Major Typhoon Damages Floating Mega Solar Plant
Causing fire, piling up of panels
Largest floating mega solar plant in Japan
In the afternoon of September 9, 2019, when typhoon No.15 passed through Chiba Prefecture, a fire broke out at the "Chiba Yamakura Floating Mega Solar Power Plant," which was constructed on the surface of "Yamakura Dam," a pond in Ichihara City, Chiba Prefecture, Japan. The floating mounting systems were broken and bent due to the strong typhoon winds, generating fires in multiple locations.
The output of solar panels floating on the water surface at the plant, which is the largest floating solar power plant in Japan, is approximately 13.7MW. The operation of the plant was started in March 2018 (Fig. 1).
The fire was reported to Ichihara City Fire Department at 1:00 pm on September 9. Seven fire engines and 21 firefighters were dispatched to the site. Water was discharged from the northern shore, which was nearest to the fire. Because the water did not reach the fire when normal fire engines with a water discharge distance of 20 to 30m were used, a large vehicle mounted with a cannon (DHCU) featuring a discharge distance of 70 to 100m was used, and the fire was distinguished at 3:24 pm. No one was injured by the fire.
In discharging water onto solar panels on fire, there is a risk of electric shock to fire fighters if water is discharged in a cylinder shape. Water in the pond was pumped up to be used on the fire, but the fire fighters did not get electric shocks. It seems that the risk of electric shock was reduced because the water discharge distance was far and the water changed to mist at the discharge destination (Fig. 2).
Operation stopped in the morning
The power producer of the damaged floating mega (large-scale) solar power plant is Kyocera TLC Solar of Chiyoda-ku, Tokyo, which is jointly financed by Tokyo Century Corp and Kyocera Corp. Yamakura Dam is a pond that supplies water for industrial use and is managed by the Enterprise Agency of Chiba Prefecture. Kyocera TLC Solar leased about 180,000m2 of the pond's surface and installed 50,904 solar panels on floating mounting systems.
The output to the grid is 11.5MW, and the power is sold to TEPCO Energy Partner Inc using the feed-in tariff (FIT) scheme. The power plant was designed and constructed by Kyocera Communication Systems Co Ltd (KCCS). The panels were manufactured by Kyocera and feature an output of 270W/sheet. The plant incorporates PV inverters (500kW units) manufactured by SMA Solar Technology AG of Germany and floating mounting systems manufactured by Ciel Terre of France. The operation and maintenance are handled by Kyocera Solar Corp.
According to a spokesperson of Kyocera, an abnormality in the Chiba Yamakura Floating Mega Solar Power Plant was detected by the remote monitoring system at sunrise after typhoon No.15 passed through Chiba Prefecture before sunrise on the 9th. The operation was stopped in the morning, disconnecting the plant from the power transmission system (Fig. 3).
The company quickly investigated and analyzed the cause.
"Solar panels at solar power plants generally generate current when solar panels are subjected to sunlight, even if the operation is stopped, posing a risk of ignition due to electrical leakage caused by damage," according to the public relations division of Kyocera. "The fire may have been caused because of such situation" (Fig. 4).
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).
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).
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).
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).
Mounting systems at southern end torn and curled up
The floating mounting systems at the southern end of the separated island were curled up by the strong wind, piling up like a roll cake (Fig. 9).
Floating mega solar power plants in Japan have been damaged by typhoons in the past. At a 1.99MW floating mega solar power plant installed on a pond in Osaka Sayama City in Osaka Prefecture, the floating mounting systems were curled up by typhoon No. 21 last year, causing warping in 733 solar panels, for example.
The phenomenon of curling up at ends of "islands" was observed generally in floating solar power plants damaged by strong wind in the past. Because of this reason, measures to prevent "curling up" were incorporated, including the increase of the weight of floats along the outer ends of islands.
In the disaster at the Yamakura Dam site caused by the typhoon, mooring wires lost their function and the "island" was pushed away significantly, in addition to "curling up" at ends of the islands. Measures including improving the design strength of the mooring wires and anchors at the bottom of the pond will be required in the future (Fig. 10 & 11).
However, the administrator of the pond does not want to make large-scale modifications to the bottom structure. Therefore, mooring wires may be connected to weights placed on the bottom depending on the case. Advanced skills for construction and technical renovation are expected for stable operation of floating mega solar power plants in the future, as strong typhoons often strike Japan.