*3.2. TEG Modules*

In the systematic search carried out, 29 articles related to TEG modules were found. We observed that one of the most commonly addressed topics is the efficiency/cost relationship presented by TE materials. This aspect is usually approached from several points of view, such as cost reduction, varying the TE material, or through a design of the TEG module that preserves its efficiency. However, another important factor that must be taken into account is the sustainability of the modules, which ranges from the analysis of their useful service life to the study of their final disposal. In Figure 6, the classification of the articles according to their content can be observed. These were classified by costs, sustainability, efficiency and modeling. In this graph, one article as found classified involving costs [42]; seven involving efficiency [27,39,44,49,52,56,57]; one in modelling [48]; and six in sustainability [18,23,37,38,50,53]. In the common areas D, E, F, G, H, it was not found papers between costs and sustainability and costs and modelling in zones D and G respectively. Between costs and efficiency, zone E, three articles were found [18,22,55]; while for zone F, between efficiency and modelling, seven were found [28,34,35,41,45–47]. Finally, ten references were found in thermoelectric modules, zone H [16,21,30–32,36,40,41,43,55].

**Figure 6.** Classification of the articles found according to the results obtained for thermoelectric modules.
