# Application of Thermoelectric Generators for Low-Temperature-Gradient Energy Harvesting
## 5 Conclusions  
IoT devices with data acquisition and processing capabilities offer solutions for health condition monitoring, which require on-line data monitoring. However, in high-voltage substations applications, as they are often in remote locations and due to harsh environments, the application of these smart devices remains a challenging task. Therefore, a proper and maintenance-free energy harvesting system is required. Thermal energy harvesting has become a hot topic due to the minimal maintenance required, compactness,  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Current** & \(\mathbf{r_{ac}}\) & \(\mathbf{\Delta T_{Hot-Ambit}}\) & \(\mathbf{\Delta T_{Hot-Cold}}\) & \(\mathbf{P_{Iot-Cold}}\) & \(\mathbf{P_{Iot-Cold}}\) & \(\mathbf{P_{Iot-Cold}}\) & \(\mathbf{P_{Iot-Cold}}\) & \(\mathbf{P_{Iot-Cold}}\) & \(\mathbf{P_{Iot-Cold}}\) & \(\mathbf{P_{Iot-Cold}}\) \\ \multicolumn{1}{c}{**(A\({}_{\text{mm}}\))**} & **(uI/m)** & **(°C)** & **(°C)** & **(W/m)** & **(W)** & **(mW)** & **(mW)** & **(°C/W)** & **(°\%)** & **(°\%)** \\ \hline
136 & 5380 & 20.7 & 3.4 & 99.5 & 0.85 & 1.24 & 0.21 & 3.964 & 0.15 & 0.025 \\
169 & 5448 & 26.1 & 3.9 & 155.6 & 1.32 & 2.50 & 0.34 & 2.914 & 0.19 & 0.026 \\
194 & 5512 & 31.7 & 4.5 & 207.5 & 1.76 & 4.47 & 0.48 & 2.534 & 0.25 & 0.027 \\
226 & 5560 & 37.7 & 5.1 & 284.0 & 2.41 & 7.34 & 0.66 & 2.095 & 0.30 & 0.027 \\
254 & 5622 & 43.7 & 5.7 & 362.7 & 3.08 & 11.2 & 0.84 & 1.841 & 0.36 & 0.027 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Steady-state performance results of the entire system.  
Figure 9: Voltage generated by TEG #1 and the voltage across the battery during a cold start situation using the TEG #1 + DC/DC converter #1 combination.  
and solid-state nature. This research work has analyzed different thermal energy harvesting systems and has conducted several experiments to characterize the behavior of each system for high-voltage transmission applications characterized by very low temperature gradients. This work has analyzed the performance of state-of-the-art of TEGs designed to operate with low temperature gradients intended for IoT systems to be applied in AC and DC tubular busbars found in high-voltage substations. Since the tubular busbars are heated by the Joule effect, there is a small temperature difference between the busbar and the ambient, so the TEG converts this heat flow into useful energy, which is used to supply low-power WSs by means of a DC/DC converter. The results presented in this paper have shown that if a temperature difference of around 5 K can be maintained between the hot and cold sides of the thermoelectric power generation modules, it will drive WSs using two 40 mm \(\times\) 40 mm modules.  
Conceptualization, Y.L., M.M.-E. and J.-R.R.; methodology, J.-R.R.; software, Y.L.; validation, Y.L. and J.S.; formal analysis, M.M.-E. and J.-R.R.; investigation, Y.L., M.M.-E. and J.-R.R.; resources, J.S., M.M.-E. and J.-R.R.; writing--original draft preparation, Y.L. and J.-R.R.; writing--review and editing, M.M.-E.; supervision, J.S. and M.M.-E.; All authors have read and agreed to the published version of the manuscript.  
This research was funded by Generalitat de Catalunya, grant numbers 2021 SGR 00392 and 2020 DI 007.  
Not applicable.  
The authors declare no conflict of interest.