Waste Heat Harvesting Using Thermoelectric Generators—Materials Sustainability Assessment

The process of conversion of energy from primary carriers to different forms of end use always results in losses. The major form of energy loss is ‘heat’ and it has been found that almost 70 % of primary energy amounting to ~ 340 PJ is wasted in the form of heat. Among the several methods of recovering and converting this waste heat, thermoelectric conversion has been prominent. The recent development of several new materials with high figure-of-merit requires that their potential from different perspectives needs to be evaluated. The objective of this work therefore has been to estimate the materials requirement, their environmental impact and also assess the materials supply chain risk. Since the waste heat ranges in intensity from < 100 C to > 300 C, the thermoelectric materials required will be different for different ranges. Hence the waste heat has been classified into 3 separate categories – low < 373 K, medium 373 K – 573 K and high > 573 K. The candidate materials which exhibit the highest figure-of-merit in these temperature ranges have been considered for evaluation. It is found that elements such as Bi, Te, Sn, Co will be required in kilo tons capacity which pose supply chain risk. Also, processing the ores of these elements can have significant environmental impact in terms of embodied energy and CO₂ emissions. All these aspects will be discussed in detail in this paper.