Effect of Shunts on Thin-Film CdTe Module Performance

A 2-D numerical circuit model is used to analyze the impact of shunts on basic performance parameters of a CdTe thin-film module. A numerical estimate of module-efficiency loss in the worst-case scenario due to shunts of different severity and fractional module area is presented. It is shown that absolute module-efficiency loss Delta eta (%) varies in systematic fashion with these shunt parameters. Estimates of Delta eta based on simple area-weighted efficiency are typically low by 3-4 times. Furthermore, the distribution pattern of shunts over the module plays a significant role in the module loss. A reliable parameter P to characterize the distribution of shunts is introduced, and its effect on module-efficiency loss, as well as individual-parameter (FF, V-OC and J(SC)) losses, is shown. Furthermore, higher transparent-conductive-oxide (TCO) sheet resistance is shown to increase shunt isolation and consequently mitigate the efficiency decrease.