A new system for integrating solar cells into the roof of an electric car will be unveiled at the Frankfurt Motor Show this September, and they promise to not only extend the driving range of an electric vehicle but also be completely indistinguishable from the rest of the vehicle’s body.

Developed by German solar research institute Fraunhofer Institute for Solar Energy Systems ISE, the system involves using solar cells in a preformed roof that can then be painted any colour, while providing extra energy for an electric vehicle.

“In order to realize a CO2-free energy supply in all sectors, we have to promote the expansion of photovoltaics vigorously, even beyond house roofs and open spaces,” said Dr. Andreas Bett, director of the institute in a note by email.

“In the future, solar modules will be integrated into our already built environment even more, for example into vehicles.”

By covering the solar cells with a special coating that mimics the surface of a Morpho butterfly’s wing (which have incredibly bright colours thanks to the interplay of numerous tiny scales and ridges), the solar car roof can match the colours of the rest of the body, albeit with a 7% loss in efficiency.

“The colour possibilities are almost endless,” said Dr. Martin Heinrich, head of PV for mobility at Fraunhofer ISE in a note.

To store the energy captured by the solar car roof, the researchers at Fraunhofer ISE have developed a way to use a “shingle interconnection” whereby overlapping monocrystalline silicon solar cells connected with a electrically conductive glue to ensure low resistance loss.

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As per Fraunhofer ISE’s press release:

The module surface can be used to the maximum for power generation and offers a homogeneous, esthetic appearance.

In addition, lower resistance losses, the avoidance of shading due to cell connectors on top of the cells and particularly high tolerance to shading ensure up to two percent higher module efficiency than for conventional solar modules.

The solar cell matrix is laminated in a polymer-film laminator between the glass panes of a commercially available, spherically curved panorama car roof. By applying a specially manufactured mold, lamination can also be carried out in a conventional laminator.

In addition to absorbing sunlight and converting it into energy to store in the vehicle’s battery, the absorption also reduces overheating inside the vehicle.

The system is certainly interesting, although whether the solar car roof developed by Fraunhofer ISE will compete against the likes of Dutch solar car roof startup Lightyear One is yet to be seen.

According to Fraunhofer ISE, the new system generates just 200 watts per square metre, adding on 10 kilometres driving range based on average daily summer sunlight in Germany’s Freiburg im Breisgau and a vehicle using 17kWh per 100km with an annual driving distance of 15,000km.

This compares to calculations by Lightyear One, which says its solar electric car officially unveiled in June can drive 35km per summer day in the same region on energy powered solely by the sun (with an average yearly driving distance of 20,000).

Fraunhofer ISE  says it sees a potential for additional research to integrate the panels into other surfaces on an electric vehicle to maximise range extension. And its solar car roof could also be used to power incidental electrical features like air conditioning or heating which can otherwise drain an electric vehicle’s battery.

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The institute also sees great potential in using integrated photovoltaic panels in commercial vehicles such as refrigerated trucks, and in 2017 completed a research project in collaboration with several truck companies using irradiation and temperature sensors that showed a potential 5,000-7,000kWh of annual power generation could provide 5,000-7000 kilometres of driving range for one typical truck.



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