The facts on the fire risks of rooftop solar arrays

By Justin Ehren, Melink Solar & Geo

Although fires from rooftop PV systems are incredibly rare, some building owners may have concerns, especially after hearing about a high-profile case in 2018 when seven of Walmart’s rooftop solar systems caught fire.

Because solar panels have live wires, there is always going to be some level of fire risk — just like with any electrical device. However, technological improvements have been made in recent years to help ensure safety and specifically avoid fire risk. Stricter electrical codes have also been enacted in many states, too. Not only is solar PV a smart investment, but it’s also safe.

Avoiding Faulty Installation

Solar PV fire incidents are extremely rare. Previous industry reports acknowledge fewer than 1 incident per 10,000 installations. In fact, it was no coincidence that Walmart experienced fires at a rate of nearly 300-times the average — it is because the same contractor (SolarCity/Tesla) performed the install at each store.

Some common mistakes that have caused issues in systems include:

• The use of incorrect crimping tools
• Using different brand connectors
• Poor wire management
• Insufficient installation training

A properly designed and installed solar PV system with correctly operating equipment presents no fire hazard, according to The Solar Nerd. For almost all fire incidents, including the Walmart incidents, there is overwhelming evidence that points to faulty installation practices as the root cause.

To help customers know that you are a quality installer and provide reassurance, consider the following actions:

• Share past projects to showcase you have worked on similar projects to theirs.
• Earn certifications from industry boards like the North American Board of Certified Energy Practitioners (NABCEP) and Solar Energy International (SEI). NABCEP is nationally recognized as the gold standard for PV certifications, providing skills and credentials required for those who work with PV and solar heating technologies.
• Be willing to put your time and money on the line to ensure you deliver a successful project, even if there are hiccups along the way.

Solar Technology Improvements to Minimize Fire Risk

Along with safer code requirements, there have been significant advances in solar design and technology that have improved fire safety. Both the proper sizing of the electrical components and the use of appropriate installation techniques are fundamental to the reduction of risk. There has been increased adoption of expansion joints to allow for thermal movement and to prevent conductors or conduit from being damaged. PV equipment technology such as modules and inverters have made significant advances in recent years as well.

PV modules are required to comply with international standards for electrical performance and safety. The design of modern inverters now includes ground fault, overload, over-temperature and arc fault protection to minimize risk. These protective elements make the system safer than most other electrical equipment on rooftops or inside buildings, such as HVAC electrical equipment, per SunPeak Power. Module-level power electronics (MLPEs) provide module-level monitoring, and this has allowed data acquisition systems to identify problems quicker.

Finally, before any array is energized, you should go through a process of commissioning and electrical inspection to ensure the system is built to the drawing set and ready to start producing efficiently and safely.

Industry Standard Improvements to Minimize Fire Risk

It is also important to note that solar systems installed earlier in the decade have notable differences from those installed today because of safety evolutions in the industry. Both technological advances in equipment, as well as more stringent electrical code requirements, have contributed to safer solar PV systems. Most of the projects that caught fire at the Walmart stores were installed around 2012, which was before states had begun adopting either the 2014 or 2017 versions of the National Electrical Code (NEC).

Rapid shutdown was first introduced in the 2014 NEC with the intent of providing a simple method for firefighters to de-energize solar arrays. In effect, the PV system could manually turn off if some problem prevented AC current from flowing to the inverters. Then in the 2017 NEC (Section 690.12), rapid shutdown rules were updated to call for module-level shutdown because even when the inverter is switched off, the DC wiring will remain energized whenever the sun is shining. To meet the module-level regulations, smart modules, microinverters or MLPEs are required to reduce the string voltage and provide manual activation of rapid shutdown features.

With all DC-based MLPEs assisting with rapid shutdown, the AC breaker is the only switch that would need to be flipped. Not only does this protect the system and ensure personnel safety, but the MLPE adds module-level monitoring functionality. As of Nov. 1, 2020, there are 38 states that have adopted 2017 NEC or above. You can research NEC adoptions by state here.

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Melink Solar is a commercial solar installer based in Cincinnati, Ohio.