Robust series resistance estimation for diagnostics of photovoltaic modules

It is well-known that the slope of the I-V curve of a photovoltaic panel at open-circuit conditions is proportional to the panel´s internal series resistance. However, the slope of the I-V characteristic is greatly affected by environmental conditions, showing an approximately linear relationship with the reciprocal of the irradiation. In this work, a simple series resistance estimation method based on the slope of of the I-V curve at open-circuit translated to standard test conditions (STC¹), is presented. Experimental test results for crystalline silicone panels show good estimation performance in a wide range of irradiation (> 200W/m²) intensities, with a worst case accuracy of ¿ 0.15¿.