Evolution of cell cracks in PV‐modules under field and laboratory conditions. (28th December 2017) - Buerhop, Claudia
Abstract: Damaged modules, especially with cell cracks, can be observed quite often in photovoltaic‐installations. Little knowledge exists about long‐term stability of precracked modules at real operating conditions. Previous investigations and existing standards focus on the degradation of new, defect‐free modules. This work highlights a twofold approach for life‐time study of precracked modules: (1) outdoor exposure of 54 precracked modules for 1 year and (2) artificial stressing of 20 representative precracked modules with a novel load test setup simulating snow and wind loads. The outdoor exposure reveals that at moderate weather conditions, no changes were detectable, neither in electric performance nor in EL‐images. However, the accelerated static load tests with stepwise increasing pressures point out that above a certain threshold, cracks grow. Below this threshold, formerly unseen cracks become visible at the loaded stage. In addition, modules with a smaller number of damaged cells have a stronger tendency to degrade further than modules with an already large number of cracked cells. Remarkably, the power output measured with a solar simulator after a stress test up to 2500 Pa (describing conservative proof conditions for severe snow loads according IEC 61215) remains unchanged for almost all modules. Abstract : This work highlights a twofold approach for life‐time study of precracked modules: (1) outdoor exposure of precracked modules for 1 year and (2) artificial stressing of precracked modules with a novel load test setup simulating snow and wind loads. The outdoor exposure reveals that at moderate weather conditions, no changes were detectable. Accelerated loading tests, performed in parallel, point out that underpressure causes severe cracks and fracture at elevated pressure. Surprisingly, cracks visible under loading disappear in the unloaded stage.