Polycrystalline Si solar cells manufactured by Kyocera Corp are used for the solar panel that comes as an option for the new Prius, which Toyota Motor Corp announced May 18, 2009, in Japan.
The solar panel is composed of a total of 36 cells arranged in six rows and six columns. Each cell is half the size of the standard 15 x 15cm cell. With a cell conversion efficiency of 16.5%, the maximum output of the entire panel reaches fifty-odd watts. The portions where three bus bars are believed to exist were covered with a black component.
Electricity generated by the solar cells directly drives the ventilation fan.
"At first, we came up with a design to charge a battery," a system demonstrator said. "But we gave up the idea because repeated charging and discharging may deteriorate the battery."
Toyota chose to use a polycrystalline Si solar cell because it was cheaper than other solar cells. The "solar panel moonroof" option, which integrates a solar panel and a sunroof, is priced at "about ¥200,000" (approx US$2,076), according to the demonstrator.
There were no major problems in adopting the solar cell, according to Toyota. For example, even when the new Prius was running on an undulant terrain, which vibrated the car, the solar cells were not cracked or detached, the company said. The solar cell has durability required for automobiles.
However, when it comes to the vehicle design, the shape of the roof had to be changed to install the solar panel. The standard model of the new Prius, which is not equipped with a solar panel, employs the "Pagoda roof" with a depressed center portion. The depressed roof reduces the frontal projected area, diminishing air resistance.
On the other hand, it is difficult to depress a solar panel whose surface is covered with glass. As a result, the frontal projected area of the Prius with the solar panel is larger than that of the standard model.
"There is no major difference in air resistance between the Pagoda roof and the solar panel moonroof," said a demonstrator who is in charge of the roof design.