Converting sunlight into power has become a trend because solar energy generation helps to preserve the environment and saves money. But now it has also become architecturally valuable: A German research institute has developed a colored solar module that is semi-transparent due to the use of nanoparticles and which can be nicely integrated into the building's facade...

The new modules that the Fraunhofer-Institut für Solare Energiesysteme (Fraunhofer Institute for Solar Energy Systems or ISE for short) introduced consist of a wafer-thin, power-generating film between two glass panes. The film is made of nanoparticles applied to silk screen. The nanoparticles are so tiny that the solar modules appear semi-transparent.

The module prototype from the Fraunhofer ISE, which was developed with well-known industrial partners in the color solar research project sponsored by the Bundesministerium für Bildung und Forschung [Federal Ministry of Education and Research or BMBF], has an amber-colored shimmer. But other colors can also be easily produced and even individual patterns can be incorporated. The result is solar modules that are so aesthetic that it would be a pity to install them on roofs as is usual. On the contrary, architects are taking advantage of the opportunity to integrate semi-transparent solar cells directly in the glass facade of a house. Here, the new technology is even fulfilling a double function: It protects against disruptive direct sunlight and simultaneously produces power.

The special challenge of the new technology was precision. The fine gap between both glass panes must be hermetically sealed so that no air can interfere with the reactive substances. For this reason, the Fraunhofer experts used glass solder instead of a polymer adhesive. For this purpose, a glass powder is applied to a silk screen and melted to the panes at temperatures of around 600 degrees. Fatigue tests under varying weather conditions have shown that the solar cells can remain fully functional even after several thousand hours.

As matters stand, the color module is, however, only a prototype. Certification of long-term stability of the colored solar modules is not yet available. And, in comparison to the conventional crystalline silicon solar cells, the four percent level of efficiency is too low.