Thermoelectric generator placed on the human body: system modeling and energy conversion improvements

¹ SATIE, ENS Cachan Bretagne, CNRS, UEB, Avenue Robert Schuman, Campus de Ker Lann, 35170 Bruz, France
² CRISMAT-CNRT ENSICAEN, 6 boulevard Maréchal Juin, 14050 Caen, France

Corresponding author: marianne.lossec@bretagne.ens-cachan.fr

Received: 5 January 2010
Revised: 24 June 2010
Accepted: 28 June 2010
Published online: 17 September 2010

Abstract

This paper focuses on the production of electricity using a thermoelectric generator placed on the human body connected to a dc-dc converter. The small difference in temperature between the hot heat source (e.g. the human body, T_b = 37 °C) and the cold heat source (e.g. ambient air, T_a = 22 °C), associated with a poor quality thermal coupling (mainly with the cold source), leads to a very low temperature gradient at the thermoelectric generator terminals and hence low productivity. Under these use conditions, the present article proposes an analysis of various ways to improve productivity given a surface capture system. Furthermore, we demonstrated, in this particular context, that maximizing the recovered electric power proves to be a different problem from that of maximizing efficiency, e.g. the figure of merit Z. We therefore define a new factor Z_E, depending on the physical characteristics of thermoelectric materials, that maximizes electric power in the particular case where the thermal coupling is poor. Finally, this study highlights the benefit of sub-optimization of the power extracted from the thermoelectric generator to further improve efficiency of the overall system. We show that, given the conversion efficiency of the dc-dc converter, the maximum power point of the overall system is no more reached when the output voltage of the thermoelectric generator is equal to half of its electromotive force.