## 1 Introduction  
Volcanoes are considered one of the most dangerous natural hazards [1]. Nowadays, more than 10% of the global population lives within 100 km of a volcano that has the potential to erupt [2]. Therefore, volcanic vigilance becomes indispensable in any volcanic system of the world, so that the damage caused by the inevitable eruptions can be reduced. Normally, volcanic eruptions are preceded by anomalous signals, known as precursors [3, 4]. Volcanic vigilance consists in the monitoring of these signals in order to, together with knowledge of past activity, predict when, where, and how the next volcanic eruption will occur. For this purpose, due to the diverse nature of the different manifestations of volcanic activity, volcano surveillance requires the combination of different techniques, the data of which needs to be analyzed together. Seismology studies the earthquakes and other generating events of seismic waves [5]; geodesy focuses on the variations in the shape and dimensions of the Earth [6]; geochemistry studies the change in temperature and composition of the volcanic products [7]; gravimetry deals with variations of the gravitational forces [8]; and magnetotellurics analyzes the fluctuations in the electromagnetic fields of the Earth [9]. In order to obtain data, most of the previous techniques use local measurements. There exist some remote methodologies such as GPS, GNSS, InSAR or satellite temperature monitoring [10; 11]. Nevertheless, local measurements are preferred due to their better accuracy and the coverage of all techniques [12]. Among local measurements, two trends can be in turn distinguished: continuous and discontinuous data acquisition [13]. In the former, permanent vigilance stations are installed in key locations, while the latter consists in performing in situ manual measurements. In general, if possible, continuous monitoring is more recommended, due to its lower cost (does not require several people taking measurements) and more information provided. Nevertheless, power supply and communication systems of such stations constitute a challenge [12], since volcanic areas are usually remote, inaccessible, and lack a power grid. This causes that only 30% of active volcanoes have instrumentation to measure their activity [14]. In order to face the previous situation, the most common alternative consists in using photovoltaic panels and, consequently, batteries, so that power supply is ensured during nights, periods of absence of sun, or episodes of volcanic ashes [15; 16]. However, sometimes, depending on the climatology and the specific conditions, the required capacity of the batteries is so high that it is preferred to lose data during some periods, rather than deal with the installation difficulties of an enormous battery in a remote and inaccessible location. This is the case of those volcanoes that record severe snowfalls during long periods in winter such as Mt. Fuji in Japan [17], or that are located at extreme latitudes where the sun does not shine for months, like Deception Island in Antarctica [18]. In the last years, with the purpose of reducing the capacity of the batteries, low-energy devices have proliferated, focusing on both data acquisition and communications. Hence, it stands out the use of systems with embedded Linux, which permit real-time monitoring with a power consumption lower than 2.5 W [16; 18; 19]. These systems are usually combined with communication technologies normally associated with Internet of Things (IoT). For instance, [PERSON] et al. developed a wireless network of thermometers to measure soil temperatures in volcanic areas based on LoRa [20]. LoRaWAN protocol was also chosen by [PERSON] et al., but in this case to control soil radon emissions [21]. Apart from reducing the consumption of the different elements that compose a vigilance station, another solution consists in using an alternative energy source, such as geothermal energy, which presents the advantage of being always available independently of weather.