Japan Electric Power Company verifies whether solar power plants can withstand heavy rain

Last month, there were heavy rains and heavy rains in many parts of Henan. Disasters such as waterlogging and mountain floods in many places have caused great damage to the safety of local residents' lives and property and the country's infrastructure such as transportation and energy.

As we all know, Japan is also a country with frequent disasters. From May to July each year, various parts of Japan enter the rainy season, and there are many typhoons approaching and landing in Japan in summer and autumn. Heavy rainfall caused by rainy seasons and typhoons caused floods and other disasters throughout Japan.

(Source: WeChat public account "PV JAPAN BRIDGE" ID: PVJapanBridge)

In order to minimize damage to solar power generation facilities and surrounding land caused by mudslides and landslides caused by heavy rains and floods, the Japanese electric power company Smart Energy has conducted research on the relationship between mudslides and solar power generation facilities.

1. The foundation is an important issue for solar power stations

Smart Energy maintains approximately 900 solar power stations across Japan. According to the company's statistics, the most common problems in these power stations are "communication abnormalities", while the second most common problems are "ground-related problems."

Due to the large area of large solar power plants, trees are often cut down and the slope is leveled during the construction process. When installing solar panels on the stand, the ground leveling work is essential, and this will lead to various land problems.

After leveling the land, even if it is constructed in accordance with the drainage plan, it still takes a certain amount of time to wait for the surface of the land to become firm. After the power station is completely completed, if it is allowed to develop, the foundation of the power station will gradually become unstable.

Therefore, maintenance of vegetation protection and growth on the ground of the power station, fine-tuning of drainage routes, and soil surface protection and treatment are essential. Therefore, soil issues are the most important "commercial basis" for large-scale solar companies, and it is also an aspect that requires special attention.

It can be seen that many solar power plants in Japan have foundation problems. So how did Japan's so many solar power plants appear? What are the land standards for solar power plants in Japan?

2. From "golf course" to "large solar power station"

In restricting the indiscriminate development of large-scale solar power plants, permits under the Forest Law play an important role. According to the Japanese Forest Law, relevant practitioners are obliged to obtain forest land development permits from relevant authorities when developing forests with an area of more than 1 hectare. Violators will be banned from forest land development in accordance with the law, and the land will be restored to its original condition under the supervision of relevant departments.

For example, some of the contents of Chiba Prefecture's review of forest land development permits:

1. The flow coefficient range of the area where the solar panels are installed is 0.9 to 1.0.

(The following values are used as a reference. For example, the discharge coefficient of farmland is 0.4-0.5 in places with a lot of rainfall, and some places in forested mountainous areas with a lot of rainfall have a discharge coefficient of 0.7 or more)

2. The area where the solar panels are installed must be equipped with drainage facilities that can safely flow down the surface. In addition, countermeasures such as grass planting projects to prevent surface erosion must be taken.

3. When installing solar panels and other equipment with an average slope of more than 30 degrees, relevant practitioners need to design disaster prevention facilities such as retaining walls and drainage facilities.

4. For the purpose of setting up solar power generation facilities, the forest coverage rate of the site should be more than 25%, and the residual forest coverage rate should be more than 15%.

5. If the height of the fill is more than 10 meters, it is necessary to manage the compactness of the fill through the density test and strength test under implementation. And in the construction plan, the quality management of the filling materials through soil testing and other methods is clearly recorded.

6. The location of the adjustment pool should be the most downstream position of the natural terrain, and a plan should be made that it can collect water.

(Excerpt)

Forests play a variety of functions in the natural environment, but forest land development permits focus on the functions of forests to protect surface soils, protect terrain, and prevent flood disasters.

Japan’s forest land development permit begins with the conversion of forest land to agricultural land. In the 1980s, the development of Japan's bubble economy reached its peak, and the sport of golf developed rapidly. Since then, a lot of woodland has been developed into land for golf courses. After 2011, the Japanese government began to purchase solar power generation at a fixed price (FIT system) in order to support solar power generation, and people began to follow suit to invest in solar power plants.

Therefore, the scene of random development of golf courses in the bubble economy era, the protagonist is replaced by today's solar power station continues to be staged.

3. How is the drainage reduced?

Whether forestland development can be licensed is determined based on whether the rainwater in the solar power station site is properly treated, and whether it will cause flood risks outside the power station site. Specifically, whether it can be 1.2 times the rainwater flow rate described in the following formula is an important criterion for obtaining permission.

Rainwater flow=1/360*flow coefficient*design rainwater intensity*catchment area area

Rainwater flow: m3/sec

Design rainwater intensity: mm/hr

Catchment area: hectares

If the rainwater runoff is large, it is necessary to build a large regulating tank, and it is required to conduct a large-scale investigation and related projects on whether there is an impact on the diversion channel of the end flow. Regardless, the construction cost will increase significantly, so how to reduce the drainage volume is the key to determining whether the project can be implemented.

The flow coefficient is a given value, and the coefficient set by the Japanese national or local government is used. In order to reduce the outflow of rainwater, the forest area with a small coefficient will not be able to be developed on a large scale, or it will not be possible to obtain additional commercial land. Since the coefficient of the solar panel installation part is 1.0, it is necessary to work hard to reduce the area.

In actual operation, even if it is to meet the minimum requirements, solar power plant practitioners need to take various measures and efforts to meet the standards. Therefore, for the owners of solar power plants, the drainage problem is always a problem that cannot be forgotten and often needs to be considered.