Materials sustainability of thermoelectric generators for waste heat utilization

Abstract

Amount of waste heat exergy generated globally (~69.058 EJ) can be divided into low temperature <373 K, 30.496 EJ; medium temperature 373–573 K, 14.431 EJ; and high temperature >573 K, 24.131 EJ. The minimum number of thermoelectric pn-junctions required to convert this high-temperature exergy into electrical power using currently known best materials is found to increase from 8.22 × 10¹¹ to 24.66 × 10¹¹ when the aspect ratio of the legs increases from 0.5 to 1.5 cm⁻¹. To convert the low-temperature exergy, 81.76 × 10¹¹ to 245.25 × 10¹¹ junctions will be required. The amount of alloys required to synthesize these is of the order of ‘millions of tons’, which means the elements Bi, Te, Pb, Sb, Sn and Se required are also of similar magnitude. The current production of these elements, however, falls far short of this requirement by several orders of magnitude, indicating significant materials supply chain risk. The production of these elements and devices, even if resources are available, will emit millions of tons of CO₂ showing that current alloys are non-sustainable. It therefore becomes clear that alternate materials with low embodied energy, emissions and toxicity footprint, as well as minimal supply chain risk, need to be pursued.