Forced arc fault detector can make rooftop PV safer

California will soon require the inclusion of an arc detector in solar system installations to reduce the risk of fire.

A warehouse fire broke out recently in New Jersey. Although the fire was not caused by the solar modules on the roof, it did cause obstacles for firefighters to fight the fire. John Kluza, Solar Market Strategy Manager at Sensata Technologies, characterized the case as "unfortunate, but increased the importance of power protection components."

Studies have shown that the probability of a fire in a rooftop PV system is small. A study in Germany showed that about 75 accidents occurred in 1.3 million installed systems, and the US study showed that there were only seven accidents in the entire country.

Arc faults are caused by air separation between electronic components, Kluza said, the most common reasons are due to production errors, installer errors, aging and connector degradation. Current causes an electric spark through these poor connections and causes a fire.

Kluza also said that the arc fault current interrupter can sense the inflow of DC current, whether it is for inverters of smaller systems or for combiners of commercial or large power plants. This additional electrical noise on arc faults will trigger before the system causes a fire to shut down the system.

Kluza explained that the 2011 National Electrical Code required the use of arc fault current interrupters in rooftop PV systems, but each state was allowed to comply with national electrical standards according to its own conditions.

“Arc fault is a serious problem, but historically it has never been a dominant issue in the market,” explains MJShiao, senior analyst at GTM Research.

According to Kluza, each arc fault interrupter device will increase the cost of a string inverter system by 25 to 100 dollars. As the largest PV market in the United States, California's enforcement of NEC licenses for civil and commercial system installations is expected to grow rapidly in the market, and the market is strongly resistant to any increase in system costs.

Jay Johnson of Sandia National Laboratory mentioned in a recent speech that some SMA inverters already contain the first arc fault detection devices in the series arc fault protection list according to UL standard 1699B.

Kluza added that products such as TigoEnerg, SensataTechnologies, Santon Holland, Eaton Corporation and ET-ACircuitBreakers are UL listed. Johnson added that MidniteSolar and SolarBOS use arc fault interrupter technology, and the Solaredge energy optimizer has a component-level arc fault interrupter function.

Shiao pointed out that the revision of the National Electrical Code requires component-level equipment.

Component level equipment is one of the most complete solutions to assist in the fire suppression of rooftop PV systems because they can potentially eliminate current in the cable even if the sun is still shining on the component. Due to the cost of component-level energy devices and limited performance records, it has not been adopted on a large scale.

Kluza said that the main difference between the emerging arc fault interrupter products and the operating cost products is that they have a robust damage avoidance function. Some arc fault interrupter technologies also cut the photovoltaic system too decisively to cope with the building's electrical activity, even if it is not due to an arc fault. Kluza explained that the cost of restarting these systems is sufficient to offset the solar economy, and SensataTechologies has spent a long time studying the problems caused by damage avoidance.

The best arc faults are those that never happen, and Johnson described the importance of arc fault current interrupters in his speech. When these devices are able to detect "predictive signals" before they need to be separated, "the photovoltaic system can monitor the signs of future arc failures and the pre-maintenance system can be supervised."

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