Suns-Vmp method for health monitoring of 110 PV modules

Abstract

One can monitor the health of the PV modules by analyzing their current-voltage (I–V) curves, which rarely are measured in commercial settings. Fortunately, nearly all PV installations measure the maximum power point current (Imp) and voltage (Vmp), along with the ambient weather conditions, which the proposed Suns-Vmp method uses to generate pseudo I–V curves. In this work, the proposed methodology was rigorously tested on 110 PV modules of various technologies installed under harsh desert conditions, for approximately 7 years and 9 months. For these modules, the fitting accuracy between the actual field measured and pseudo I–V curves, did not exceed an RMSE value of 0.35 A. The median power degradation of the mono-crystalline, poly-crystalline, and thin-film technologies were estimated to be around 0.21 %/year, 0.49 %/year, and 1.51 %/year. From the root-cause analysis using the fitted PV parameters, it was found that the dominant degradation contribution in all the modules came from series resistance, followed by shunt resistance. For mono-crystalline, poly-crystalline, and thin-film technologies, the mean yearly rate of change for series resistance was 1.47 %, 4.37 % and 13.37 %, while for shunt resistance these values were 0.68 %, 1.26 % and 3.95 % respectively. As field measured I–V curves are seldom available, techniques like the Suns-Vmp method can offer valuable insights for effective solar farm management and maintenance, without any interruption in the operation.