PV inverters stopped operation after being submerged by the flooding

The situation of the damage to the solar power plant in Mabi Town, Kurashiki City, Okayama Prefecture is considerably different from that damage in other areas, although the cause was the same – the flooding of rivers. Many of the PV inverters for rooftop solar power equipment for household and business use became inoperable after being submerged, as wide swaths of the city were flooded. Solar panels at ground-based low-voltage solar power plants for business use were also flooded.

A river bank collapsed before dawn of July 7 in Mabi Town. One-quarter of the town and three-quarters of the urban areas concentrated with houses were submerged, and about 4,600 houses were flooded. The water depth reached a maximum of 4.8m. The majority of the solar panels installed on roofs of buildings including houses were not affected by the flood, but the PV inverters on the walls of the first floor were submerged and became inoperable.

At group home Chojunosato Mabi (in Kurashiki City), solar panels with an output of 34kW in total were on the roof of the two-storey building and two PV inverters were set up on the roof of the first floor. The generated power is sold under the FIT scheme. The facility was designed and constructed by Sanix Inc (Fig. 15).

Fig. 15: The group home was equipped with a rooftop solar power generation facility. (picture: Nikkei BP)

The two PV inverters were submerged by the flood on July 7. Engineers at Sanix visited the group home after the disaster to stop and disconnect the PV inverters to ensure safety. On this occasion, the engineers inspected the solar panels and confirmed that they were free from abnormalities (Fig. 16).

Fig. 16: The PV inverters were submerged and became unusable. (picture: Nikkei BP)

The company will reconstruct the building because it was damaged by the flood. After it is reconstructed, the existing solar panels will be installed on the rooftop, and the PV inverters will be replaced with new ones.

The majority of the districts affected by the flood in Mabi Town are urban areas and the number of on-ground solar power plants is limited. There is a low-voltage solar power plant for business use, which has 240 solar panels with a total output of about 50kW. All of the equipment and the panels were flooded (Fig. 17).

Fig. 17: Solar panels at the flooded low-voltage solar power plant for business use (picture: Nikkei BP)

Two arrays were arranged on land that was formerly used as a parking lot. Eight compact PV inverters (manufactured by Kyocera Corp) were installed on the mounting systems at a height of 50cm above the ground and under the arrays. Large-area panels were arrayed in the latitudinal direction in 6 columns and 20 rows (120 panels in total), at an angle of about 10 degrees. The top parts of the arrays are 2m to 3m above the ground. It is estimated that the PV inverters and the solar panels were totally submerged by the flood.

When we visited the disaster site in late July, all of the PV inverter connection cables were disconnected and power was not being generated. According to residents near the site, the panels were covered with mud when they were seen shortly after being submerged, but they were cleaned by the operator a few days after the disaster (Fig. 18).

Fig. 18: The PV inverter cables were disconnected to stop power generation (picture: Nikkei BP)

The low-voltage solar power plant for business use incorporates mounting systems built by connecting pipes with joints. There are some concerns about mounting systems made of pipes, in terms of the durability and strength, but the foundations at the power plant are fixed by concrete and resisted the streams caused by the flood. No damage was observed to the appearance of the mounting bases.

The PV inverters cannot be used once they are submerged, even if they are dried, and have to be replaced. As for the solar panels, problems may not occur immediately when they are used for power generation, if they are used after being dried, even if they have been submerged. But they are generally replaced because the risk of problems in the future is high.