Fraunhofer Institute for Solar Energy Systems ISE (Fraunhofer ISE), Freiburg, Germany, has developed a process to produce solar panels with a homogeneous and brightly colored surface. The colored components could be integrated almost invisibly into facades or roofs.
The principle was borrowed from the wing of the Morpho butterfly. According to Fraunhofer, the idea for the development was not to color the cover glasses of the modules with colored pigments, but to imitate the physical effect of the butterfly’s wing. If glass were coated with pigments, it would lose much of its efficiency because the light would no longer be able to pass the module’s surface unhindered.
In contrast, the Morpho butterflies that live in the tropical rainforests of Central and South America create a color impression not through colored pigments, but through an optical effect. The butterfly wings have a micrometer-fine surface structure that specifically reflects a narrow wavelength range, for example a color.
The Fraunhofer ISE experts have succeeded in applying a similar surface structure to the back of the cover glass of their photovoltaic panels using a vacuum process. Depending on the fine structure, cover glasses in blue, green or red can be produced in this way. Fraunhofer ISE explains that around 93% of the light can penetrate this layer – only around 7% is reflected and triggers the color effect. Therefore, the Freiburg researchers named their technology Morpho color after the blue Morpho butterfly.
The cover glasses, which are vaporized in a vacuum process, can be laminated into photovoltaic modules or integrated into a collector for solar heat generation. In the future, photovoltaics and solar thermal energy could be provided with the same color and mounted virtually invisibly next to each other on roofs or facades. Moreover, the Fraunhofer researchers have found a new approach for mounting solar cells. To prevent the photovoltaic cells, which are soldered together, from shimmering through the colored cover glass like a checkerboard, they have developed a method very similar to the principle to roof shingles. Roof shingles are laid overlapping on top of each other to allow rain to run off. Accordingly, the Freiburg solar researchers produce photovoltaic cells in strips, which they glue together overlapping by a few millimeters to form a larger module. This creates a homogeneous whole without any disturbing gaps or visible contact wires. One can look at the photovoltaic shingles with Morpho color coating from different angles and still the uniform and homogeneous appearance remains the same.