Angewandte Werkstofftechnik

In this work, 1.25 t of AB₂-commercially available hydride-forming alloy is taken as a case study for material selection for large-scale systems. Systematic experimental characterizations, modeling, and life cycle-cost assessment at this industrial scale are performed. Based on the thermodynamic characterization, the equilibrium pressure is calculated by applying the most used Nishizaki and novel 3D representation with 2D-bilinear interpolation approaches, giving accurate values. The kinetic model is comprehensively and successfully developed in a wide range of temperatures and pressures by applying the separable variable method. Life cycle assessment shows that the CO₂ emissions of these kinds of systems can be minimized by increasing the share of recycled material and by using waste heat sources for dehydrogenation. The economic analysis clarifies the influence of the components on the economic viability of large hydride-based systems for emergency power supply. Finally, guidelines are proposed for the development of hydride-based integrated renewable energy systems.

The integration of increasing shares of intermittent renewable energy necessitates flexibility in both energy generation and consumption. Typically, the operation of flexible energy resources is orchestrated through optimization models. However, the manual creation of these models is a complex and error-prone task, often requiring the expertise of domain specialists. This work introduces a methodology for the automatic generation of optimization models for systems of flexible energy resources to simplify the modeling process and increase the use of energy flexibility. This methodology utilizes a modular, generic model structure designed to depict systems of flexible energy resources. It incorporates algorithms for model parameter derivation from operational data and an information model that represents the system’s structure and dependencies of resources. The efficacy of this methodology is demonstrated in two case studies, highlighting its relevance and ability to significantly streamline the optimization modeling process by minimizing the need for manual intervention.

In metal hydride beds (MHBs), reaction heat transfer often limits the dynamic performance. Heat transfer within the MHB usually involves solid and gas phases. To account for both, an effective thermal conductivity (ETC) is defined. Measuring and predicting the ETC of metal hydride beds is of primary importance when designing hydride-based systems for high dynamics. This review paper presents an integral overview of the experimental and modeling approaches to characterize the ETC in MHBs. The most relevant methods for measuring the ETC of metal hydride beds are described, and the results and scopes are shown. A comprehensive description of the models applied to calculate the ETC of the MHBs under different conditions is developed. Moreover, the effects of operation parameters such as P, T, and composition on the ETC of the presented models are analyzed. Finally, a summary and conclusions about experimental techniques, a historical overview with a classification of the ETC models, a discussion about the needed parameters, and a comparison between ETC experimental and calculated results are provided.

With the integration of renewable energy production into grids, hydrogen storage is an effective solution for coping with the fluctuating nature of the resources and reliably providing energy demands. Metal hydride storage is seen as a key technology due to its low operating pressure and temperatures near ambient, while it has a significant volumetric capacity (for room temperature hydrides: 50-110 kg/m³) compared to pressurized (40 kg/m³ under 700 bar and room temperature) or even liquified hydrogen (70 kg/m³ at – 253 ºC and 1 bar). One potential application with metal hydride storage lies in the flexibilization of residential energy demand. Excess photovoltaic generation from a house can power an electrolyser to produce hydrogen, which is then stored in the metal hydride storage. When power and heat are needed in the building, the hydrogen is released into a fuel cell. This case study investigates the dispatch optimization of a metal hydride storage system within a residential household energy system. The interaction of the electrolyser, metal hydride storage, and fuel cell, all components of a container solution called Smart Energy Transform Unit, was studied during summer and winter. Results show that in an exemplary period in winter, from 21 December 2021 to 28 December 2021, the total electricity demand is 98% covered by supply from the grid due to the low photovoltaic generation, which also yields a low hydrogen production; the total heat demand is 90% covered by the heat pump and the thermal storage as a buffer. During an exemplary period in summer, from 20 June 2021 to 27 June 2021, the system is self-sufficient, as hydrogen was stored during the day due to the high yield of photovoltaic generation, and hydrogen is used in a fuel cell at night to provide energy demands. In addition, heat pump operation during summer is small due to the heat provided by the electrolyser, the fuel cell, and the thermal buffer storage. The PV system, together with the Smart Energy Transform Unit, covers 99% of the total electric demand during this period in summer, while for the total heat demand, a coverage of 85% is observed, and the heat pump covers 15%.

Die rasche Expansion erneuerbarer Energiequellen führt zu erheblicher Volatilität und Unvorhersehbarkeit in der Energieversorgungskette, was die Stabilität und Zuverlässigkeit des Stromnetzes herausfordert. Diese Arbeit präsentiert daher eine Methode, die bestehende statische Optimierungsmodelle flexibler Energiequellen echtzeitfähig macht und damit ermöglicht, dass diese sowohl für die mittelfristige Planung als auch für Echtzeitanwendungen eingesetzt werden können. Durch die Anpassung statischer Modelle für die Echtzeitanwendung ermöglicht eine in diesem Beitrag vorgeschlagene zweistufige Optimierungsstrategie flexible Anpassungen von Betriebsplänen, wodurch erneuerbare Energien auch trotz unvorhergesehener Schwankungen bestmöglich genutzt werden können. Dieser Ansatz gewährleistet nicht nur die Zuverlässigkeit des Netzes, sondern verbessert auch die wirtschaftliche Effizienz durch die Optimierung der Ressourcennutzung. Die Wirksamkeit dieser Methode wird durch eine Fallstudie mit einem System von Elektrolyseuren demonstriert, die deutliche Vorteile gegenüber traditionellen statischen Optimierungsmethoden bei der Ausrichtung des Energieverbrauchs auf die Erzeugung erneuerbarer Energie aufzeigt.

Effective hydrogen storage is vital for the widespread adoption of hydrogen in energy systems, as it enables flexibility across various sectors. However, assessing such energy storage systems' suitability in future energy system configurations presents several challenges. One such challenge is the identification of representative operational scenarios for experimental testing of storage systems. Against this background, this paper presents an approach to derive such operational scenarios with the help of energy system modelling and optimization. Using the open-source energy system model and data set of Europe, PyPSA-Eur, cost-optimal future energy system configurations are identified, allowing the derivation of operational scenarios for energy storage facilities from the operation of the overall energy system. For this purpose, the methodology provides a way to identify a representative storage system from the entirety of corresponding storages in the energy system. Further, it allows determining representative time series sections using a segment identification algorithm, providing a basis for experimental technology testing. For an exemplary application of this methodology, further post-processing is implemented to consider the feasibility limits of subsystem components. The results showcase the effectiveness of the approach, offering a transparent and reproducible framework for defining operational scenarios for storage testing aligned with future energy system requirements.

The Digi-HyPro (Digitalized Hydrogen Process Chain for the Energy Transition) project's conceptual development of the SET-Unit investigates and facilitates the connection between the electric, gas, and mobility grid. This application report describes the experimental design of the Smart Energy Transition unit (SET-Unit), contemplating the bottom-up and top-down approaches. For the bottom-up approach, the design of core devices such as metal hydride-based hydrogen storage (MHS) and compressor (MHC) systems are shown. The gas separation system (GSS) concept is based on a hybrid process composed of membrane and pressure swing adsorption (PSA) for the gas grid coupling. Commercial anion exchange membrane electrolyzer (AEM-EL) and polymer exchange membrane fuel cell (PEM-FC) are assembled for the power grid connection. For the top-down approach, the first experimental SET-Unit composed of AEM-EL–MHS–PEM-FC in the nominal power range between 5 and 10 kWel and its control strategy for the optimal hydrogen and heat coupling is presented. All experimental development is carried out in the facilities of the Helmholtz-Zentrum Hereon in the frame of a cooperation agreement with the Helmut Schmidt University/University of the Federal Armed Forces.

Constrained Friction Processing (CFP) is a novel solid-state processing technique suitable for lightweight materials, such Mg- and Al-alloys. The technique enables grain size refinement to fine or even ultrafine scale. In this study, the effect of CFP on the microstructural refinement of AM50 rods is investigated in terms of particle size and morphology of the eutectic and secondary phases originally present in the base material, in particular the eutectic ß-Mg17Al12 and Al-Mn phases. For that purpose, as-cast and solution heat-treated base material and processed samples were analyzed. The AlMn intermetallic phase was identified as the main secondary phase present in all samples before and after the processing. A notorious refinement of these particles was observed, starting from particles with an average equivalent length of a few micrometers to around 560 nm after the processing. The refinement of the secondary phase refinement is attributed to a mechanism analogous to the attrition comminution, where the combination of temperature increase and shearing of the material enables the continuous breaking of the brittle intermetallic particles into smaller pieces. As for the eutectic phase, the results indicate the presence of the partially divorced ß-Mg17Al12 particles exclusively in the as-cast base material, indicating that no further phase transformations regarding the eutectic phase, such as dynamic precipitation, occurred after the CFP. In the case of the processed as-cast material analyzed after the CFP, the thermal energy generated during the processing led to temperature values above the solvus limit of the eutectic phase, which associated with the mechanical breakage of the particles, enabled the complete dissolution of this phase. Therefore, CFP was successfully demonstrated to promote an extensive microstructure refinement in multiple aspects, in terms of grain sizes of the -Mg phase and presence and morphology of the Al-Mn and eutectic ß-Mg17Al12 .

Hydrogen storage is expected to play a crucial role in the comprehensive defossilization of energy systems. In this context, the focus is typically on underground hydrogen storage (e.g., in salt caverns). However, aboveground storage, which is independent of geological conditions and might offer other technical advantages, could provide systemic benefits and, thereby, gain shares in the hydrogen storage market. Against this background, this paper examines the market relevance of aboveground compared to underground hydrogen storage. Using the open-source energy system model and optimization framework of Europe, PyPSA-Eur, the influence of geological independence, storage cost relations, and technical storage characteristics (i.e., efficiencies) on mentioned market relevance of aboveground hydrogen storage are investigated. Further, the expectable market relevance based on current cost projections for the future is assessed. The studies show that in terms of hydrogen capacities, aboveground hydrogen storage plays a considerably smaller role compared to underground hydrogen storage. Even when assuming comparatively low aboveground storage cost, it will not exceed 1.7% (1.9 TWhH2,LHV) of total hydrogen storage capacities in a cost-optimal European energy system. Regarding the amounts of annually stored hydrogen, aboveground storage could play a larger role, reaching a maximum share of 32.5% (168 TWhH2,LHV a-1) of total stored hydrogen throughout Europe. However, these shares are only achievable for low cost storage in particularly suited energy system supply configurations. For higher aboveground storage costs or lower efficiencies, shares drop below 10% sharply. The analysis identifies some especially influential factors for achieving higher market relevance. Besides storage costs, the demand-orientation of a particular aboveground storage system (e.g., hydrogen storage at demand pressure levels) plays an essential role in market relevance. Further, overall efficiency can be a beneficial factor. Still, current projections of future techno-economic characteristics show that aboveground hydrogen storage is too expensive or too inefficient compared to underground storage. Therefore, to achieve notable market relevance, rather drastic cost reductions beyond current expectations would be needed for all assessed aboveground hydrogen storage technologies.

The storage of hydrogen in metal alloys as an alternative to hydrogen storage in pressurized or liquid form has the advantage of high volumetric storage capacity and less complex storage systems due to lower pressure and moderate temperature conditions. The later leads to an improved safety and reduced cost of the storage vessel. However, when considering their utilization in hydrogen storage tanks, swelling-induced stress and heat management are challenges that still require to be addressed. Several strategies have been published in the past to address these problems, however it can be challenging to scale them up. In this work, we propose an easily scalable approach to overcome these drawbacks. The commercially available AB2 room-temperature metal alloy Hydralloy C5 was modified by applying a wash coating-like methodology. The surface of the metal alloy was coated with a mixture of a conductive material like expanded natural graphite (ENG) or aluminum and the elastomeric ethylene-vinyl acetate copolymer (EVA). The performance of this modified metal alloy was investigated by in situ measurement of hydrogen capacity, heat dissipation and swelling-induced stress during 50 hydrogenation/dehydrogenation cycles. The coated metal alloy maintained a satisfactory hydrogen capacity with slightly improved heat dissipation. The swelling-induced stress behavior of the treated material was greatly improved. Especially the addition of a mixture of 10 wt% ENG and 10 wt% EVA allowed to completely compensate for the swelling-induced stress during hydrogenation.