Fault identification in crystalline silicon PV modules by complementary analysis of the light and dark current-voltage characteristics

Photovoltaic system (PV) maintenance and diagnostic tools are often based on performance models of the system, complemented with light current-voltage (I-V) measurements, visual inspection and/or thermal imaging. Although these are invaluable tools in diagnosing PV system performance losses and faults, it is often difficult to distinguish between types of faults and to schedule appropriate maintenance actions, without combining them and performing on-the-spot inspection, for example determining if a PV module needs to be cleaned (is affected by soiling), or if it needs to be replaced (cells or contacts are damaged/degraded).
With the recent growth and development of new module level dc-dc optimizers and micro inverters, capable of bidirectional current flow, it is now possible to implement both dark I-V and light I-V measurements as complementary diagnostic tools. By complementing light I-V measurements, which reflect both the optical and electrical performance parameters of the PV device, with dark I-V measurements, which focus only on the electrical characteristic of the PV device, the optical factors determining power loss (such as partial shadows, soiling, discoloration of the plastic encapsulates), can be separated from the electrical factors (such series losses due to corrosion, cell interconnect break) or degradation of the solar cells through potential induced degradation (PID), cell cracks and breaks. In this way maintenance operations can be optimized by scheduling appropriate maintenance actions in function of severity and type of fault affecting the PV modules.
This work focuses on determining PV module parameters such as series resistance, shunt resistance and fill factor from dark I-V measurements, and comparing them with the ones obtained from light I-V measurements. The goal of the comparison is to distinguish between performance losses due to solar cell related factors (increased series resistance, shunting, cell degradation/damage, PID), and those due to the effects of partial shadows or irradiance effects on the PV module parameters.