UL Takes a 'Shot' at Predicting Solar PV Module Reliability

There is no question that the solar photovoltaic market is expanding as it matures, largely due to the rapid decline in prices (as well as tax incentives). Most solar electricity buyers tend to look at panel affordability and the amount of power that panels can generate. But price projections are based on the assumption of a product life that is not always achieved.

Not all solar panels are created equal. A number of factors can contribute to deterioration of performance or outright failure over time.

Back in 2013, Fraunhofer began testing solar modules for durability. Using highly accelerated life testing (HALT), the organization evaluated a number of commercially available PV modules. Its test results generated "bathtub curves" that divided product life into three phases: infant mortality, random failures, and wear out, showing the failure rate for each. The test procedure concentrated on five specific failure modes:

- Potential-induced degradation

- Damp heat

- Loading/temperature cycling

- Thermal cycling

- Outdoor exposure

Early results showed significant differences between manufacturers, particularly with respect to thermal cycling durability. The two existing standards for solar panels and modules, UL 1703 and IEC 61215, primarily relate to build quality/infant mortality as opposed to long-term durability.

Last month the DoE announced a new round of funding in its SunShot Initiative, with the intent of improving scientific understanding of the factors affecting the performance of solar PV systems. Among the funds allocated, $1.35 million was given to Underwriters Laboratories (UL) to "advance the mechanistic understanding of PV module backsheet degradation in fielded modules and develop improved laboratory weathering exposures with results correlated to field performance."

The grant was part of a $102 million federal package to support clean energy innovation.

As its name suggests, the backsheet is the bottom layer of the module, which, according to Dunmore, an engineered films company making coated, metallized, and laminated foils, films, and fabrics, "is designed to protect the inner components of the module, specifically the photovoltaic cells and electrical components from external stresses as well as act as an electric insulator."

According to National Renewable Energy Laboratory, backsheets, which are generally made of resin-based laminates, degrade due to yellowing in the presence of UV light, an effect that is difficult to simulate through accelerated testing. Breakdown of the backsheet could contribute to mechanical stress failure or cause the module to short out and fail.

Under the grant, UL will "develop new scientific methods for predicting PV module material performance and reliability over time."

"UL is pleased to gather a group of distinguished scientists to examine the performance expectations of PV materials that affects everyone from module manufacturers, and developers, to investors and insurers," said Lisa Salley, vice president and general manager for Energy & Power Technologies at the organization.

"This project," said Ken Boyce, principal engineer manager at UL, "will examine the correlation between data in the laboratory and data that's collected from modules in the field. This will provide some missing links so that realistic models can be built to better predict lifetime performance."

UL will collaborate with several partners on this project, including: 3M, Arkema Inc., Case Western Reserve University, NREL, National Institute of Standards and Technology (NIST), and Northeastern University.

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RP Siegel, PE, has a master's degree in mechanical engineering and worked for 20 years in R&D at Xerox Corp. An inventor with 50 patents, and now a full-time writer, RP finds his primary interest at the intersection of technology and society. His work has appeared in multiple consumer and industry outlets, and he also co-authored the eco-thriller Vapor Trails.

[image via graur codrin at FreeDigitalPhotos.net]