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.     

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.     

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.     

Stand-alone PEM water electrolysis system for fail safe operation with a renewable energy source

A complete stand-alone electrolyser system has been constructed as a transportable unit for demonstration of a sustainable energy facility based on hydrogen and a renewable energy source. The stand-alone unit is designed to support a polymer electrolyte membrane (PEM) stack operating at up to ∼4 kW input power with a stack efficiency of about 80% based on HHV of hydrogen. It is self-pressurizing and intended for operation initially at a differential pressure of less than 6 bar across the membrane electrode assembly with the hydrogen generation side being at a higher pressure. With a slightly smaller stack, the system has been operated at an off-site facility where it was directly coupled to a 2.4 kW photovoltaic (PV) solar array. Because of its potential use in remote areas, the balance-of-plant operates entirely on 12 V DC power for all monitoring, control and safety requirements. It utilises a separate high-current supply as the main electrolyser input, typically 30–40 V at 100 A from a renewable source such as solar PV or wind. The system has multiple levels of built-in operator and stack safety redundancy. Control and safety systems monitor all flows, levels and temperatures of significance. All fault conditions are failsafe and are duplicated, triggering latching relays which shut the system down. Process indicators monitor several key variables and allow operating limits to be easily adjusted in response to experience of system performance gained in the field.     

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.     

Electrolysers for mitigating wind curtailment and producing ‘green’ merchant hydrogen

The implementation electrolysis plant in combination with wind power plant is proposed, to absorb wind generation otherwise curtailed while generating ‘green’ hydrogen for the merchant hydrogen market. The objective are to (i) achieve exceptionally high wind power penetrations in future power systems, and (ii) derive hydrogen for sale in the existing merchant industrial market from surplus (zero cost) renewable electricity. The economic rationale is investigated for an isolated power system as a function wind penetration, wind curtailment target, electrolyser cost, hydrogen system efficiency and hydrogen sales price. The main outputs are the total annualized cost of wind power plant with electrolysis plant, net annual revenues and discounted pay-back periods. Unprecedented low values of pay-back period are attainable, relative to the implementation of wind power plant at low wind penetrations (Φ_W). For example, at Φ_W = 50%, a wind curtailment target of 80% allows the investment to be recovered after 4-7 years, provided the hydrogen system efficiency is ≥50% and the hydrogen sales price is 20-30 $/kg. Making use of some non-curtailed wind electricity to boost the utilization of the electrolyser stock is also investigated as a means for improving the return on investment.     

Parameter study for dimensioning of a PV optimized hydrogen supply plant

Green hydrogen produced from intermittent renewable energy sources is a key component on the way to a carbon neutral planet. In order to achieve the most sustainable, efficient and cost-effective solutions, it is necessary to match the dimensioning of the renewable energy source, the capacity of the hydrogen production and the size of the hydrogen storage to the hydrogen demand of the application.For optimized dimensioning of a PV powered hydrogen production system, fulfilling a specific hydrogen demand, a detailed plant simulation model has been developed. In this study the model was used to conduct a parameter study to optimize a plant that should serve 5 hydrogen fuel cell buses with a daily hydrogen demand of 90 kg overall with photovoltaics (PV) as renewable energy source. Furthermore, the influence of the parameters PV system size, electrolyser capacity and hydrogen storage size on the hydrogen production costs and other key indicators is investigated. The plant primarily uses the PV produced energy but can also use grid energy for production.The results show that the most cost-efficient design primarily depends on the grid electricity price that is available to supplement the PV system if necessary. Higher grid electricity prices make it economically sensible to invest into higher hydrogen production and storage capacity. For a grid electricity price of 200 €/MWh the most cost-efficient design was found to be a plant with a 2000 kWp PV system, an electrolyser with 360 kW capacity and a hydrogen storage of 575 kg.     

Influence of the power supply on the energy efficiency of an alkaline water electrolyser

Electric energy consumption represents the greatest part of the cost of the hydrogen produced by water electrolysis. An effort is being carried out to reduce this electric consumption and improve the global efficiency of commercial electrolysers. Whereas relevant progresses are being achieved in cell stack configurations and electrodes performance, there are practically no studies on the effect of the electric power supply topology on the electrolyser energy efficiency. This paper presents an analysis on the energy consumption and efficiency of a 1 N m³ h⁻¹ commercial alkaline water electrolyser and their dependence on the power supply topology. The different topologies of power supplies are first summarised, analysed and classified into two groups: thyristor-based (ThPS) and transistor-based power supplies (TrPS). An Electrolyser Power Supply Emulator (EPSE) is then designed, developed and satisfactorily validated by means of simulation and experimental tests. With the EPSE, the electrolyser is characterised both obtaining its I–V curves for different temperatures and measuring the useful hydrogen production. The electrolyser is then supplied by means of two different emulated electric profiles that are characteristic of typical ThPS and TrPS. Results show that the cell stack energy consumption is up to 495 W h N m⁻³ lower when it is supplied by the TrPS, which means 10% greater in terms of efficiency.     

Review of research on autonomous wind farms and solar parks and their feasibility for commercial loads in hot regions

In the wake of rising cost of oil and fears of its exhaustion coupled with increased pollution, the governments world-wide are deliberating and making huge strides to promote renewable energy sources such as solar–photovoltaic (solar–PV) and wind energy. Integration of diesel systems with hybrid wind–PV systems is pursued widely to reduce dependence on fossil-fuel produced energy and to reduce the release of carbon gases that cause global climate change. Literature indicates that commercial/residential buildings in the Kingdom of Saudi Arabia (KSA) consume an estimated 10–40% of the total electric energy generated. The study reviews research work carried out world-wide on wind farms and solar parks. The work also analyzes wind speed and solar radiation data of East-Coast (Dhahran), KSA, to assess the technical and economic potential of wind farm and solar PV park (hybrid wind–PV–diesel power systems) to meet the load requirements of a typical commercial building (with annual electrical energy demand of 620,000 kWh). The monthly average wind speeds range from 3.3 to 5.6 m/s. The monthly average daily solar global radiation ranges from 3.61 to 7.96 kWh/m². The hybrid systems simulated consist of different combinations of 100 kW wind machines, PV panels, supplemented by diesel generators. NREL (and HOMER Energy's) HOMER software has been used to perform the techno-economic study. The simulation results indicate that for a hybrid system comprising of 100 kW wind capacity (37 m hub-height) and 40 kW of PV capacity together with 175 kW diesel system, the renewable energy fraction (with 0% annual capacity shortage) is 36% (24% wind + 12% PV). The cost of generating energy (COE, $/kWh) from this hybrid wind–PV–diesel system has been found to be 0.154 $/kWh (assuming diesel fuel price of 0.1$/L). The study exhibits that for a given hybrid configuration, the number of operational hours of diesel generators decreases with increase in wind farm and PV capacity. Attention has also been focused on wind/PV penetration, un-met load, excess electricity generation, percentage fuel savings and reduction in carbon emissions (relative to diesel-only situation) of different hybrid systems, cost break-down of wind–PV–diesel systems, COE of different hybrid systems, etc.     

Techno-economic optimisation of hydrogen production by PV - electrolysis: “RenHydrogen” simulation program

The work concerns the optimisation of hydrogen production by electrolysis using renewable energy resources. To achieve this aim, the techno-economic analysis was dedicated to a system composed of PV panels and an electrolyser, including all associated technology such as the chopper circuit¹. The first step was to complete a LabVIEW simulation program which was able to reproduce a photovoltaic (PV) plant connected to the alkaline electrolyser. The virtual instrument was developed on the basis of the models of incident radiation, PV cells and electrolyser. After the indication of PV cell type and number, tilt of all panels, number of strings², latitude and main characteristics of the electrolyser (e.g. nominal power, number of electrolytic cells, working temperature and pressure), the program computes the hydrogen produced, the electrolyser running hours and other data, for a chosen period of the year.Differently tilted photovoltaic panels were considered either directly coupled with the electrolyser or connected via a DC converter between the two systems.The simulation program, called “RenHydrogen”, provides a qualitative calculation of the hydrogen production during the whole year, comparing different technological options and leading to the techno-economic optimisation of the PV-electrolysis system.     

From wave to jet and from jet to hydrogen: A promising hybrid system

One of the main challenges that our society must overcome in this century is that of finding alternative energy sources to fossil fuels. These, ideally, must be inexpensive, less polluting than current fuels and available for a substantial time. One promising alternative is hydrogen, which has the great advantage that it can be produced by coupling renewable energy devices with water electrolysis. Several projects devoted to connecting photovoltaic and wind systems with electrolysis devices have been successful; however, little research has been done into the coupling of ocean wave energy converters with water electrolysis. The work here proposes a basic system that stores the energy from waves in the form of hydrogen. The WEC considered is a novel design known as a Blow-Jet, which captures waves and converts them into a water jet. The performance of the Blow-Jet is found to depend more on wavelength than on wave height. The electrolyser results show, at 0.200 A and 1.88 V, that the electrolysis of water produces 0.082 Nl h⁻¹ of hydrogen and a current efficiency (η_I) of 90.58%.     

Performance investigation of hydrogen production from a hybrid wind-PV system

In this study, a hybrid system consisted of 10 kW wind and 1 kWp PV array is built to meet the load demand of a raise chucker partridge raising facility by renewable energy sources. The facility has an average energy consumption of about 20.33 kWh/day, with a peak demand of 2.4 kW. The solar radiation data and wind data of the region are analyzed for sizing of the renewable energy system. The performance of each alternative system is examined in terms of energy efficiency, and H₂ production capacity of the hybrid system from due to excessive electrical energy is studied. A Matlab-Simulink Software is used for analyzing the system performance. The average range of state of charge varies between 56.6% and 88.3% monthly from April to July. The amount of hydrogen production by excess electricity is 14.4 kg in the month of July, due to the high wind speed and solar radiation. Energy efficiency of the electrolyser is found to be varying between 64% and 70% percent. Energy efficiency of each hybrid system is calculated. The overall energy efficiency of wind-electrolyser system varies between 5% and 14% while the energy efficiency of PV-electrolyser system changes within a narrower range, as between 7.9% to and 8.5%, respectively.     

Simulation of design and operation of hydrogen energy utilization system for a zero emission building

Nearly 40% of the total greenhouse gases (GHGs) are emitted from the energy consumption in buildings in Japan, which should be reduced to address global warming. A hydrogen energy utilization system with renewable energy (RE) was designed by MATLAB/Simulink simulations for realizing a zero emission building (ZEB), comprising a hydrogen-producing electrolyzer, a hydrogen storage tank, fuel cell, and battery for short-term power storage with estimated specifications of 3.0 Nm³/h, 36 Nm³, 4.2 kW, and 10 kW/17 kWh, respectively. We identified a small low-rise building (total floor area: ∼1000 m², demand: ∼5 kW) as the planned ZEB to construct and operate a bench-scale system. A 20-kW photovoltaic (PV) system was selected as the RE source. Two hydrogen production processes (constant power of 10 kW or with excess PV power) were evaluated by simulating 48-h operations on fine and cloudy days, where the former showed higher efficiency. The results with excess power on a fine day agreed well with that of actual operation, validating our simulation models. Further, the constant case was suitable for practical application.     

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.     

A mobile off-grid platform powered with photovoltaic/wind/battery/fuel cell hybrid power systems

Cross utilization of photovoltaic/wind/battery/fuel cell hybrid-power-system has been demonstrated to power an off-grid mobile living space. This concept shows that different renewable energy sources can be used simultaneously to power off-grid applications together with battery and hydrogen energy storage options. Photovoltaic (PV) and wind energy are used as primary sources and a fuel cell is used as backup power. A total of 2.7 kW energy production (wind and PV panels) along with 1.2 kW fuel cell power is supported with 17.2 kWh battery and 15 kWh hydrogen storage capacities. Supply/demand scenarios are prepared based on wind and solar data for Istanbul. Primary energy sources supply load and charge batteries. When there is energy excess, it is used to electrolyse water for hydrogen production, which in turn can either be used to power fuel cells or burnt as fuel by the hydrogen cooker. Power-to-gas and gas-to-power schemes are effectively utilized and shown in this study. Power demand by the installed equipment is supplied by batteries if no renewable energy is available. If there is high demand beyond battery capacity, fuel cell supplies energy in parallel. Automatic and manual controllable hydraulic systems are designed and installed to increase the photovoltaic efficiency by vertical axis control, to lift up & down wind turbine and to prevent vibrations on vehicle. Automatic control, data acquisition, monitoring, telemetry hardware and software are established. In order to increase public awareness of renewable energy sources and its applications, system has been demonstrated in various exhibitions, conferences, energy forums, universities, governmental and nongovernmental organizations in Turkey, Austria, United Arab Emirates and Romania.     

Electrolysers as a load management mechanism for power systems with wind power and zero-carbon thermal power plant

For an isolated power system the deployment of a large stock of electrolysers is investigated as a means for increasing the penetrations of wind power plant and zero-carbon thermal power plant. Consideration is given to the sizing and utilization of an electrolyser stock for three electrolyser implementation cases and three operational strategies, installed capacity ranges of 20–100% for wind power and 10–35% for zero-carbon thermal power plant (as proportions of the power system’s maximum electrical demand) were investigated. Relative to wind-hydrogen alone, hydrogen yields are substantially increased especially on low-wind days. The average load placed on fossil-fuelled power plant is substantially decreased (while achieving a virtually flat load profile) and the carbon intensity of electricity can be reduced to values of <0.1 kg CO₂/kWh_e. The trade-offs between the carbon intensity of the electricity delivered, the carbon intensity of the hydrogen produced and the daily hydrogen yield are explored. For example (on the variable wind day for Strategy C with respective wind power and zero-carbon thermal power penetrations of 100% and 35%), if the carbon intensity of hydrogen is relaxed from 0 to 3 kg CO₂/kg H₂, the hydrogen yield can be increased from 435 tonnes to 1115 tonnes (which is the energy equivalent of 120% of consumer demand for electricity on that day). The findings suggest that the deployment of electrolysers on both the supply and demand-side of the power system can contribute nationally-significant amounts of zero or low-carbon hydrogen without exceeding the power system’s current maximum system demand.     

Levelized costs of energy and hydrogen of wind farms and concentrated photovoltaic thermal systems. A case study in Morocco

This work deals with the evaluation of levelized costs of energy and hydrogen of wind farms and concentrated photovoltaic thermal systems. The production of hydrogen is ensured by an alkaline water electrolyser supplied by the electric current generated by the renewable energy sources. The study is carried out on the basis of meteorological data from the Tangier region, in Morocco. Mathematical models are developed to assess the performance and efficiency of renewable sources in terms of energy and hydrogen production for different installed powers. The comparison between the current results and those of previous work shows that the discrepancy did not exceed 6% for both electrical and thermal efficiency of the concentrated photovoltaic/thermal system. The results show that the energy consumption ratios of the electrolyzer are 61 and 64 kWh.kg⁻¹ for wind and solar energy, respectively. Wind and solar hydrogen production efficiencies are also 66 and 62%, respectively. Results show that levelized costs of energy and hydrogen decrease with the increase in installed wind and photovoltaic capacity. The overall results also show that the Tangier region can produce energy and hydrogen at low cost using wind energy compared to concentrated photovoltaic installations. For the hybridization of the two green sources studied, this is highly recommended provided that the capacity of the electrolyzer to be installed is optimal in order to effectively improve the production of hydrogen.     

H2RES,Energy planning tool for island energy systems – The case of the Island of Mljet

When it comes to the energy planning, computer programs like H₂RES are becoming valuable tools. H₂RES has been designed as support for simulation of different scenarios devised by RenewIsland methodology with specific purpose to increase integration of renewable sources and hydrogen into island energy systems. The model can use wind, solar, hydro, biomass, geothermal as renewable energy sources and fossil fuel blocks and grid connection with mainland as back up. The load in the model can be represented by hourly and deferrable electricity loads of the power system, by hourly heat load, by hydrogen load for transport and by water load depending on water consumption. The H₂RES model also has ability to integrate different storages into island energy system in order to increase the penetration of intermittent renewable energy sources or to achieve a 100% renewable island. Energy storages could vary from hydrogen loop (fuel cell, electrolyser and hydrogen storage) to reversible hydro or batteries for smaller energy systems. The H₂RES model was tested on the power system of the Island of Porto Santo – Madeira, the islands of Corvo, Graciosa, and Terrciera – Azores, Sal Island – Cape Verde, Portugal, the Island of Mljet, Croatia and on the energy system of the Malta. Beside energy planning of the islands, H₂RES model could be successfully applied for simulation of other energy systems like villages in mountain regions or for simulation of different individual energy producers or consumers.     

Development of an ambient temperature alkaline electrolyser for dynamic operation with renewable energy sources

A comparison is made between the ambient and conventional temperature alkaline electrolysers in terms of operational system, voltage efficiency and corrosion rates. The capital, operational and maintenance costs are reduced by reducing auxiliary equipment as well as auxiliary utilities in the ambient temperature alkaline electrolyser. Also, since auxiliary electricity consumption is reduced, the alkaline electrolyser is capable for dynamic, continuous and fast-response operation with renewable energy sources. The ambient temperature alkaline electrolyser is capable for wider operational range and faster response time when powered by wind energy sources. Although the voltage efficiency for hydrogen production is increased by about 12% at the conventional operating temperature, corrosion rate of the electrode is increased by a factor of about 6.3. The voltage efficiency for hydrogen production, however, is increased by about 12% by employing electrocatalyst in the ambient temperature alkaline electrolyser, and there is benefit of enhancing lifetime durability of the electrode as well as cell components at relatively lower operating temperature.     

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%.