1.4MW Solar Plant in Toyama Directly Hit by Ferocious Winter Lightning (page 3)
Annual power sale affected by snow accumulation
Checked for aging by asking Hokuden Group to inspect by drone
Only three solar panels have been replaced so far due to cracking of cover glasses, including the damage caused by winter lightning. Panels are replaced as soon as cracking is discovered. The cost is covered by insurance.
The company also has a strong interest in age-related deterioration of solar panels. In August 2017, the company checked for abnormalities in the solar panels using a drone (unmanned compact aircraft) (Fig. 5).
The company checks the panels by measuring insulation resistance and I-V characteristics of each string via input terminals in the combiner boxes, in addition to visual exterior inspection. However, the company knew that panels with overheating of hot spots and deterioration in conversion efficiency could not be identified by these inspections. As a measure to solve the problem, the company entrusted an external company to inspect the panels with a drone.
The inspection detected temperature distribution abnormalities in 52 of the 4,800 solar panels. Heat distribution images of the 52 panels, in which temperature distribution abnormalities were discovered, were obtained by shooting the images with a hand-held infrared camera by walking around the site after the inspection using a drone (Fig. 6).
Images of the panels were shot from the back side of panels in the inspection performed on the ground. This was owing to the difficulty of obtaining appropriate data by shooting the panels from the front side, because panels at mega solar power plants with measures against snow accumulation are installed at a higher position and a higher angle. The height of the bottom of the panels at the mega solar power plant is 1.5 m and the installation angle is 30 degrees.
By shooting the images from the ground, significant temperature differences due to hot spots were detected in 21 of the 52 panels. However, the results of I-V characteristics measurement were not below the standard specified by the manufacturer, and, therefore, the panels did not fall into the replacement category covered by the manufacturer.