Extracting parameters from semi-log plots of polycrystalline silicon PV modules outdoor I–V data: Double-exponential model revisited

This paper presents a method for extracting physically meaningful parameters from measured I-V curves of PV modules. The 7-parameter double-exponential model is applied in the modeling. The method is based on linear fitting of semi-logarithmic plots. The paper demonstrates a new technique to estimate the series resistance of a module with high accuracy from such plots. As a result, also the reverse saturation current and the quality factor of the diffusion diode can be determined. The method is applied to outdoor I-V data from a test station with three similar, but not identical, polycrystalline-Si modules. The values of the series resistances found with this method deviate somewhat from the values found by indoor measurements by an independent laboratory. The quality factors of the diffusion diodes were in this case found to be somewhat larger than 1, indicating a good, but not perfect quality of the material.