# IoT Sensor Challenges for Geothermal Energy Installations Monitoring: A Survey
## 4 Research Challenges
### Technological Innovations  
The process of constructing an underground geothermal structure requires many technological components. Most of these components do not support direct monitoring, and deploying sensors in existing installations is therefore problematic. The next generation of components could integrate physical sensors directly into equipment. A solution such as this not only permits IoT monitoring but also provides a sensory interface for any type of analytical equipment, such as DTS technology. In principle, components with embedded sensors add value at minimal cost. Technological improvements would involve the installation of optical fibres directly into the underground geothermal structure and the positioning of temperature sensors in the borehole at various depths. These improvements have the potential benefit of optimizing the efficiency of the installation. While this solution addresses certain aspects of the problem, such as improving functionality or performance, it does not still provide a comprehensive solution for maintenance or replacement requirements. In order to ensure sustained effectiveness, it is crucial to consider the high reliability of components involved. Moreover, a key expectation for this solution is its ability to support long-term deployment without significant interruptions or failures.  
Energy harvesting transducers can power IoT sensors, but the transducer design must be optimized and aligned with the installation to establish the best energy gains. Thermoelectric generators are a promising technology, but they must be deployed in environments with effective temperature gradients. Temperature gradients for thermoelectric generator purposes are found in environments that fluctuate between medium and ambient temperatures, between warm and cold branches, and between shallow soil (50 cm below ground) and ambient air.  
Underground monitoring generally faces problems with data transmission. Regular connections with the cloud can be solved in two ways: a transmission antenna can be placed on the surface, or new types of underground antennae suitable for IoT communications must be developed.  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Energy Harvesting Method** & **Application** & **Features** \\ \hline Thermoelectric generator & Underground IoT & Fixed to the current technology \\ Water pipeline energy harvesting & IoT sensors near pipes & Inside pipe \\ Solar and wind & IoT sensors located on the ground & External technology \\ \hline \hline \end{tabular}
\end{table}
Table 12: List of energy harvesting methods suitable for powering sensors used to monitor underground geothermal structure parameters.  
The final research challenge involves innovating the communication interface and cloud data processing. Computationally limited, low-power IoT nodes require effective data transmission solutions that can be delivered through edge computing techniques or event-based approaches (Table 13).  
Edge computing allows metadata analysis in situ and provides significant benefits for data transmission; for example, IoT nodes monitoring a geothermal energy installation conserve energy and resources by transmitting data only if a hazardous state arises. The data transmission time and the volume of data stored in the cloud are reduced by storing raw sensor data locally, and the use of cloud computational resources is minimized.  
IoT monitoring systems designed for the real-time collection of data from geothermal energy installations can also be optimized with edge computing data compression methods to reduce the total volume of transmitted data. Truncated data can also be uploaded when energy for transmission is limited, followed by detailed data transmission in the future when energy is sufficient.