Snail trails appear on panels

As the polycrystalline silicon panels of ReneSola bore the burden of snow after a heavy snowfall, its impact was a concern. Accordingly, since then, the plant has been paying close attention as to whether the panels have micro-cracks and other problems.

Amid such circumstances, the plant discovered numerous snail trails on many solar cells (power generation elements) in the summer of 2016. Snail trails were found on many cells of most panels (Fig. 5). Snail trails are rarely seen on a significant scale.

Fig. 5: Snail trails found on many cells of most panels. Snail trails were found on many cells of most panels. (source: Nikkei BP)

Snail trails are linear patterns that look like the trails of snails. They are found along the micro-cracks on cells.

The amount of power generation will not sharply decrease immediately after the snail trails appear on solar cells. Accordingly, solar panel manufacturers do not consider snail trails as "defects" or "failures." It is difficult to request solar panel manufacturers to accept snail trails as being eligible for their product warranties.

However, snail trails might cause the amount of power generation to decrease in the future. For power producers, snail trails are a phenomenon that they cannot ignore as long as they have clearly changed the appearance of panels and could cause the amount of power generation to decrease.

Moreover, ReneSola, the panel supplier, withdrew its bases from Japan in the fall of 2017. The plant could continue to receive after-sales services from ReneSola's bases in China, but, taking this opportunity, it undertook an inspection using a drone (unmanned small aerial vehicle) in January 2018 as part of its efforts to understand the current state of polycrystalline silicon panels at Uenohara (Fig. 6).

Fig. 6: An inspection using a drone in January 2018 (source: Nikkei BP)

I visited the site to report on the inspection by a drone when it was undertaken. Failures were found at 31 locations, three of which were immediately fixed as they had been caused by blown fuses inside the combiner box.

The company that inspected the plant using a drone explained the situation on the site to MDI-SB Solar, restoring power transmission by replacing the fuses after gaining approval from MDI-SB Solar.

As for solar panels, MDI-SB Solar said it has not been able to identify in any of the inspections, including the recent one using a drone, whether problems during the manufacturing process or the damage accompanied by the heavy snow caused the snail trails.

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