Fraunhofer Institute integrates solar cells into cars

In recent years, several car manufacturers have already presented vehicle models with integrated photovoltaic roofs. Researchers from Freiburg have now gone one step further and built solar cells directly into the bonnet of a car. With the help of the institute's MorphoColor® technology, the solar-active surface can be adapted to the colour of the car.

Dr Martin Heinrich, coordinator for PV mobility at Fraunhofer ISE, explains the process: "We applied the solar cells to the bonnet panel of a car model often sold in Germany, interconnected them and laminated them with foil. In doing so, we carefully optimised the lamination process to minimise air gaps, avoid wrinkling of the foil module due to the curved surface and maintain the overall integrity of the bonnet structure."

Different solar cell technologies such as IBC, PERC shingle and TOPCon shingle were used for the prototypes to make the best use of the available surface area on the bonnet. The surface structure is textured by laminating it with foil, and this can be colour-matched to the vehicle colour using MorphoColor® technology. Heinrich emphasises: "It already looks very good, and we are currently working on improving the surface appearance even further. To do this, we are looking for project partners who are interested in a joint development.

One feature of this PV bonnet technology is the substrate made of metal, sheet metal to be precise, instead of a classic backing made of foil or glass. This presented the researchers with the challenge of identifying suitable material combinations and investigating the adhesion properties. The research team developed prototypes with different numbers of solar cells and different cell and interconnection technologies. All prototypes were tested in the laboratory to ensure the electrical performance, reliability and durability of the PV bonnet demonstrators. At the IAA MOBILITY, a bonnet with a rated power of 115 watts was presented, equipped with 120 PERC shingle solar cells and finished in the MorphoColor® colour grey.

Dr. Harry Wirth, Division Manager Power Solutions at Fraunhofer ISE, sees great potential in this development "The technology would also be applicable for metal roofs of vehicles. This would have the advantage of being much lighter than photovoltaic car roofs made of glass. Expanding the technical possibilities for integrating photovoltaics into vehicle shells will convince more and more customers; there is still a lot of potential to be tapped here."