The Heat Is On: Fault Detection and Fire Prevention

Could PV-involved fires dampen a hot solar market?

On the evening of June 19, 2015, a KOB 4 Eyewitness News anchor in an Albuquerque, New Mexico, studio teased a developing story with a video montage running behind his back. “This video shows smoke pouring from the roof of a community center,” he explained, as the footage cross-faded from fire engines with flashing lights to firefighters hosing down the roof of a broad building from an aerial ladder. Before the video cut to helicopter footage showing a smoldering and blackened roof, the anchor intoned: “Tonight a fire there is blamed on solar panels.”

One bad news report like this can counterbalance a hundred positive stories. News of the Solyndra bankruptcy, after all, made more of an impression on the public than two decades’ worth of sustained solar market growth and job creation. For the solar industry to continue to enjoy broad public and political support, we must do everything in our power to eliminate fires in PV systems.

In this article, I provide a brief history of PV-involved fires, exploring both their causes and effects. I describe specific design and installation practices that can help prevent PV-initiated fires by minimizing ground faults and series arc faults. I summarize efforts to improve fault detection in fielded PV systems with new codes and standards, and provide troubleshooting tips for identifying and remedying detected faults. Lastly, I consider some actions integrators and asset managers can take to limit liability and financial exposure associated with possible future fires in legacy PV systems that are not built to the latest codes and standards.

Brief History of PV-Involved Fires

Though fires involving PV systems are very rare, they occur on a continual basis. In April 2009, for example, a fire began with a PV array on the roof of a big box store in Bakersfield, California. When I subsequently analyzed this fire in SolarPro, I foresaw that the same type of event could happen again unless the industry changed the ground-fault detectors used in these systems. (See “The Bakersfield Fire: A Lesson in Ground-Fault Protection,” February/March 2011.) Approximately 2 years later, in April 2011, a fire originating within an array on the roof of a manufacturing facility in Mount Holly, North Carolina, damaged 20 PV modules, two combiner boxes and portions of the roof.

In May 2013, a PV-involved fire occurred at the headquarters of a dairy co-op in La Forge, Wisconsin, causing roughly $12 million in damages. The local fire department classified the cause as undetermined. However, a fire investigator for the National Fire Protection Association (NFPA) wrote an article (see Resources) contending that the site’s green building technologies and construction materials—including the PV array on the roof and recycled cotton-based insulation in the wall cavities—contributed to the spread of the fire and presented safety issues for firefighters.

Perhaps the most publicized PV-involved fire occurred in September 2013 at a 300,000-square-foot food warehouse in Delanco, New Jersey. While the origin of this fire is still under investigation, the fire was linked closely with the PV system. Media outlets reported that firefighters did not fight the blaze more aggressively because they were afraid that the PV system would injure them.

While the community center in Albuquerque is perhaps the most recent PV-involved fire to make the news, a similar event occurred in May 2015 on the roof of a large industrial facility in Mesa, Arizona. Though investigators are still determining their causes, it is likely that both were PV-initiated fires. Further, both resulted in severe damage, with the Mesa fire creating millions of dollars of fire loss.

Causes. Until recently, the manner in which PV systems started fires was subject to speculation and hypothesis. Now, however, after dozens of examples of PV-initiated fires in fielded systems, there is general consensus regarding the primary causes. We can categorize the vast majority of fires originating within PV arrays as either ground-fault detection blind spot fires on the one hand or series arc-fault fires on the other.

The Bakersfield and Mount Holly fires, for instance, are examples of fires caused by a blind spot in a ground-fault detection system. While ground-fault detection blind spot fires are unique to certain PV systems, fires caused by arc faults are not. An arcing fault can cause a fire in a dc circuit even more easily than it can in an ac circuit. Common causes of series arc faults in PV circuits are loose or separated connections in modules, connectors or combiner boxes. 

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