Solar/wind Power Facilities Hit by Abnormal Weather in Japan (1)

Risks in 'disaster archipelago' exposed by torrential rains, typhoons, earthquake

2018/10/15 11:24
Kenji Kaneko & Shinichi Kato, Nikkei BP Intelligence Group, CleanTech Labo

The Japanese archipelago was stricken by a series of serious natural disasters this summer, including the repeated torrential rains and typhoons that hit western Japan, as well as a major earthquake in Hokkaido. Disasters at solar power plants and wind power plants were also reported by the mass media and SNS.

The Ministry of Economy, Trade and Industry (METI) announced on Aug 28, 2018, that 15 solar power plants in six prefectures, namely Hyogo, Hiroshima, Okayama, Yamaguchi, Shimane and Ehime prefectures, were damaged by the torrential rains in western Japan (known as the "Torrential rains in July 2018"), in respect to plants larger than 50kW, which are required to submit reports.

It is estimated, however, that most of the plants affected by the disaster were low-voltage solar power plants for business use between 10kW and 50kW, and the overall picture of the damage, including damage to equipment mounted on houses, cannot be fully grasped.

In this troubleshooting report, we are covering solar power and wind power plants damaged by the western Japan torrential rains in early July and typhoons No. 21 and No. 22 that hit Japan in late August and early September, as well as the impact of the Hokkaido Eastern Iburi Earthquake on the renewable energy generation business.

Contacts Shinkansen line fence

The Shinkansen line was stopped due to the collapse of solar power generation equipment caused by the torrential rains in western Japan.

On the night of July 5, 2018, a slope beside the railway tracks collapsed near the exit of a tunnel along the Sanyo Shinkansen Line in Suma-ku, Kobe City, Hyogo Prefecture. The collapse occurred between Shin-Kobe Station and Nishi-Akashi Station. According to an announcement by Kobe City, solar power equipment that was installed on the slope also collapsed (Fig.1).

Fig. 1: The solar power equipment in Suma-ku, Kobe City, collapsed due to the torrential rains. (source: Kobe City)

An entire array (a unit for fixing solar panels on a mounting system) of six panels arranged in latitudinal direction on the slope collapsed. The solar power plant is believed to be a low-voltage solar power plant for business connected to a low-voltage transmission line. There are fences that separate the Shinkansen railway tracks from the external areas on the land adjacent to the east of the array and at the bottom of the slope. Part of the array that collapsed hit the fence, bending it significantly.

Although the solar power generation equipment did not break through the fence or protrude into the railway track area, West Japan Railway Company (JR West) determined that the equipment could reach the area near the railway tracks or it could contact the overhead lines if the collapse worsened, and the operation of the Sanyo Shinkansen Line was stopped temporarily.

When we later visited the site, the slope was repaired and the solar power generation equipment had been removed. The slope was fairly steep (Fig.2).

Fig. 2: The site in Suma-ku, Kobe City, from which the damaged equipment was removed (picture: Nikkei BP)

Drain water flows like a stream below the bottom of the slope and the top side of the slope is adjacent to a residential area. A fence made of pipes stood between the residential area and the slope and color cones had been placed along the fence to prevent access to the slope. They are new and appear to have been installed after the removal of the solar power generation equipment.

Resin parts for water collection and drainage could be on the slope and a fence made from layers of wooden boards was installed near the fence of the Shinkansen Line. They are also new and appear to have been installed after the collapse.

Responding to the serious accident of the collapse of the solar power generation system, which stopped the operation of the Shinkansen Line and had a significant influence on society at large, Kobe City announced its plan to establish an ordinance that specifies regulations on the installation of ground-based solar power generation equipment and requirements on reporting the management situation, aiming to prevent accidents of this kind. The ordinance will be applied to power generation equipment with an output of 10kW or more.

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)

60 of 75 distributed PV inverters were damaged

Among the arrays (36 panels arranged in 6 rows and 6 levels) above the retaining wall, six arrays were damaged due to the collapse of the ground caused by the breakage of the blocks in the retaining wall due to the torrential rains while the arrays below the retaining wall were crushed by blocks that came sliding down the slope. The solar panels were installed on special mounting systems, and the mounting systems above the retaining wall were fixed on pile foundations while the mounting systems below the retaining wall were fixed on concrete foundations.

The damage was worsened by the collapse of the blocks, and 1,344 of the 3,534 panels (918kW) installed on the site were broken. The plant incorporated distributed-type PV inverters, and 60 of the 75 units (totaling 10kW of output) were broken.

The detailed cause of the accident is currently being investigated, but it is likely that the amount of water drained via the U-shaped gutter could not handle the rainfall which exceeded the rated value per hour. The plant used the "block wall method," which is expensive but features a high slope-protection effect, placing priority on measures against disasters, but the structure failed to resist the concentrated heavy rain.

As one of the plans for the repair of the plant, the company is considering the possibility of reducing the capacity of the PV inverters and solar panels installed at the site, aiming to place a higher priority on safety measures. However, when the capacity of the equipment is changed by more than a certain rate, certification of the changes is required under the feed-in tariff (FIT) scheme, and the purchase price will drop, which is a bottleneck, according to the company.

It may be necessary to improve the management of the FIT scheme; for example, in a case that the certified output of a plant is reduced, maybe the plant should not be allowed to have the certification of changes for safety reasons.

Completely destroyed by mountainside landslide

In Daiwa Town, Mihara City, Hiroshima Prefecture, which was hit by a series of disasters due to a landslide on July 5 caused by torrential rains, a solar power plant for business use connected to a low-voltage transmission line was nearly completely destroyed by earth and sand that flowed into the site (Fig.6).

Fig. 6: The damaged site in Daiwa Town, Mihara City, Hiroshima Prefecture (picture: Nikkei BP)

Daiwa Town is in the northern part of Mihara City and is on a gently-sloped plateau, where a number of buildings, roads and fields are located between small hills. Low-voltage solar power plants for business use with an output of about 50kW, as well as mega (large-scale) solar power plants, are scattered among the fields along the roads and at the foot of the mountains.

When we visited the site in late July after the disaster, traces of the landslide could be seen on mountainsides along the roads, and earth and sand containing trees covered roads in some areas. According to a survey by Mihara City, roads in the city were damaged at 1,114 spots by the torrential rains in western Japan, of which 349 locations are in Daiwa Town.

Houses and offices hit by the earth and sand were damaged. Throughout the city, the number of damaged houses totaled 399 while 187 office buildings were also hit. The solar power plant was one of the damaged buildings. The panels were installed on a narrow site that extends from north to south between an agricultural road and a forest.

The panels were arranged in a latitudinal direction in 4 levels and 6 rows (24 panels in total) in one array. The arrays were installed on mounting bases, which were fixed on pile foundations consisting of two piles in the north-south direction and three piles in east-west direction. Around 10 arrays were laid out from north to south. It seems that the earth, sand and fallen trees hit the middle of the arranged arrays and washed away the panels together with the mounting systems (Fig.7).

Fig. 7: The panels were washed away together with the mounting systems by earth and soil that flowed down from the mountain. (picture: Nikkei BP)

Two arrays, one at the southern end and the other at the northern end, barely kept its shape, but they are tilted and twisted, and the plant was nearly completely destroyed. Some of the pile foundations remain in place. It is thought that the mounting systems were disconnected from the pile foundations, while some of the pile foundations were pulled out due to the weight of earth, sand and fallen trees, and they were destroyed after being pushed toward the road (Fig. 8).

Fig. 8: Some of the pile foundations remain in place (picture: Nikkei BP)

In Daiwa Town, there is a solar power plant that was not damaged at all although earth and sand from a landslide reached the area several meters away from the plant (Fig. 9). Solar power plants are easily damaged when earth and sand flow into the sites. The importance of careful investigation of the risks of damage caused by earth and soil in constructing power plants in front of mountains was re-acknowledged.

Fig. 9: The power plant that escaped damage from landslide by a narrow margin (picture: Nikkei BP)

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