During their lifetime, photovoltaic (PV) plants are subject to a normal degradation of their components, and they are consequently characterized by decrease of the expected production. In order to prevent and evaluate failures and loss of production, specific tests can be carried out on the PV modules. Non-destructive methods, such as visual inspection and infrared thermography, can be performed in order to determine production failures or defects on the PV modules. I-V curves allow to estimate the performance of photovoltaic modules and strings, estimating the deviation between the power of the examined module and that declared by the manufacturer. The aim of this work is to evaluate the efficiency loss of photovoltaic modules associated to specific defects, causing in a systematic way some faults on a set of brand-new modules and assessing the relative decrease of power. The set of brand-new photovoltaic modules, after being damaged, was experimentally characterized determining their I-V curves by means of an indoor solar flash test device based on a class A+ AM 1.5 solar simulator. Using the I-V curves as a dataset, it was possible to estimate the incidence of different defects on the power of the photovoltaic module being considered.