Japanese Firm Testing Solar Panel-embedded Road Surface

2019/07/24 05:57
Kenji Kaneko, Nikkei BP Intelligence Group, CleanTech Labo

Test conducted by laying 20 modules

Nippo Corp (a major construction company) and Mirai-Labo Co Ltd (Hachioji City, Tokyo) co-developed a pavement system embedded with solar cells.

The system was made by covering thin-film silicon (amorphous silicon) solar cells with a transparent plastic plate. Nippo aims to commercialize the system by 2022.

The system was installed in an area of about 20m2 on the premises of Nippo General Technology Center on a trial basis in November 2018. And the durability, power generation performance, etc have been tested.

The newly-developed module (panel) has a structure that protects film-like thin-film silicon (Si) solar cells with a transparent high-strength plastic plate. And it measures 1 x 1m. On an asphalt pavement, 20 units of the module were fixed by using resin mortar. The system generates about 3kWh of electricity per year, according to Nippo.

The "solar power generation pavement" being tested (source: Nippo)

According to Nippo, a system that consumes electricity generated on a road surface in house (as an independent power source) instead of transferring it to the grid of a power company is promising. So, in the verification test, the company also installed a storage battery system, employing a mechanism that stores electricity generated during daylight hours in a lithium-ion (Li-ion) battery with a capacity of 4kWh and uses it to power LED lamps for illuminating the road surface at night.

The system is used to illuminate the road surface with LED lamps at night. Dividing lines and a stop line were illuminated. (source: Nippo)

The storage battery system incorporates a compact, portable battery. (source: Nippo)

The introduced storage battery system is compact and portable. It can be carried to a shelter, etc at the time of disaster for charging, for example, mobile phones.

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.