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Solar Panel Inspection Employs Drone, AI, Automatic Reporting (2) (page 2)

Mosaic abnormalities caused by lightning can be detected

2019/07/31 10:16
Shinichi Kato, Nikkei BP Intelligence Group, CleanTech Labo
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Damage due to reverse current caused by lightning strike also detectable

According to actual analyses, abnormalities that are rarely detected by drone inspection were discovered in the validation test stage. They are problems where mosaic thermal distribution abnormalities appear on solar panels (Fig. 4).

Fig. 4: Mosaic temperature distribution abnormalities are generated by damage due to a reverse current caused by a lightning strike. (source: NESIC)

It is believed that the abnormalities were caused by a reverse current flowing to solar panels, which is generated by a lightning strike or failure of an anti-backflow diode. Cells are damaged by backflow of current to panels, resulting in thermal distribution abnormalities with contrasting density similar to mosaic patterns depending on the degree of the damage, according to estimations. The cells were overheated to 100°C or higher and needed to be replaced immediately.

Abnormalities detected by NESIC services are evaluated for urgency by three levels in the reports. Overheating of 80°C or more is classified as the top urgency level. Therefore, the level 100°C or higher due to mosaic abnormality mentioned above was the top urgency level.

The company shoots still images. Many companies shoot moving images in their services, but still images are more advantageous for reporting urgency levels because information on absolute temperatures is recorded in all pixels, according to the company. Absolute temperatures are not recorded in moving images, which leads to significant limitations in mapping on layout drawings.

At the power plant where mosaic abnormalities were discovered in panels, which seem to have been caused by a lightning strike, the actual power generation amount was much less than the amount estimated at the time of working out the business plan for three consecutive years, but the situation was left unchecked.

For the hardware side, the speed of the analysis engine was increased and its weight was reduced by using special technology developed by NEC Laboratories America Inc to improve the analysis environment. Following this improvement, only a single server is required for analysis, without the need for a large-scale hardware environment, according to the company.

The company uses infrared cameras manufactured by a US company for mounting on the drones although infrared cameras for mounting on drones are also manufactured by Nippon Avionics Co Ltd of the NEC Group (See related article).

Products of the US manufacturer, which are widely used, were incorporated because infrared camera modules manufactured by Nippon Avionics have yet to satisfy the requirements of NESIC in terms of downsizing and weight reduction.

Going forward, the company plans to offer the solar panel inspection services using drones to many power plants, not limiting the targets to solar power plants from which the company is entrusted with EPC and O&M services. The company emphasized that it can diagnose solar panels based on a wide variety of experiences because it handles a wide range of EPC and O&M services and has abundant knowledge on panel abnormalities.