The Consumer Affairs Agency (CAA) released a report on fires started by residential photovoltaic systems Jan 28, 2019.

In our previous report, 13 cases of fires generated by solar panels or cables in residential solar power generation facilities were introduced based on the survey report. Fires caused by ignition of cables seem to be attributable to defective installation in many cases while fires caused by ignition of panels seem to be attributable to defective panels, not defective installation, in many cases, as we pointed out in our previous report.

It was also learned that the degree of damage due to the spread of fires to roofing materials depends on the installation method on the roof, when the fire source is a solar panel or a cable. Damage due to fire is serious when the fire extends to "sheathing roof boards" that constitute part of the roof. Seven cases of this kind were reported, and all of them occurred in facilities installed by the "method where panels are not integrated with steel plates," in which non-combustible materials such as steel plates are not placed between solar panels and sheathing roof boards.

In the survey report, the process leading to fire was inferred through investigation of the accident, in respect to each of the 13 cases of fires, and so forth. We introduce the processes in our latest report. Residential solar power facilities that are in operation that have not had fire-related accidents were examined based on the presumption, and it was discovered that some of the facilities were starting to have the same problems that could lead to fires.

Investigation reports of the fire department, the National Institute of Technology and Evaluation (NITE) and manufacturers were analyzed in respect to the 13 cases of accidents including fires. And estimated ignition sources were classified into solar panels and cables to analyze the causes of the fires, and so forth.

As for solar panels, on-site investigation was performed for residential PV facilities in operation to check whether the analyzed content was valid. Tests were also carried out to validate the process of fire spreading to sheathing roof boards.

Five of the 13 accidents including fires were presumed to have been caused by solar panels catching fire. The panels had been used for more than seven years in all of the five cases. The process leading to panel ignition was estimated based on the cases, which is shown below (Fig. 1).

Fig. 1: Estimated process of ignition (source: CAA)