Long-Range Radio for Underground Sensors in Geothermal Energy Systems

The paper presents the design of a temperature monitoring system in a very harsh environment, such as Shallow Geothermal Systems (SGS), where the information of underground temperature is necessary to assess the thermal potential of the soil, for maximizing the efficiency of the SGS. The challenge is to get information at different depths (sometimes up to −100 m), to transmit data wirelessly in rural areas where conventional wireless connections (e.g. WiFi, GSM) are not guaranteed and energy availability poses severe limits. Our design exploits a recent new modulation protocol developed for long-range transmission, at the minimum energy cost, and a two-tier hardware architecture for measuring underground temperature. Aggressive duty cycling permits to achieve lifetime of several years. Experimental results demonstrate the utility of such a system during the design and the operational activity of a SGS.