Effects of electrode size on the voltage of a tree-based energy generator

Abstract

A standing tree and its surrounding soil form a sustainable energy generator, which is expected to decrease the need for in-the-field battery changes of low-power sensors used in forests, thereby enhancing forest monitoring technologies. Although various tree-powered circuits and sensors have already been invented, the low voltage of such a generator still causes great difficulty in energy harvesting and utilization. Hence, a key issue that must be addressed is the increasing voltage level. A larger electrode may generate a higher voltage level. However, the relationship between the electrode size and voltage remains unclear. Moreover, larger electrodes will incur higher costs and worsen portability. Therefore, this study aims to preliminarily ascertain the effect of the electrode size on voltage and to provide a reference for optimally using such a generator. Six plate-shaped ground electrodes of different side lengths were used to measure the tree-soil voltage. The measured data show that voltage has a logarithmic relationship with the effective surface area of the ground electrode. With the increasing area of the electrode, the voltage rises by at least 57% relative to the initial value; however, its growth rate declines markedly. Therefore, a larger electrode size is not always better for a generator when considering efficiency, cost, and portability. In this study, an electrode size of 10 cm × 10 cm × 0.3 cm was found to be optimal.