UR-SolarCap: An Open Source Intelligent Auto-Wakeup Solar Energy Harvesting System for Supercapacitor-Based Energy Buffering
Energy harvesting systems that couple solar panels with supercapacitor buffers offer an attractive option for powering computational systems deployed in field settings, where power infrastructure is inaccessible. Supercapacitors offer a particularly compelling advantage over electrochemical batteries for such settings because of their ability to survive many more charge-discharge cycles. We share UR-SolarCap-a versatile open source design for such a harvesting system that targets embedded system applications requiring power in the 1-10 W range. Our system is designed for high efficiency and controllability and, importantly, supports auto-wakeup from a state of complete energy depletion. This paper summarizes our design methodology, and the rationale behind our design and configuration decisions. Results from the operation and testing of a system realized with our design demonstrate: 1) an achievable harvester efficiency of 85%; 2) the ability to maintain sustained operation over a two week period when the solar panel and buffer are sized appropriately; and 3) a robust auto-wakeup functionality that resumes system operation upon the availability of harvestable energy after a period in which the system has been forced into a dormant state because of a lack of usable energy. To facilitate the use of the system by researchers exploring embedded system applications in environments that lack a power infrastructure, our designs are available for download as an archive containing design schematics, Printed Circuit Board (PCB) files, firmware code, and a component list for assembly of the system. In addition, a limited number of pre-assembled kits are available upon request.