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, Δ T [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 V open = 53.17 × Δ T [mV] and an internal resistance of R 0 = 3.88 Ω with a tolerance of Δ R int = 0.13 Ω such that R int = R 0 ± Δ R int = 3.88 ± 0.13 Ω. The measurements done under the maximum output power delivery condition (for the maximum temperature gradient of Δ T = 51 °C) resulted in the maximum output power of P out = 500 mW, as well as in the output current and voltage of I out = 357 mA and V out = 1.40 V, respectively. The load resistance of 3.92 Ω ( V out / I out ) is also in accordance with the measurements because it is located in the range [ μ − σ, μ + σ] Ω, where μ = R 0 = 3.88 Ω and σ = Δ R int = 0.13 Ω. An Agilent multimeter model 34410A with 6½ digits was used for measuring the voltages at the TEG’s output and the respective currents.