Experimental Evidence of the Viability of Thermoelectric Generators to Power Volcanic Monitoring Stations

Abstract

Although there is an important lack of commercial thermoelectric applications mainly due to their low efficiency, there exist some cases in which thermoelectric generators are the best option thanks to their well-known advantages, such as reliability, lack of maintenance and scalability. In this sense, the present paper develops a novel application in order to supply power to volcanic monitoring stations, making them completely autonomous. These stations become indispensable in any volcano since they are able to predict eruptions. Nevertheless, they present energy supply difficulties due to the absence of the power grid, the remote access, and the climatology. As a solution, this work has designed a new integral system composed of thermoelectric generators with high efficiency heat exchangers, and its associated electronics, developed thanks to Internet of Things (IoT) technologies. Thus, the heat emitted from volcanic fumaroles is transformed directly into electricity with thermoelectric generators with passive heat exchangers based on phase change, leading to a continuous generation without moving parts that powers different sensors, the information of which is emitted via LoRa. The viability of the solution has been demonstrated both at the laboratory and at a real volcano, Teide (Canary Islands, Spain), where a compact prototype has been installed in an 82 °C fumarole. The results obtained during more than five months of operation prove the robustness and durability of the developed generator, which has been in operation without maintenance and under all kinds of meteorological conditions, leading to an average generation of 0.54 W and a continuous emission over more than 14 km.

Keywords: LoRa; autonomous; geothermal; heat pipe; power supply; thermoelectric generator; volcano surveillance.

Figure 1

Schematics of a geothermal thermoelectric generator (GTEG) with heat pipes as heat exchangers.

Figure 2

Designed thermoelectric generator composed of two thermoelectric modules and heat pipes as heat exchangers.

Figure 3

Thermal resistance of the cold side heat exchanger for different heat fluxes, considering natural and forced convection.

Figure 4

Thermal bath used as heat source in the laboratory experiments to determine the power generated by the designed prototype.

Figure 5

Voltage (left axis) and power generated (right axis) of the two thermoelectric modules studied, M1 and M2, with respect the intensity. The values correspond, from left to right, to open-circuit (OC), $4.7$ $\Omega$, $3.2$ $\Omega$, $2.2$ $\Omega$, 1 $\Omega$ and short-circuit (SC).

Figure 6

Diagram of the electronics installed with the prototype, which represents the node of the LoRa communication system.

Figure 7

Schematics of a communication system implemented with LoRa.

Figure 8

Detail of the protection boxes to avoid corrosion in the PCB.

Figure 9

Prototype installed at Teide volcano on December 2019, composed of 4 thermoelectric modules.

Figure 10

Location of the prototype node and the gateway, and their associated elevation profile. Images taken from Google Earth ©.

Figure 11

(a) Temperature of the ground T_ground, the hot and the cold side of two thermoelectric modules M1 and M2 (T_H and T_C) and the ambient T_amb, (b) power, (c) voltage and (d) intensity measurements during typical operation.

Figure 12

(a) Temperature, (b) power, (c) voltage and (d) intensity measurements during several hot days.

Figure 13

Ambient temperature $T_{amb}$ (left axis), power generated by M2 and total generation (right axis) between 21 and 23 May 2020.

Figure 14

(a) Temperature, (b) power, (c) voltage and (d) intensity measurements during several cold days.

Figure 15

Power generated by M2 versus the temperature difference between their sides $\Delta T=T_H-T_C$ between 19 December 2019 and 20 August.