Monday, November 05, 2007

Secret of Solar Cell System on Mitsubishi 'i MiEV' Sport

Mitsubishi's "i MiEV Sport" concept car (Tech-On!)

"I knew someone would point it out," said a Mitsubishi attendant in response to my question.

Mitsubishi Motor Corp is drawing interest by displaying its "i MiEV Sport" concept electric vehicle equipped with a thin-film solar cell system at the 40th Tokyo Motor Show. I was interested in the thin-film cells' fat wires like those in crystal Si cells. So I asked the booth attendant about it, and he gave me a secret of the solar cell system, starting with the phrase above.

The solar cell system mounted on the i MiEV Sport is a 13%-efficiency CIGS system. CIGS and other thin-film solar cells use extremely slim wires and usually look black. The objects on the i MiEV Sport that looked like wires are, in fact, not wires, the attendant said.

When it comes to solar cells, many consumers think of crystal Si type, which features outstanding fat wires. Therefore, Mitsubishi discussed with designers and added lines that are compared to wires so the system can be easily recognized as a solar system.

Mitsubishi chose thin-film type instead of crystal Si type because of its slimness and shock resistance. Furthermore, the company was attracted by the logical possibility of increasing conversion rates and therefore chose CIGS type among thin-film solar cell technologies.

The latest prototype can drive 20km per 1-week charge. This is, however, not worth the cost of a solar cell system. The company expects the solar cell system manufacturer to lower system costs further, Mitsubishi said.

The manufacturer of the CIGS solar cells has not been specified. The attendant, however, stressed the cells were "CIS type, not CIGS." In Japan, Honda Motor Co Ltd calls the same technology CIGS, while Showa Shell Solar KK calls it CIS.


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