“…Alegría et al [12] characterized in laboratory a GTEG for medium temperature geothermal anomalies (MT) without moving parts, and were able to install it in Timanfaya National Park, demonstrating the feasibility of the technology for the first time in real conditions, working for more than 2 years in perfect operation without the need for maintenance and generating between 2.09 and 2.78 W per module [22]. Thank to this development, they could finally install a thermoelectric generator in the area with the highest temperature (HT) geothermal anomalies recorded in Lanzarote, reaching a generation of 4.5 W per module, 36 W total, working also without maintenance and generating more than 280 kWh of energy per year [23]. These include thermosyphons as heat exchangers, which makes them totally passive, with no auxiliary consumption, and are the only geothermal thermoelectric generators installed an operating in a real geothermal field.…”