In recent years, some car manufacturers have already presented the first car models with photovoltaic panels integrated into the roof. The roof is the easiest surface to use for on-board solar power generation. Researchers at the Fraunhofer Institute for Solar Energy Systems ISE have now gone a step further by integrating solar cells into bonnets as well.
As part of two government-funded research projects, researchers from the Fraunhofer ISE integrated solar cells into the standard metal bonnet of an ordinary passenger car. "We applied the solar cells to the bonnet panel of a popular car model in Germany. We connected them together and laminated them with foil." So says Dr Martin Heinrich, coordinator for PV mobility at Fraunhofer ISE. "To achieve this, we carefully optimised the lamination process. This was necessary to minimise air pockets and prevent wrinkling of the film module. This can occur due to the curved surface. We also had to maintain the overall integrity of the hood structure."
Solar cell selection
To make the most efficient use of the available surface area on the hood, the Fraunhofer ISE team built their prototypes with a selection of IBC, PERC shingle and TOPCon shingle solar cells. In principle, any solar cell technology can be used. Laminating the surface with foil results in a structured surface structure. It is possible to match it to the colour of the vehicle using MorphoColor technology. "We have already achieved very good aesthetics with this," continues Dr Heinrich. "And we are currently working on improving the surface appearance even further. For this, we are actively looking for project partners interested in joint development."
Curved shape
Besides the curved shape, the substrate in this case is also unique to the hood's PV module. This is because it is made of sheet metal instead of a classic back surface of foil or glass. This led the scientists to investigate the adhesive properties of different material combinations.
Prototypes
After identifying suitable materials, the research team built prototypes with different amounts of solar cells and different cell and interconnection technologies. The team tested all prototypes intensively in the laboratory to ensure the electrical performance, reliability and durability of the PV bonnet demonstrators. The bonnet with 115 watts of power contains more than 120 PERC shingle solar cells and is finished in MorphoColor grey.
Roofs of vehicles
"The technology can also be applied to the metal roofs of vehicles. The advantage is that they are much lighter than photovoltaic roofs made of glass." So says Dr Harry Wirth, director of the Power Solutions division at Fraunhofer ISE. "Expanding the technical possibilities for integrating photovoltaics into vehicle shields will appeal to more and more customers. There is still a lot of potential to tap into here."
HighLite
PV bonnet development is part of the "HighLite" research project. This project was supported by the European Union's Horizon 2020 programme, and the research project "3D - PV Modules with Contour for Integrated Photovoltaics", supported by the German Federal Ministry of Economics and Climate Action (BMWK).
Opening photo: The 115-watt vehicle hood has more than 120 PERC shingle solar cells and is finished in MorphoColor grey. (Photo: Fraunhofer ISE)
