The fourth case was a fire that occurred in June 2013 in Niigata Prefecture. A neighbor of the house discovered smoke and fire coming from the roof and told the resident. The resident extinguished the fire by climbing up to the roof and using a hose connected to the water supply and called 119. Solar panels and the peripheral area were burnt in this case (Fig. 7 & 8). The panels were installed by the "method where panels are placed on roof."
According to the analysis of the fire department, sparks generated from an extension cable connected to a panel cable ignited dry cedar leaves on the roof, resulting in the spread of fire. A portion with continuous and wave-shaped gashes was discovered on a cable. The gashes were caused due to gnawing by small mammals such as flying squirrels. It was inferred that the cable coating was broken, causing a short circuit near the PF tube (plastic flexible tube) where extension cables are concentrated, generating a situation where sparks tend to fly easily.
The fifth case occurred in August 2013 in Nara Prefecture. A fire alarm was activated when no one was at home and an employee of a security company rushed to the house. Smoke was in the house, but the alarm stopped when the second floor windows were opened. The employee left the house after obtaining approval.
The resident came back later and checked the interior of the house. A trace of burning was discovered in the storage space in the loft, and the resident reported the accident to the fire department. Parts of cables and part of the loft were burnt (Fig. 9). The panels were installed by the "method where panels are integrated with steel plates."
The fire department inferred the cause of the fire to be as follows. A subsidiary of the company that sold the house was entrusted with reconstruction of the existing wiring for construction of the loft around January 2012. On this occasion, the cables for the solar power facility had to be passed above the ridge beam. The originally installed cables were cut and the cable cores were press fitted using ring sleeves, pasting vinyl insulation tape on the terminals. Then, plasterboard was installed on the rafters by a construction company before completing the work.
As a result, the cables were enclosed in a narrow space, with roofing material on top, plasterboard at the bottom and rafters to the left and right. The cables were heated every day in the daytime due to the generated solar power passing through the narrow space, with no measures to release the heat.
The cables were subjected to such environment continuously and heat accumulated inside the bundled cables, causing overheating and melting the vinyl tapes on the terminals. The connected copper wires were exposed due to press fitting by ring sleeves, which resulted in a short circuit due to contact between the copper wires. This generated sparks and burned the cable coating, causing the fire.
The sixth case occurred in August 2014 in Kanagawa Prefecture. A person passing by the house told the resident that "smoke is rising from the house," and the resident reported it to the fire department. Parts of solar panels, sheathing roof boards and the loft were burnt (Fig. 10 & 11). The solar panels were installed by the "method where panels are not integrated with steel plates."
The first department inferred that damage occurred in multiple locations in the covering of solar panel cables of different poles due to inadequate installation, which caused a short circuit via aluminum frames of the panels and metal brackets for fixing on the roof, causing electrical discharge and igniting the resin construction material for fixing the panels.
Before the fire, the circuit breaker tripping and the alarm indicating a DC ground fault of the PV inverter were observed. Responding to the circuit breaker tripping, two systems in which electrical leakage was detected were shut down, but the fire was not prevented. If appropriate actions such as shielding the panels were taken on this occasion, the fire could have been prevented, according to the fire department.