The seventh case occurred in August 2014 in Tokyo. The resident heard a crackling noise coming from the second floor. An unusual smell was detected when the window was opened, but the resident did not think the smell came from the house. Later, a neighbor told the resident that smoke was rising from the roof, and the resident contacted the fire department. Part of the loft and seven solar panels were burnt (Fig. 12 & 13). The panels were installed by the "method where panels are not integrated with steel plates."

Fig. 12: Damage to roof of house in Tokyo. Right-hand photo shows situation after removal of solar panels. (source: CAA)

Fig. 13: Pinched cable. Left-hand picture shows trace of pinching; right-hand picture shows state of being pinched. (source: CAA)

Sparks generated from panel cables ignited the roofing materials and caused the fire, according to the analysis by the fire department.

The NITE inferred that a cable was pinched in the mounting system at the time of installation and load and vibration stress was applied to the cable due to changes in the weather after installation, which accelerated deterioration in insulation performance of the cable at the pinched portion, causing breakdown at the maximum power generation amount and forming a short circuit using the mounting system as the path, which led to the flow of excessive current and heating, resulting in the fire.

The eighth case occurred in February 2015 in Tochigi Prefecture. The residents were not at home, but children in the neighborhood discovered smoke coming from the roof and contacted the fire department. When a panel in the area where smoke was being generated was removed, a fire was about to start near the cables. Cables and one panel were burnt and roof tiles were cracked by the heat (Fig. 14).

Fig. 14: Solar panel burnt on roof of house in Tochigi Prefecture. Right-hand photo shows burnt cables (source: CAA)

The fire department inferred the cause of the fire to be as follows. When the conduit was replaced about 6 months before the fire, the cables of two systems were detached from the coupler joint and five cables including one ground wire were cut, followed by press fitting and coating of the cables. Defective press fitting existed in these areas, which generated heat over time and resulted in the fire.

The ninth case occurred in December 2015 in Kanagawa Prefecture. A neighbor discovered a fire in the area around the PV inverter installed on the outer wall. The fire was reported to the fire department by the resident. The fire was extinguished by the resident using a fire extinguisher and a firefighter confirmed that the fire had been controlled. Cables, part of the PF tube and part of the outer wall were burnt (Fig. 15).

Fig. 15: Damage to house in Kanagawa Prefecture After removal of cables (source: CAA)

The fire department inferred the cause of the fire to be as follows. Connectors of the cables that connect panels with the PV invertor were inside an outdoor cable protection tube made of resin, which is not supposed to house joints. The joints became loose due to deterioration of connectors, and so forth, causing defective contact and generating heat due to increase in contact resistance, resulting in melting of the insulating portion and a fire due to a short circuit between opposing poles.