Estimation of PV module degradation through extraction of I–V curve at inverter pre-startup condition

Decline in photovoltaic (PV) output power is observed due to aging factors such as solder bond failure, corrosion of busbars, formation of cracks in solar cell, failures of bypass diode etc. Furthermore, these happenings reflect changes in PV module parameters such as increment in series resistance/reduction in open-circuit voltage and/or decrease in fill factor etc. However, these parameter variations can be easily examined with the module level I–V curve. This study proposes a new approach of exploring the I–V curve of the PV module using an inverter pre-startup condition, i.e. just before sending the PV power to the grid. From this pre-startup I–V curve, one of the important parameters, i.e. module series resistance is estimated. The proposed method is investigated through simulations in MATLAB/Simulink and is experimentally tested on a PV output coupled to a grid-connected micro-inverter. The key advantage of the proposed method is that it does not require any additional circuitry/sensors to extract the I–V curve. Furthermore, there is no need to disconnect the PV from its normal operation.