The black uniformity of photovoltaic (PV) cells is an increasingly common sight on the rooftops of European buildings. They are a sign of our growing desire for renewable energy, but their appearance has not been welcomed in regions where traditional tiling is valued.
In Italy, which is famous for its terracotta rooftops, Wegaplast SpA has answered the problem with a plastic roof tile with integrated PV cells which is colored to match traditional ceramic tiles.
Wegaplast, based in Toscanella di Dozza, near Bologna, injection molds its Wegalux tile in Luran S, Styrolution's UV-stabilized acrylonitrile styrene acrylate (ASA) copolymer. The Wegalux tile comprises the molded housing and a solar module with two polycrystalline cells. The tile is the same size as a normal tile and can be integrated seamlessly into new or existing roofs.
Ugo Rigon, sales director of Wegaplast's Wegalux division, said: "The PV system can be applied to any sloping or ribbed roof that has Marseille terracotta tiles, which are very common in Italy. Our Wegalux tile is the perfect way to obtain energy from sunlight – even in historical districts and places where it is essential not to obstruct the local scenery."
Styrolution, based in Germany, worked closely with Wegaplast to ensure UV-resistance and weathering performance would enable the tile to withstand the Italian weather. The Luran S grade has high dimensional stability and good resistance to temperature fluctuations.
Luran S grades and their blends with polycarbonate have been impact-modified with acrylic ester rubber, making them suitable for components that are exposed to rain, wind and weather.
Marko Blinzler, product manager, specialties, at Styrolution, said: "As well as being resistant to sunlight, our product also withstands adverse weather conditions, thus offering optimal solutions to even the most demanding architects, designers and builders in terms of surface quality."
The need to meet aesthetic requirements was crucial for Wegaplast.
Rigon said: "Luran S' aesthetic qualities were a decisive factor for us, as Styrolution was able to provide us with the exact shade we needed to make our solar tiles fit in harmoniously with non-PV ones. This pre-colored solution saves us time and costs."
He told European Plastics News: "The basic idea was to make the solar cell 'disappear' on the roof, so it does not disturb the aesthetic of Italian villages with black solar cells, but instead it is integrated into the shape and color of existing tiles."
The PV cells are easy to mount on any roof because they are part of the tiles.
A major challenge for outdoor applications is color change over the lifetime of the product's use. ASA has good resistance to yellowing and Styrolution also supplies UV protection packages that are added to Luran S.
For the Wegalux tile, Styrolution conducted xenon tests which simulated 10,000 hours of sunlight exposure. Testing has continued to gather data for longer periods.
The Wegalux plastic tiles will be mounted close to ceramic ones. It is likely that after a large number of years there will be some color deviation as the two materials age in different ways and the shades of terracotta start to vary. But Styrolution does not think this will be significant.
"We believe the color deviation will be acceptable and it will be small enough that you can combine ceramic and plastic on one roof," said Pieper.
He said that after five years of exposure to sunlight, Styrolution expects the tile's color deviation to have a dE value below 5 in the CIELAB color space system. A value above 5 indicates a visible difference in color.
Styrolution is supporting Wegaplast as it develops the second generation of Wegalux tiles, which aim to be more efficient. The first generation already achieves a good performance – producing 1kWp of electric energy requires 10 square meters of Wegalux roofing, equivalent to 128 tiles.
Luran S is targeted at a number of sectors, including automotive exterior parts. In the housing and construction sector, Styrolution is seeking out niche applications. Pieper said the company's targets in the sector are linked to special outdoor applications which are still in development.