Featured Publications Q2-2025

Energy and Buildings | Volume 320 | 1 October 2024 | 114592

Helen Rose Wilson, Tilmann E. Kuhn, Hisashi Ishii, Daniel Valencia-Caballero, Nuria Martin Chivelet, Jinqing Peng, Rebecca Jing Yang, Yukun Zang, Hua Ge, Kai Ye, Jacob C. Jonsson, Konstantinos Kapsis

The Solar Heat Gain Coefficient (SHGC) typically quantifies the proportion of incident solar radiation that is transmitted – directly or indirectly –  through building envelope components into the interior of the building. There is a need to modify it for building-integrated photovoltaics (BIPV) because photovoltaic power generation reduces the amount of absorbed solar energy that would otherwise be transferred as heat into indoor spaces.

“Understanding this effect is essential for optimizing energy efficiency in buildings, reducing cooling demand, and supporting the broader adoption of BIPV solutions,” said the authors.

BIPV systems are intrinsically designed to generate electricity and to provide at least one building-related function. When BIPV modules act as glazing products in windows, skylights or curtain walls, their ability to control the transmission of solar energy into the building must be characterised by a Solar Heat Gain Coefficient (SHGC) or g value (also known as Total Solar Energy Transmittance – TSET – or “solar factor”). For the comparison of BIPV glazing products consisting of one PV laminate and possibly further, conventional glazing layers separated by gas-filled cavities, the procedures documented in international standards to determine the SHGC for architectural glazing (e.g. ISO 9050 and EN 410) form a suitable starting point. Easily implemented modifications to these procedures are proposed in the paper to take both optical inhomogeneity due to the combination of PV cells and transparent areas, and extraction of electricity from BIPV glazing units, into account. The basic approach is to calculate the SHGC of the BIPV glazing unit from the optical and thermal properties of its components and the photovoltaic conversion efficiency of the PV module.

The paper also presents results and conclusions from an implementation exercise and sensitivity study carried out by participants of the IEA-PVPS Task 15 on BIPV. The cell coverage ratio in the PV laminate, the thermal resistance offered by the glazing configuration, the choice of boundary conditions and the effect of extracting electricity were all identified as parameters which significantly affect the SHGC value determined for a given type of BIPV glazing. A practicable approach to accommodate the great variety of dimensions typical for BIPV glazing is also proposed. 

Based on the findings reported in the paper, a new Annex to take the specific features of BIPV glazing into account has been included in the current revision of EN 410, the existing component-based European standard for architectural glazing. The revised version of EN 410 with the new BIPV Annex should be published in 2026. It is expected that the next revision of the equivalent international standard, ISO 9050, will also include a BIPV Annex based on the work reported in the paper.

Renewable and Sustainable Energy Reviews | Volume 213 | May 2025 | 115469

Salome Hauger, Vanessa Lieb, Rüdiger Glaser

Agrivoltaics describes the synergistic concept of using agricultural land for both food production and solar energy generation. This dual use not only allows for a significant increase in land efficiency but also offers potential protection for crops against extreme weather events.

This study conducts a geodata-based analysis of agrivoltaic potential and site selection in Germany for the first time, aiming to estimate the possible contribution of the technology to climate goals. By integrating geographic information systems with the Analytical Hierarchy Process, the study quantifies available agricultural land and identifies optimal sites regarding economic viability. Criteria catalogs have been developed that include geographical, technical, economic, and particularly legal and regulatory criteria. With a land use index, a potential of 7900 GWp and 5600 GWp (Scenario 1 and 2) as well as a synergy potential of 136 GWp and 98 GWp (Scenario 1 and 2) were determined, which represent 2.5 times and 3.5 times the photovoltaic expansion targets for 2030, respectively.

Journal of Power Sources | Volume 591 | 30 January 2024 | 233780

Yuze Hou, Johannes Schall, Steve Dietze, Timo Kurz, Dietmar Gerteisen

Degradation during start-up and shut-down (SUSD) of proton exchange membrane (PEM) fuel cells is investigated both experimentally and numerically. In order to understand spatial degradation, the local cell voltage and electrochemical surface area (ECSA) during SUSD are measured using a segmented cell. Novel phenomena such as undegraded inlet segments and a gradual rise in resting potential at the start of the test are hence observed. To further interpret the experimental data, an advanced SUSD model is developed, which accurately reproduces detailed experimental phenomena. The local potential is calculated independently based on the mixture gas concentration and kinetics, without imposing an artificial hydrogen/air interface, allowing for a more realistic transition of the membrane phase potential. The study shows that hydrogen has a greater influence on local membrane phase potential than air due to its faster reaction kinetics and residual hydrogen in inlet gas during shutdown can safeguard the inlet segments against degradation.

Solar Energy Materials and Solar Cells | Volume 282 | April 2025 | 113432

Benjamin Hammann, Florian Schindler, Jonas Schön, Wolfram Kwapil, Martin C. Schubert, Stefan W. Glunz

Hydrogen is known to passivate defects in silicon and therefore plays an important role in highly efficient silicon solar cells. An example of this are TOPCon solar cells, whose excellent surface passivation is only possible with the help of hydrogen. On the other hand, hydrogen is responsible for long-term instabilities such as ‘light- and elevated-temperature-induced degradation’ (LeTID) or ‘surface-related degradation’ (SRD). For high-efficient and long-term stable solar cells, it is important to avoid the negative aspects of hydrogen while retaining the positive ones.

Therefore, in this review paper, we provide an overview of hydrogen research in recent years. We discuss the findings on the role of hydrogen in various degradation phenomena. This leads to the need to reduce the hydrogen concentration below a threshold value, which particularly concerns the concentration of molecular hydrogen. For such an adjustment it is necessary to understand the influence of the different process steps. Therefore, in the second part of this review paper, the findings on various processes that influence the hydrogen concentration are described. These are in particular

1.) The hydrogen source, typically silicon nitride,

2.) layers that influence hydrogen diffusion, such as aluminum oxide and highly doped layers, and 

3.) the firing step, whose peak temperature and cooling ramp are essential parameters for controlling the diffusion and thus the concentration of hydrogen.

Metrology and Simulation