Inspecting series resistance effects and bypass diode failure using contactless outdoor photoluminescence imaging

Operation of photovoltaic systems in the most economical way requires monitoring the modules' performance in order to ensure that the maximum power output is obtained. Existing methods for field inspection have limited capability of detecting various electronic defects that can, however, be identified with luminescence-based methods. This study presents a fully contactless outdoor photoluminescence imaging based measurement that uses the sun as the excitation source. This is achieved by modulating the module bias and hence luminescence signal by shading a single cell. We show that this technique can identify: (a) isolated areas, by modulating the cells in a sub-string between different operating points; and (b) open-circuit bypass diode failure, which is impossible to identify in contactless fashion using conventional field-inspection methods. The main merit of this method is that it can be used when the module is under normal operation in the field, without having to change any of the electrical wirings of the photovoltaic array.