From pv magazine Germany
In 2024, researchers at Fraunhofer ISE analyzed the stability of TOPCon, passivated emitter and rear cell (PERC), and heterojunction solar cells under UV irradiation and found that all three cell technologies can suffer significant losses in implied voltage and efficiency. Practical experience has confirmed this finding.
With that in mind, other Fraunhofer ISE researchers assessed the validity of standard UV testing methods for TOPCon modules. The result – surprising at first glance – is that conventional UV tests can significantly exaggerate the degradation effect.
In these lab tests, experts simulate the natural UV exposure photovoltaic modules face in the field and on rooftops. They increase the irradiation intensity to accelerate aging and estimate long-term performance losses.
Testing limits
Fraunhofer ISE said modules must be stabilized after testing to produce results that reflect real-world degradation more accurately. Only then can researchers distinguish between UV-sensitive and more stable module types for comparable evaluations. Scientists attributed this to the metastable behavior of commercial TOPCon modules, prompting a reassessment of test procedures and additional field testing.
“Many module types of the current generation of commercial TOPCon photovoltaic modules unfortunately react sensitively to UV irradiation. ‘Field returns' and comparisons between laboratory-aged and field-aged modules also confirm this. However, the degradation rate does not appear to be as drastic as previously assumed,” stated Daniel Philipp, head of Fraunhofer ISE’s Module Characterization and Reliability Department. “We recommend that users test photovoltaic modules according to the latest findings.”
Researchers said they must further investigate the phenomenon to better predict long-term impacts of solar exposure on module yield.
Relative power loss of commercial TOPCon modules after UV testing (same-color lines indicate same module types), measured before and after stabilization
Image: Fraunhofer ISE
Efficiency rebound
The Fraunhofer ISE researchers found that UV irradiation during testing destabilizes modules to the point that they lose significant efficiency during dark storage. Sunlight exposure afterward, however, triggers a marked recovery effect.
Field tests at Fraunhofer ISE’s Outdoor Performance Lab and analysis of field returns in the institute’s CalLab PV Modules lab showed that this stabilization process yields degradation values much closer to real-world outcomes.
Some modules showed little to no degradation after 60 kWh/m² of UV exposure – roughly equivalent to one year in Germany – and subsequent stabilization under sunlight. Others still showed performance declines of up to 5% post-stabilization. Overall, degradation was significantly lower than suggested by standard UV tests, said Fraunhofer ISE.
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