A 2-D numerical circuit model is used to study the effect of weak-diodes on the efficiency of a CdTe thin-film module. Numerical calculations of module-efficiency loss due to weak-diodes of different levels of voltage loss and fractional module area are shown. It is shown that absolute module-efficiency loss Δη (%) varies in systematic fashion with these weak-diode parameters. It was also shown that for given values of fractional area and severity of weak-diodes Δη is a strong function of the distribution pattern. A reliable parameter P to characterize the distribution of weak-diodes is introduced, and its effect on Δη, as well as individual-parameter (FF, VOC) losses, is presented. The partial isolation effect of weak-diodes due to higher transparent-conductive-oxide (TCO) sheet resistance is demonstrated.