A procedure is detailed in which the effects of series resistance and diode quality factors are separately analyzed and quantified using current-voltage (IV) data gathered in situ from three photovoltaic (PV) modules. Series resistance losses are implicated to be largely responsible for reduction in the fill factor values for intensities of 60% of one sun or greater. The data presented are from one cadmium telluride (CdTe) and two amorphous silicon (a-Si) modules and were taken in held deployment with a data acquisition system.