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We use the fluorescence effect of the lamination material of photovoltaic (PV) modules to detect cracks in wafer-based solar cells in a power plant. For this purpose, the PV modules are irradiated by ultraviolet (UV) light, and the fluorescence light is measured by a camera. The measurement is realized in the dark. This new application of the fluorescence method allows new insight into cracks of a huge amount of PV modules during service life without remounting or touching the PV modules. We found that the frequency distribution of so-called cross cracks is almost homogenous in the PV modules. These cracks are frequently induced by crumbs or needle-shaped production equipment and not introduced after production. We show that the measured distribution of “cross cracks” in the PV modules fits to the binominal frequency distribution, as expected for production-induced cell failures. The measured crack frequency distribution for other crack types is compared with a finite-element simulation of a simplified PV module. We find that the lateral crack distribution correlates with the simulated strain distribution induced by module vibrations. In total, we found that 4.1% of the solar cells in the PV modules show at least one crack.