Shift from crystalline Si to thin film
Nippo considered that a high durability and function as a paved road are important for the commercialization of the "solar power generation pavement," and it gave consideration to it at the time of the modularization.
In fact, when Nippo started the research and development in 2017, the company employed a crystalline Si solar cell, which is commonly used now, and developed and tested a prototype having a structure covered with reinforced glass.
As a result, the company judged that it is not enough for realizing (1) a high enough durability for withstanding the weight of a vehicle and (2) skid resistance necessary for a road surface. Crystalline Si cells and glass are vulnerable to flexure deformation caused by a load and can be fractured by it.
In view of this, Nippo newly made a prototype by combining a film-like solar cell and transparent plastic plate in cooperation with Mirai-Labo, which owns thin-film solar cell technologies. Nippo found that, with this combination, the prototype is resilient to flexure and is not fractured.
Though its power generation efficiency is lower than that of a crystalline Si-based prototype, the company put priority on durability and safety for a road surface.
In the verification test at Nippo General Technology Center, vehicles including 6t-class vehicles run on the pavement system on a daily basis. But there has been no problem since it started operation six months ago, and it has been steadily generating electricity. There is even a possibility that the commercialization of the system can be pushed forward from 2022, according to Nippo.