// Accelerated ageing of photovoltaic modules

// CIGS modules in damp heat test

The damp heat test (DH), which is carried out at 85°C and 85% relative humidity, is among the more stringent tests PV modules have to undergo in the context of the IEC 61646, 61215 design and quality certification. During the test, which is carried out in climate chambers over a period of 1,000 hours, the PV modules are subjected to much stricter requirements than in outdoor conditions. Ageing-related faults, such as lower performance, delamination of the sealing material or corrosion of thin layers, can thus be caused in much shorter time.

A generally valid estimate of the modules’ useful lifetime cannot be derived from the DH test since such deduction requires knowledge of both the respective micro climate and the temperature dependency and activation energy of the fault mechanism. However, it is assumed that the 1,000-hour DH test simulates several years or decades of service in outdoor conditions. For comparative quality analysis and test-to-failure studies, the test duration is extended significantly beyond the 1,000 hours. In one study, CIGS modules were subjected to a 4,000-hour DH test involving regular quality and performance assessments. Up until around 2,000 hours of DH, CIGS modules show very little degradation of performance. After 4,000 hours, their average performance declines to 80%. The stability behaviour of CIGS modules is thus superior to that of typical c-Si modules which show a significant degradation of performance after 3,000 hours of DH testing.

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Peter Lechner
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Relative performance of commercial CIGS modules (above), and c-Si modules (below), as a function of DH test duration.