Featured Publications Q1-2025

Wafer-bonded two-terminal III-V//Si triple-junction solar cell with power conversion efficiency of 36.1% at AM1.5g

Division Photovoltaics

© 2024 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.

Progress in Photovoltaics | Volume33, Issue 1 EU PVSEC 2023 | January 2025 | Pages 100-108

Patrick Schygulla, Ralph Müller, Oliver Höhn, Michael Schachtner, David Chojniak, Andrea Cordaro, Stefan Tabernig, Benedikt Bläsi, Albert Polman, Gerald Siefer, David Lackner, Frank Dimroth

 

To increase the efficiency of silicon solar cells above 30 %, the introduction of additional absorber layers is necessary. Semiconductor materials with higher band gaps can utilise the short-wavelength part of the solar spectrum more efficiently so that less energy is lost as heat. 

In this article, we have presented a triple-junction solar cell whose efficiency of 36.1 % under the AM1.5g standard spectrum is currently the highest of all silicon-based solar cells. We used a thin top cell layer stack of III-V compound semiconductors, i.e. elements such as gallium, indium, arsenic and phosphorus, which we bonded directly to a silicon sub-cell after crystal growth. However, this only increased the overall thickness of the cell by around 1 %. 

A photonic lattice structure on the back, developed and implemented jointly with the Dutch research institute AMOLF in a successful international cooperation, led to an increased light absorptance in the silicon sub-cell. We also succeeded in improving the material quality of the III-V sub-cells so that the voltage of the solar cell increased by 60 mV compared to previous generations. Both measures together made the new record possible. Furthermore, we established a new measuring technology to analyse the light coupling between the individual sub-cells of the solar cell. Thereby we show how we can achieve even higher values in future by adjusting the layer thicknesses.

Methanol Synthesis from Sustainable Feedstocks– A Quantitative Side Product Analysis

Division Hydrogen Technologies

© 2024 The Author(s). Chemie Ingenieur Technik published by Wiley-VCH GmbH

Chemie Ingenieur Technik | Volume 96, Issue 9 | Special Issue: Carbon2Chem® Teil 4 | September 2024 | Pages 1166-1176

Dr. Florian Nestler, Johannes Voß, Dr. Anna Fastabend, Dr. Tammarat Niemeier, Dr. Holger Ruland, Max J. Hadrich

 

Methanol synthesis from sustainably produced hydrogen and atmospheric or biogenic CO2 will play a crucial role in the future energy and raw material transition due to the high significance of methanol in the chemical and fuel market. Unlike conventionally produced methanol based on fossil raw materials such as natural gas, coal, and petroleum, the synthesis conditions for its sustainable production change due to new gas compositions and process framework conditions. Among other issues, this leads to uncertainties regarding by-product formation.

For the first time, a systematic correlation analysis of various influencing factors on the formation of carbon-containing by-products is conducted in this publication using proprietary experimental data collected in the project Carbon2Chem® as well as literature-based data. The analysis identifies the CO2 content of the synthesis gas at the reactor inlet as the most important factor for by-product formation – the higher the CO2 content in the synthesis gas, the lower the proportion of undesired by-products in the liquid crude methanol. Trend functions based on the experimental data were derived for the identified by-products, enabling the prediction of the by-product content in crude methanol for consideration in the downstream process chain.

In this publication, a systematic correlation analysis of various influencing factors on the formation of carbon-containing by-products is conducted for the first time using proprietary measurement data collected within the framework of the Carbon2Chem® project and literature-based data. The analysis identifies the CO2 content of the synthesis gas at the reactor inlet as the most important factor for by-product formation – the higher the CO2 content in the synthesis gas, the lower the proportion of undesirable by-products in the liquid crude methanol. Measurement data-based trend functions for the identified by-products are established, which for the first time enable the prediction of the by-product content in crude methanol and consideration in the downstream process chain.

Evaluating low-temperature heat sources for large-scale heat pump integration: A method using open-source data and indicators

Division Power Solutions

© 2024 The Authors. Published by Elsevier Ltd.

Applied Energy | Volume 377, Part B, 1 | January 2025 | 124487

Nicolas Fuchs, Guillermo Yanez, Bertrand Nkongdem, Jessica Thomsen

 

Large heat pumps are an important technology for the decarbonization of district heating. To utilize large heat pumps, they require suitable heat sources from which environmental heat can be efficiently converted into usable heat. The paper presents a method for evaluating low-temperature heat sources such as air, water (rivers, lakes, wastewater), and ground (shallow and deep geothermal) solely using publicly available data. The developed evaluation method consists of five steps:

1. Identification of potential natural heat sources

2. Assessment of the availability and potential of these sources based on technical, economic, ecological, and regulatory indicators using freely available public data.

3. Cost estimation for the development and provision of the heat sources.

4. Comparison of potentials and costs to determine the most suitable heat sources.

5. Recommendations for decision-makers for optimal integration into existing district heating systems. 

The method allows for the identification and evaluation of local renewable heat sources, which is crucial for the decarbonization of district heating systems and the promotion of sustainable energy supply. By utilizing open-source data, the approach provides a cost-effective and easily accessible way for municipalities, planners, and decision-makers to make informed decisions in the planning of their energy systems.

Analysis of the performance and operation of a photovoltaic-battery heat pump system based on field measurement data

Division Heat and Buildings

© 2023 The Authors. Published by Elsevier Ltd.

Solar Energy Advances | Volume 4 | 5 January 2024 | 100047

Shubham Baraskar, Danny Günther, Jeannette Wapler, Manuel Lämmle

 

Electrically driven compression heat pumps are considered a key technology to achieve climate protection goals in the building sector. Additionally, utilizing on-site produced PV electricity can yield further ecological and economic benefits. In the BMWK-funded project "WP-QS in Existing Buildings" (FKZ: 03EN2029A), up to ten PV/heat pump combinations are analyzed based on a detailed measurement study in real existing buildings. Various system and control concepts are examined with regard to self-sufficiencyand self-consumption. At the same time, the influence of PV-optimized operation on efficiency and operational behavior is to be investigated. Since the results are based on measured field data, this work distinguishes itself from the current literature, which is mostly based on model-based approaches.

This work addresses the evaluation of a supply system consisting of a non-capacitycapacity-controlled ground source heat pump, a PV system, and a battery storage. The system is operated in a single-family house built in 1960, with a measured heating energy consumption of 84 kWh/(m²a). The control strategy to increase self-consumption through the heat pump involves raising the setpoint temperature for space heating and domestic hot water heating, activated when a certain level of PV output is available. Over the 12-month evaluation period, 43% of the electricity produced by the PV system was used on-site. The electricity used by the heat pump came 36% from the PV system. This solar coverage rate ranged from over 90% in the summer months to only 5% in December of the considered year. As a result of the setpoint temperature increase when PV output was available, the annual performance factor of the heat pump decreased by 4.0% in space heating mode and by 5.7% in domestic hot water preparation.