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Multi-level Hill Transformed Into Slope at Island Solar Plant (page 3)

Innovative measures for environment, soil in remote island

2020/02/12 13:47
Shinichi Kato, Nikkei BP Intelligence Group, CleanTech Labo
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This red soil is one of Fukuejima's characteristics. It differs from ground soil at most solar power plants in Honshu and mainland Kyushu. Red soil in Fukuejima and other Goto Islands is easily eroded and washed away by rainwater, etc because its particles are less adhesive. The company said its design also kept red soil from running out of the site.

The crushed stones around the top area not only helped with the delivery of PV inverters and other heavy facilities and protecting them but also limiting red soil erosion by rainwater. The company also built "water blocks" by solidifying crushed stones to keep red soil from being washed away following a sharp rise in rainwater running down the slopes including the mountain forests outside the site (Fig. 5).

Fig. 5: "Water blocks" formed by solidifying crushed stones (source: Nikkei BP)

Remote islands in Kyushu are mostly hit by heavy rain when a fierce typhoon strikes. What are such circumstances like in reality?

Given the different circumstances from those in Honshu and mainland Kyushu, it is difficult to imagine heavy rain and strong winds on a remote island in a typhoon without experiencing them. Therefore, Comsys Create developed countermeasures from the design phase, gaining knowledge from the local community.

The company requests the landlord to inspect the site after a typhoon or heavy rain and to restore things to their original state if something unusual is found.

There was a concern that, if rainwater starts running down the slope before pouring into the drainage ditches following heavy rain, soil on the surface might be removed or water pathways might be formed. The water blocks were built to counter such risks, and partly thanks to them, soil has never been largely washed away thus far.

In summer 2019, however, the slope adjacent to the bottom fences collapsed following heavy rain during a typhoon. This consequently caused the fences and side slopes that supported the fences to collapse. When restoring this damage, Comsys Create added stone walls to further enhance the resistance, making it difficult for similar damage to take place again (Fig. 6).

Fig. 6: Restored and reinforced by adding stone walls (source: Nikkei BP)

Some solar panels were also detached from the mounting systems and blown away by strong winds in a typhoon. This typhoon caused wind-related and flood-related damage throughout the Goto Islands. Although the company had taken preparatory measures, some panels were blown off from the mounting systems by winds stronger than expected at the time of design.

However, the detached panels stayed within the site and did not scatter across the surrounding area. Using reserve panels as replacements, Comsys Create immediately restored operation.