2004 35th Annual IEEE Power Electronics Specialists Conference Aachen, Germany. 2W4 A Novel Modeling Method for Photovoltaic Cells Weidong Xiao William G. Dunford Antoine Capel University of British Columbia University of British Columbia Vancouver, BC Canada Vancouver, BC Canada Tarragona,Spain weidongx@ece.ubc.ca wgd@ece.ubc.ca antoine.capel I @wanadoo.ti llniversity Rovira i Virgili Absfracr-The mathematical description of current-voltage characteristics for photovoltaic cells are generally represented by a coupled nonlinear equation, which is diliicult to solve by analytical methods. In this paper, a novel modeling process is proposed to configure a computer simulation model, which is able to demonstrate the cell’s output features in terms of environment changes in irradiance and temperature. Based on a simplified single-diode model, the parameters are determined in the sense of minimum model error and temperature effect. It is tested to simulate three popular types of photovoltaic panels made of different materials, CIS thin film, muti- crystalline silicon, and mono-crystalline silicon. The effectiveness of this approach is evaluated through comparison of simulation results to the data provided by product’s manufacturer. NOMENCLATURE A Ideality factor y Charge on an electron AM Airmass I+, Photo current G. insolation (W/m’) k Boltnnan wnstant C, Standard insolation T Cell temperature (iOOOW/m’) (degrees Kelvin) I, Saturation current V, Thermal voltage (volt) STC Standard test condition T, Standard temperature (29810 I. INTRODUCTION The performance of solar cell is normally evaluated under the standard test condition (STC), where an average solar spectrum at AM I .5 is used, the irradiance is normalized to 1000W/m2, and the cell temperature is defined as 25%. To satisfy the requirement of temperature and insolation in STC, the test usually needs specified environment and some special testing equipment, such as an expensive solar simulator. Simple experiments may not be sufficient to reproduce the electrical characteristics of solar cell accurately. In this study, the modeling method is based on the specification data provided in the manufacturers’ datasheets. The traditional equivalent circuits of a solar cell represented by a current source in parallel with one or two diodes are shown in Fig.1. The single-diode model [I] includes four components: a photo current source, a diode parallel to the source, a series resistor R, and a shunt resistor Rp. In double-diode model [2] shown in Fig.l(b), an additional diode is added for better curve fitting. In most cases, it is difficult to determine the 5 parameters in single-diode model and 6 parameters in double-diode V rr + I (b) Fig. I The cell equivalent circuits: (a) the single-diode model; (b) the double-diodemodel model mathematically, due to the exponential equation of a p-n diode junction. In [I], the solar model was developed through the coupled multi-physical processes of photovoltaic energy conversion. In 121, the Levenberg- Marquardt method was chosen to solve the double- exponential model equation. To avoid the modeling sophistication, a datzi-based approach is presented in this paper. Some researchers [3],[4] on photovoltaic models use constant parameters (i.e. ideality factor A, series resistance R, and shunt resistance R,,), which result in modeling inaccuracy. In realiiy, these parameters vary with the temperature change. To prevent this problem, this proposed modeling method considers temperature effect on the important parameters of solar cells. The modeling process is divided into three steps. First, the simulation modet. is presented and the parameters are determined. Second, a computer simulation model is created to illustrate the electrical features of a solar cell. Finally, the accuracy of modeling method is evaluated through comparison of simulation results to the practical data. 11. MODELING This model requks four parameters derived from data that can be obtained (iom commercial photovoltaic modules under three condition:jshort circuit current (Isc), open circuit 0-7803-8399-0/04/$20.00 02004 IEEE. 1950