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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]

Graphical abstract Highlights • Hydrocarbon production directly from water, solar energy, and air is demonstrated. • Pilot plant operated 300 h with production of oil and wax 6.2 kg per day. • A conceptual plant can achieve energy and carbon efficiencies of 47% and 94%. Abstract This work demonstrates hydrocarbon production directly from water, solar energy, and air—called SOLETAIR. The plant includes direct air capture (DAC) of carbon dioxide, hydrogen production by water electrolysis, and two-step synthesis bench-scale units that operate using grid-connected solar photovoltaic (PV) electricity. In addition, co-feeding of hydrogen and carbon monoxide from gas bundles are utilized to enable scaling between units. This pilot plant achieved a total operating time of approx. 300 h with a combined production of oil and wax of 6.2 kg per day. The mass and energy balances in integration of the units are studied. According to the experiments and studies, potential and bottlenecks to improve the individual units and their integration are found. Finally, a conceptual Power-to-X plant is presented, which can achieve energy and carbon efficiencies of 47% and 94%, respectively, considering liquid and solid hydrocarbons as products. [ABSTRACT FROM AUTHOR]

A modular power-hardware-in-loop (PHIL) simulator for water electrolyzers is developed to study the electrolyzer as part of a smart grid and to examine the characteristics of various electrolyzer power supply electronics. A PHIL simulator up to 405 A of continuous current is built using commercially available power electronic converters. The design and operating principle of the emulator are analyzed. The experimental dynamics tests are performed to verify the PHIL simulator operation and suitability for water electrolysis emulation considering the effect of supply power quality. Finally, the PEM stack model is implemented, and the PHIL simulator is used to emulate a commercial PEM electrolyzer following the measured solar photovoltaic (PV) output power. [ABSTRACT FROM AUTHOR]

The pace at which the human population is growing raises serious concerns related to food security while at the same time conventional agriculture-based food production is becoming a major cause of environmental pollution and greenhouse gas emissions. Numerous solutions have been proposed to boost food production among which edible microbial biomass is considered a promising alternative to conventional sources of food and feed with lower environmental footprint. This work introduces the Neo-Carbon Food concept that is a pilot-scale hybrid biological–inorganic process suitable for the production of microbial biomass. The concept includes integrated hydrogen production by water electrolysis, direct air capture (DAC) of carbon dioxide, and its subsequent assimilation by autotrophic hydrogen-oxidizing bacteria (HOB). The hydrogen production with in situ electrolysis achieved specific energy consumption just below 100 kWh/kgH 2 while the specific energy consumption of DAC was around 20 kWh/kg CO 2. Image 1 • Microbial protein could be a sustainable source of protein. • A pilot-scale hybrid biological-inorganic system is presented. • Novel in situ water electrolysis stack is introduced. • Energy consumption of hydrogen production and direct air capture of CO2 is studied. [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]

Industrial water electrolyzers apply direct current in kiloampere ranges. Therefore, rectifiers are typically based on thyristors despite the high amplitude current fluctuation excited by the rectifier. This paper studies the effect of thyristor rectifiers on the power quality of the electrolyzer stack and the supplying AC grid. The thyristor bridge excites high current and power fluctuation causing additional losses in the electrolytic cells. Further, the both AC supply side and DC output power factors are low especially under partial load conditions. The reactive power is divided into phase shift and distortion components. In the case of thyristor rectifier without any passive filter components the distortion reactive power component is dominating. The simulated results are supported by the power factor measurements of an industrial alkaline water electrolyzer. It is proposed that electrolyzer stack manufacturers should give requirements for the DC power quality to maximize the stack energy efficiency and lifetime. • DC current harmonics increase the specific energy consumption of water electrolyzers. • Thyristor rectifier has poor input and output power factor at partial loads. • Thyristor rectifier has high distortion reactive power component. • High AC reactive power component indicates poor DC quality. [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]

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]

Owing to the ongoing energy crisis, increasing shares of renewables, and climate mitigation targets, a green hydrogen economy through water electrolysis has gained interest. Hydrogen can be directly utilised or converted via different Power-to-X pathways to produce fossil-free substitutable products; therefore, their life-cycle emissions were studied to determine whether these solutions could provide sustainable alternatives. Thus, understanding which Power-to-X solution can provide the greatest greenhouse gas emission reduction is crucial. This study provides nine meta-analyses of different pathways to compare climate emissions reductions based on the literature. The minimum, maximum, and average values were estimated for each investigated Power-to-X pathway. The direct use of hydrogen or its service to produce steel, biogas upgrading, protein, or ammonia resulted in over 10 kg CO2 kg H2 −1 reductions on average while using low-carbon energy sources. Co-electrolysis can potentially provide higher emission savings owing to lower electricity consumption compared with low-temperature electrolysers. In addition, the possibility of integrating electrochemical synthesis with hydrogen production has great potential, but the usability depends on the advancement of the technology in the future. Selections of carbon dioxide sources, substitutable products, and other assumptions of the investigated studies significantly impact the reduction potential. Low-emission-factor electric grid mixes containing fossil sources can result in emission savings in many Power-to-X systems. However, using grid mixes that result in emission savings is system-dependent, and the largest emission savings are achieved through renewables or nuclear energy. • Emission reductions were evaluated in the different pathways using hydrogen. • Power-to-X solutions using carbon dioxide resulted in the least reductions. • Co-electrolysis is an interesting option but is unmatured technology. • Green hydrogen is not the only hydrogen source capable of emission reduction. • LCA studies using primary data are desirable. [ABSTRACT FROM AUTHOR]

The demand for green hydrogen is growing as the increasing production of pure hydrogen can no longer be based on fossil hydrocarbons. As water electrolysis would move from niche to a significant consumer of emission-free electricity, the efficiency of electrolytic gas production, lifetime of water electrolysis systems, and balance in the electricity grid become essential. The operational and investment costs of an industrial-scale alkaline water electrolyzer with four practical rectifier topologies are investigated. The results show thyristor-based rectifiers provide poor quality for the AC and DC sides, which leads to nonoptimal specific energy consumption (SEC) of the water electrolyzer and a notable reactive power component. Transistor-based topologies may offer up to 4.5% lower SEC of the electrolyzer than the conventional 6-pulse thyristor bridge. The reactive power results in additional costs in either investments in compensation equipment or regular allowance costs. An additional DC/DC converter can be installed to improve the power quality for the electrolyzer, but the second conversion stage adds to the system complexity and cost without eliminating reactive power. A modular single-stage rectifier based on insulated-gate bipolar transistor (IGBT) bridges is suggested as an alternative to provide improved power quality for both the electrolyzer and the electricity grid. • Four power supply topologies are studied in industrial green hydrogen production. • Thyristor rectifiers have poor AC power factor especially at partial loads. • Transistor-based topologies can minimize the stack SEC at wider partial loads. • A novel modular single-stage IGBT rectifier is presented for electrolysis applications. • The novel rectifier can be the most competitive solution in green hydrogen production. [ABSTRACT FROM AUTHOR]