Mega Solar Plants Submerged Underwater in Hokkaido (1)
About 10,000 panels replaced at cost of 500 million yen
Damage from flooding due to unexpectedly heavy rain is one of the risks that solar power plants near rivers in Japan face. In recent years, a number of regions in Japan have been hit one after another by torrential rains that are "the heaviest recorded" or "once in several hundred years." Rivers flooded and their levees collapsed due to the extreme weather conditions, damaging solar power plants in some cases.
Many rivers in the Tokachi region of Hokkaido were flooded on August 30 and 31 by Typhoon No. 10, which hit the Tohoku region and Hokkaido, and multiple mega (large-scale) solar power plants in the areas were damaged by the flooding.
The damage to a mega solar power plant in Nakajima Town of Obihiro City, one of such mega solar power plants, and the restoration carried out at the plant are covered in this article (Fig. 1).
Typhoon No. 10 brought heavy rain to a wide area of the Tokachi region including Obihiro City. Because of the rain, water levels of tributaries to the Tokachi River including the Satsunai, Tottabetsu, Sarubetsu, Toshibetsu, Otofuke, Memuro, Bisei, Pekerebetsu, Shin-Obihiro and Sahoro rivers as well as many other rivers exceeded the height of the levees, breaking them in some cases.
Muddy water flowed across the entire area, burying roads, houses and fields under mud. Bridges collapsed in some areas (Fig. 2). Because of the damage, many roads and railroads were blocked. In some areas, there was no running water for a long period because water pipes are routed under bridges.
A large-scale slope failure occurred at the Nissho pass between the Tokachi region and the Hidaka region. The pass is on Route 274, a major route that connects central Hokkaido and eastern Hokkaido. The restoration work is still in progress. It is expected that traffic will be able to use the Nissho pass again by the end of October 2017.
The Tokachi region is one of the major agricultural areas in Japan, and vegetables produced in the region are delivered to all areas in Japan. Potatoes, onions, beets, red beans, etc were severely damaged by the typhoon.
Levees near fields collapsed
Two mega solar power plants, one with an output of 1.35MW and the other 1MW, were damaged by the disaster (Fig. 3). Levees of nearby rivers collapsed, and muddy water and driftwood rushed into the plants. The fences, mounting systems and solar power generation equipment were destroyed or submerged underwater because of the disaster.
These mega solar power plants are located near the point where the Tottabetsu and Satsunai rivers meet and stand between the two rivers.
The two rivers are administered by different entities. The Satsunai River is administered by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) while the Tottabetsu River is administered by the Hokkaido Government. In respect to the collapse of levees of the Satsunai River, the Obihiro Development and Construction Department at the Hokkaido Regional Development Bureau of MLIT presented the progress and measures in September 2016 (Fig. 4) (See related article).
The levee on the right side of the Tottabetsu River, which is administered by the Hokkaido Government, collapsed first. The levee was destroyed for a distance of about 500m, according to reports (Fig. 5).
The destroyed portions are located between the Tottabetsu and Satsunai rivers. Fields, agricultural warehouses and mega solar power plants are between the two rivers and were damaged by flooding caused by the collapse of the levees.
When the levee on the right side of the Tottabetsu River collapsed, water containing soil and driftwood flowed from the Tottabetsu River into the area between the Tottabetsu and Satsunai rivers.
The majority of the areas near the collapsed portions along the Tottabetsu River are occupied by fields, and beets from which sugar is produced and potatoes were grown on the fields. The floodwater reached the mega solar sites, eroding the soil and covering the beets and potatoes.
The water from the flooded river flowed mainly to the southwestern side of the mega solar power plants. The fences and mounting systems blocked the entry of some driftwood, beets and potatoes, but the force of the water didn't wane and the water flowed further toward the north.
The water reached the area near the point where the Tottabetsu River joins the Satsunai River. The floodwater that reached this area destroyed the levee of the Satsunai River, flowing from the land side (Fig. 6).
The levee on the left side of the Satsunai River was destroyed for a distance of about 200m in the area adjacent to the point where the Satsunai River joins the Tottabetsu River, according to the announcement by the Obihiro Development and Construction Department of MLIT.
1.35MW mega solar in operation and 1MW mega solar completed on former sites of gravel plants
The two mega solar power plants that were damaged stand adjacent to each other. Both of them were developed by Technical Yield Co Ltd of Kasai Village, Sarabetsu-gun, Hokkaido. The sites were formerly occupied by gravel plants operated by an external company in the same business. The company developed the solar power plants on the sites, which were owned by the company and had remained idle for many years.
When they were damaged in the disaster, the 1.35MW power plant was in operation and the power generated by the plant was being sold. It was completed about three years and six months before the disaster. The 1MW power plant had been completed, and the commercial operation of the plant was about to start when the disaster occurred.
Technical Yield is engaged in the construction business, the production and sale of civil engineering materials, IT consulting and the waste treatment business in the Tokachi region.
The company also develops solar power plants in the Tokachi region. It operates four mega solar power plants for connection to high-voltage power distribution lines. They are the two plants in Nakajima Town in Obihiro City, a plant with an output of about 1.39MW in Shimizu Town (See related article 2) and a plant with an output of 1.55MW in Sarabetsu Town (See related article 3). The company also develops and operates solar power plants that are connected to low-voltage power distribution lines.
All of them were constructed on idle land that the company owns, including former sites of gravel quarries.
Regarding the two damaged mega solar power plants in Nakajima Town, Obihiro City, the power producer of the plant that was already in operation is Technical Yield while the power producer of the power plant that has yet to start commercial operation is Tokachi Kousan, a group company of Technical Yield.
The 1.35MW plant operated by Technical Yield mainly uses single crystal silicon panels manufactured by Yingli Green Energy Holding Co Ltd of China. The 1MW plant operated by Tokachi Kousan uses CIS compound-type panels manufactured by Solar Frontier KK.
The plant operated by Technical Yield incorporated PV inverters of GS Yuasa Co while the plant operated by Tokachi Kousan incorporated those of Toshiba Mitsubishi-Electric Industrial Systems Corp (TMEIC).
Fences covered with driftwood, beets and muddy water and foundations lifted up
As for the fences along the outer circumference of the site, the fences hit by floodwater had collapsed and were covered with mud, fallen trees, beets and potatoes when pictures of the site were taken in early September 2016, immediately after the disaster. Some of the foundations of the fences had been pulled out (Fig. 7).
The floodwater that was not blocked by the fences reached the internal area of the mega solar site. Many of the fallen trees that flowed into the site looked 10m or more in length.
Solar power plants in Hokkaido incorporate higher installation levels and stronger mounting systems, compared with plants in other regions, so that the equipment can withstand the accumulation of snow. However, the mounting systems were covered with fallen trees, weeds, beets and potatoes above the height of a human.
In the area between the southern side and the southwestern side, which seems to have been subjected to the fastest and strongest water flow, some of the mounting systems near the solar panels were bent, and the entire array (unit of solar panels installed on a mounting system) was damaged in some cases, indicating the strength of the floodwater.
Damage varies depending on the site
The damage was slightly different between the two mega solar power plants because of the difference in the flow of the floodwater, according to Technical Yield (Fig. 8).
The water that flowed from the collapsed portion along the Tottabetsu River passed through the field and hit the fences of the mega solar power plant, eroding the soil and covering the beets and potatoes being grown (Fig. 9).
Driftwood and crops were caught in the point area at the southernmost part of the mega solar site (Fig. 10).
Panels manufactured by Solar Frontier are arranged at the point of the site. Panels of the same manufacturer are also installed on the area to the east of the point. This area was severely damaged by driftwood and crops while damage due to flooding and submerging was comparatively minor.
Panels manufactured by Yingli Green Energy are arranged adjacent to the west of the area. The panels along the fences were significantly damaged by driftwood and crops, but damage due to flooding and submergence was worse in other sections.
The floodwater that flowed into the mega solar site spread to the west side of the site and hit the levee near the meeting point with the Satsunai River. The muddy water with the force to break the levee from the land side was pushed back by the levee and had no route to escape and so accumulated in the area.
The power plant that incorporated solar panels of Yingli Green Energy was close to the muddy water "pond," which resulted in significant damage due to flooding and submergence (Fig. 11).