  We study the physical processes at work at the interface of two
thermoelectric generators (TEGs) thermally and electrically connected in
series. We show and explain how these processes impact on the system's
performance: the derivation of the equivalent electrical series resistance
yields a term whose physical meaning is thoroughly discussed. We demonstrate
that this term must exist as a consequence of thermal continuity at the
interface, since it is related to the variation of the junction temperature
between the two TEGs associated in series as the electrical current varies. We
then derive an expression for the equivalent series figure of merit. Finally we
highlight the strong thermal/electrical symmetry between the parallel and
series configurations and we compare our derivation with recent published
results for the parallel configuration.
