Featured Publications Q4-2023

Solar Energy | Volume 269 | February 2024 | 112319

Nils Straub, Wiebke Herzberg, Anna Dittmann, Elke Lorenz

In this paper, we present a novel all sky imager (ASI) method for high-resolution irradiance forecasting. Our AI-based model uses pixel values and various other image features from ASI images directly to calculate irradiance forecasts within a radius of about 10 km around the camera position.

Throughout the test period (May 2021-April 2022), our novel method showed significantly lower forecasting error than various established reference models. By blending our new model with the reference models into one compact hybrid forecasting model, we were able to significantly reduce forecasting errors even further.

Scientific Reports | Volume 13 | Article number: 15745 | September 2023

Jörg Schube, Oliver Höhn, Patrick Schygulla, Ralph Müller, Mike Jahn, Gabriele Mikolasch, Marc Steiner, Felix Predan, Jonas Bartsch, Frank Dimroth, Florian Clement & Roman Keding

In recent years, new applications for III-V photovoltaics are rising, e.g., in vehicle-integrated PV (cars, planes, drones etc.). One major challenge for such solar cells to be utilized in these emerging fields is cost. This work aims for a low-cost metallization of III-V cells, which has been an unchartered regime until now. For the first time we successfully applied a mask and plate approach without precious metals to III-V-on-silicon tandem solar cells and demonstrate its potential on high-efficiency devices. A photoconversion efficiency of 31.6 % was reached. It turns out that the significantly cheaper mask and plate metal contacts with potential feature sizes of 10 µm enable similar efficiencies as the photolithographically realized reference metallization.

Since our approach is directly applicable to any III-V-based solar cell concept, we believe that it can fundamentally change such devices’ whole microfabrication and cost structure.

Energy Technology | Volume 11, Issue 12 | December 2023 | 2300379

Manuel Lämmle, Jakob Metz, Michael Kropp, Jeannette Wapler, Thore Oltersdorf, Danny Günther, Sebastian Herkel, Constanze Bongs

While heat pumps are already state of the art in smaller new buildings, there are still various challenges in older buildings that hinder a rapid ramp-up, including the higher temperatures required or the development of suitable heat sources, especially in densely populated urban areas. The special feature of the article described here is the intersection of results from eight Fraunhofer ISE research projects in order to describe the challenges for heat pumps in existing buildings in a well-founded manner and to point out possible solutions. The field studies taken into account allow a statistical evaluation of the source and sink temperatures and their influence on the efficiency of heat pumps in both single-family and multi-family houses. Alternative refrigerants as well as bivalent operating modes or multi-source systems are considered as optimization options. In summary, the article describes the great potential of heat pumps in existing buildings, especially if the possibilities in the areas of device development and the planning, installation and parameterization of heat pump systems are fully exploited.

Chemie Ingenieur Technik | Volume 96 | Issue 1-2 Special Issue: Hydrogen | January / February 2024 | 86-99

Tobias Eißler, Gwendolyn Schumacher, Jochen Behrens, Friedrich Mendler, Christopher Voglstätter

In the paper "Detailed Cost Analysis of Hydrogen Refuelling Costs for Fleets", the team of authors led by Tobias Eißler calculated the costs of hydrogen refuelling for fleets of vehicles in a two-stage approach. First, various system configurations of hydrogen refuelling stations (HRS) were simulated and optimised for different HRS sizes and 350 bar pressure using the H2ProSim toolkit from Fraunhofer ISE. According to the results, pipeline-supplied HRS with a high hydrogen throughput (> 4000 kg/d) can reduce hydrogen refuelling costs even with lower capacity utilisation.

As customer travel costs to hydrogen refuelling stations play an important role, particularly in the activation phase of the hydrogen market, the positioning and dimensioning of the refuelling station network was optimised in a case study for the Upper Rhine region. The analysis shows possible network structures and hydrogen supply costs for a number of specific customers.