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.