Solar energy harvesting for autonomous field devices

The energy required to power an autonomous field device can be drawn from its environment by means of energy harvesting. Outdoors, one abundant and ubiquitous source of energy is solar irradiation, which can be reliably converted into electricity by solar cells. In principle, this is also true indoors if artificial light sources produce sufficient optical irradiation. Different solar cell materials can play off their individual strengths in these different use cases. Since ambient optical irradiation usually is an intermittent phenomenon, a solar powered field device has to include an energy storage solution for bridging gaps that occur in energy harvesting. In this study, different solar cell materials and energy storage solutions are discussed and evaluated quantitatively according to data sheet information. According to calculations for an assumed continuous power consumption of an autonomous field device of 1 mW for a period of 10 years, a solar panel of 4 × 4 cm² in the outdoor case and 20 × 20 cm² in the indoor case can deliver the required energy. Along with an energy storage system consisting of a 100 F supercapacitor and a primary backup cell, solar energy harvesting for autonomous field devices seems technically feasible.