The facade of the new institute building for the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) is furnished with CIGS modules.© ZSW – Zentrum für Sonnenenergie und Wasserstoffforschung, Baden-Württemberg

Building-integrated photovoltaics – BIPV 24.07.2018

Coloured demonstration solar modules, presented in the ISE Annual Report 2017/2018© Fraunhofer ISE

CIGS thin-film modules beautify house wallsIn order to achieve the goal of meeting Germany's energy demand almost completely with renewables by 2050, it is planned that facades and partially shaded surfaces should also be used for generating electricity by photovoltaic means. The modules that can be used for building-integrated photovoltaics (BIPV) have to meet considerable requirements in terms of their appearance, performance and costs. Experts have summarised this need for action in their recommendations for the German federal government's 7th Energy Research Programme.

Photovoltaic facade systems, also known as BIPV (building-integrated photovoltaics), can expand the usable area for economic power generation. Based on studies, the Centre for Solar Energy and Hydrogen Research Baden-Wuerttemberg (ZSW) calculates that this area is equivalent to about ten per cent of the economically usable roof area in Germany. Although building-integrated modules are more expensive than roof-mounted modules, these extra costs are offset by not having to install a conventional building envelope.

In particular, photovoltaic facade systems on existing buildings have to cope with the existing changing light conditions and shading. Further development work is needed to adapt modules and systems to these specific conditions for integration into building facades. Solar facades with a payback period of ten years are therefore possible.

Facade-integrated CIGS thin-film PV systemsResearchers want to develop a shading-tolerant CIGS thin-film module that can make better use of the special irradiation conditions on building facades. They are aiming to improve the yield and ease of assembly, and to realize flexible module sizes. Researchers from ZSW, the Centre for Applied Research – Sustainable Energy Technology (zafh.net) at Stuttgart

Detailed view of the ZSW institute building with CIGS modules© ZSW – Zentrum für Sonnenenergie und Wasserstoffforschung, Baden-Württemberg

The solar cells are visible under the coloured cover glazing when viewed from a short distance. © Fraunhofer ISE

Researchers want to develop a shading-tolerant CIGS thin-film module that can make better use of the special irradiation conditions on building facades. They are aiming to improve the yield and ease of assembly, and to realize flexible module sizes. Researchers from ZSW, the Centre for Applied Research – Sustainable Energy Technology (zafh.net) at Stuttgart University of Applied Sciences and the module manufacturer, NICE Solar Energy GmbH, are jointly pursuing the goal of making CIGS thin-film systems market-ready for facade applications.

Many different requirements need to be taken into account in this regard: modules for use on facades must meet not only structural requirements but also specific safety, reliability and longevity criteria resulting from the shading of the facades. These requirements also apply to components such as inverters. In addition, it is also intended that the waste heat from the facades should serve as a source for heat pumps. Another goal is to use the facade system in summer for natural ventilation.

ZSW is collecting the operating data for the CIGS test facade at its new institute building in Stuttgart. It is using it to simulate the energy potential of CIGS facade systems from an economic perspective.

Standard BIPV facadeIn the Standard-BIPV project, researchers from the Fraunhofer Institute for Solar Energy Systems (ISE) are working on developing a prefabricated

standard BIPV facade for the energy-efficient refurbishment of existing buildings. In this context, they carried out a detailed analysis of the existing building stock in Germany. The aim was to identify building categories that could be refurbished with prefabricated and standardised BIPV facades. One focus was on industrial sheds, whose facades in Germany cover more than 100 million m2 in area.

Facade design with coloured PV modulesIn the case of solar cells for facades, it is not just the efficiency that plays an important role but also the colour design. With a new coating process, a large variety of colours for solar modules will be possible without causing major output losses.

Only a few colours for solar cells or cover glazing were previously available, which also considerably impeded the efficiency. The Innovative Coatings team at Fraunhofer ISE has therefore developed a new coating for the cover glass for PV modules. The coloured coating on the back of the cover glazing only reduces the output by about 7% compared with uncoated cover glass. The colour layer on BIPV modules covers the otherwise visible structure of the module. It combines high saturation with good angular stability of the colour impression, whereby there is only a slight loss of efficiency. The coating can be produced with cost-effective industrial coating processes. The researchers are now working together with module and glass manufacturers to improve the manufacturing process and adapt it to an industrial production scale.

The researchers based their surface design on the three-dimensional surface structure that is a feature of Morpho butterfly wings. Here nanoscale lamellae create the iridescent blue colour. These reflect the incident light, and the reflections reinforce one another. At the same time this structure remains permeable to other wavelengths. By changing the distances between the lamellae, the researchers achieve strong colouration with high light transmission.

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