Hydrogen generation by electrolysis and storage in salt caverns: Potentials,economics and systems aspects with regard to the German energy transition

The Plan-DelyKaD project focused on an in-depth comparison of relevant electrolysis technologies, identified criteria for and selected most relevant salt cavern sites in Germany, studied business case potentials for applying hydrogen taken from storage to different end-users and engaged in identifying the future role of hydrogen from large scale storage in the German energy system. The focus of this paper is on the latter three topics above. The bottom-up investigation of most suitable salt cavern sites was used as input for a model-based analysis of microeconomic and macroeconomic aspects. The results identify dimensions and locations of possible hydrogen storages mostly in Northern Germany with ample potential to support the integration of fluctuating renewable electricity into the German power system. The microeconomic analysis demonstrates that the most promising early business case for hydrogen energy from large scale storage is its application as a fuel for the mobility sector. From a system perspective the analysis reveals that an optimized implementation of hydrogen generation via electrolysis and storage in salt caverns will have a positive impact on the power system in terms of reduced curtailments of wind power plants and lower residual peak loads.     

Study of SOFC-SOE transition on a RSOFC stack

Reversible Solid Oxide Fuel Cell (RSOFC) can perform both power production and electricity storage with high efficiency and reduced cost using the same device for both functions. Within the frame of a small scale application and distributed generation, RSOFC systems operate connected to the grid switching from electrolysis to fuel cell and vice versa depending on load and grid peculiarities. The study aims to investigate the behavior of RSOFC in the two operation modes and in the transition phase. The analysis moves from the thermal equilibrium and electrical performances data gathered during the test of a six cells SOFC short stack. In particular, the effect of gas composition was deeply investigated. A mapping of performances was realized through polarization curves. Dilution of reactants, both in SOFC and SOE brings to reduction in performances while different compositions during SOE-SOFC transition did not give any significant effect to stack voltages. The dynamic model was derived from experimental results; thermal and electrical transient response to current variation was determined under several operating conditions and related transfer functions were identified characterizing the device dynamic behavior.     

Developing a mathematical tool for hydrogen production,compression and storage

Among the few lessons learned presented in the literature, authors put in evidence the on-going need to investigate on station components and their integration. The specific power consumption of station units with on-site hydrogen generation is often subject to uncertainty, and it would have been desirable to find more details about the energy contribution of each component. To address this gap, this paper focuses on the development of a mathematical modeling as a dynamic and multi-physical design tool to predict the energy performance of hydrogen production systems. Particularly, the model aims to describe and analyze the energy performance of two different electrolyzer technologies (PEM and Alkaline), integrated with a compressor system and gaseous buffer storage. Multiple tank options and a switching strategy are investigated, as well as a control system to simulate a real infrastructure operation. Auxiliaries and components related to the thermal management system have been also included. A carbon-footprint analysis follows the energy one, focusing on the CO₂ emission reduction. Comparisons between literature data and model show that the hydrogen system proposed model is suitable to evaluate systems with respect to energy efficiency and system performance. The model could be a powerful tool for exploring control strategies and understanding the contributions to the overall energy consumption from the various internal components as a guide to researchers aiming for improved performance.     

Enhanced reversible hydrogen storage performance of light metal-decorated boron-doped siligene: A DFT study

The use of nanomaterials for hydrogen storage could play a very important role in the large-scale utilization of hydrogen as an energy source. However, nowadays several potential hydrogen storage nanomaterials do not have a large gravimetric density and stability at room temperature. In this work, we have investigated the hydrogen storage performances of Na-, K- and Ca-decorated B-doped siligene monolayer (BSiGeML) using density functional theory calculations. The results show that boron doping improves the interaction between the metal adatom and the siligene monolayer (SiGeML). The K- and Ca-decorated BSiGeMLs can bind up to seven H₂ molecules per metal adatom, whereas Na-decorated BSiGeML only adsorb four H₂ molecules per adsorption site. The effect of temperature and pressure on the hydrogen storage capacity of BSiGeMLs was also evaluated. At room temperature, all the H₂ molecules adsorbed on Na-, and Ca-decorated BSiGeML are stable at mild pressure. The metal decoration of both sides of BSiGeML may lead to hydrogen gravimetric densities exceeding the target of 5.5 wt% proposed by DOE for the year 2025. K- and Ca-decorated BSiGeML could be efficient hydrogen molecular storage media compared to undoped SiGeML and other 2D pristine materials.     

A hybrid method for hydrogen storage and generation from water

This communication describes a new hybrid method for storing hydrogen in solid inorganic hydride materials as well as producing it from water based on the reaction between LiOH/LiOH·H₂O and LiH. As a hydrogen storage method, the release and uptake of hydrogen in this method are accomplished via a series of simple reactions with good kinetics within a practically reasonable temperature range. The reversible hydrogen storage capacity of the material system is 6–8.8 wt.% at <350 °C. This capacity is one of the highest among all other metal hydrides known to date in the same temperature range. As a hydrogen production method, 100% of hydrogen generated by this method comes from water by its reaction with alkali metal oxides. This method is also an environmentally friendly alternative to the current commercial processes for hydrogen production. The preliminary thermodynamic calculation on energy required for complete regeneration shows that the current system is energetically favorable.     

Hydrogen storage in binary and ternary Mg-based alloys: A comprehensive experimental study

This study focused on hydrogen sorption properties of 1.5 μm thick Mg-based films with Al, Fe and Ti as alloying elements. The binary alloys are used to establish as baseline case for the ternary Mg–Al–Ti, Mg–Fe–Ti and Mg–Al–Fe compositions. We show that the ternary alloys in particular display remarkable sorption behavior: at 200 °C the films are capable of absorbing 4–6 wt% hydrogen in seconds, and desorbing in minutes. Furthermore, this sorption behavior is stable over cycling for the Mg–Al–Ti and Mg–Fe–Ti alloys. Even after 100 absorption/desorption cycles, no degradation in capacity or kinetics is observed. For Mg–Al–Fe, the properties are clearly worse compared to the other ternary combinations. These differences are explained by considering the properties of all the different phases present during cycling in terms of their hydrogen affinity and catalytic activity. Based on these considerations, some general design principles for Mg-based hydrogen storage alloys are suggested.     

Hydrogen-based systems for integration of renewable energy in power systems: Achievements and perspectives

This paper is a critical review of selected real-world energy storage systems based on hydrogen, ranging from lab-scale systems to full-scale systems in continuous operation. 15 projects are presented with a critical overview of their concept and performance. A review of research related to power electronics, control systems and energy management strategies has been added to integrate the findings with outlooks usually described in separate literature. Results show that while hydrogen energy storage systems are technically feasible, they still require large cost reductions to become commercially attractive. A challenge that affects the cost per unit of energy is the low energy efficiency of some of the system components in real-world operating conditions. Due to losses in the conversion and storage processes, hydrogen energy storage systems lose anywhere between 60 and 85% of the incoming electricity with current technology. However, there are currently very few alternatives for long-term storage of electricity in power systems so the interest in hydrogen for this application remains high from both industry and academia. Additionally, it is expected that the share of intermittent renewable energy in power systems will increase in the coming decades. This could lead to technology development and cost reductions within hydrogen technology if this technology is needed to store excess renewable energy. Results from the reviewed projects indicate that the best solution from a technical viewpoint consists in hybrid systems where hydrogen is combined with short-term energy storage technologies like batteries and supercapacitors. In these hybrid systems the advantages with each storage technology can be fully exploited to maximize efficiency if the system is specifically tailored to the given situation. The disadvantage is that this will obviously increase the complexity and total cost of the energy system. Therefore, control systems and energy management strategies are important factors to achieve optimal results, both in terms of efficiency and cost. By considering the reviewed projects and evaluating operation modes and control systems, new hybrid energy systems could be tailored to fit each situation and to reduce energy losses.     

Air compressor efficiency in a Vietnamese enterprise

Compressed air systems in a Vietnamese footwear manufacturing enterprise consume about 10% of enterprise's total electric power supply. Energy efficiency of these air compressor systems, either equipped with new and efficient compressors or old and inefficient ones, can only reach between 5% and 10%. In other words, regardless whatever air compressors were installed, energy loss from the compressor systems was over 80%. This study discovered that energy loss was due to non-optimized operations of the air compressor systems and air leakages. The objectives of the paper are to uncover energy saving potential in Vietnamese air compressor systems, demonstrate methodologies used in the auditing and assessment, share auditing and assessment results, and serve a guide on how to analyze energy efficiency in a compressed air system. This paper concludes that energy efficiency investment in air compressor systems in the Vietnamese enterprise could be extremely cost-effective. If the enterprise invests USD 84,000 in the air compressors to improve efficiency performance, the investment capital will be recovered in about six months. The net present value of the investment will be about USD 864,000 at a discount rate of 12%.     

Mechanochemical modification of LiAlH4 with Fe2O3 - A combined DFT and experimental study

LiAlH₄ is a promising material for hydrogen storage, having the theoretical gravimetric density of 10.6 wt% H₂. In order to decrease the temperature where hydrogen is released, we investigated the catalytic influence of Fe₂O₃ on LiAlH₄ dehydrogenation, as a model case for understanding the effects transition oxide additives have in the catalysis process. Quick mechanochemical synthesis of LiAlH₄ + 5 wt% Fe₂O₃ led to the significant decrease of the hydrogen desorption temperature, and desorption of over 7 wt%H₂ in the temperature range 143–154 °C. Density functional theory (DFT)-based calculations with Tran-Blaha modified Becke-Johnson functional (TBmBJ) address the electronic structure of LiAlH₄ and Li₃AlH₆. ⁵⁷Fe Mössbauer study shows the change in the oxidational state of iron during hydrogen desorption, while the ¹H NMR study reveals the presence of paramagnetic species that affect relaxation. The electron transfer from hydrides is discussed as the proposed mechanism of destabilization of LiAlH₄ + 5 wt% Fe₂O₃.     

High temperature electrolysis using Molten Carbonate Electrolyzer

Molten Carbonate Fuel Cells (MCFC) are a well-developed and commercial technology that can operate also as an electrolyzer producing hydrogen from steam. In this study, a system for the production of hydrogen based on Molten Carbonate Electrolyzer (MCE) is presented. The system receives, as an external input, water and recovers internally the additional gas streams required as input to the electrolyzer. The system products are, separately, pure oxygen and hydrogen. A calculation sheet was implemented to analyze the energy equilibrium and gas mix compositions. The system can produce 0.074 Nl h^?1 cm^?2 of hydrogen with an inlet power density of 0.213 W cm^?2 for an energy consumption of 3.40 kWh Nm_H2^?3. Sensitivity studies on current density, utilization factors of both steam and CO₂ were analyzed considering energy equilibrium of the stack unit and the post processing processes. Results show how current density has higher impact on system equilibrium compared to the other parameters.     

Hydrogen strategy as an energy transition and economic transformation avenue for natural gas exporting countries: Qatar as a case study

In the wake of the apparent impacts of climate change, the world is searching for clean energy transformations and a consequent transition to a carbon-neutral economy and life. The intermittent nature of renewable energy sources introduces several risks, and efficient energy storage technologies are developed to circumvent such issues. However, these storage methods also come with additional costs and uncertainties. Hydrogen is considered a viable option as an energy carrier and storage medium, offering versatility to the energy mix. This study reviews hydrogen production, storage, transmission, and applications avenues, describes the current global hydrogen market and compares national hydrogen strategies. A framework for evaluating the relative competitiveness of natural gas-exporting countries as hydrogen exporters is developed. Qatar's national hydrogen strategy should focus on blue and turquoise hydrogen production in the short/medium term with a mix of green hydrogen in the future term and investment in technological research and development to compete with other gas exporters that have abundant renewable energy potential.     

Beyond Haber-Bosch: The renaissance of the Claude process

Ammonia may be one of the energy carriers in the hydrogen economy. Although research has mostly focused on electrochemical ammonia synthesis, this however remains a scientific challenge. In the current article, we discuss the feasibility of single-pass thermochemical ammonia synthesis as an alternative to the high-temperature, high-pressure Haber-Bosch synthesis loop. We provide an overview of recently developed low temperature ammonia synthesis catalysts, as well as an overview of solid ammonia sorbents. We show that the low temperature, low pressure single-pass ammonia synthesis process can produce ammonia at a lower cost than the Haber-Bosch synthesis loop for small-scale ammonia synthesis (<40 t-NH₃ d^?1).     

压缩空气蓄能（CAES）系统综述

介绍了一种新型的大规模蓄能技术——压缩空气蓄能（Compressed Air Energy Storage,CAES）,CAES系统响应快、容量大、成本低、寿命长,逐渐成为了全球第二大蓄能技术。根据CAES系统的容量不同,将CAES系统划分为大型CAES、小型CAES和微型CAES3种,并针对3种不同容量级的CAES,详细介绍了其组成及现状,对技术特点与难点和应用领域及场景进行了分析与概述。对CAES系统的研究方向与发展前景进行了展望。     

Thermally integrated energy storage system for hybrid fuel cell electric bike: An experimental study

The hybrid fuel cell/battery technology is an attractive option for a sustainable mobility with zero emissions. In fact, this solution owns system scalability features and high efficiency and, compared to battery electric solutions, it offers advantages in terms of flexibility of use and fast charging times. However, the thermal management for the battery in this type of powertrain is a crucial issue, since operating temperatures can significantly affect safety and performance. In this study, an innovative system aimed at providing high storage energy density and improving the battery pack performance of hybrid fuel cell/battery vehicles is investigated for use on-board of a plug-in fuel cell electric bike. The proposed system, developed by the authors in previous studies, integrates the battery pack with a hydrogen storage based on metal hydrides. The idea behind this solution is to exploit the endothermic desorption processes of hydrogen in metal hydrides to cool down the battery pack during operation. An experimental analysis is conducted to assess the thermal management capabilities of this system: by considering a typical duty cycle designed on the base of road test measurements, battery pack temperature profiles are evaluated and compared against those from a control experiment where no battery thermal management is enabled (i.e. no hydrogen desorption from the metal hydride tank). The results show that, beside enhancing the on-board stored energy capacity, the proposed system represents an effective solution to provide an efficient thermal management for the battery pack, with significant advantages in terms of attainable riding range.     

Yttrium-decorated C48B12 as hydrogen storage media: A DFT study

We report a density functional theory calculation dedicated to analyze the behavior of hydrogen adsorption on Yttrium-decorated C₄₈B₁₂. Electron deficient C₄₈B₁₂ is found to promote charge transfer between Y atom and substrate leading to an enhanced local electric field which can significantly improve the hydrogen adsorption. The analysis shows that Y atoms can be individually adsorbed on the pentagonal sites without clustering of the metal atoms, and each Y atom can bind up to six H₂. molecules with an average binding energy of −0.46 eV/H₂, which is suitable for ambient condition hydrogen storage. The Y atoms are found to trap H₂ molecules through well-known “Kubas-type” interaction. Our simulations not only clarify the mechanism of the reaction among C₄₈. B₁₂, Y atoms and H₂ molecules, but also predict a promising candidate for hydrogen storage application with high gravimetric density (7.51%).     

A critical review on the current technologies for the generation,storage, and transportation of hydrogen

Hydrogen production, storage, and transportation are the key issues to be addressed to realize a so-called clean and sustainable hydrogen economy. Various production methods, storage methods, and hydrogen transportations have been listed in the literature, along with their limitations. Therefore, to summarize the state of the art of these proposed technologies, a detailed discussion on hydrogen production, storage, and transportation is presented in this review. Also, to discuss the recent advancements of these methods including, hydrogen production, storage, and transportation on their kinetics, cyclic behavior, toxicity, pressure, thermal response, and cost-effectiveness. Moreover, new techniques such as ball milling, ultrasonic irradiation, ultrasonication, alloying, additives, cold rolling, alloying, and plasma metal reaction have been highlighted to address those drawbacks.Furthermore, the development of modern hydrogen infrastructure (reliability, safety, and low cost) is needed to scale up hydrogen delivery. This review summarizes promising techniques to enhance kinetic hydrogen production, storage, and transportation. Nevertheless, the search for the materials is still far from meeting the aimed target for production, storage, and transportation application. Therefore, more investigations are needed to identify promising areas for future H₂ production, storage, and transportation developments.     

螺杆式空压机变频节能技术的应用

文章论述高压变频调速装置的原理,通过压缩机变频恒压控制节能分析和计算,阐述变频调速技术在空压机供气领域的应用。节省电能的同时改善空压机性能,提高供气品质。     

并联冰蓄冷空调在汽车上的应用

本文分析了汽车空调采用冰蓄冷技术的优点：降低油耗并且可以满足制冷负荷增大时的舒适性，并对其与汽车运行工况的匹配控制作了探讨。     

Thermodynamic analysis and experimental investigation of a unique photoelectrochemical hydrogen production system

In this study, we thermodynamically analyze and experimentally investigate a continuous type hybrid photoelectrochemical H₂ generation reactor. This system enhances solar spectrum use by employing photocatalysis and PV/T. Additionally, by replacing electron donors with electrodes to drive the photocatalysis, the potential of pollutant emissions are minimized. In this study, the present reactor is tested under electrolysis operation during which the present reactor is investigated under three different inlet mass flow rates (0.25, 0.50, and 0.75 g/s) and four different operating temperatures (20, 40, 60, and 80 °C). Some parametric studies are run by varying the environmental temperature between 0 and 40 °C. In addition, the impact of coating the membrane electrode assembly of the reactor with Cu₂O is investigated. The present results show that the highest energy and exergy efficiencies occur at the environmental temperature of 20 °C which is about 60% and 50%, respectively. The Cu₂O coated membrane gives a lot higher current readings, meaning that the coating makes the membrane more conductive and increases H₂ production by permitting ions at a higher rate.