True Colours: Solar Panels to Enhance the Exteriors of Buildings

Photovoltaic modules that can be produced in a spectrum of single colors, through a technology inspired by butterfly wings, are being developed by the Fraunhofer Institute for Solar Energy Systems (ISE).

The aim, explains Dr. Thomas Kroyer, Head of Group Coating Technology and Systems at the organization, is to make solar panels more aesthetically pleasing to encourage designers to incorporate them into buildings.

“We see a lot of potential for these panels in building-integrated photovoltaics (BIPV). BIPV is a technology that can significantly improve the CO2 balance of a building, ideally to the point of a zero-energy or plus-energy building.”

Butterfly Wings

BIPV involves using photovoltaic modules instead of conventional building materials in areas such as roofs, skylights, and facades. Yet despite its benefits and the improved aesthetics of solar panels in recent times, photovoltaic modules are still not popular design features among developers, planners, and architects.

The Fraunhofer ISE modules, however, marry functionality with beauty and will be available in a range of colors to enhance or blend with the building on which they are mounted, Dr. Kroyer explains:

“Conventional methods to color solar cells or cover glass offer a limited selection of colors and have a decisive disadvantage – namely they cause comparatively high energy losses. Our procedure produces coloured modules with minimal transmission losses and thus minimised losses in energy yield.”

The Fraunhofer ISE process sees a layer of dielectric materials added to the backside of the photovoltaic glass that has a photonic 3D structure.

“This structure is inspired by the morpho butterfly whose brilliant blue wing is not created by pigments as with other butterflies, but rather by a surface structure with lamellae [a thin layer of organic tissue] in the nanometer range. The miniature lamellae, which can only be seen under an electron microscope, cause light to diffract and interfere. The many lamellae reflect light of a specific wavelength, in this case, blue; the reflections reinforce one another so that a truly brilliant color is achieved.”

Light Transmission

The special highlight of this structure is that it remains transparent for the other wavelengths. It is therefore ideal for producing brilliant colors while maintaining a high light transmission. In comparison to uncoated cover glass, the colored modules exhibit a relative power loss of only seven percent, an efficiency that is unique in the construction sector. Shades can be specified by adjusting the distance between the lamellae within the 3D structure on the surface of the glass, enabling any color to be manufactured, says Dr. Kroyer:

“The more complex the photonic structure used, the better the quality of the color, eg in terms of angular stability, and the efficiency.”

Prototypes are expected to be produced later this year. The panels could be on the market in 2022.

“The biggest challenge in the project is to find a compromise between the production effort – cost and time – and the color effect. Our current research focus is to achieve the best possible color effect at a reasonable cost for solar module manufacturers.”