A flexible analytical model for operational investigation of solar hydrogen plants

Hydrogen will become a dominant energy carrier in the future and the efficiency and lifetime cost of its production through water electrolysis is a major research focus. Alongside efforts to offer optimum solutions through plant design and sizing, it is also necessary to develop a flexible virtualised replica of renewable hydrogen plants, that not only models compatibility with the “plug-and-play” nature of many facilities, but that also identifies key elements for optimisation of system operation. This study presents a model for a renewable hydrogen production plant based on real-time historical and present-day datasets of PV connected to a virtualised grid-connected AC microgrid comprising different technologies of batteries, electrolysers, and fuel cells. Mathematical models for each technology were developed from chemical and physical metrics of the plant. The virtualised replica is the first step toward the implementation of a digital twin of the system, and accurate validation of the system behaviour when updated with real-time data. As a case study, a solar hydrogen pilot plant consisting of a 60 kW Solar PV, a 40 kW PEM electrolyser, a 15 kW LIB battery and a 5 kW PEM fuel cell were simulated and analysed. Two effective operational factors on the plant's performance are defined: (i) electrolyser power settings to determine appropriate hydrogen production over twilight periods and/or overnight and (ii) a user-defined minimum threshold for battery state of charge to prevent charge depletion overnight if the electrolyser load is higher than its capacity. The objective of this modelling is to maximise hydrogen yield while both loss of power supply probability (LPSP) and microgrid excess power are minimised. This analysis determined: (i) a hydrogen yield of 38–39% from solar DC energy to hydrogen energy produced, (ii) an LPSP <2.6 × 10^?4 and (iii) < 2% renewable energy lost to the grid as excess electricity for the case study.     

Performance of a PV–wind hybrid system for hydrogen production

This paper describes the performance of an integrated PV–wind hydrogen energy production system. The system consists of photovoltaic array, wind turbine, PEM electrolyser, battery bank, hydrogen storage tank, and an automatic control system for battery charging and discharging conditions. The system produced 130–140 ml/min of hydrogen, for an average global solar radiation and wind speed ranging between 200 and 800 W/m² and 2.0 and 5.0 m/s respectively. A mathematical model for each component in the system was developed and compared to the experimental results.     

Comparative performance analysis of a grid connected PV system for hydrogen production using PEM water,methanol and hybrid sulfur electrolysis

This paper presents comparative performance analysis of photovoltaic (PV) hydrogen production using water, methanol and hybrid sulfur (SO₂) electrolysis processes. Proton exchange membrane (PEM) electrolysers are powered by grid connected PV system. In this system design, electrical grid is considered as a virtual energy storage system (VESS) where the surplus of PV production can be injected and subsequently taken to support the electrolyser. Methanol (ME) and hybrid sulfur (HSE) electrolysis are compared to the conventional water electrolysis (WE) in term of operating cell voltage. Based on the experimental results reported in the literature, semi-empirical models describing the relationship between the hydrogen production rate and the electrolyser cell power input are proposed. Furthermore, power and hydrogen management strategy (PHMS) is developed. Case study is carried out to show the impact of each type of electrolysis on the system component sizes and evaluate the hydrogen production potentialities. Results show that the use of ME allows to produce 65% more hydrogen than with using WE. Moreover, the amount of hydrogen produced is almost double in the case of HSE. At Algiers city, based on a grid connected PV/Electrolyser system, it is possible to produce about 25 g/m² d and 29 g/m² d of hydrogen, respectively, through ME and HSE compared to 15 g/m² d of hydrogen when using WE.     

Direct coupling of an electrolyser to a solar PV system for generating hydrogen

Hydrogen as an energy currency, carrier and storage medium may be a key component of the solution to problems of global warming, poor air quality and dwindling reserves of liquid hydrocarbon fuels. Hydrogen is a flexible storage medium and can be generated by the electrolysis of water. It is particularly advantageous if an electrolyser may be simply and efficiently coupled to a source of renewable electrical energy. This paper examines direct coupling of a polymer electrolyte membrane (PEM) electrolyser to a matched solar photovoltaic (PV) source for hydrogen generation and storage. Such direct coupling with minimum interfacing electronics would lead to substantial cost reduction and thereby enhance the economic viability of solar-hydrogen systems. The electrolyser is designed for fail-safe operation with multiple levels of safety and operational redundancy. A control system in the electrolyser unit provides for disconnection when required and for auto-start in the morning and auto shut-down at night, simultaneously addressing the goals of minimum energy loss and maximum safety. The PV system is a 2.4 kW array (20.4 m² total area) comprising 30, 12 V, 80 W, Solarex polycrystalline modules in a series–parallel configuration. The integrated system has been operated for approximately 60 days over a 4-month period from September 2007 to January 2008 with many periods of unattended operation for multiple days, experiencing weather ranging from hot and sunny (above 40 °C) to cool and cloudy. The principle and practicality of direct coupling of a suitably matched PV array and PEM electrolyser have been successfully demonstrated. Details of electrolyser operation coupled to a PV array along with modelling work to match current–voltage characteristics of the electrolyser and PV system are described.     

Off-grid solar-hydrogen generation by passive electrolysis

A novel embodiment of a polymer electrolyte membrane (PEM) electrolyser is presented as a means for producing hydrogen off-grid by the efficient absorption of the time-varying power output of a solar photovoltaic (PV) panel or array. The balance-of-plant power load was minimised using passive design principles to ensure efficient operation under cloudy, sunset and wintry conditions. Heat generated during the electrolysis process is stored when appropriate to significantly enhance the efficiency of hydrogen production after a period of darkness. A prototype field trial demonstrated the electrolyser's ability to track closely the highly variable output of the PV year-round under a wide range of operating conditions. Hydrogen yields for various geographical locations were estimated to vary from 25 to 65 kg p.a. for a 1.6 kW electrolyser with fixed-tilt PV panels depending on local levels of solar insolation. This could be increased to over 100 kg p.a. by employing a PV panel of greater capacity and a battery for absorbing the peak generation and then discharging it overnight to the electrolyser.     

Optimization and sensitivity analysis of a photovoltaic-electrolyser direct-coupling system in Beijing

Hydrogen as a clean energy carrier for solar energy can be produced by using photovoltaic-electrolyser (PVE) direct-coupling system that is well known as a kind of simple and low investment but unstable system for solar energy conversion. The key to improve hydrogen yield of a direct-coupling system is to keep its working points around maximum power point (MPP) of photovoltaic (PV) modules. The coupling of three different connection patterns of six PV modules with one electrolyser were investigated in summer, autumn and winter, three typical seasons in a year, to seek the optimum arrangement for higher system efficiency in Beijing (116°E, 40°N). A corresponding mathematics model of the system is applied to simulate and analyze the instantaneous efficiency of the system, which agreed well with the experimental results. The variation rate of the system instantaneous efficiency varies with the solar irradiation intensity, the ambient temperature and the resistance of the electrolyser. The working point that distinguishes the variation trends of the system efficiency is called the efficiency changing point (ECP). The author use a parameter V/V_m, the ratio between the voltage of the working point to the voltage of the maximum power point, to analyze the respective ECP of each factor above. It can be concluded that the variation rate of system instantaneous efficiency changes little with the above factors when the value of V/V_m of working point is smaller than that of the ECP and is sensitive to those factors when the value of V/V_m is larger than that of the ECP. Following the annual historical climate data in Beijing, the result of the annual analysis is that the best scheme for the experiment system with a 1 m² PV panel covering 1.05 m² areas of ground can convert 78.4 kWh of solar energy to hydrogen energy in 2012.     

Experimental investigation of solar hydrogen production PV/PEM electrolyser performance in the Algerian Sahara regions

This paper presents experimental results on the solar photovoltaic/PEM water electrolytes system performance in the Algerian Sahara regions. The first step is to present a photovoltaic module characterization under different conditions then validate the results by comparing the measured and calculated values. The main objective of this study is to develop a parametric study on the system performance (open-circuit voltage Voc, short circuit current Is, fill factor FF, maximum power Pm and the efficiency η) under hot climate conditions (Ouargla, Algeria). The ambient temperature effects and solar radiation on the solar PV performance characteristics were investigated using modeling and simulation analysis as well as experimental studies. The results show that the root mean squared error (RMSE) error of the currents and voltages and the mean bias error (MBE) are respectively 0.71%, 0.37% and 0.12%, 0.15%. The relative errors in the current and the voltage are respectively 0.83%–1.76%, and −0.58% to 0.83%. The second part provide some general characteristics concerning the indirect coupling of a lab scale proton exchange membrane (PEM) water electrolyser (HG60) powered by a set of our photovoltaic panels. Experimental results provide practical information for the modules and the electrolysis cells by the indirect coupling. The weather conditions effect on hydrogen production from the electrolyser was also investigated. The results showed a high hydrogen production of 284 L in one day for 08 h of running and the electrolyser power efficiency with solar PV system was between 18 and 40%.     

An experimental and modelling study of a photovoltaic/proton-exchange membrane electrolyser system

An experimental model of a photovoltaic (PV) module-proton exchange membrane (PEM) electrolyser system has been built. A model has been developed for each device separately based on the experimental results. Output current–voltage (I–V) characteristics of the PV module are modelled in respect to different irradiance and temperature conditions by experimental tests. Similarly, input I–V characteristic and hydrogen formation characteristic of the PEM electrolyser are measured and modelled. After these studies, combined PV module–PEM electrolyser system model is defined. There is a good agreement between model predictions and measurements. At 18–100% irradiance interval, operating points of PEM electrolyser on the PV module are predicted with relative errors of 0.1–0.8%. Furthermore, the study shows that these simple model system devices can easily be defined in MATLAB/Simulink and used to model similar systems of different size.     

Stand-alone operation of an alkaline water electrolyser fed by wind and photovoltaic systems

Over the last few years, hydrogen technologies have established themselves as key enablers in the medium and long-term development of a new energy model that offers greater sustainability and independence than the present-day one. In this respect, the integration of water electrolysis with renewable energy-based systems can play an important part in the large-scale production of sustainable hydrogen. This paper reports on the complete experimental characterisation of a 1 Nm³ h⁻¹ alkaline water electrolyser located in the Public University of Navarre (UPNa). Specifically, a study was made of the electrical performance, hydrogen production rate, purity of the gases generated and energy efficiency, for a range of operating currents (40–120 A), temperatures (35–65 °C) and pressures (5–25 bar). Additionally, an experimental study was conducted on the electrolyser operation under conditions that are characteristic of a stand-alone wind power and PV-based renewable energy system, installed at the UPNa. The results obtained for the wind power and PV emulations showed that the electrolyser performed correctly, with regard to balance of plant and its principal electrochemical characteristics. Furthermore, the mean energy efficiency of the electrolyser was 77.7% for the wind power emulation, and 78.6% for the PV emulation on a day with stable irradiance, and 78.1% on a day with highly variable irradiance (day with scattered clouds).     

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.     

Meeting the electricity demand for the heating of greenhouses with hydrogen: Solar photovoltaic-hydrogen-heat pump system application in Turkey

Providing the heating system with coal in greenhouses causes harmful results in terms of carbon emissions. In this study, analyzes were performed to meet the electrical energy required for the heating system with a heat pump from a solar photovoltaic-hydrogen system. For floor area 25000 m² where greenhouses the required energy is obtained directly from hydrogen without using a heat pump 3000 m² solar panel area required. The use of a heat pump reduces energy needs but it is also not feasible for large greenhouses. For convenience, a solar photovoltaic-hydrogen-heat pump system analysis was also made for 1000 m² floor area greenhouses and it is found that the 24 m² solar panel area is adequate in terms of meeting energy demand. Using a solar-hydrogen-heat pump system reduces carbon emissions by 86.5 tons per 1000 m² floor area greenhouse. Considering the hydrogen storage system becomes unfeasible. We normalized the greenhouse floor area to 1 m² and proposed reference values for hydrogen to be produced in 1 h, storage, and PV area. In addition, an analysis was made for the use of hydrogen energy for greenhouses that do not require a heating system and only work with a water pump.     

Investigation of photovoltaic-hydrogen power system for a real house in Turkey: Hydrogen blending to natural gas effects on system design

In the study, the effects of hydrogen mixing studies at the rate of 20% to the natural gas system which is an ongoing study in Turkey, on the photovoltaic system (PV) is investigated using a real house consumption. Providing the annual electrical energy consumption (1936,83  kWh) and 20% of natural gas consumption (62,4 m³) of a real house with hydrogen is included in the study. A PV-hydrogen system is theoretically investigated to provide the energy required for hydrogen production from solar panels. Hydrogen blending effects on PV size, capacity usage, and carbon footprint are analyzed. Thus, the contribution was also made to the “green hydrogen” works and reduction of the carbon footprint of the house. It was found that the required hydrogen for electricity can be provided 52,5 m² solar panel area and 14,28% increase in this area and installed power can provide an amount of hydrogen that need for 20% hydrogen blending to the natural gas system. The overall system capacity usage decreased when the system is used for 20% hydrogen blending to the natural gas system. The carbon footprint of the house was decreased by 67,5%. If the hydrogen has not been blended with 20% natural gas, this ratio would have been 59,2%.     

Techno-economic assessment of a synthetic fuel production facility by hydrogenation of CO2 captured from biogas

In this study, a thermodynamic and economic analysis of a synthetic fuel production facility by utilizing the hydrogenation of CO₂ captured from biogas is carried out. It is aimed to produce methanol, a synthetic fuel by hydrogenation of carbon dioxide. A PEM electrolyzer driven by grid-tie solar PV modules is used to supply the hydrogen need of methanol. The CO₂ is captured from biogas produced in an actual wastewater treatment plant by a water washing unit which is a method of biogas purification. The required power which is generated by PV panels, in order to produce methanol, is found to be 2923 kW. Herein, the electricity consumption of 2875 kW, which is the main part of the total electricity generation, belongs to the PEM system. As a result of the study, the daily methanol production is found to be as 1674 kg. The electricity, hydrogen and methanol production costs are found to be $ 0.043 kWh^?1, $ 3.156 kg^?1, and $ 0.693 kg^?1, respectively. Solar availability, methanol yield from the reactor, and PEM overpotentials are significant factors effecting the product cost. The results of the study presents feasible methanol production costs with reasonable investment requirements. Moreover, the efficiency of the cogeneration plant could be increased via enriching the biogas while emissions are reduced.     

Off-grid hybrid renewable energy system with hydrogen storage for South African rural community health clinic

Most inhabitants of rural communities in Africa lack access to clean and reliable electricity. This has deprived the rural dwellers access to modern healthcare delivery. In this paper, an off-grid renewable energy system consisting of solar PV and wind turbine with hydrogen storage scheme has been explored to meet the electrical energy demands of a health clinic. The health clinic proposed is a group II with 10 beds located in a typical village in South Africa. First, the wind and solar energy resources of the village were analysed. Thereafter, the microgrid architecture that would meet the energy demand of the clinic (18.67 kWh/day) was determined. Some of the key results reveal that the average annual wind speed at 60 m anemometer height and solar irradiation of the village are 7.9 m/s and 4.779 kWh/m²/day, respectively. The required architecture for the clinic composes of 40 kW solar PV system, 3 numbers of 10 kW wind turbines, 8.6 kW fuel cell, 25 kW electrolyser and 40 kg hydrogen tank capacity. The capital cost of the microgrid was found to be $177,600 with a net present cost of $206,323. The levelised cost of energy of the system was determined to be 2.34 $/kWh. The project has a breakeven grid extension distance of 8.81 km. Since this distance is less than the nearest grid extension distance of 21.35 km, it is established that the proposed renewable energy microgrid with a hydrogen storage system is a viable option for the rural community health clinic.     

Exploring the feasibility of green hydrogen production using excess energy from a country-scale 100% solar-wind renewable energy system

When planning large-scale 100% renewable energy systems (RES) for the year 2050, the system capacity is usually oversized for better supply-demand matching of electrical energy since solar and wind resources are highly intermittent. This causes excessive excess energy that is typically dissipated, curtailed, or sold directly. The public literature shows a lack of studies on the feasibility of using this excess for country-scale co-generation. This study presents the first investigation of utilizing this excess to generate green hydrogen gas. The concept is demonstrated for Jordan using three solar photovoltaic (PV), wind, and hybrid PV-wind RESs, all equipped with Lithium-Ion battery energy storage systems (ESSs), for hydrogen production using a polymer electrolyte membrane (PEM) system. The results show that the PV-based system has the highest demand-supply fraction (>99%). However, the wind-based system is more favorable economically, with installed RES, ESS, and PEM capacities of only 23.88 GW, 2542 GWh, and 20.66 GW. It also shows the highest hydrogen annual production rate (172.1 × 10³ tons) and the lowest hydrogen cost (1.082 USD/kg). The three systems were a better option than selling excess energy directly, where they ensure annual incomes up to 2.68 billion USD while having payback periods of as low as 1.78 years. Furthermore, the hydrogen cost does not exceed 2.03 USD/kg, which is significantly lower than the expected cost of hydrogen (3 USD/kg) produced using energy from fossil fuel-based systems in 2050.     

Assessment of power and hydrogen production performance of an integrated system based on middle-grade geothermal source and solar energy

In this study, power and hydrogen production performance of an integrated system is investigated. The system consists of an organic Rankine cycle (ORC), parabolic trough solar collectors (PTSCs) having a surface area of 545 m², middle-grade geothermal source (MGGS), cooling tower and proton exchange membrane (PEM). The final product of this system is hydrogen that produced via PEM. For this purpose, the fluid temperature of the geothermal source is upgraded by the solar collectors to drive the ORC. To improve the electricity generation efficiency, four working fluids namely n-butane, n-pentane, n-hexane, and cyclohexane are tried in the ORC. The mass flow rate of each working fluid is set as 0.1, 0.2, 0.3, 0.4 kg/s and calculations are made for 16 different situations (four types of working fluids and four different mass flow rates for each). As a result, n-butane with a mass flow rate of 0.4 kg/s is found to be the best option. The average electricity generation is 66.02 kW between the hours of 11⁰⁰-13⁰⁰. The total hydrogen production is 9807.1 g for a day. The energy and exergy efficiency is calculated to be 5.85% and 8.27%, respectively.     

A parametric study on thermodynamic performance of a SOFC oriented hybrid energy system

In this paper, a parametric study of the performance of a SOFC system for several types of supplied fuels is carried out. A SOFC system which is assisted by some energy resources, namely biomass, solar energy and natural gas, i.e. methane, is designed in order to realize this study.This system consists of four main components which are Solid Oxide Fuel Cell (SOFC), Proton Exchange Membrane Electrolyser (PEME), Photovoltaic system (PV), and Anaerobic Digester for biogas production (AD). The system is designed by considering three fundamental operation modes which are day-time (M1), night-time (M2), and winter-time (M3), in accordance with the duration of solar irradiation period. In order to evaluate the performance of the system, comprehensive energy and exergy analyses are performed, as major system parameters are changed for the operation modes considered. In this study, maximum total energy and exergy efficiency values of 0.60 and 0.49, respectively, are achieved when the overall energy and exergy performance of the system is evaluated, at 5500 A/m² current density for M3 operation mode among the three operation modes considered. Finally, the maximum net electrical energy and exergy efficiencies are achieved for 633 °C SOFC fuel inlet temperature and 8000 A/m² current density, in this study.     

A solar and wind driven energy system for hydrogen and urea production with CO2 capturing

A novel solar PV and wind energy based system is proposed in this study for capturing carbon dioxide as well as producing hydrogen, urea and power. Both Aspen Plus and EES software packages are employed for analyses and simulations. The present system is designed in a way that PEM electrolyzer is powered by the wind turbines for hydrogen production, which is further converted into ammonia and then synthesizes urea by capturing CO₂ and additional power is supplied to the community. The solar PV is employed to power the cryogenic air separation unit and the additional power is used for the industrial purpose. In the proposed system, ammonia does not only capture CO₂ but also synthesizes urea for fertilizer industry. The amount of electrical power produced by the system is 2.14 MW. The designed system produces 518.4 kmol/d of hydrogen and synthesizes 86.4 kmol/d of urea. Furthermore, several parametric studies are employed to investigate the system performance.     

Hydrogen production through an ocean thermal energy conversion system operating at an optimum temperature drop

Storage of electrical energy produced from an ocean thermal energy conversion (OTEC) system is considered to be extremely essential, since the conversion process could take place in a remote offshore area and distant from the actual utilization sites. Energy conversion from an OTEC system into hydrogen energy, which is used for power generation through fuel cells, is an important approach of storing such energy for further utilizations. In this paper, a technical analysis of hydrogen production through an OTEC system coupled with a polymer electrolyte membrane electrolyser (PEM), which is developed by the Japanese international clean energy network using hydrogen conversion (WE-NET), is performed. The analysis is conducted at an optimum temperature drop between the working fluid and seawater, δT_op. Furthermore, the analysis is carried out at various temperature differences between the surface and deep sea water, ΔT. The calculated results demonstrated the significance of temperature drop and temperature difference on the electrical power output and conversion efficiency. Moreover, the actual rate of hydrogen production varied from 2.5 N m³/h to 60 N m³/h as ΔT raised from 5 °C to 25 °C, respectively.     

Thermodynamic assessment of modified Organic Rankine Cycle integrated with parabolic trough collector for hydrogen production

Hydrogen is one of the most clean energy carrier and the best alternative for fossil fuels. In this study, thermodynamic analysis of modified Organic Rankine Cycle (ORC) integrated with Parabolic Trough Collector (PTC) for hydrogen production is investigated. The integrated system investigated in this study consists of a parabolic trough collector, a modified ORC, a single effect absorption cooling system and a PEM electrolyzer. By using parabolic trough collector, solar energy is converted heat energy and then produced heat energy is used in modified ORC to produce electricity. Electricity is then used for hydrogen production. The outputs of this integrated system are electricity, cooling and hydrogen. By performing a parametric study, the effects of design parameters of PTC, modified ORC and PEM electrolyzer on hydrogen production is evaluated. According to the analysis results, solar radiation is one of the most important factor affecting system exergy efficiency and hydrogen production rate. As solar radiation increases from 400?W/m² to 1000?W/m², exergy efficiency of the system increases 58%–64% and hydrogen production rate increases from 0.1016?kg/h to 0.1028?kg/h.