Angewandte Werkstofftechnik

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.

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%.

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.

In the transition from fossil fuels to renewable energy, efficient energy conversion and storage systems are required. One of the promising technologies that can support this transition is photoelectrochemical (PEC) water-splitting, in which solar energy is directly used to split water into oxygen and hydrogen. One of the main challenges in the design of efficient PEC systems is the optimization of the semiconductor material systems on the electrodes, which convert sunlight into electrochemical energy. The photoelectrochemical performance of these materials is significantly affected by the microstructure at the interface to the electrolyte, including the distribution of grains, grain boundaries and surface defects. Scanning probe microscopy (SPM) allows to simultaneously analyze and correlate morphological, mechanical, electrical and electrochemical properties at the nanometer scale. In this work, a series SPM methods were employed to investigate, with high spatial resolution, the effect of film morphology on the electrical and electrochemical properties of semiconductor photoelectrodes. Thin TiO2 films synthesized by atomic layer deposition (ALD) were used as model systems. Conductive atomic force microscopy (CAFM) measurements revealed anisotropy in the photocurrent activity, which was correlated with underlaying crystalline orientations with the help of high-resolution topography and complementary microscopy techniques. Kelvin probe force microscopy (KPFM) studies revealed a slow charge redistribution upon and after illumination due to the trapping and detrapping of photogenerated charges. Current-voltage (I-V) characterization was employed to investigate charge carrier transport mechanisms occurring at the metal tip and crystalline TiO2 nanojuction. Finally, electrochemical AFM (EC-AFM) was used to study the photocorrosion of partially crystalline TiO2 in-situ under the working conditions of the photoanode. The results thus provide new insights into the fundamental microscopic processes in photoelectrodes, from which strategies for further efficiency improvements can be derived.