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Industrial water electrolyzers mainly use old thyristor-based rectifiers to obtain the DC current required to run because of the low voltage level and high current requirements of the processes. These rectifiers cause significant ripple in the electrolyzer input current, leading to dynamic operation of the electrolyzer. Even though industrial-scale water electrolyzers are operated under such dynamic conditions, the effect on the electrolyzer performance is not well explored. In this study, current measurements from an industrial alkaline electrolyzer plant were used to define the common current ripple amplitude and frequency caused by the thyristor-based rectification. Based on the parameters obtained, laboratory measurements were conducted using an alkaline water electrolyzer to define the power losses incurred at various ripple amplitudes and frequencies. Additionally, the linearization of the electrolyzer current–voltage behavior as a function of frequency was studied using two electrode sets made of different materials. The laboratory measurements carried out in the study show that the ripple amplitude has a significant effect on increasing the losses, whereas the ripple frequency counteracts this. Thus, dynamic operation can have a large impact on losses, especially at partial loads, where the ripple current amplitudes increase significantly when using thyristor rectifiers. Lastly, the frequencies where the electrolyzer starts to behave linearly were observed to be at 68 Hz with the first electrode set and at 5 Hz with the second one. The considerable difference between the electrode sets indicates that the electrode materials and microstructure play a significant role in defining the electrolyzer frequency behavior. Because common thyristor-based power delivery systems operate at 300 Hz or 600 Hz, the results also imply that when modeling these systems, a linear model can be used for the electrolyzer to simplify the simulation. [Display omitted] • Large amplitude current ripple on alkaline electrolyzers is studied. • Ripple amplitude increases power losses, while frequency counteracts it. • As ripple frequency is increased, the electrolyzer starts to behave linearly. • The linear slope is determined purely based on the impedance. • At high frequencies, power usage can be determined from EIS measurement. [ABSTRACT FROM AUTHOR]

Water electrolysis will be used to produce renewable hydrogen for energy storage and Power-to-X applications in the future renewable-energy-based energy systems. Therefore, the energy efficiency of hydrogen production will probably become a major issue. In this study, the effect of practical supply power converters on the specific energy consumption of megawatt (MW)-scale alkaline electrolyzers is studied and compared with an ideal dc power supply. The current quality and the stack specific energy consumption are studied in the case of traditional thyristor rectifiers and a transistor-based converter. The stack specific energy consumption is analyzed based on the simulated current waveforms and the electrical equivalent circuit of the electrolyzer stack. It is found that the transistor-based converter offers up to 14% lower electrolyzer stack specific energy consumption than the 6-pulse thyristor rectifier and up to 9.2% lower electrolyzer stack specific energy consumption than the 12-pulse thyristor rectifier as the current varies between 5000 and 1000 A. The simulated change in the stack specific energy consumption of the MW-scale alkaline water electrolyzer outweighs the losses occurring in the rectifiers. Further, selection of the ac voltage level may have a more adverse effect on the stack specific energy consumption with the thyristor rectifier topologies compared with the transistor-based topologies. [ABSTRACT FROM AUTHOR]

The interest in green hydrogen has been increasing in recent years for several applications, such as energy storage and different industrial sectors. The green hydrogen is produced from water electrolysis supplied by renewable electricity. The operation of industrial large-scale water electrolysis is characterized by a high DC current in the kiloampere range and a few hundred volts. Therefore, the rectifier unit plays an important role in converting AC current of the electricity grid into DC current supplied to the electrolyzer. The power electronic converters are also considered as one of the main cost components of the water electrolyzer system. The objective of this paper is to study whether the operation at a higher voltage than typical values (200 V–300 V) can be beneficial both for the cost and energy efficiency of the power converters in water electrolyzer systems. In this study, three different rectifier topologies considered for an industrial-scale electrolyzer are analyzed and compared in terms of energy efficiency and cost. The simulation models of each topology are carried out in the Matlab/Simulink environment. • The effect of voltage elevation on industrial water electrolyzer system is studied. • Thyristor and transistor-based rectifiers for water electrolyzers are analyzed. • Voltage elevation improves the energy efficiency and cost of rectifiers. • Buck-rectifier provides lowest specific energy consumption of electrolyzer stack. [ABSTRACT FROM AUTHOR]

Power-electronics-based power-hardware-in-loop (PHIL) simulator for water electrolyzer emulation with a nominal current of 405 A is developed to study the electrolyzer as part of a smart grid and to analyze the characteristics of various electrolyzer power supply electronics. A simplified model of a proton exchange membrane (PEM) electrolyzer is implemented into the PHIL simulator to describe the voltage and current characteristics of the electrolyzer stack. The model is verified comparing the current and the estimated hydrogen production of the PHIL simulator with the measured values of the commercial PEM electrolyzer following the measured solar photovoltaic (PV) system output power. [ABSTRACT FROM AUTHOR]

• The effect of current ripple on PEM water electrolysis is analyzed. • A semi empirical PEM electrolyzer cell model is presented. • Higher power quality lowers energy consumption for water electrolysis. • High power quality reduces cell area up to five times at the same efficiency. Water electrolyzer technologies may play a key role in the decarbonization of the fossil-fueled world economy. Electrolytic hydrogen production could bridge emission-free power generation and various energy end-use sectors to drive the energy system towards a net zero-emission level. In order to reduce the economic cost of the required energy transition, both the overall system efficiency in converting electrical energy into the chemical energy carried by hydrogen, and the material used to build electrolytic cell stacks, should be optimal. The effect of power quality on the specific energy consumption of proton exchange membrane (PEM) water electrolyzers is investigated with a semi-empirical cell model. An experimentally-defined polarization curve is applied to analyze cell-specific energy consumption as a function of time in the case of sinusoidal current ripples and ripples excited by an industrial 12-pulse thyristor bridge. The results show that the effective electrolyzer cell area should be up to five times as high as an ideal DC power supply when powered by the 12-pulse thyristor rectifier supply to match the specific energy consumption between the two power supply configurations. Therefore, the improvement of power quality is crucial for industrial PEM water electrolyzer systems. The presented approach is applicable to simulate the effect of power quality for different proton exchange membrane electolyzers. [ABSTRACT FROM AUTHOR]

The ripple of the supplied direct current has a significant effect on the energy efficiency of the water electrolyzer cell. Hydrogen production is defined by the current mean value, but current harmonics generate additional losses in the electrolyzer cell. However, the direct measurement of the DC current in the kiloampere range may be a challenging task compared with the voltage, which is practically in the range of a few hundreds volts in the electrolyzer stack. The effect of current harmonics on the energy efficiency and the voltage mean and root-mean-square (RMS) values is analyzed analytically based on the measured polarization curve of the PEM electrolyzer cell. The results show that both in the case of a theoretical sinusoidal current ripple and a practical thyristor bridge supply, the voltage mean or RMS values do not give a reliable estimate of the power quality. Instead, the voltage waveform as a function of time or the difference between the current mean and RMS values should be monitored. • Current quality has significant effect on the energy efficiency of electrolytic cells. • Sinusoidal and thyristor rectifier-induced current ripples cause additional losses. • Current RMS value differing from the mean value indicates poor power quality. • Cell voltage mean or RMS values do not indicate power quality. [ABSTRACT FROM AUTHOR]

The practical dynamic properties and operational limitations of a commercial differential pressure 1 Nm 3 h −1 proton exchange membrane (PEM) water electrolyzer are studied from the viewpoint of renewable power production. Measured values from a 5 kW p solar photovoltaic (PV) power plant and PEM electrolyzer are analyzed to study factors affecting the control of PEM water electrolyzers operating as a part of renewable power production systems. Specific energy consumption of the PEM stack as a function of stack hydrogen outlet pressure is estimated based on measured values from two different measurement systems. Electrical energy consumption of the stack does not show any notable increase as the hydrogen outlet pressure is increased from 2.0 MPa to 4.0 MPa. However, the stack specific energy consumption increases by a maximum of 0.2 kWh/Nm 3 when hydrogen outlet pressure is increased from 2.0 MPa to 4.0 MPa. The increase in specific energy consumption at high differential pressure operation is due to a decrease in Faraday efficiency. Selection and control of the hydrogen outlet pressure can minimize the specific energy consumption and maximize the real hydrogen production in dynamic PEM water electrolyzer operation. [ABSTRACT FROM AUTHOR]

A comprehensive literature review of current water electrolyzer modelling research was conducted and presented models critically evaluated. Based on the literature review this paper presents an open-source MATLAB toolbox for water electrolyzer polarisation curve parametrization and modelling. The modelling capabilities of the tooling were verified using measured PEM and alkaline water electrolyzer polarisation data. As real-world measurement data is rarely ideal, tests were also conducted using suboptimal data, first with data sets that have a low number of measurement points and secondly with data sets that have low or high current densities missing. The tooling is shown to work with a wide variety of use cases and provides an automated method for modelling and parametrization of electrolyzer polarisation curves. • Critical review of the water electrolyzer polarisation curve modelling is conducted. • Open source MATLAB toolbox for automated parametrization of models is presented. • Measured alkaline and PEM water electrolyzer data is used to verify fit accuracy. • Data sets of variable quality are used to verify fitting robustness. [ABSTRACT FROM AUTHOR]