A group of scientists from the U.S. Department of Energy’s Sandia National Laboratories has conducted a failure analysis of 6,276 photovoltaic connectors used in rooftop PV systems, in an effort to increase publicly available data on the rates and types of connector failures.
“The primary objective is to establish a fielded connector database that encompasses installations representative of the entire PV industry, providing insights into installation practices, connector models, climates, and other system variables associated with the highest failure rates,” the academics explained. “The research will also include forensic analysis to identify the root causes of failures.”
The group sourced all the connectors for the analysis from an undisclosed PV system installer operating in the U.S. market. The devices were installed between 2014 and 2017 and were taken from 265 individual rooftop systems spread across seven U.S. regions, with California providing the highest number.
For their failure analysis, the researchers implemented a framework including barcoding, wire stripping, visual inspection, 4-wire resistance measurements, and X-ray imaging.
“This characterization procedure prioritized high efficiency and rapid connector processing over high-precision measurements,” they specified. “The complete dataset from this work is hosted on the DuraMAT data hub. All data analysis was conducted using Python scripts, and outliers were identified using the interquartile range (IQR) method.”
The analysis showed that tight wire bending radius, extra dirty connectors, and loose nuts are the most common failure causes in rooftop PV systems, with percentages of 2.2%, 1.3%, and 1.1%, respectively. Furthermore, the scientists found that loose nuts had a critical failure rate of 41 % for fiber optic connectors.
They also found that high current levels are often associated with connectors’ higher resistance ranges and critical failure rates, which were attributed to resistive heating.
Moreover, the research team carried out a performance assessment of cross-mated connector models. “The analysis did not reveal a definitive performance trend between cross-mated and non-cross-mated connectors; some cross-mated connectors performed adequately, while others did not,” they pointed out.
The analysis also revealed that connector types designed to limit heat dissipation from the contact to the housing are often associated with higher failure rates, and that rounded contact barbs used in some connectors can lead to retainer failures.
The connector analysis was presented in the study “Rapid characterization and failure analysis of 6276 rooftop-harvested photovoltaic connectors,” published in Solar Energy. “Future work will leverage the techniques developed in this paper to characterize a more diverse range of PV installations,” the team concluded.
Other researchers from Sandia National Labs have recently created a standardized terminology for PV connectors in an effort to reduce confusion and offer best practices for their deployment.
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