Policies for predictive energy management with supercapacitors

This paper presents an algorithm to dynamically determine the maximum supported uniform demand for energy of sensor nodes powered by energy harvesters using supercapacitors as energy buffers. Knowledge about the maximum uniform consumption is required to adapt the sensor node´s duty cycle or task schedule to achieve uniform, utility-maximizing, and depletion-safe operation. Our algorithm makes use of a supercapacitors´ relationship between state-of-charge and voltage, is particularly designed to handle the non-linear system model, and is lightweight enough to run on low-power sensor node hardware. We define three energy policies, evaluate their performance using a real-world solar-harvesting trace, and analyze the influence of the supercapacitor´s capacity and errors of the energy forecast.