Method for analyzing series resistance and diode quality factors from field data Part II: Applications to crystalline silicon

The method described in a prior journal publication [1] is applied to the determination of module series resistance and diode quality factors for several crystalline silicon (c-Si) technology photovoltaic (PV) modules. This method makes use of the functional dependence of the slope of the current-voltage (I-V) characteristics at open circuit (R-oc) against the reciprocal of the short-circuit current density (J(sc)), from multiple I-V curves taken under variable illumination. It is shown that calculations of the series resistance for six modules yield values in the range 1.0-1.6 Omega-cm(2), expressed in unit-cell area terms. The derived values for the series resistance (R-s) determined from the data are investigated for their effect on the module fill factor (FF) values and their dependence at higher light intensity levels. The diode quality factors also derived from the same data are shown to be somewhat larger than those obtained from the more canonical method - slope of the fit of the open-circuit voltage (V-oc) versus logarithm of J(sc). The differences between the two methods are explored within a two-diode model for c-Si. Deriving average values of diode quality factors for series-connected cells using either method is shown to exhibit problematic issues. (C) 1999 Elsevier Science B.V. All rights reserved.