Featured Publications Q2-2024

Progress in Photovoltaics | Volume 32, Issue 6 | June 2024

David Chojniak, Michael Schachtner, S. Kasimir Reichmuth, Alexander J. Bett, Michael Rauer, Jochen Hohl-Ebinger, Alexandra Schmid, Gerald Siefer, Stefan W. Glunz

Tandem solar cells offer the potential to surpass the maximum efficiency of the silicon single-junction technology currently established in the market. However, due to their spectral sensitivity and the resulting need for spectral adjustment of the solar simulator used for the measurement, tandem devices also place significantly higher demands on the measurement technology and methods used. Nowadays, LED-based solar simulators are increasingly used for measuring solar cells. The typically high number of spectrally different LEDs and the resulting mutual influence of individual light sources, however, increases the complexity of measuring tandem solar cells.

Therefore, this publication presents a new methodology for the precise spectral adjustment of LED-based solar simulators. In addition to a calculation routine to solve the optimization problem resulting from the high number of light sources, it also includes an adapted method for calibrating the individual LED spectra. This represents a significant step for the use of LED-based solar simulators for the calibration of tandem solar cells. Due to the continuous light capability and scalability of LED-based simulator systems, this is particularly relevant for the currently emerging perovskite on silicon tandem technology.

Scientific Data | 11 | 828 | 27 July 2024

Patrick Schneider, Anne-Christine Scherzer, Linda Ney, Ha-Kyung Kwon, Brian D. Storey, Dietmar Gerteisen & Nada Zamel

In collaboration with the Toyota Research Institute, we investigated the impact of the composition and morphology of the cathode catalyst layer on the performance and stability of polymer electrolyte membrane fuel cells. With this publication we present comprehensive in-situ characterization data focused on cathode catalyst degradation, drawn from 36 unique durability tests spanning over 4000 hours of testing. The study examines variations in the cathode ionomer to carbon ratio, platinum on carbon ratio, ionomer equivalent weight, and carbon support type. The applied accelerated stress tests were conducted under different upper potential limits and relative gas humidities. Characterization techniques, including IV-curves, limiting current measurements, electrochemical impedance spectroscopy, and cyclic voltammetry, were employed to analyze changes in performance, charge and mass transfer, and the electrochemically active surface area of the catalyst. By making this dataset public, we aim to enhance the understanding of catalyst degradation in the community, allowing other researchers to utilize the data for their own research.

Solar Energy | Volume 273 | 1 May 2024 | 112486

Thomas Kraft, Gregor Bern, Mark Schmitz, Werner Platzer

To maximize the thermal efficiency of solar thermal power plants (Concentrating Solar Power, CSP) with a Parabolic Trough Collector (PTC) field, precise control of the mass flow in individual loops is necessary to achieve optimal outlet temperatures. Individual mass flow control has only been introduced in recent power plants, while mass flow measurement with high temporal and spatial resolution has not yet been implemented. This paper presents the "Time-of-Flight" (ToF) method for determining the mass flow distribution through the individual loops of the solar field in a CSP plant. This method is based on measuring thermal step responses using temperature sensors typically found in standard power plant configurations. The ToF method is presented in a form specifically adapted for this application and validated with exemplary operational data from the Andasol III power plant. The mass flow distribution was successfully determined for the solar field with a deviation of less than 5% for 94% of the analyzed operational data. By combining mass flow and outlet temperature data, inefficient collectors can be identified in existing plants without the need for additional measuring equipment, thereby improving predictive maintenance. This demonstrates the high potential of the simple, safe and effective ToF method to enhance the efficiency of CSP plant operation. 

Applied Energy | Volume 372 | 15 October 2024 (available online 3 July 2024) | 123809

Julian Brandes, Patrick Jürgens, Markus Kaiser, Christoph Kost, Hans-Martin Henning

Sector-coupled energy system models describe the transformation of the entire energy system, taking into account the end-use sectors transportation, buildings and industry. A current challenge is the integration of a high temporal and spatial resolution in a model with a detailed representation of the technologies in all transformation and end-use sectors. This article describes how the spatial resolution of the sector-coupled energy system model REMod can be increased so that the energy, transport and heating transition can be analyzed in an integrated manner in one model at the level of the German federal states. Simulation-based optimization is used for this purpose and the exchange of electricity and hydrogen between the model regions is made possible.

The article emphasizes the importance of taking the overall system perspective into account when transforming the energy system at the federal state level. The challenge is to reconcile the high energy demand in federal states such as North Rhine-Westphalia, Bavaria and Baden-Württemberg with the great potential of renewable energies in federal states such as Lower Saxony, Schleswig-Holstein and Mecklenburg-Vorpommern. The transformation of the demand sectors and grid expansion as well as energy storage, power-to-X technologies (especially electrolysis) and flexible power plants are taken into account.