The Beauty of Invisible Solar: How custom-colored modules increase social acceptance

Until now.

Solar modules for building-integrated applications need to behave optically like a traditionally- colored element (i.e., black or very dark) while still generating as much power as possible. However, taking inspiration from the 3D photonic structures on a Morpho butterfly’s shimmering blue wings, scientists in Germany have developed colored solar panels that can be incorporated into a building’s exterior — practically invisibly — while maintaining high efficiency. This is especially important when integrating PV into more historic buildings, where visible renovations can prompt disapproval from the local communities. In fact, a recent study found that when PV modules are colored to match the roof or façade of an existing building, social acceptance increases.

In 2024, a joint study on the social acceptance of building-integrated photovoltaics (BIPV) concluded that the acceptance of integrated photovoltaics in urban areas is generally very high, and that PV on modern buildings is viewed more positively than on historic buildings. The study also showed, however, that when PV modules are colored to match the building's roof or façade so that they are practically invisible, the social acceptance is increased to the point where no difference is detected between the different building types. 

Historic building in Eppingen, Germany, with a red roof-integrated PV system. It has been shown that a color-matched, homogeneous PV integration increases the acceptance.  © Fraunhofer ISE / Photo: Sarah de Carvalho

The study analyzed two surveys: An online survey based on photos, and a survey in person, where differently colored PV modules were shown. “An important finding of the study is that the social acceptance of PV systems depends on the type of building and visual impression. These two factors weigh much more heavily than personal variables such as personal values, political attitudes, or environmental concerns," summarized the authors of the study. “The findings confirm that the acceptance of PV systems can actually be increased through good visual integration with colored modules, especially for historic buildings."

Market expectations for building-integrated PV

In Germany, 75 percent of installed PV is located on buildings, a market that is growing continuously. For Germany’s energy transition to succeed, around 400 gigawatts-peak of installed PV power will be required by 2045. With a technical potential of around 1000 gigawatts-peak, photovoltaics on buildings can make a significant contribution to the decarbonization of the building sector and built infrastructure — all without taking up additional land area. 

This “double use” of already sealed surfaces appeals to urban areas all over the world, allowing cheap electricity to be generated where it is needed. However, solar panels can sometimes look out of place when installed on roofs and facades, especially in the historical centers of cities. It makes more sense to select colored PV modules that blend homogeneously into the building's appearance rather than using them as an architectural detail. To that end, the PV industry would greatly benefit from offering a wide range of aesthetically different PV modules that match existing buildings. 

A special structure on the Morpho butterfly’s wing gives the impression of saturated color. Scientists from Fraunhofer ISE copied this structure to develop colored solar modules with almost no efficiency losses. 

Color inspired by a butterfly

Historically, the sticking point for colored BIPV products has been their lack of efficiency; simply painting the cover glass of a PV module results in the color pigments blocking out the sun and inhibiting it from reaching the solar cells. To avoid this, the researchers looked to nature for inspiration. They found it in the Morpho butterfly. The 3D photonic structures on the butterfly’s wings allow for an intensive, angularly stable colored impression thanks to a fundamentally low-loss interference effect. Following this biological model, the scientists succeeded in using a vacuum process to apply a similar surface structure to the back of the glass covering their solar panels. Depending on the fine structure, glass coverings in a large variety of colors and colored foils can be produced.

A Green PV system integrated into the façade of Fraunhofer ISE’s laboratory building built in 2022. Building-integrated photovoltaics on new buildings was not examined in the study, so restrictions need not apply. Colored PV modules can be employed as architectural details here. © Fraunhofer ISE / Photo: Guido Kirsch

The coating system developed for colored solar panels has now surpassed the biological model in terms of its properties. Independent measurements confirm that the colored solar panels with the structural properties (rather than painted coatings) can achieve about 95 percent of the power of a comparable uncoated panel. The plug-in solution can be used with all standard commercially available solar technologies as well as those foreseeable in the future, plus it can be manufactured industrially at low cost. Cell and panel technologies such as rear contact solar cells with a uniform appearance are an especially good fit.

Dr. Thomas Kroyer is head of the Coating Technology and Systems group at Fraunhofer ISE, Europe’s largest solar energy research organization. His research focus is on PV coating technologies, optical design and characterization of thin film coatings, and low emissivity and solar control coatings on glass and film substrates.

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