Thermoelectric generation systems for utilizing waste heat and ambient temperature swings have been proposed that would involve temperature differences on the order of 1-10 K. The inherently low thermodynamic efficiency of such systems requires that a relatively large amount of heat pass through the system for a given rate of electricity production. The coupled design of the thermoelectric module and the hot side and cold side heat exchangers is fundamental to the creation of a useful device. An approximate optimal design is derived that is applicable to systems with a small temperature difference between the reservoirs, For a fixed thermal resistance in the heat exchangers, the optimal configuration splits the total temperature drop evenly between the thermoelectric module and the heat exchangers. For heat exchanger thermal resistances that vary with time, optimal configuration are derived for linear, sawtooth function and sinusoidal variations. The application of these equations to a typical system design is described. (C) 2000 Elsevier Science Ltd. All rights reserved.