Heavy Rain in Kyushu Damages Mega Solar Plant (2)

Causing collapse of ground, slopes

2019/08/13 11:57
Kenji Kaneko, Nikkei BP Intelligence Group, CleanTech Labo
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Continued from Heavy Rain in Kyushu Damages Mega Solar Plant (1)

About 2MW of solar panels stopped operation

The Kirishima Sunday Power Plant started operation in August 2017, and this is the second summer after its start. A large typhoon passed through the area last summer, but no serious damage was caused. Erosion of the ground due to rainwater also occurred during construction of the plant, and measures against erosion due to water flow on the ground were taken, including planting of grass over almost the entire site.

According to a rain gauge at the power plant, rainfall during the period from June 26 to July 4 reached 789mm in total. The rainfall on July 3, when the highest rainfall was recorded, was 276mm. The maximum rainfall per hour was 52 mm, which was recorded at 3am on July 1.

The rainfall per hour did not exceed the range estimated at the time of designing, according to Tokyo Energy & Systems. However, "the level of concentrated heavy rainfall over a short period such as 10 minutes or 20 minutes cannot be obtained from the figures indicated by the rain gauge," according to the company.

Details on the scale of damage to the entire power plant were not explained to the mayor during his visit to the site. Judging from the damage, facilities corresponding to about 2MW out of the approximately 41.3MW facilities seem to have stopped, and the power generation loss caused by the damage is limited to about 5%.

In the area filled with soil from the first landslide, some of the solar panels and a concrete foundation of the PV inverter installed on the southern edge of the area sank significantly below the surface, and the equipment in this area, which generates 1MW of power, has stopped (Fig. 6).

Fig. 6: Foundation of substation including PV inverter sank significantly. PV inverter and transformer already removed, and only foundation concrete panel remains unremoved (center of picture) (source: Nikkei BP)

In other areas, where PV inverters were not damaged, strings (panel DC circuits) with damaged panels have stopped. Erosion had occurred on some of the slopes we observed, in addition to the serious damage, and strings near such slopes had stopped. Therefore, the power generation loss of the entire power plant is estimated at 2MW, including the loss of 1MW due to damage to one of the PV inverters (Fig. 7).

Fig. 7: In addition to large-scale damage to three areas, small collapses observed on multiple slopes (source: Nikkei BP)