Research shows repaired PV modules can perform with acceptable losses

A group of researchers led by Spain's Centre for Energy, Environmental and Technological Research (CIEMAT) has assessed the performance of 23 partially repaired crystalline silicon solar modules at a 12-year-old PV plant in Spain and has found these panels can operate with minimal losses.

“This research employs a comprehensive standardized approach,” the scientists explained. “It integrates visual inspection, electrical testing, electroluminescence imaging, and thermal imaging techniques to thoroughly evaluate the functional status of these modules and define the nature and extent of defects that persist post-repair.”

The test was conducted following IEC 61215 standard on 18 monocrystalline panels and 5 polycrystalline devices. The monocrystalline products came from two different manufacturers. All panels had a backsheet-glass configuration and their weight ranged from 21 kg to 25 kg. The group also applied the MQT 03 and MQT 15 Module Quality Test standards.

Module failures were identified according to the following classification: snail trails; browned EVA and broken cell; burnt cell; delamination and corrosion as a consequence of EVA degradation; bubbles formation, cracking and burn in the backsheet. “This categorization delineates the progression of power loss from the initial level to a specific point in the operational lifespan of a PV module,” the academics specified. 

Through the visual inspections, the team found that the modules showed optical degradation due to delamination and discoloration of the encapsulant. Moreover, it also ascertained that all of the 23 PV modules evaluated passed the dry insulation test, while only one passed the wet leakage current test.

“All modules analyzed exhibit exposed welds on the back sheet, due to bus bar interruption repair,” the researchers stressed. “This condition is not a failure due to the degradation of the module itself but rather a result of the subsequent partial repair, which caused the insulation to fail, making electrical isolation impossible. To fix the insulation of these modules, it is necessary to continue with the backsheet repair, sealing the exposed solder joints and re-testing the modules for wet leakage current.”

The I-V Curve measurements showed that the modules did not suffer from anomalies, although a power reduction was detected, while electroluminescence imaging (EL) demonstrated that around 73% of the panels presented microcracks and darker areas on the periphery of the solar cells.

When they used infrared thermography imaging, the researchers found that “strong hot spots” were detected for 4.35% of the analyzed panels, while “light hot spots” were identified for 74% of the modules. “In this last group, we found that 47 % had featured high temperatures in the junction boxes, attributable to the diode’s activation and further energy dissipation,” they added.

All in all, the analysis showed that the most common defect in the repaired modules is moisture-induced degradation (MID), followed by cracked cells and disconnected areas in cells.

“However, despite the presence of defects, around 87 % of these modules exhibit a reduction of less than 20 % in power,” the scientists stated. “This significant finding suggests that the repaired modules successfully meet the manufacturer's warranty criteria, indicating their potential for reuse.”

The group also warned, however, that there is an urgent need to define a protocol for evaluating the features of a “viable” repaired panel. “Additionally, it is necessary to raise awareness regarding international standards and Cradle-to-Cradle certification, as this has the potential to stimulate the market demand for second-hand modules with improved sustainability and circularity attributes,” it concluded.

Their findings are available in the paper “Enhancing Photovoltaic Module Sustainability: Defect Analysis on Partially Repaired Modules from Spanish PV Plants,” published in the Journal of Cleaner Production.

Another research team at CIEMAT recently developed a set of techniques to repair ribbon busbar interruptions in PV panels without resorting to expensive electroluminescence images.