The Chinese manufacturer said it has developed a new circuit model-based method to accurately detect hotspot risks in TOPCon backcontact modules, overcoming the limitations of the IEC 61215 approach caused by low shunt resistance. The method, validated by indoor and outdoor testing, predicts temperature rise under shade and reportedly allows for faster, more accurate risk assessment of hotspots.
A group of researchers from Chinese PV module manufacturer DAS Solar has developed a new methodology to detect hotspot risks in TOPCon solar cells and modules based on back-contact (BC) architecture.
“We found that the inherently low shunt resistance of TOPCon BC cells makes the conventional inflection point method specified in IEC 61215 MQT09 ineffective at identifying the modules’ hotspot risks, which in turn leads to an evaluation process that is both time-consuming and less accurate,” says the study’s lead author, D.engyuan Song, narrated pv magazine. “To address this technical bottleneck, our research team proposed a collaborative two-level equivalent circuit model for substring module systems, which directly solves the no-inflection point problem encountered in IEC 61215 MQT09 testing caused by the low shunt resistance of TOPCon BC cells.”
Image: DAS Solar
The scientists constructed a special substring-level equivalent circuit model to simulate the power dissipation characteristics under different partial shading conditions, establishing a direct quantitative correlation between the hotspot power density and the temperature rise. “The accuracy and robustness of the proposed model were extensively validated through double verification of indoor controlled experiments and outdoor field measurements,” Song said. “The results showed that the predicted trends in temperature variations closely matched real-world test data, confirming the practical reliability and industrial applicability of the proposed method.”
For their experiments and experimental validation, the scientists chose TOPCon BC solar cells with an area of 191.37 cm² from the same production line, providing consistent production parameters. The cells were categorized according to the following criteria: 0.1% efficiency interval, 5 mV open circuit voltage interval, and uniform film color. Cells showing abnormal photoluminescence (PL), electroluminescence (EL), or appearance defects were excluded. Qualified cells were subjected to the standard TOPCon BC module manufacturing process, including ink printing, solder paste application, series welding, laminate stacking, laminate curing, EL testing, frame assembly, junction box installation, and final current voltage (IV) testing.
As encapsulation materials, the scientists used coated semi-toughened ultra-white front relief glass with a thickness of 2.0 mm and high transmittance, an ethylene-vinyl acetate (EVA) film, and uncoated semi-toughened ultra-white back relief glass with a thickness of 2.0 mm with three center holes and grid glazing.
“All other components were of the same model and same batch,” Song specified. “To ensure experimental consistency, all modules were manufactured on the same production line under identical process parameters, resulting in three modules designated A, B and C.”
Image: DAS Solar
Hot-spot temperature tests were conducted under two sets of conditions: stable indoor conditions and outdoor operating conditions at the company’s demonstration base in Quzhou, China.
The results showed that the peak hotspot temperatures of TBC modules reached 119 C (indoor) and 114 C (outdoor), respectively. Furthermore, consistent trends in temperature variation were observed in substring-level shading tests, module-level shading tests, and open-air field shading tests, verifying the repeatability and stability of the test results.
“In conclusion, this study validates the reliability of the proposed hotspot assessment method and provides important technical guidelines for the standardized assessment of hotspot risks in TOPCon BC modules,” Song concluded. “It is worth noting that factors such as natural air convection and array inverter control under actual outdoor conditions exert complex coupling effects on the temperature behavior of TOPCon BC modules. Importantly, the proposed method enables rapid and accurate identification of the shadow area corresponding to the maximum power dissipation of the modules, which significantly improves the efficiency of hotspot risk testing compared to conventional methods.”
The study findings are presented in “Circuit model-driven research into hotspot behavior in n-type TBC photovoltaic modules”, published in Solar energy materials and solar cells.
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