When considering electric energy harvesting from waste heat, two different solutions of direct conversion are possible: pyroelectric and thermoelectric conversions. This paper presents a study of the thermoelectric conversion by two different approaches: analytical and experimental. Furthermore, a brief historical description of the discovery and early years of development of thermoelectricity is presented. The essential objective of this work is to develop a numerical tool that can estimate the output quantities of a thermoelectric converter, without knowing all its features. For this, two analytical models were developed, based on electrical and thermal phenomena occurring within the active element. The results obtained by this model were compared successfully with experiments carried out on an industrial thermoelectric element. Considering the centimetric size of the device (16cm ~2 area), the electrical power recovered by this conversion varies from 16 to 80mW for a temperature difference between 2 and 18°C and according to the load value. In addition, both models transcribe the behavior of the active element with an accuracy of about 10%. In agreement with this, the output voltages reached are of the same magnitude for the models and the experimental values and vary from 0.1 to 0.8V depending on the load connected and the type of convection. Another issue which is discussed for the two cases is that an optimal recovered energy is obtained for a given electric load taking into account the physical characteristics of the considered thermoelectric element. Finally, a conversion efficiency calculation has shown that it is possible to reach 45% of the Carnot efficiency. This denotes the interest to perform load matching to optimize the output power.
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