Novel Measurements and Analysis for Thermoelectric Devices

Abstract

Thermoelectric power generation is the premiere solid-state energy conversion technology for two very interesting niche applications: (1) low-temperature, ΔT < ~ 700 K, conversion of heat energy into electrical energy and (2) extremely small geometrical form factor cooling and refrigeration. However, evaluation, interpretation, and analysis of thermoelectric (TE) devices are not straightforward. In this work, we introduce two new methods of analyses that provide new simple experimental methods to obtain validation of TE device performance. For cooling devices, we introduce a new test where small ΔT divergence from room temperature (ΔT< 20 K) is determined in the range where ΔT changes linearly with respect to current. The test compares ΔT and the transient cooling/heating with theoretical predictions based on measured properties and thus can confirm materials’ measurements with very high accuracy. The second new analysis and empirical test allow for directly determining and, hence, validating TE figure of merit ZT_max. The significance of this new method is that it provides fast experimental method to confirm the validity of basic materials’ measurements. The measured conversion efficiency is used to extract TE device ZT_max which can be compared to individual material ZT_max measurement claims. Therefore, this approach minimizes systemic error. We demonstrate the efficacy of this method by three cases of thermoelectric power generation modules (TEGs) fabricated from different materials: low-cost module produced by the former Alphabet Energy that demonstrates ZT = 0.4, commercial module from Marlow that shows ZT = 0.7, and specialty module made by NASA JPL that has ZT = 0.95.