Anchors Coming Away Cause Fire at Floating Solar Plant in Chiba

2019/11/19 19:29
Kenji Kaneko & Shinichi Kato, Nikkei BP Intelligence Group, CleanTech Labo
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77% of solar panels damaged

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 Oct 28, 2019. At the meeting, Kyocera TCL Solar LLC, the power producer of the "Chiba Yamakura Floating Mega Solar Power Plant," reported the background and situation of the accident, the progress in investigating the cause and findings that have been confirmed so far, in respect to the plant damaged by Typhoon 15.

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. In the afternoon of September 9 after Typhoon 15 had passed through Chiba Prefecture, a fire broke out. Floating mounting systems were swept away and damaged by the strong winds of the typhoon, causing fires at multiple locations (Related article: Major Typhoon Damages Floating Mega Solar Plant).

The progress of the accident is as follows, according to Kyocera TLC Solar. At about 6:30 in the morning of September 9, a "DC leakage" alarms were activated at the monitoring center in Sakura City, Chiba Prefecture, and at a mobile terminal of the chief electrical engineer.

The engineer hurried to the site and arrived there at about 7:30 and confirmed the damage, stopping all PV inverters during the period from 7:50 to 8:30. Fire was detected at 13:00 and reported to the fire department. Firefighting started at 14:00 and the fire was extinguished at 17:20.

No injuries were reported, but about 77% of the 50,904 solar panels were swept away and damaged by the winds, with some of them burnt due to the fire (Fig. 1 & 2).

Fig. 1: More than 70% of panels pushed to northern shore (source: Nikkei BP)

Fig. 2: Panels overlapped and short circuited, causing fires (source: Nikkei BP)

Connected to 420 anchors by 828 mooring wires

At the mega solar power plant, one solar panel was mounted on one main resin float, using fixing brackets, and main floats were connected placing "second floats" between them. Resin pins were used to connect the main floats with second floats (Fig. 3).

Fig. 3: Components of solar panel island and mooring method (source: Kyocera TCL Solar)

The shape of the island made of solar panels connected by the above method is wider in width from east to west at the southern end, measuring 503.1m at the widest part. The length from south to north is longer on the western side, and the maximum south-north width is 487m (Fig. 4).

Fig. 4: Outline of power plant and size of island (source: Kyocera TCL Solar)

The outer circumference of the island is connected to anchors fixed to the pond bottom by 828 mooring wires to prevent it from being pushed away by the wind. Two mooring wires were generally connected to one anchor. Therefore, 420 anchors were used in total (112 locations on the northern end, 133 locations on the eastern end, 68 locations on the southern end and 107 locations on the western end) (Fig. 5).

Fig. 5: Float components and island mooring method (source: Kyocera TCL Solar)