Investigation of Pulsed Thermoelectric Performance by Impedance Spectroscopy

A widespread use of thermoelectric technology usually collides with their limited efficiency. Efforts to overcome this limitation face difficulties in decoupling the thermal conductivity from the electrical conductivity (because of the Wiedeman-Franz law) and to obtain simultaneously high values of electrical conductivity and Seebeck coefficient (because of the Pisarenko relation). Some efforts to circumvent partially these limitations have been oriented to non-equilibrium solutions. These have been proved for cooling and in the last decade have been proposed as a means to increase power conversion from time varying thermal gradients. Another possibility that has been explored is the enhancement of thermal conversion efficiency obtained by periodically modulating the electronic load applied to a thermoelectric generator. Using impedance spectroscopy and pulsed loads applied to thermoelectric modules under adiabatic and non-adiabatic test conditions, we explored the role of several experimental parameters on the output power and conversion efficiency. We discuss operating limits and realistic perspectives of thermoelectric pulsed load application. Moreover, we examined the difference between air and vacuum impedance measurement for a thermoelectric module figure of merit determination and discussed the possible use of impedance spectroscopy as a tool for the study of thermal contact resistance by means of direct measurements under operating conditions.