Explicit Expressions for Solar Panel Equivalent Circuit Parameters Based on Analytical Formulation and the Lambert W-Function

Abstract

Due to the high dependence of the photovoltaic energy efficiency on environmental conditions (temperature, irradiation...), it is quite important to perform some analysis just focusing on the photovoltaic device characteristics in order to optimize the energy production, even in case of small-scale users. The use of equivalent circuits is the preferred option to analyze solar cells/panels performance. However, the aforementioned small-scale users rarely have the equipment or expertise to perform large testing/calculation campaigns, the only information available for them being the manufacturer datasheet which normally refers to fixed irradiation and temperature levels. The solution to this problem is the development of new and simple methods to define equivalent circuits able to reproduce the behavior of the panel for any working condition, from a very small amount of information. In the present work a direct and completely explicit method to extract solar cell parameters from the manufacturer datasheet is presented and tested. This method is based on analytical formulation which includes the use of the Lambert W-function to turn the series resistance equation explicit. Therefore, the calculations involving this parameter are simplified. The presented explicit method is used to analyze the performance (i.e., the I-V curve) of a commercial solar panel at different levels of irradiation and temperature. The analysis performed is based only on the information included in the manufacturer's datasheet. Results indicate a good correlation level with experimental data.