Sustainability of large scale waste heat harvesting using thermoelectric

TL;DR

This paper evaluates the feasibility of large-scale waste heat harvesting using thermoelectric devices, highlighting significant material and environmental challenges due to the high element requirements and CO2 emissions involved.

Contribution

It provides a quantitative analysis of the material and energy requirements for thermoelectric waste heat recovery at scale, emphasizing sustainability issues.

Findings

High temperature exergy requires billions of junctions.

Element requirements exceed current global production.

Significant CO2 emissions make current alloys unsustainable.

Abstract

The amount of waste heat exergy generated globally is 69.058 EJ which can be divided into, low temperature 373 K, 30.496 EJ, medium temperature 373 K to 573 K, 14.431 EJ and high temperature 573 K, 24.131 EJ. These values of exergy have been used to determine the minimum number of pn junctions required to convert the exergy into electrical power. It is found that the number of junctions required to convert high temperature exergy increases from 8.22x10^11 to 24.66x10^11 when the aspect ratio of the legs increases from 0.5 cm^1 to 1.5 cm^1. To convert the low temperature exergy, 81.76x10^11 to 245.25x10^11 junctions will be required depending on the legs aspect ratio. The quantity of alloys containing elements such as Pb, Bi, Te, Sb, Se and Sn required to synthesize these junctions therefore is of the order of millions of tons which means the elements required is also of similar magnitude. The current world production of these elements however falls far short of this requirement, indicating significant supply chain risk. The production of these elements, even if resources are available, will emit millions of tons of CO2 showing that current alloys are non-sustainable for waste heat recovery.