Modeling and parameter calculation of photovoltaic fields in irregular weather conditions

In this paper, a model for photovoltaic (PV) fields and a procedure for calculating theparameters of the modules of a string (a group of PV modules connected in series)are presented. The proposed model considers the series and parallel resistors of thephotovoltaic modules, the bypass diodes as ideal switches and represents theblocking diodes with the Shockley equation, which allow to express the string voltageas an explicit function of the load current by using the Lambert-W function; in thisway it is possible to construct one equation per string for calculating its current for agiven voltage. That procedure is repeated for each string and the current of the fieldis evaluated by adding the currents of all strings. The parameter calculationprocedure evaluates the voltage and current of each active module from the currentand voltage of the string and fits the current equation of a module to theexperimental data. The accuracy of the proposed model was tested experimentallywith a string of two modules obtaining an accuracy improvement near to 50%