Evaluation the Accuracy of One-Diode and Two-Diode Models for a Solar Panel Based Open-Air Climate Measurements

Increasingly, using lower energy cost system to overcome the need of human beings is of interest in today's energy conservation environment. To address the solution, several approaches have been undertaken in past. Where, renewable energy sources such as photovoltaic systems are one of the suitable options that will study in this paper. Furthermore, significant work has been carried out in the area of photovoltaic system as one of the main types of renewable energy sources whose utilization becomes more common due to its nature. On the other hand, modeling and simulation of a photovoltaic system could be used to predict system electrical behaviour in various environmental and load conditions. In this modeling, solar panels are one of the essential parts of a photovoltaic system which convert solar energy to electrical energy and have nonlinear I-V characteristic curves. Accurate prediction of the system electrical behaviour needs to have comprehensive and precise models for all parts of the system especially their solar panels. Consequently, it provides a valuable tool in order to investigate the electrical behaviour of the solar cell/panel. In the literature, models that used to express electrical behaviour of a solar cell/panel are mostly one-diode or two-diode models with a specific and close accuracy with respect to each other. One-diode model has five variable parameters and two-diode model has seven variable parameters in different environmental conditions respectively. During the last decades, different approaches have been developed in order to identify electrical characteristics of both models. (Castaner & Silvestre, 2002) have introduced and evaluated two separate models (one-diode and two-diode models) for a solar cell but dependency of the models parameters on environmental conditions has not been fully considered. Hence, the proposed models are not completely accurate. (Sera et al., 2007) have introduced a photovoltaic panel model based on datasheet values; however with some restrict assumptions. Series and shunt resistances of the proposed model have been stated constant and their dependencies on environmental conditions have been ignored. Furthermore, dark-saturation current has been considered as a variable which depend on the temperature but its variations with irradiance has been also neglected. Model equations have been merely stated for a solar panel which composed by several series cells.