Capacity over capacitance for reliable energy harvesting sensors

Abstract

Today, most sensors that harvest energy from indoor solar, ambient RF, or thermal gradients buffer small amounts of energy in capacitors as they intermittently work through a sensing task. While the utilization of capacitors for energy storage affords these systems indefinite lifetimes, their low energy capacity necessitates complex intermittent programming models for state retention and energy management. However, recent advances in battery technology lead us to reevaluate the impact that increased energy storage capacity may have on the necessity of these programming models and the reliability of energy harvesting sensors.In this paper, we propose a capacity-based framework to help structure energy harvesting sensor design, analyze the impact of capacity on key reliability metrics using a data-driven simulation, and consider how backup energy storage alters the design space. We find that for many designs that utilize solar energy harvesting, increasing energy storage capacity to 1-10 mWh can obviate the need for intermittent programming techniques, augment the total harvested energy by 1.4-2.3x, and improve the availability of a sensor by 1.3-2.6x. We also show that a hybrid design using energy harvesting with a secondary-cell battery and a backup primary-cell battery can achieve 2-4x the lifetime of primary-cell only designs while eliminating the failure modes present in energy harvesting systems. Finally, we implement an indoor, solar energy harvesting sensor based on our analysis and find that its behavior aligns with our simulation's predictions.

Continuous Sensing on Intermittent Power

“…Figure 12 captures CIS availability on a time window of 5 seconds for thee different ambient energy conditions. In these experiments, the average power cycles of the CIS nodes are (3,18), (3.9,12.3), and (4.3,11.5) seconds when ambient light intensity are 500, 800, and 900 lux, respectively. If we focus on the line graphs associated with 500 and 800 lux and compare the system availability within the interval [20,50] seconds and the rest, we can observe that the CIS gradually alternates between low and high collective availability; nodes' on-times gradually transition from maximum to minimum separation and vice versa (Section 3.1.1).…”

“…One way to increase the system availability is by using multiple nodes. However, coordinating the nodes' awake 1 An alternative approach is to combine EH with a (small) rechargeable battery [17,18]. times using communication may introduce prohibitive overhead as a scattering algorithm must be regularly executed, and messages for synchronizing nodes' clocks and reserving time slots need to be repeatedly exchanged.…”

Feasibility of Wireless Horse Monitoring Using a Kinetic Energy Harvester Model

“…In the wireless node, generally a battery or capacitor will be included for storing limited amounts of energy for reliable performance of the node. Figure 13 shows the feasibility of the energy harvester node which is based on the harvester input and the capacity of the rechargeable battery [52]. Three different operational regions can be distinguished:…”

Camaroptera

“…Recent work [1] advocates for using batteries to avoid managing capacitive energy storage and to store surplus energy. While simpler and appropriate for some tasks with low duty cycle and low compute intensity, battery-powered devices are larger, heavier, contribute to battery waste, and face lifetime issues, as fixed batteries fail and rechargeable batteries wear out with recharge cycles.…”

“…: Camaroptera prototype buffering the energy in a battery [1] or capacitor [2]. After collecting sufficient energy, the system activates and performs some sensing, computing, or communication for its application.…”