Theoretical limits of thermoelectric power generation from exhaust gases

The recovery of energy from exhaust gases using thermoelectric generators is of growing interest. The electrical loading of the thermoelectric system impacts the amount of energy that can be recovered. This paper presents a model for the theoretical limit of electrical power generation that provides optimal electrical loading conditions for a given exhaust stream and system configuration. The analysis of a sample heat recovery configuration indicates that the simple isothermal modeling approach often applied to individual thermoelectric leg pairs is not sufficient to optimize power generation when a significant amount of energy is removed from the exhaust stream via a sequence of leg pairs. The analysis establishes that ZT, the thermoelectric figure of merit, is not a sufficient metric to describe system level performance. The analysis predicts that there is an optimum number of thermoelectric leg pairs that maximize the power extracted for any system, and that adding more leg pairs beyond this optimum can degrade system performance. The theoretical limit for power generation is compared to proposed electrically loading strategies found in the literature. The developed model has low computational load and is suitable for use in system optimization models.