Design and Measurement of a 24.5-mW, 33-mWh, 1.8-V-Output Solar Energy Harvester for Bluetooth Sensor Nodes

This paper presents the design and measurement of a solar energy harvester capable of powering a Bluetooth sensor node indefinitely. The harvester consists of a PMIC that integrates the battery charger, maximum power point tracker (MPPT), low-dropout (LDO), and battery over/under-voltage protection. The miniature solar cell harvests sunlight to charge a miniature lithium-ion battery. The harvester has a peak solar cell power output of 24.5 mW, a storage capacity of 33mWh, and an output voltage of 1.8 V. Measurement results show that the harvester successfully powers the load under various conditions including large 7.5-mA transient demand, 40hour long duration without solar energy, and 7-day continuous operation under a dynamically lighted indoor environment. We also demonstrate the harvester powering a Bluetooth module to wirelessly communicate with a smartphone app.