This work describes an experimental study on the possibilities of harvesting energy from tree trunks in order to power sensor nodes for environmental monitoring, particularly in wild forests. As the trunk of a living tree can be divided into isothermal subvolumes, which are generally referred to as annual rings, and the trunk is a good heat storage material, depending on the tree dimensions and its species, it can potentially offer different temperature gradients according to the tree trunk depths. The hypothesis is to consider the application of this temperature gradient on the faces of a Peltier cell to obtain electrical energy. In order to evaluate this hypothesis, a wireless sensor network was developed for measuring internal temperature of trunks from different trees. The experimental results show that it is possible to obtain a sufficient temperature gradient to harvest energy from tree trunks. Additionally, it is also shown that it is possible to harvest thermal energy during the day and during the night while photovoltaic cell only works under sunlight.

As solar radiation is the most plentiful energy source on earth, thermoelectric energy harvesting emerges as an interesting solution for the Internet of Things (IoTs) in outdoor applications, particularly using semiconductor thermoelectric generators (TEGs) to power IoT devices. However, when a TEG is under solar radiation, the temperature gradient through TEG is minor, meaning that the TEG is useless. A method to keep a significant temperature gradient on a TEG is by using a solar absorber on one side for heating and a heat sink on the other side. In this paper, a compact TEG-based energy harvester that features a solar absorber based on a new class of solid matter, the so-called quasicrystal (QC), is presented. In addition, a water-cooled heat sink to improve the temperature gradient on the TEG is also proposed. The harvester is connected to a power management circuit that can provide an output voltage of 3 V and store up to 1.38 J in a supercapacitor per day. An experimental evaluation was carried out to compare the performance of the proposed QC-based harvester with another similar harvester but with a solar absorber based on conventional black paint. As a result, the QC-based harvester achieved 28.6% more efficient energy generation and achieved full charge of a supercapacitor around two hours earlier. At last, a study on how much the harvested energy can supply power to a sensor node for Smart agriculture during a day while considering a trade-off between the maximum number of measurements and the maximum number of transmission per day is presented.

The Internet of Things (IoT) revolution is getting attention of all kinds of enterprises and industries: from the big ones to the startups. From the energy point of view, deploying IoT devices in urban or industrial environments is not a dramatic problem since electrical outlets and chemical batteries are easily available almost everywhere. However, why not tap into natural resources first? The future may bring an Internet of Natural Things (IoNaT). If so, the agricultural and forestry industries will certainly take advantage of such technology. The question will then be how to power the IoNaT. Chemical batteries are not an environment-friendly option in an agricultural field or in a forest. In this chapter, we suggest different and innovative, natural and easily available energy sources and the main processes to harvest them. The use of these natural and revolutionary technologies may ensure that monitored data could be obtained in a sustainable way.

Thermoelectricity energy harvesting based on the thermoelectric generator (TEG) has had a prominent role in energy harvesting solutions since they have dramatically grown recently due to the existence of significant thermal gradients $\Delta{{\mathrm {T}}}$ in both natural and industrial environments. However, to prove that a given environment is adequate to generate energy is a hard task. In order to early evaluate the potential of a given environment to get enough thermal energy to be converted to electric energy, we propose in this paper an automatic emulation system of thermal energy that can be used with any thermal source in a simple way. Experimental results show that the proposed platform can emulate any thermal gradient pattern, apply this pattern on a TEG and measure the actual electric energy generated by the TEG. An example of application is described, and the results are shown. The example is an experiment to harvest energy from tree trunks.