Thermoelectric generators: from design to applications

Recovering waste heat to generate electricity on on-board systems, and generating electricity in areas or locations not connected to a centralized power generation system, are important issues in today's environmental context. The thermoelectric effect is one way of contributing to the production of electricity from heat.

Thermoelectric generators consist of a set of thermoelectric modules inserted between two heat exchangers. Each thermoelectric module is then made up of several dozen to hundreds of pairs of semiconductor materials, enabling part of the heat passing through them to be converted directly into electrical energy.

For many years, thermoelectric generators were confined to space applications: their extreme reliability justified their use to supply electricity to the vast majority of probes sent into space (Voyager, Apollo, Pioneer, Curiosity...). However, their high cost and low efficiency have been a brake on their development for more common applications. The arrival on the market in 2015 of new thermoelectric modules offering extended operating ranges, using low-cost, non-toxic materials with a small ecological footprint, opens up immense prospects for manufacturers.

There are three main obstacles to the development of thermoelectric generators: thermoelectric materials, the production of thermoelectric modules and the integration of modules into systems to create efficient thermoelectric generators.

At present, many laboratories are studying new solid or nanostructured materials to improve performance and reduce costs. Until recently, the only material available was bismuth tellurium (Bi ₂ Te ₃ ), with interesting performance characteristics, but in limited quantities (rare materials). Very recently, laboratories have announced low-cost, large-scale production methods for new materials including skutterudites, Half-Heuslers, oxides as well as silicon-based materials. In addition, some very promising performance materials have recently been announced. However, from a medium-term industrial perspective, it is much more sensible to study the prospects offered by materials that are reaching the module production stage, with performances close to those of current bismuth telluride, but which are compatible with our environmental requirements, have wider operating temperature ranges, are lighter, available in very large quantities and should enable us to develop economically profitable thermoelectric generators in the short to medium term.

Electricity generation using thermoelectric modules requires optimization of the entire chain, from the thermal energy generator (hot source and cold source)...