Characterization of thermoelectric generators by measuring the load-dependence behavior

Abstract

Solid-state thermoelectric generators (TEGs) based on the Seebeck effect to convert temperature gradients, DT [K], into electrical energy are being used in an increased number of stand-alone microsystems applications. These generators are composed by at least one pair of p- and n-type thermoelectric elements with high figures-of-merit, ZT, to perform such a conversion. The exact behavior knowledge of generators is mandatory in order to decide the most suitable for the target application. The focus of this paper is to present a methodology to characterize thermoelectric generators, by measuring their behavior for different types of loads. The measurements were done with the help of commercial thermoelectric generators (thermoelectric modules TEC1-12707) and a measurement setup composed by a controlled hot-plate, a controlled cooling fan (above an heat dissipator), a set of two thermistors for measuring the temperature, a personal computer with the data acquisition board model NI USB-6009 and the LabView software from National Instruments for acquiring the measures and for controlling both the hot-plate and the cooling fan. The thermoelectric modules TEC1-12707 was selected due to its compact size (e.g., 40 mm 40 mm) and because it can withstand temperatures up to 450 K without degrading the quality of measurements. A SPICE model for thermoelectric modules TEC1-12707 was also obtained: an open-circuit voltage of Vopen = 53.17 DT [mV] and an internal resistance of R0 = 3.88 X with a tolerance of DRint = 0.13 X such that Rint = R0 ± DRint = 3.88 ± 0.13 X. The measurements done under the maximum output power delivery condition (for the maximum temperature gradient of DT = 51 C) resulted in the maximum output power of Pout = 500 mW, as well as in the output current and voltage of Iout = 357 mA and Vout = 1.40 V, respectively. The load resistance of 3.92 X (Vout/Iout) is also in accordance with the measurements because it is located in the range [l r, l + r] X, where l = R0 = 3.88 X and r = DRint = 0.13 X. An Agilent multimeter model 34410A with 6½ digits was used for measuring the voltages at the TEG’s output and the respective currents.