Using solar energy to power onboard electronics or auxiliary functions such as air-conditioning, or even to charge batteries, seems to be gaining some momentum. Proof of that was on display at REVA Electric Car’s booth at the Frankfurt Motor Show. The Indian automaker revealed the REVA NXR three-door hatchback with an optional solar roof panel that provides a trickle charge to top off the battery.
And the new Toyota Prius offers an available sliding glass moonroof packaged with Kyocera-developed solar panels to generate power for interior ventilation while the car is parked in sunlight (see “A cool solution to a hot Prius” in the August issue of AEI or at www.sae.org/mags/aei/6622).
But solar modules in vehicles are still very much niche products.
One reason is glass-based module manufacturing limits the use of photovoltaic cells in size and weight, according to Proof Design and Innovation Management. The German company presented a plastic-based solution, the Composite Solar Module (CSM), at the Frankfurt show.
“With Proof CSM solar modules, the generation of energy is for the first time possible on engine bonnets as well as on dashboards or rear shelves,” said Denis le Maire, Head of Advanced Engineering for Proof Design and Innovation Management, adding that a 50% weight savings can be realized compared to traditional glass modules.
To produce the CSM, solar cells are embedded in a patented Sunovation process between highly transparent thermoformed plastic panels. High-performance plastics such as Plexiglas from Evonik and Makrolon from Bayer MaterialScience are used.
The process accommodates all available solar cell technologies, according to Bettina Weiss, Product Developer at Proof Design, noting that the company works with cell manufacturers such as Sunways, Uni-Solar, and SolarWorld on the modules.
Enabling the use of plastics is a silicon-based gel layer between the panels and the cells, which are also made of silicon. “Silicon does not expand very much, and plastic expands in the heat and high temperature a lot,” Weiss explained. “So if you stick the cell directly on the plastic sheet, it will crack. So we developed a layer between that is able to take the tension off the materials and provides good isolation.”
CSM panels resist mechanical stress very well, Weiss noted, and compared to glass modules are not only lighter but also more flexible and have higher breaking resistance. Such characteristics make the technology suitable for not just passenger vehicles but also heavy trucks and even boats, she said.
Another aspect Proof Design brings to the solar module is in the design—in particular, the ability to custom-laser-cut solar cells. “We are a design studio, so we try to influence the solar industry that they have to vary their design,” said Weiss. “Each car manufacturer likes to have its own design and not a fixed design of the cell. We have a laser process where we can cut the cell and make other geometries so that it’s more individual for each customer.”
By the end of 2010, the plastic solar modules will be in mass production for architectural applications, “but not yet on mobile applications like cars,” Weiss said. “We’re working with several OEMs on the prototype phase at the moment. On the first pre-series cars, there are functional modules already.”
One challenge to widespread adoption of such modules is getting automakers to first accept the plastic, she explained: “If you need the quality of a glass, we have to improve the plastic. But companies like Bayer, they’re working on this so that we offer the same quality as glass. If this glazing is accepted, the way is open for this type of module.”