‘TOPCon technology comes with three or four relevant risks that should be known’

From pv magazine Spain

Last week, solar panel manufacturers JinkoSolar and Trina Solar reported that field tests show that tunnel oxide passivated contact (TOPCon) solar modules outperform p-type rear contact PV modules in monthly power generation. These studies were conducted by the manufacturers individually, and in the case of Jinko Solar, the results were confirmed by German agency TÜV Nord.

While the data from a generation perspective is encouraging, the results of this year's Kiwa PVEL scorecard have shown that the technology is more vulnerable. Researchers at the University of New South Wales in Australia have also recently published the results of new research showing the vulnerability of TOPCon solar cells to contact corrosion, as previously reported by pv magazine in 2023.

In the case of the tests carried out by Kiwa PVEL, the results depend largely on the type of bills of materials (BOM) used.

“This year’s results have surprised us,” Asier Ukar, managing director of Kiwa PI Berlin in Spain, told pv magazine. In particular, less than 6% of the 388 models tested were top performers in all reliability tests (TC, DH, MSS, HSS, PID and LID+LETID); and 66% of module manufacturers experienced at least one failure in the tests. “The failure rate at BOM level also increased to 41%, the highest ever,” he explained. PV modules with the same model type can be manufactured from completely different BOMs, and these changes in PV module components can have a major impact on reliability and performance. On the other hand, “industry certification tests according to standard regulations are often not strict enough to identify these potential problems,” Ukar added.

For example, the International Electrotechnical Commission (IEC) test for Thermal Cycling is 200 cycles in a climatic chamber, while the Kiwa PVEL test is 600 cycles. This test models the behaviour under hot-cold thermal cycles, and the requirement to pass the test is that the module degrades less than 2%, and 84% of the modules tested passed the test; 11 manufacturers suffered a failure in this test. “The average degradation rate for PERC and TOPCon was 0.6% and 0.7%, respectively, but 5 TOPCon BOMs registered a power degradation failure compared to only 1 PERC BOM,” Ukar said.

Another test, Damp Heat, subjects the panels to moist heat in a climate chamber. Kiwa PI Berlin subjects them to 2,000 hours – compared to 1,000 for the IEC – and the requirement to pass the test is that the module degrades less than 2%. “In this case, 31% of the BOMs tested failed the test, and TOPCon is more affected than PERC,” Ukar explained.

The mechanical stress, hail, Potential Induced Degradation (PID) and LID – LeTID tests generally yielded good results, but problems were observed in the UV-induced degradation (UVID) tests: “The power loss after 120 kWh/m2 of UVID ranged from 0.6% to 16.6%. While HJT is affected and PERC degrades more than expected, TOPCon suffers much more,” he added.

Everything points to TOPCon being the dominant technology in the next five years and, as with every technological advancement introduced by the sector, this improvement also comes with certain risks and challenges that must be understood and addressed.

“One of the main objectives in the race to deploy this technology in a way that meets expectations is to focus on its long-term durability, that is, how this technology behaves under the influence of environmental factors such as humidity or UV radiation,” Ukar stated. This approach brings with it the need to include extended-duration tests in the prequalification processes of manufacturers and their models, as well as adapting laboratory testing procedures with tests adapted to the risks that TOPCon introduces. “The good news is that both the tools and the knowledge exist and are at the service of the industry,” he concluded.

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