The Fraunhofer Institute for Solar Energy Systems ISE clad the facade of one of its laboratory buildings with 70 photovoltaic modules that were developed together with its partner, Bystronic glass, under the name TPedge, and which were manufactured in its own pilot production.© Fraunhofer ISE

Building-integrated photovoltaics 05.07.2018

The wafer-thin solar films from the production plant weigh only 500 g/m² and are less than 1 mm thick. This enables the films to be integrated into a diverse range of applications.© Heliatek/Tim Deussen, Berlin

Roof of the largest shopping centre in Europe, Dolce Vita Tejo in Lisbon, Portugal, with 5-layer foil cushions made of 200,000 m² of ETFE. The roofing was manufactured by Hightex GmbH – a specialist provider of textile architecture which is also now involved in the FLEX-G project. Each roof element can be optionally furnished with solar cells or electrochromic films.© Hightex GmbH

Photovoltaic elements for facades and flexible roofsModern building facades can do more than provide insulation and outer envelopes for buildings. New photovoltaic modules give designers considerable scope when designing the colour of facade surfaces. Unlike standard solutions, such energy facades make a considerable contribution to improving the energy balance of buildings. Standard silicon, thin-film and organic PV elements can be used.

PV facade elements are particularly suitable for covering larger office or factory buildings. These have large surfaces that need to be clad. They can also be used for re-cladding and energy efficiently refurbishing old buildings in need of renovation. The spread of these facade systems is being fuelled by the trend towards energy-plus buildings as well as the new statutory requirements for energy efficient buildings, such as the Minimum Energy Standard and the expansion goals of Germany’s Renewable Energy Sources Act (EEG).

Making PV facades fit for the mass marketHowever, there are still several obstacles that need to be overcome before their broad market introduction: the requirements for PV facade elements differ significantly from those for standard modules. On the one hand, they have to fulfil additional building physics- and safety-related criteria. On the other hand, architects and developers have high aesthetic and design requirements in terms of the colour, surface design and shape. They are not purely investment projects. PV facades are primarily a construction product and must be comparable to conventional facades. Researchers

from the systems engineering and grid integration division at the Fraunhofer Institute for Energy Economics and Energy Systems IEE Kassel have investigated how building technology and building regulations can be improved for PV facade components. The aim was to create guidelines that help to summarise the building code requirements for PV modules as a construction product for national technical approval. Before being used as an

However, there are still several obstacles that need to be overcome before their broad market introduction: the requirements for PV facade elements differ significantly from those for standard modules. On the one hand, they have to fulfil additional building physics- and safety-related criteria. On the other hand, architects and developers have high aesthetic and design requirements in terms of the colour, surface design and shape. They are not purely investment projects. PV facades are primarily a construction product and must be comparable to conventional facades. Researchers

from the systems engineering and grid integration division at the Fraunhofer Institute for Energy Economics and Energy Systems IEE Kassel have investigated how building technology and building regulations can be improved for PV facade components. The aim was to create guidelines that help to summarise the building code requirements for PV modules as a construction product for national technical approval. Before being used as an energy-optimised, high-quality building envelope, not only the durability of the modules but also the system components used must be tested and documented under operating conditions.

Development of a comparative, holistic evaluation schemeThe researchers focussed on finding out which building code requirements photovoltaic facade modules have to fulfil and which added value they offer over conventional facade systems. The aim is to provide engineers with planning software for facade projects with multifunctional photovoltaic components. This will enable designers, clients, investors, architects and facade constructors to consider and compare different facade systems with and without PV in a holistic way.

The focus is not on the highest possible yield but on activating the building envelope for the use of local energy resources. Decisive for a PV facade system is the creative integration into the building concept.

Higher requirements for system componentsAt the same time, the safety, quality and long-term stability of the components must be guaranteed. Not only the PV modules have to be adapted to the field of application in the facade but also the complete system technology, ranging from the bypass diode energy conversion units and wiring to the monitoring.

In cooperation with several industrial partners, the work is focussing on the high demands placed on the quality of PV facade elements and integrated system components. The common goal has been to eliminate technical and normative barriers that currently hamper the further dissemination of PV facades.

For this purpose, quality standards have been developed that specifically relate to the use of PV components in facades. On the one hand, this concerns the development of draft standards and directives that can either complement existing standards or be included in the European BIPV standard. It is equally important to develop design criteria for the appropriate dimensioning of PV facade elements and PV system components in different applications.

According to the researchers, successful marketing of the new technology requires the development and publication of safe, building physics-efficient, energy efficient and economically optimised PV facade systems for new construction and refurbishment. As part of the Multielement II research project, Fraunhofer IEE managed to promote the transfer of knowledge between research and industry and contribute to continuous product improvement. In addition, the institute supported the networking of the players as well as the foundation of Allianz BIPV.

Flexible organic photovoltaic elements for membrane roofsAnother possible field of application for using photovoltaics could be large-scale roofs and facades such as on railway stations, airports and stadiums where large, translucent facade and roof elements are used. These consist, for example, of weather-resistant fluoropolymer plastics such as ethylene-tetra-fluoro-ethylene (ETFE). These are lighter and more flexible than glass, but in contrast difficult to coat. In the FLEX-G project, researchers are investigating how this material can be furnished with functional layers, for example with a heat-insulating coating or integrated solar modules. They are aiming to develop roll-to-roll coating processes that enable large-area functional layers to be applied directly onto flexible ETFE film.

The project partner and manufacturer of organic thin-film solar cells, Heliatek, is investigating how large-area flexible organic solar cells can be integrated directly into ETFE membranes. The researchers are working to embed OPV solar films into ETFE cushions and to prepare their series production, adapted to the specific requirements of membrane construction. Researchers from the Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP are investigating the roll-to-roll coating of the film with opto-electronically active layers. The new functional layers will be tested on a 36 m2 membrane roof in which flexible organic solar cells and electrochromic devices for switching the total energy transmittance will be integrated.

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