Thresher Test
Developed by and for industry stakeholders, the first consensus commercial reliability and durability test standard for PV module product qualification has been “separating the wheat from the chaff” since 2011.
Developed by and for industry stakeholders, the first consensus reliability and durability test standard for PV modules has been separating the wheat from the chaff since 2011. Much as the Jet Propulsion Laboratory’s Flat-Plate Solar Array (FSA) Project marked the genesis of the terrestrial solar industry, the introduction of the Thresher Test marked a pivotal moment of market maturation, the birth of a science- and engineering-based approach to bankability. Though both initiatives relied on similar analytical methodologies, the delivery processes could not have been more different. Whereas the FSA Program was a top-down initiative led by government-funded scientists, the Thresher Test was the product of a bottom-up collaboration involving an ad hoc team of industry stakeholders led in part by RETC.
On July 15, 2011, Hugh Kuhn and RETC’s Alelie Funcell introduced the cooperatively developed Thresher Test to the world as part of the International PV Module Quality Assurance Forum in San Francisco. Having grown up in a farming community, Kuhn named the extended test protocol after a type of farm equipment used to separate seed and grain (high-quality materials) from straw and chaff (low-quality materials). Much as a threshing machine beats a plant to separate useful materials from waste, the Thresher Test uses stress sequences to separate high-quality PV module designs from low-quality ones.
As the program coordinator, RETC was the first independent testing laboratory to offer the Thresher Test product qualification program. Other laboratories, such as TÜV SÜD, followed suit, making the Thresher Test the solar industry’s original commercial test standard for characterizing PV module designs based on long-term performance, reliability, and durability. In the years since the Thresher Test’s introduction and adoption as the de facto standard for comparative PV module testing, RETC has adapted or added test sequences to better align test outcomes with the latest field-failure data. However, the core extended test sequences—thermal cycling, humidity freeze, damp heat, and damp heat with system voltage bias—are still used today to characterize product-specific design vulnerabilities, wearout and failure modes, and long-term degradation patterns.