  There are few exact results on optimal power conditions for a thermoelectric
generator in the presence of both external and internal
irreversibilities---modelled as non-ideal thermal contacts and Joule heating,
respectively. Simplified cases, where only one kind of irreversibility is
assumed, yield some well-known expressions for efficiency at maximum power
(EMP), such as Curzon-Ahlborn efficiency for endoreversible model. In this
work, we analyze situations under the simultaneous presence of internal and
external irreversibilities. To simplify, we neglect heat leaks, and each kind
of irreversibility is assumed only on the side of one of the thermal contacts.
We also present the symmetric case---where each kind of irreversibility
contributes with equal strengths towards the side of each thermal contact. We
show the bounds satisfied by EMP in each of these regimes and compare its
properties for thermal impedence matching and close to equilibrium, where we
find step-wise changes in EMP.
