Voltage-Matched Strings using 3-Terminal Tandems: Fundamentals and End Losses

Strings constructed from 3-terminal tandems (3TT) offer the performance benefits of voltage-matching (which reduces sensitivity to spectral variation), but without the subcell voltage isolation required by 4-terminal cells. However, the circuitry for a 3TT string can become complex, making circuit analysis more challenging. Here we illustrate the essential features of “single-polarity” voltage-matched (VM) 3TT strings using representative examples. End losses are intrinsic to this type of string, but can be reduced by minimizing the integers m and n in the VM ratio m/n = Vtop/Vbot, and further mitigated by increasing the string length. This analysis agrees with preliminary experimental results.