**Nomenclature**

**Figure 14.** Percentage of heat loss through insulation for different heat powers in the case of introducing heat extenders.

In summary, losses due to thermal bridges definitely need to be taken into account: around one-fourth of the power provided from the source goes through the insulation instead of the

In order to decrease the thermal losses, it has been demonstrated that it is better to increase the thickness of the insulation, despite adding two additional contacts. Among the materials studied, the best one is acrylic wool. Nonetheless, air (equivalent to not adding any insulation) should be considered, since the cost is reduced and there is not such a significant difference among them. However, it presents the disadvantage of a more complicated assembly.

Although the assembly is not generally considered in the optimization of thermoelectric generators, the present chapter has demonstrated that it is an aspect that cannot be forgotten since it deteriorates the performance of generators. Thus, the assembly needs to incorporate thermal interface materials that counteract microscopic imperfections, being graphite sheets the most recommended one between the studied. In order to ensure this microscopic contact and reduce the temperature drop that appears in the interface, it is also important to apply some pressure to the assembly. The easiest way to achieve this is the use of screws. Pressure measurement films have shown that each module needs to have its own tightening. Assemblies that share this tightening can cause a contact in only some parts of the module. However, the implementation of these screws has a counter effect: they represent a thermal bridge themselves and part of the heat is lost through them. Therefore, the insertion of nylon rings is recommended. The other important source of losses due to thermal bridges occurs between the heat exchangers, since the distance between them is too small. Placing an insulating material between the exchangers slightly reduces the losses, but it is better to

thermoelectric modules. As a consequence, the generation is reduced.

**5. Conclusions**

138 Bringing Thermoelectricity into Reality


