The risk of fire in solar panel systems is extremely low: according to research by TNO, fires occur in just 0.014% of installations. Zonnefabriek has never experienced a fire in the tens of thousands of systems we have installed over the past fifteen years. A correct installation is the best way to prevent fires.
After a number of fires in solar power systems in 2018, an investigation was launched to determine the cause(s). The results are now available, and the main conclusion is that the vast majority of fires likely originated from poor electrical connections on the DC side (direct current side).
A melted DC connector on a roof due to arcing
AC and DC React Differently
When an electrical connection is not properly made, extra resistance occurs at that point. The current passing through has more difficulty flowing, causing the connection to heat up. If this were an alternating current (AC) connection, it would create sparking, where small arcs jump across intermittently. In a direct current (DC) connection, however, a phenomenon called an arc fault occurs: a continuous stream of energy that keeps heating the poor connection until components begin to melt.
In a faulty AC connection, the occasional sparks pose a minor risk, but since there is no significant heat buildup and the sparks usually remain within insulation materials, the chance of fire is low. In DC, however, the arc fault can last longer and generate significant heat. These days most inverters are equipped with an 'arc fault circuit interruption' system (AFCI) which detects an arc fault in a DC circuit and then interrupts the circuit, however: prevention is always better than cure.
The Right Connectors
This is why it is crucial to properly assemble and connect DC connectors. Cables must be stripped to the correct length (removing exactly the right amount of insulation), the connector must be securely attached to the cable using the correct crimping tool, and connectors must be fully inserted into each other until they click into place. When done correctly, the connection is safe and remains reliable for years, even under exposure to the elements.
The report also emphasizes that only connectors of the same type should be used together. Apparently, some of the fires occurred because different types of connectors were improperly combined. At Zonnefabriek, we only use so-called MC4 connectors, which match those pre-installed on our solar panels.
On the Roof or Integrated into the Roof
Even if a connection is poorly made, the risk of fire is low in a standard system where panels are mounted on the roof. In such cases, a faulty connection will eventually melt away, breaking the circuit and stopping the flow of electricity—eliminating the danger.
However, the TNO study found that most fires occurred in integrated roof systems. In these setups, panels are built directly into the roof rather than mounted on top. The cables connecting the panels lie directly on the roof structure, near insulation materials and membranes. In the worst-case scenario, a severely overheated connector could come into contact with flammable materials, potentially causing a fire.
in an 'integrated roof' system the panels are sunken into the plane of the roof
Expertise Matters
Integrated roof systems are most commonly used in new construction projects and can have a sleek, seamless appearance. However, extra care must be taken to ensure correct installation. A challenge with new builds is that both the house and the solar power system are often installed by a general construction company rather than a specialist in solar energy. This lack of expertise can lead to mistakes.
TNO has provided several recommendations to further reduce the already low fire risk. These include paying extra attention to DC connectors, ensuring only matching connector types are used, and ensuring proper training for installers. Zonnefabriek has been prioritizing these best practices for years, which is why we are proud to say that in over a decade, we have never experienced a fire in any of our solar power systems.
For those interested in reading the full report, a downloadable version is available on the Holland Solar website.
