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Major Typhoon Damages Floating Mega Solar Plant (page 3)

Causing fire, piling up of panels

2019/09/30 13:12
Kenji Kaneko, Nikkei BP Intelligence Group, CleanTech Labo
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Island broken into 3 parts

At the Chiba Yamakura Floating Mega Solar Power Plant, about 50,000 solar panels were fixed on floating mounting systems, which were connected to form a large "island" floating on the northern part of the pond.

When the situation after the disaster was observed, the "island" had broken into three parts, and the "largest island" among the three had been pushed toward the northern shore, stopping when it hit the shore. About two-thirds of the entire "island" seems to have been moved (Fig. 5).

Fig. 5: The "island" was broken into three parts. The areas inside the blue circles remained unmoved while the other area enclosed by the yellow circle was pushed to the north. (source: Image provided by Kyocera, and explanation added by Nikkei BP)

At the plant, the floating mounting systems were connected to anchors fixed to the bottom of the pond, using more than 400 mooring wires, to prevent the "island" of panels from moving due to wind. To ensure the pull-out strength of the anchors, tests were repeated by trial installation before final installation, according to the company. The mooring wires were strong enough to resist a wind velocity of up to 41.5m/second.

A strong wind exceeding the maximum instantaneous wind speed of 50m/s was recorded in Chiba City during typhoon No. 15. It is possible that the maximum instantaneous wind speed exceeded 50m/s at Yamakura Dam because some of the trees lining the pond fell over to the south and large branches were broken.

It is believed that some of the mooring wires and anchors could not withstand the unexpectedly strong wind and were broken, and the panels began to be pushed by the wind, which caused portions connected to functioning wires to be pulled by the portions with broken wires, causing separation of the island into multiple islands and resulting in the separated island drifting like a kite released from its string (Fig. 6).

Fig. 6: Some panels pushed to the shore (source: Nikkei BP)

The depth of Yamakura Dam is more than 10m at the deepest point. The wires were installed with certain tolerances in consideration of the fluctuation in the height of the water surface depending on the season. It is possible that some of the wires were functioning in the part that was carried away by the wind. It is likely that the functioning wires were pulled by the anchors at the bottom of the pond, resulting in the mounting systems bending at the pulled portions (Fig. 7).

Fig. 7: Possible that rear mounting systems pushed up mounting systems in front of them (source: Nikkei BP)

The northern end of the separated part near the shore seems to have curled downward into the water. It is likely that the mounting systems were pulled by functioning cables (Fig. 8).

Fig. 8: Mounting systems at northern end curl downward into water (source: Nikkei BP)