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Defective Solar Panels Can Cause Fires at Residential PV Facilities (1)

Survey of fires caused by panels, cables

2019/03/19 17:45
Shinichi Kato, Nikkei BP Intelligence Group, CleanTech Labo
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On January 28, the Consumer Affairs Agency (CAA) released a report on fires generated from residential solar power generation systems.

The survey was conducted by the Consumer Safety Investigation Commission and the report is titled "Report on the survey of causes of accidents, etc., based on the specifications in Consumer Safety Act Article 23 Section 1." The investigation commission tried to identify the causes of accidents and hazards based on the specifications in the abovementioned section and from the standpoint of consumers. The purpose of the survey was to prevent hazards that could affect the life or health of consumers and to prevent expansion of such hazards, not to accuse anyone of causing the accidents.

The survey was conducted because accidents including fires generated by residential solar power facilities could result in house fires, and as the number of residential solar power facilities exceeded 2 million as of the end of 2016, the possibility of avoiding such accidents seems to be low because it is difficult for consumers to stop these facilities generating power.

As for fires generated by solar panels and cables among the accidents involving residential solar power facilities, in many cases where cables are believed to be the ignition sources, the alleged cause is inadequate installation. On the other hand, when solar panels are believed to be the ignition sources, in many cases, the accidents are alleged to be caused by defective panels, not inadequate installation, according to the survey.

It is estimated that solar panels become ignition sources when defects in cable joints or bypass circuits deteriorate due to aging, based on survey reports of panel manufacturers.

The "process leading to panel ignition" was looked at in the report. Upon surveying residential solar power facilities in operation, problems that prove the validity of the process were actually discovered. Problems of this kind were observed in products of multiple manufacturers.

Among these problems, those in cable joints inside panels are caused by aging or problems in manufacturing. The duration after introduction is also an important factor because fires that are believed to have been ignited by panels occurred in residential solar power facilities that are older than about 10 years.

As for fires ignited by panels or cables, the degree of damage due to the spread of fires to roofing materials varies depending on how the panels and cables are installed on the roof.

Solar panels are usually installed on roofs by four methods (Fig. 1 & 2). In the "method where panels are placed on a roof," panels are fixed on mounting systems that are installed on roof covering materials such as tiles, slates and metal sheets. In the "method where panels are placed on steel plates," panels are integrated in roof covering materials or panels are fixed on the entire roof surface, with incombustible materials such as steel plates placed on roofing materials (waterproof materials for roofing) directly below the panels.

In the "method where panels are integrated with steel plates," panels that have incombustible materials such as steel plates on the back are fixed directly to roofing materials. In the "method where panels are not integrated with steel plates," panels without steel plates on the back are fixed directly to roofing materials.

Fig. 1: Basic roof structure of houses (source: CAA)

Fig. 2: Methods of solar panel installation on roofs (source: CAA)

The fire damage is serious when the fire extends to sheathing roof boards that constitute part of the roof. The damage was serious in seven fires where the fire extended to sheathing roof boards.

Sheathing roof boards are fixed on rafters and are generally made of wood. All of the seven fires that caused serious damage due to the spread of fire to sheathing roof boards occurred in the "method where panels are not integrated with steel plates," in which noncombustible materials such as steel plates are not placed between solar panels and sheathing roof boards.

Fires are also caused by PV inverters and combiner boxes. The causes were also analyzed.

The Consumer Affairs Agency also disclosed the opinions submitted to the Minister of Economy, Trade and Industry and the Secretary of the Consumer Affairs Agency based on the survey results. The ministry and the agency will take action responding to the opinions and will report the details of the action to the Consumer Affairs Agency.