Hybrid RF-Solar Energy Harvesting for IoT

This work studies hybrid radio frequency (RF)-solar energy harvesting, which stacks a layer of radio frequency energy harvester (RFEH) beneath a layer of solar panel, with a boost converter combining them. The aim is to minimize the size of the whole energy harvester, while acquiring a sufficient amount of energy for realizing net-zero energy Internet of Things (IoT). Driven by this, a novel patch antenna is designed and fabricated with a single-stage rectifier, forming a compact-sized RFEH (3.5cm by 5cm) with a gain of 5.6 dBi. To the best knowledge of the authors, this is the highest gain that has been achieved with a similar size of RFEH in the existing literature. A hybrid RF-solar energy harvester is built upon the newly designed RFEH and an off-the-shelf solar panel with a similar size (5cm by 5cm). Experimental results show that the hybrid energy harvester can reduce the charging time by up to about 60% in comparison to a stand-alone solar panel. The hybrid energy harvester spends less than 50s to fully charge a 0.01 F supercapacitor, which can store 125mJ and support an IoT device to operate at a low level of power consumption (∼1 mW) for 125s. This indicates that the hybrid energy harvester is capable of supporting such an IoT device to work continuously.