  We study how maximum output power can be obtained from a thermoelectric
generator(TEG) with nonideal heat exchangers. We demonstrate with an analytic
approach based on a force-flux formalism that the sole improvement of the
intrinsic characteristics of thermoelectric modules including the enhancement
of the figure of merit is of limited interest: the constraints imposed by the
working conditions of the TEG must be considered on the same footing.
Introducing an effective thermal conductance we derive the conditions which
permit maximization of both efficiency and power production of the TEG
dissipatively coupled to heat reservoirs. Thermal impedance matching must be
accounted for as well as electrical impedance matching in order to maximize the
output power. Our calculations also show that the thermal impedance does not
only depend on the thermal conductivity at zero electrical current: it also
depends on the TEG figure of merit. Our analysis thus yields both electrical
and thermal conditions permitting optimal use of a thermoelectric generator.
