Glass-free lightweight PV building elements: solutions to minimize weight and maximize durability

In densely populated countries, little free land is available for the deployment of photovoltaics (PV) in field installations. In addition, 40% of the world's demand for electricity is related to buildings. These facts provide a strong argument for the accelerated development of building-integrated PV (BIPV), as it enables electricity production with a minimal impact on free land. However, BIPV elements currently on the market show some limitations, which includes their relatively high prices, as most products are custom-made and produced in small volumes. Moreover, the relatively high weight (15-20 kg/m2) of these products may preclude their use in the potentially promising market of renovations of older buildings, for which excessive load could be a serious constraint.

With the aim of limiting the module weight while preserving excellent mechanical stability and durability, we demonstrate that, with careful material selection and a proper adaptation of the manufacturing processes, we are able to manufacture lightweight modules with a weight of 6 kg/m2. The weight reduction is achieved by replacing the backsheet, conventionally glass or polymer, with a rigid composite sandwich structure and by replacing the front cover glass with a thin polymer foil. In our approach, the conventional liquid epoxy used to glue skins and core is substituted with a thermoplastic adhesive foil (polyolefin) that ensures a good adhesion and stress transfer between the sandwich components. By associating this adhesive with a high-thermal-conductivity honeycomb core (aluminum), we can employ conventional lamination processes used in the PV industry to manufacture the backsheet and the full solar module stack simultaneously during a single process. These modules show an excellent resistance and stability when subjected to mechanical, climatic and electrical stress tests used in the solar industry. In fact, these solutions show a reduced power loss (lower than -5%), no major visual changes and preserve a good insulation resistance. These results demonstrate the potential of our design to successfully comply with the relevant PV qualification standards (e.g. IEC 61215).

We further demonstrate that our lightweight modules can successfully pass hail tests without cracked cells by tuning the mechanical properties of the frontsheet and backsheet simultaneously. The design of the lightweight PV modules is successfully scaled up to a sixteen-cell 0.81 × 0.81 m2 module.

Furthermore, the BIPV elements need to comply not only with PV standards but also with construction and safety standards, e.g. fire resistance. Preliminary results indicate that the proposed design in this thesis may successfully pass the relevant fire tests used for building elements (CEN/TS 1187). These first results also give indications on how to optimize the product further.

Finally, to reach a commercial market, some challenges must still be addressed: we must scale up to standard module sizes (1.6 m2), and we must develop an ideal mounting solution for a good integration of the modules into the building.