When she left the Peruvian port of Callao on January 12 earlier this year and headed out to sea in the direction of Polynesia, Maud Fontenoy, the first woman to row solo across the North Atlantic and who has now set her sights on the Pacific, had around 8,000 kilometers of empty ocean in front of her. The journey is scheduled to take around four to six months. The electricity required to operate her satellite telephone, the lights to study her charts and the GPS navigation system for setting her course is generated from solar modules supplied by Duisburg, Germany-based SunWare Solartechnik GmbH & Co KG. The special feature of the modules is a new film called ETIMEX® TPU Film VISTASOLAR® from Dietenheim, Germany-based Etimex PP GmbH, which is used to encapsulate the individual module components. The film consists of the thermoplastic polyurethane (TPU) Desmopan® from Bayer MaterialScience AG.
"We decided to use this TPU film because it offers a considerably better bond with the silicon wafers, the various module films and the glass rear panel than the ethylene vinyl acetate copolymer (EVA) materials formerly used. This means that the encapsulated structure does not become delaminated, resulting in a longer and calculable service life for the modules and thus improving the benefit to the customer. The TPU film also enables us to manufacture the modules more cost-effectively," says Julian Schüren, Managing Director and owner of SunWare.
"The VISTASOLAR® film has the advantage that it can be processed like a thermoplastic in a vacuum-free environment using a continuous process. In contrast, when EVA is used to encapsulate modules in the vacuum laminator, it has to undergo the time-consuming process of three-dimensional crosslinking and this results in cycle times of between 10 and 20 minutes," says Dr. Gunther Stollwerck, an expert on plastic encapsulation for solar modules at Bayer MaterialScience. Thanks to the TPU film, SunWare was able to reduce cycle times for module manufacturing by around a half, resulting in a significant increase in productivity and reduced costs.
Due to the fact that the TPU film is not chemically crosslinked, but rather is only fused on at around 120 °C, it can be softened again and removed by heating. This not only enables comparatively simple repair of the modules, but also allows them to be recycled, which is particularly beneficial given the high value of the silicon wafers. In contrast to EVA, the TPU material does not contain any reactive crosslinking agents. The extruded films are already cut to size and can therefore be stored almost anywhere prior to processing without outgassing additives.
The optical and mechanical properties of the TPU film are very similar to those of EVA. "A further strength is its long-lasting transparency, due to the fact that it is a light-stable version of the TPU Desmopan®. It is also flexible over a large temperature range. In severe cold, it does not become brittle and liable to crack. This also helps to prolong the service life of the solar modules," says Jens Ufermann, specialist in TPU films and coating materials at Bayer MaterialScience.