Thermoelectric power generation is the premier solid-state technology for low-temperature, greater than approximately 900 K, conversion of heat energy into electrical energy. However, the evaluation, interpretation, and analysis of thermoelectric devices is not straightforward. In this work, we introduce a new device analysis that provides a simple new experimental method to obtain the usual quantifiable metric for device performance, ZTmaximum. The significance of this new method is that it provides a fast experimental method to confirm the validity of basic materials measurements. The new method directly connects basic materials properties to conversion efficiency and, employing differential measurements, minimizes systemic error. We demonstrate the efficacy of this method by 3 separate cases of thermoelectric power generation modules fabricated from different materials a low-cost technology demonstrates ZT 0.4, a commercial module shows ZT 0.7, and a precommercial lead tellurideTAGS technology has ZT 0.7 by the proposed technique.