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Stress Concentration due to Rocking Causes Fire, Breakage at Floating Solar Plant

2020/02/24 15:32
Kenji Kaneko, Nikkei BP Intelligence Group, CleanTech Labo
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Japan's Ministry of Economy, Trade and Industry (METI) held a meeting of the Working Group (WG) for Accident Response for Renewable Energy-based Power Generation Facilities and Structural Strength Feb 5, 2020. Kyocera TCL Solar LLC, the power producer of the "Chiba Yamakura Floating Mega Solar Power Plant," which was damaged by Typhoon 15, reported the details of an investigation into the cause of the accident and analysis results at the meeting. It was the third report made by the company.

According to the company, the major cause of the damage was "concentration of stress at the center of the southern side due to rocking of the island (island of solar panels) caused by strong winds." The company also announced that panels will be installed on multiple islands that are rectangular in shape in reconstruction of the facility, instead of the conventional method where panels formed a single large island, to prevent recurrence of the accident.

The "Chiba Yamakura Floating Mega Solar Power Plant," which was constructed on the surface of "Yamakura Dam," a pond in Ichihara City, Chiba Prefecture, started operation in March 2018. The plant features an output of about 13.7MW and is one of the largest floating solar power plants in Japan. A fire broke out in the afternoon of September 9 after Typhoon 15 had passed through Chiba Prefecture. Floating mounting systems were swept away by the strong winds and a single island was broken into three parts, causing fires at multiple locations and generating flames and smoke (Fig. 1).

Fig. 1: "Chiba Yamakura Floating Mega Solar Power Plant" severely damaged by Typhoon 15 (source: Nikkei BP)

At the mega solar power plant, one solar panel was mounted on one main resin float, using fixing brackets, and the main floats were connected placing "second floats," which are smaller than the main floats, between them. Resin pins were used to connect the main floats with the second floats.

As such, one large island was formed by connecting the panels in the method explained above. The profile of the island was complex and looked like multiple rectangles had been combined to form it. The length from east to west is longer on the southern side, measuring 503.1m at the widest part. The length from south to north is longer on the western side, which extends further than the eastern side toward south, and the maximum south-north width is 487m.

The outer circumference of the island was connected to anchors fixed to the pond bottom using 828 mooring wires to prevent it from being pushed away by winds (Fig. 2).

Fig. 2: Whole view of "Chiba Yamakura Floating Mega Solar Power Plant" before disaster. Panels installed on large complex-shaped island (source: Kyocera TCL Solar)