Retaining walls on slope collapsed due to torrential rains

Part of the site of a solar power plant in Hayashida Town, Himeji City, Hyogo Prefecture, which features an output of about 900kW and is connected to a high-voltage distribution line, collapsed and was damaged July 7, 2018. The "Tainavi Himeji Solar Power Plant" features a grid output of 750kW and the capacity of the solar panels at the plant is 918kW. The plant started generating power in December 2015.

Tainavi Power of Shinagawa-ku, Tokyo, the power generator, is part of the Goodfellows Group of Shinagawa-ku, Tokyo. The company operates the "Tainavi power generation plant," a property search site for on-ground solar power plants. The website has covered properties with a total output of about 2GW so far and is believed to boast the top share among solar power property matching sites.

Solar panels at the damaged site were installed on the slope of a mountain along a road. Seen from below immediately after the disaster, the arrays arranged along the mountainside appear to have collapsed and fell with the soil (Fig. 3).

Fig. 3: The slope collapsed at a solar power plant connected to a high-voltage transmission line in Himeji City, Hyogo Prefecture. (picture: Nikkei BP)

According to Goodfellows, large concrete blocks were used, and U-shaped gutters were installed above the retaining walls to prevent the flowing of rainwater along the slope because the middle area of the mountainside was steep (Fig. 4 & 5).

Fig. 4: The retaining wall at the middle of the mountainside of the site before the collapse (source: Goodfellows)

Fig. 5: The water drainage channel and plants at the top of the retaining wall at the middle of the mountainside of the site before the collapse (source: Goodfellows)