Klassen, Thomas

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.

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.

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.

Das Kaltgasspritzen entwickelt sich zu einem Verfahren mit großem Potenzial für die Reparatur metallischer Bauteile, insbesondere für das Aufbringen von hitze- und oxidationsempfindlichen Materialien. In diesem Zusammenhang ermöglicht der Einsatz von Automatisierung und Robotik eine flexible Steuerung des Reparaturprozesses. Um einen optimalen Reparaturprozess zu gewährleisten, müssen die verschiedenen Anforderungen des robotergeführten Kaltgasspritzens bereits in der simulativen Planungsphase berücksichtigt werden. Herkömmliche Trajektorien zum Materialauftrag berücksichtigen jedoch oft nicht die bei Reparaturen zu beachtenden geometrischen Randbedingungen des Materialaufbaus, den effizienten Materialeinsatz und die zugrundeliegenden Einschränkungen der Roboterkinematik. In dieser Arbeit wird daher ein Konzept zur automatisierten Trajektorienplanung und anschließenden Trajektorienoptimierung zur Reparatur durch robotergeführtes Kaltgasspritzen beschrieben. Das Ziel ist es, eine optimierte Trajektorie zu erzeugen, die die Anforderungen des Kaltgasspritzens und der Roboterkinematik berücksichtigt, um eine qualitativ hochwertige Reparatur und einen effizienten Materialeinsatz zu gewährleisten. Dazu gehören die Minimierung des überschüssigen Materials und die Minimierung des Rucks bei der Roboterbewegung. Die Ergebnisse zeigen die erfolgreiche Anwendung der initialen Trajektorienplanung und der anschließenden Trajektorienoptimierung für die Bauteilreparatur durch Kaltgasspritzen.

Material deposition in cold spraying occurs in solid state and thus avoids undesired effects of melting and solidification. However, residual stress conditions in cold sprayed coatings could limit possible part performance. The temperature distribution and thermal history of the cold sprayed components has significant influence on stress distribution and thus deposition and part quality. The present study investigates the effect of substrate material and nozzle traverse speed (as a secondary parameter) on effective temperatures and residual stress distributions of titanium-grade 1 deposits. The results demonstrate that substrate material properties and nozzle traverse speeds have significant influence on residual stresses of the cold spray deposit. It is understood that coefficient of thermal expansion (CTE) difference of the coating and substrate materials has significant effect on residual stress state. On the other hand, the residual stresses change from more compressive to more tensile state as the temperature of the components increases by decreasing the nozzle traverse speed. These findings indicate that thermal parameters affect residual stresses substantially. Thus, by adjusting the kinematic parameters and reducing maximum reached local temperatures within the part, more favorable stress states of the finished component can be obtained. The attained knowledge is essential for the development of high-quality deposits and the selection of the best strategies for repair and additive manufacturing applications.

Rotational symmetry parts are common and essential in industrial applications. Cold spray additive manufacturing (CSAM) is an attractive and rapidly developing solid-state material deposition process, providing an efficient and convenient method for producing such parts, as it allows for the rapid formation of high-quality, large-volume 3D objects. Since there is no highly reactive liquid phase involved in this process, the deposited material is free of oxides. As compared to conventional additive manufacturing methods, cold spraying enables to reduce the production costs and times. In this work, a general implementation method for CSAM of rotating symmetry casing parts is presented. Here, the developed application can handle rotational symmetry parts of arbitrary geometry in the form of CAD files to generate precise toolpaths. Robot offline programming allows for process simulation, analysis, and optimization. Additionally, modelling of robot kinematics is employed to evaluate the effect of the planned toolpaths on the spraying process, ensuring efficient and precise manufacturing processes.

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%.

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.