PEM water electrolyzer model for a power-hardware-in-loop simulator

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.     

Performance assessment of an electrochemical hydrogen production and storage system for solar hydrogen refueling station

This paper investigates the performance of a hydrogen refueling system that consists of a polymer electrolyte membrane electrolyzer integrated with photovoltaic arrays, and an electrochemical compressor to increase the hydrogen pressure. The energetic and exergetic performance of the hydrogen refueling station is analyzed at different working conditions. The exergy cost of hydrogen production is studied in three different case scenarios; that consist of i) off-grid station with the photovoltaic system and a battery bank to supply the required electric power, ii) on-grid station but the required power is supplied by the electric grid only when solar energy is not available and iii) on-grid station without energy storage. The efficiency of the station significantly increases when the electric grid empowers the system. The maximum energy and exergy efficiencies of the photovoltaic system at solar irradiation of 850 W m-2 are 13.57% and 14.51%, respectively. The exergy cost of hydrogen production in the on-grid station with energy storage is almost 30% higher than the off-grid station. Moreover, the exergy cost of hydrogen in the on-grid station without energy storage is almost 4 times higher than the off-grid station and the energy and exergy efficiencies are considerably higher.     

阴离子交换膜电解水制氢技术的研究进展

氢能是我国2060年“碳中和”的关键支撑,氢气制备又是氢能产业链“制、储、输、用”四大环节中的首要环节,绿色高效地制取氢气是氢能发展的基础。阴离子交换膜电解水（AEMWE）作为新兴的“绿氢”技术,充分结合了碱性水电解技术与质子交换膜电解技术的优势,有望成为最具发展潜力的可再生能源制氢技术。对AEMWE的原理与研究现状做了简要分析,详细论述阴离子交换膜（AEM）水电解槽关键部件的研究进展与发展方向,包括阴离子交换膜、阳极、阴极催化剂、双功能催化剂、离聚物、膜电极、多孔传输层、双极板及电解液。最后结合研究现状,展望了AEMWE制氢技术的研究方向。     

New multi-physics approach for modelling and design of alkaline electrolyzers

This work presents a multi-physics model used for the design and diagnosis of the alkaline electrolyzers. The model is based on a new approach that allows to choose precisely the design parameters of a new electrolyzer even if it is not commercially available and predicting energy consumption, efficiency and rate of hydrogen production, taking into account to their physical state and various operating conditions. The approach differs from those of conventional models of the following: It allows the characterization of the electrolyzer based on its structural parameters in a relatively short time (few minutes) compared with the conventional approach which need experimental data collected for few weeks (Ulleberg). The approach allows describing a range of alkaline electrolyzers, while semi-empirical models found in literature are inherent to a specific electrolyzer. In addition, the model takes into account the variation of all structural parameters (geometry, materials and their evolution depending on operating conditions) and operational parameters of the electrolyzer (temperature, pressure, concentration, bulk bubbling and recovery rate of electrode surface by the bubble), while the models in the literature involve only the temperature. The developed multi-physics model was programmed in a Matlab Simulink^® environment and an alkaline electrolyzer’s simulation tool was developed. The simulation tool was validated using two industrial (Stuart and Phoebus) electrolyzers with different structures and power rates. Simulation results reproduced experimental data with good accuracy (less than 0.9%). The simulation tool was also used to compare the energy efficiency of two hydrogen production systems. The first one is based on atmospheric electrolyzer with a compressor for hydrogen storage and the second one is a barometric electrolyzer (under pressure) with its auxiliary devices to identify the effective mode of hydrogen production according to the physical state and operating conditions of the electrolyzer. The analysis of results revealed that the second mode of hydrogen production is more efficient and confirms the results of the literature based solely on the thermodynamic approach (K. Onda et al) without the input of the power consumed by power overvoltages.     

Hydrogen production using alkaline electrolyzer and photovoltaic (PV) module

In this paper it is presented hydrogen production using alkaline water electrolysis where a 30 W photovoltaic (PV) module was involved as a source of electric energy. Therefore, the process is without emitting CO₂. There is constructed and tested an alkaline electrolyzer with 50 × 50 × 2 mm Ni metal foam electrodes, 50 × 50 × 0.4 mm Zirphon^® membrane and 25% alkaline (KOH) solution electrolyte. Electrolyzer UI characteristics for natural and forced flow of electrolyte with PV module UI characteristics are presented. The results are in favor of forced flow circulation, and these are better if the flow velocities are higher. Calculated Energy efficiency (based on hydrogen high heating value) for both types of circulation is above 55%. There are much evidence for further improvement of the system components and consequently electrolyzer and system efficiency.     

Operation of first solar-hydrogen system in China

The first solar-hydrogen (S-H) system in China, which consists a 2 kW PV cell array, a 48 V/300Ah lead-acid battery bank, an 0.5 Nm³/h hydrogen production capacity alkaline water electrolyzer, a 10 Nm³ LaNi₅ alloy hydrogen storage tank and a 200 W H₂/air PEM fuel cell, was installed in the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University and has been operated for several months. The goal of the system was to study the technical and economical feasibility of using such a system to produce hydrogen in large scale for the future hydrogen energy society. With two months operation, experimental results reveal 40.68% energy transformed to hydrogen with 7.21 kWh/Nm³ H₂ electricity consumption. Economic analysis results illustrate that the present system is not cost-efficient and the energy conversion efficiencies of PV panel and electrolyzer are suggested to increase in technology improvement to cut down cost.     

Experimentally tuned dual stage hydrogen compressor for improved compression ratio

An experiment-driven design procedure for optimizing the combination of stages of a dual stage hydrogen compressor with enhanced compression ratio is presented herein. Three different combinations of reactors were used using LaNi₅, Ca_0.6Mm_0.4Ni₅ and Ca_0.2Mm_0.8Ni₅ as hydrogen storage materials. Compression ratios were found to be similar for low supply pressure conditions, which improved significantly for high supply pressure conditions in single stage experiments. A dual stage compressor system with LaNi₅ in first stage and Ca_0.2Mm_0.8Ni₅ in the second stage was proposed based on single stage results, which was found to be very effective for enhancing compression ratio. Results show that 53% higher compression ratio can be attained by selecting appropriate storage materials for stages, compared to LaNi₅ based economic dual stage system.     

Optimal operation of a photovoltaic generation-powered hydrogen production system at a hydrogen refueling station

As the popularity of fuel cell vehicles continues to rise in the global market, production and supply of low-carbon hydrogen are important to mitigate CO₂ emissions. We propose a design for a hydrogen refueling station with a proton exchange membrane electrolyzer (PEM-EL)-based electrolysis system (EL-System) and photovoltaic generation (PV) to supply low-carbon hydrogen. Hydrogen is produced by the EL-System using electricity from PV and the power grid. The system was formulated as a mixed integer linear programming (MILP) model to allow analysis of optimal operational strategies. Case studies with different objective functions, CO₂ emission targets, and capacity utilization of the EL-System were evaluated. Efficiency characteristics of the EL-System were obtained through measurements. The optimized operational strategies were evaluated with reference to three evaluation indices: CO₂ emissions, capacity utilization, and operational cost of the system. The results were as follows: 1) Regardless of the objective function, the EL-System generally operated in highest efficiency state, and optimal operation depended on the efficiency characteristics of the EL-System; 2) mitigation of CO₂ emissions and increase in capacity utilization of the EL-System required trade-offs; and 3) increased capacity utilization of the EL-System showed two opposing effects on hydrogen retail price.     

Thermal performance of a commercial alkaline water electrolyzer: Experimental study and mathematical modeling

In this paper a study of the thermal performance of a commercial alkaline water electrolyzer (HySTAT from Hydrogenics) designed for a rated hydrogen production of 1 N m³ H₂/h at an overall power consumption of 4.90 kW h/N m³ H₂ is presented. The thermal behaviour of the electrolyzer has been analyzed under different operating conditions with an IR camera and several thermocouples placed on the external surface of the main electrolyzer components. It has been found that the power dissipated as heat can be reduced by 50–67% replacing the commercial electric power supply unit provided together with the electrolyzer by an electronic converter capable of supplying the electrolyzer with a truly constant DC current. A lumped capacitance method has been adopted to mathematically describe the thermal performance of the electrolyzer, resulting in a thermal capacitance of 174 kJ °C⁻¹. The effect of the AC/DC converter characteristics on the power dissipated as heat has been considered. Heat losses to the ambient were governed by natural convection and have been modeled through an overall heat transfer coefficient that has been found to be 4.3 W m⁻² °C⁻¹. The model has been implemented using ANSYS^® V10.0 software code, reasonably describing the performance of the electrolyzer. A significant portion of the energy dissipated as heat allows the electrolyzer operating at temperatures suitable to reduce the cell overvoltages.     

Methylcyclohexane production under fluctuating hydrogen flow rate conditions

Energy storage using liquid organic hydrogen carrier (LOHC) is a long-term method to store renewable energy with high hydrogen energy density. This study investigated a simple and low-cost system to produce methylcyclohexane (MCH) from toluene and hydrogen using fluctuating electric power, and developed its control method. In the current system, hydrogen generated by an alkaline water electrolyzer was directly supplied to hydrogenation reactors, where hydrogen purification equipment such as PSA and TSA is not installed to decrease costs. Hydrogen buffer tanks and compressors are not equipped. In order to enable MCH production using fluctuating electricity, a feed-forward toluene supply control method was developed and introduced to the system. The electrolyzer was operated under triangular waves and power generation patterns of photovoltaic cells and produced hydrogen with fluctuating flow rates up to 7.5 Nm³/h. Consequently, relatively high purity of MCH (more than 90% of MCH mole fraction) was successfully produced. Therefore, the simplified system has enough potential to produce MCH using fluctuating renewable electricity.     

Prospects of the European gas market

This paper discusses prospects for increased consumption of natural gas within the European Union (EU) up to 2030. Particular emphasis is on the power generation sector, where the main growth in demand is expected to occur, on supply and infrastructural constraints and on future price of natural gas.     

有源逆变器的研究现状与发展

有源逆变技术是将直流电能变为交流电能并回馈至电网,从而实现电能回收利用的技术,是电源性能测试中的最新技术手段.文中对大功率电子负载技术中的核心技术——有源逆变并联技术的研究现状和发展进行了介绍.     

Educational electrolyzer prototype: Improving engineering students' knowledge in renewable energies

This article aims to demonstrate the process of building a low-cost water electrolyzer using common materials and to analyze the influence of practical experiments on students' knowledge. Practical classroom experiments are of great importance to students' learning and problems such as bureaucracy in the teaching department, high cost of equipment and lack of teacher time are some of the factors responsible for the delay in performing them in the classroom. Applying the Advanced Product Quality Planning methodology, Active Learning, thermodynamic and electrochemical modeling, it was possible to build an electrolyzer with about 150 US$. In the electrolyzer, the electrolytic solutions with 1 M concentration of NaOH and KOH were used, i.e., 39 g L^?1 and 64 g L^?1, respectively, to produce the gases hydrogen and oxygen. The flow of hydrogen and oxygen for the KOH electrolytic solution was 1.22 L min^?1 and for the NaOH solution, 1.07 L min^?1 was found using a 9–12 V and 8–15 A adjustable transformer. Among the undergraduate students who were interviewed, 54% did not know electrolysis and 46% knew just the basic concepts. After the practical experiment, it was observed that 94% of the students understood the concepts of the electrochemical reaction. Based on the averages of the two tests applied to students, before and after the practical experiment, an increase of 58% in the correctness of the questions was found for students who had not heard of electrolysis before and a 13% increase was observed for those who already knew the basic concepts. With this experiment, it was possible to observe how much practical activities in the classroom can positively influence the understanding of electrolysis and make students aware of this renewable energy production process.     

Sustainable energy systems: Role of optimization modeling techniques in power generation and supply—A review

Electricity is conceivably the most multipurpose energy carrier in modern global economy, and therefore primarily linked to human and economic development. Energy sector reform is critical to sustainable energy development and includes reviewing and reforming subsidies, establishing credible regulatory frameworks, developing policy environments through regulatory interventions, and creating market-based approaches. Energy security has recently become an important policy driver and privatization of the electricity sector has secured energy supply and provided cheaper energy services in some countries in the short term, but has led to contrary effects elsewhere due to increasing competition, resulting in deferred investments in plant and infrastructure due to longer-term uncertainties. On the other hand global dependence on fossil fuels has led to the release of over 1100 GtCO₂ into the atmosphere since the mid-19th century. Currently, energy-related GHG emissions, mainly from fossil fuel combustion for heat supply, electricity generation and transport, account for around 70% of total emissions including carbon dioxide, methane and some traces of nitrous oxide. This multitude of aspects play a role in societal debate in comparing electricity generating and supply options, such as cost, GHG emissions, radiological and toxicological exposure, occupational health and safety, employment, domestic energy security, and social impressions. Energy systems engineering provides a methodological scientific framework to arrive at realistic integrated solutions to complex energy problems, by adopting a holistic, systems-based approach, especially at decision making and planning stage. Modeling and optimization found widespread applications in the study of physical and chemical systems, production planning and scheduling systems, location and transportation problems, resource allocation in financial systems, and engineering design. This article reviews the literature on power and supply sector developments and analyzes the role of modeling and optimization in this sector as well as the future prospective of optimization modeling as a tool for sustainable energy systems.