BI-FACE High-efficiency bifacial PV Modules and Systems for flat roofs

The scope of the project BI-FACE was to develop innovative bifacial modules and systems for flat roofs. The results included three novel variations for bifacial modules and systems which were tested in three different climate areas: subtropical (Cyprus), temperate (Austria) and maritime temperate (Netherlands). The ultimate design of these systems was challenging due to the large number of parameters that influence the energy yield (e. g. tilt and distance between modules, reflecting surfaces, shading, cell spacing, materials used and weather conditions).

A holistic approach to energy performance needed to take the aspect of standardization into account pusing rapid market introduction. Therefore, critical effort were put in to harmonized performance characterization of bifacial PV modules in a factory and laboratory settings.

The layout and mounting design of a bifacial system is critical to obtain the maximum possible performance on flat roofs. The construction demands with respect to wind load, stability, total weight (incl. ballast) and maximum allowed weight on a roof are directly influenced by this and need to be critically examined in parallel. The used approach compared theoretical investigations with tests in the laboratory and in the field.

The project BI-FACE aimed to develop technically as well as economically novel bifacial PV systems to exploit the enormous potential of this technology.

Ausgangssituation

Although bifacial cells need some additional manufacturing steps, from an economical point of view the production costs are comparable
and the yield increase can be approximated by up to 30%. Today one of the most effective ways to include PV is the usage of solar
panels on manufacturing sites and public buildings, where the generated power is used immediately. In many of these buildings, flat roofs are state of the art. Therefore the project BI-FACE focused on optimized lightweight bifacial PV systems for flat roofs.
The first main challenge was the optimization of the module itself, such as the used components and design rules. Novel materials for i.e. encapsulation and glass / foil were evaluated for costs as well as reliability. Furthermore, the manufacturing process was not well analyzed and needded optimization. Besides that, also the characterization of the built modules was still challenging. At the Begining of the project the characterization
of bifacial modules was not well defined, labelling was therefore unprecise and unsatisfactory for customers as well as for manufacturers.
Especially the lack of harmony between laboratory and manufacturing characterization was huge. Parallel to these module aspects the second main challenge was the optimization of the overall system design, where a focus had to be on the layout and mounting design of the system and its effects on energy performance. Energy performance of a system, is critically influenced by, for example,structure and albedo of the roof, influences of surrounding modules and shape of the modules and should be evaluated and optimized to achieve maximum performance. The structure of the system directly influences the construction demands that are related to it, for example
its effect on ballast needed due to added wind load. This contradicts the requirements of many flat roofs, as many cannot handle heavy
weights. This combined optimization of module, system and construction needs to be combined with the economic need to have high energy yield at low costs.