydrogen production

Decomposition of sulphuric acid is a key step of sulphur based thermochemical cycles for hydrogen production by thermal splitting of water. The Hybrid Sulphur Cycle (HyS) consisting of two reaction steps is considered as one of the most promising cycles: firstly, sulphuric acid is decomposed by high temperature heat of 800–1200 °C forming sulphur dioxide, which in a second step is used to electrochemically split water. Compared to conventional water electrolysis only about a tenth of the theoretical voltage is required making the HyS one of the most efficient processes to produce hydrogen by concentrated solar radiation. As a result, this thermochemical cycle has the potential to significantly reduce the amount of energy required for water splitting and to efficiently generate hydrogen free of carbon dioxide emissions. The European research project HycycleS aims at a technical realisation of the HyS. One objective of the project is to develop and qualify a solar interface, meaning a device to couple concentrated solar radiation into the endothermal steps of the chemical process. Therefore, a test reactor for decomposition of sulphuric acid by concentrated solar radiation was developed and tested in the solar furnace of DLR in Cologne. Tests in concentrated solar radiation were carried out for temperatures of the honeycomb up to 950 °C decomposing sulphuric acid of 50 and 96 weight-percent. Mass and energy flow of the process were calculated in order to determine energy efficiency and chemical conversion. The influence of process parameters like temperature, flow rates and space velocity on chemical conversion and reactor efficiency was analysed in detail. If catalysts like iron oxide (Fe₂O₃) and mixed oxides (i.e. CuFe₂O₄) were used a conversion of SO₃ to SO₂ of more than 80% at a thermal efficiency of over 25% could be reached.     

Solar enriched methane production by steam reforming process: Reactor design

A novel hybrid plant for a mixture of methane and hydrogen (enriched methane) production from a steam reforming reactor whose heat duty is supplied by a molten salt stream heated up by a concentrating solar power (CSP) plant developed by ENEA is here presented. By this way, a hydrogen stream, mixed with natural gas, is produced from solar energy by a consolidated production method as the steam reforming process and by a pre-commercial technology as molten salts parabolic mirrors solar plant. After the hydrogen production plant, the residual heat stored in molten salt stream is used to produce electricity and the plant is co-generative (hydrogen + electricity).The heat-exchanger-shaped reactor is dimensioned by a design tool developed in MatLab environment. A reactor 3.5 m long and with a diameter of 2″ is the most efficient in terms of methane conversion (14.8%) and catalyst efficiency (4.7 Nm³/h of hydrogen produced per kg_cat).     

Performance evaluation of a photoelectrochemical hydrogen production reactor under concentrated and non-concentrated sunlight conditions

In this paper, we present the experimental performance evaluations of a newly developed photoelectrochemical (PEC) reactor for the production of hydrogen under no-light and concentrated solar radiation conditions. With a newly developed experimental setup, the solar light is concentrated about ten times, and the spectrum is divided using cold mirrors for better sunlight utilization. The photoelectrochemical reactor is examined at different applied potentials and the hydrogen production quantities are measured. Copper oxide, which is used as a light-sensitive material, is electrochemically coated on the cathode metal plate to increase the rate of hydrogen evolution under illumination. The present experiments are conducted to investigate the variation of reactor performance with intensified light conditions and the obtained results are compared with the dark conditions. The results of this study reveal that the hydrogen evolution rate was 41.34 mg/h for concentrated light measurement and 34.73 mg/h for no-light measurements at 2.5 V applied potential. The corresponding photocurrent generated under concentrated light at 2.5 V is found to be 0.63 mA/cm². Under the concentrated sunlight, the hydrogen production rates increase considerably which is led by the positive effect of the photocurrent contribution.     

The dynamic modeling and the exergy assessment of hydrogen synthesize and storage system with the power-to-gas concept for various locations

In this article, the solar hydrogen storage is modeled and hourly investigated with TRNSYS software. The Photovoltaic (PV) panel is employed for green power generation that is consumed in the electrolyzer subsystem and produced hydrogen. Additionally, the required electricity at the lack of enough solar irradiation is supplied from the grid. The performance of the system is comparatively analyzed for three main cities. Results show that the maximum power generation by PV panel is about 1670 kW in June which approximately is the same for two cities. The energy and Faraday efficiency of electrolyzer changes between 0.85-0.89 and 0.89–0.92 respectively. The amount of hydrogen production reaches 1235 m³/h for one of them in May. The total amount of hydrogen production is 13,181 m³/year in Yazd, 13,143 m³/year in hot city, and 13,141 m³/year in most populated city.     

Coupled hydrodynamic and kinetic model of liquid metal bubble reactor for hydrogen production by noncatalytic thermal decomposition of methane

Industrial-scale implementation of liquid metal bubble reactors (LMBRs) to produce hydrogen by methane decomposition will require large gas holdups (e.g., 20–30 vol%) and elevated gas pressures (>20 bar) to allow for practical reactor sizes. A realistic reactor design must account for the coupling between reaction kinetics and hydrodynamic effects. The gas holdup is predicted from the superficial gas velocity with a drift flux model that was experimentally corroborated in gas-molten metal mixtures. Large superficial gas velocities (>0.40 m s⁻¹) are required to achieve gas holdups of about 25 vol% in liquid metal baths (LMBs). A noncatalytic kinetic model is developed to provide thermodynamically consistent decomposition rates at methane conversions approaching equilibrium. The coupled model optimizes the LMB dimensions (diameter and length) and the inlet pressure to minimize the volume of liquid metal when the hydrogen production rate, bath temperature, methane conversion, metal composition, and maximum gas holdup are specified. For example, 200 kt a⁻¹ of hydrogen can be produced in an LMBR containing at least 96.5 m³ of molten tin held at 1100 °C in a bath measuring 3.50 m in diameter and 14.3 m in length, with an inlet methane pressure of 57.8 bar resulting in an average gas holdup of 29.7 vol% and a methane conversion of 65%.     

PDMA cryogel beads as a catalyst for hydrogen generation from NaBH4 alcoholysis

Poly[2-(dimethylamino)ethyl methacrylate] cryogel beads were prepared under cryogenic conditions via free radical polymerization and used as a catalyst in the production hydrogen (H₂) from NaBH₄ by alcoholysis. The efficiency of the catalyst was investigated in the range of 0–40 °C by both methanolysis and ethylene glycolysis reactions, and its reuse was tested. Accordingly, it was observed that the methanolysis reaction was faster than the ethylene glycolysis reaction. When the hydrogen generation rate (HGR) values between 0 and 40 °C were compared, it was concluded that the methanolysis reaction rate increased from 1550 to 4800 mL.min⁻¹g⁻¹ and the ethylene glycolysis reaction rate increased from 923 to 3551 mL.min⁻¹g⁻¹. In the alcoholysis reaction catalyzed by PDMA cryogel beads, the activation energy was calculated as 19.34 and 22.77 kJ.mol⁻¹ for the methanolysis and ethylene glycolysis reactions, respectively. After six repetitions, the catalyst activity was calculated over 50% for NaBH₄ methanolysis and ethylene glycolysis.     

Energy and exergy analyses and optimization study of an integrated solar heliostat field system for hydrogen production

In this paper, we propose an integrated system, consisting of a heliostat field, a steam cycle, an organic Rankine cycle (ORC) and an electrolyzer for hydrogen production. Some parameters, such as the heliostat field area and the solar flux are varied to investigate their effect on the power output, the rate of hydrogen produced, and energy and exergy efficiencies of the individual systems and the overall system. An optimization study using direct search method is also carried out to obtain the highest energy and exergy efficiencies and rate of hydrogen produced by choosing several independent variables. The results show that the power and rate of hydrogen produced increase with increase in the heliostat field area and the solar flux. The rate of hydrogen produced increases from 0.006 kg/s to 0.063 kg/s with increase in the heliostat field area from 8000 m² to 50,000 m². Moreover, when the solar flux is increased from 400 W/m² to 1200 W/m², the rate of hydrogen produced increases from 0.005 kg/s to 0.018 kg/s. The optimization study yields maximum energy and exergy efficiencies and the rate of hydrogen produced of 18.74%, 39.55% and 1571 L/s, respectively.