Acronyms

converted into electrical power by the TEG. A heat sink rejects the excess heat at the

Due to the development of the thermoelectric materials, a solar TEG with an incident flux of 100 kW/m<sup>2</sup> and a hot side temperature of 1000°C could obtain 15.9% conversion efficiency. The solar TEG is very attractive for standalone power conversion. The efficiency of a solar TEG depends on both the efficiency with which sunlight is absorbed and converted into heat, and the TEG efficiency η TEG. Furthermore, the total efficiency of a solar TEG is also influenced by the heat lost from the surface. The efficiency of solar TEG systems is relatively small due to the low Carnot efficiency provoked by the reduced temperature difference across the TEG and the reduced ZT [116]. Its improvement needs to rise temperature differences and to develop new materials with high ZT like nanostructured and complex bulk materials (e.g., a device with ZT = 2 and a temperature of 1500°C would lead to obtain a conversion efficiency about 30.6%) [117]. According to the literature survey, both residential and commercial applications gain much more interest in the regions of incident solar radiation of solar TEGs. This can be explained by the fact that most of the heat released at the cold side of the TEG can be used for domestic

Most TEG applications have been designed for autonomous operation within a local system. Of course, the TEG output may be connected to different types of loads. In general, a TEG can be seen as a renewable energy power generation source that supplies an autonomous system or a grid-connected system. To be suitable for grid connection, the TEG needs an appropriate power conditioning system. This power conditioning system has to be a power electronic system, with specific regulation capabilities, different with respect to the ones used for solar photovoltaic and wind power systems [114], because the TEG operating conditions are different with respect to the other renewable energy sources. Molina et al. [118] proposed a control strategy to perform energy conversion from DC to AC output voltage, which maintains the operation of the thermoelectric device at the MPP. In the same proposal, active and reactive power controls are addressed by using a dedicated

This chapter has addressed the structures and applications of TEGs in various contexts. It has emerged that the TEG is a viable solution for energy harvesting, able to supply electrical loads in relatively low-power applications. The TEG efficiency is also typically low. Thereby, the advantages of using TEG have to be found in the characteristics of specific applications in which there is a significantly hightemperature difference across the TEG system, and other solutions with higher efficiency cannot be applied because of various limitations. These limitations may be the relatively high temperatures for the materials adopted, the strict requirements on the system to be used (regarding the type of operation, emissions of pollutants, the position of the device during operation or noise). In these cases,

In particular, the use of TEGs is entirely consistent with the provision of green energy through energy harvesting from even small temperature differences. Some low-power applications have been identified on electronic circuits, sensors, waste heat recovery, residential energy harvesting and automotive systems. In other

TEGs may be fully competitive with the other solutions.

cold junction of the TEG to keep a proper ΔT across the TEG [115].

hot water and space heating [115].

3.2.6 Grid integration of TEG

Green Energy Advances

power conditioning system.

4. Conclusions

26


## Symbols


