Photovoltaic Energy Harvesting Wireless Sensor Node for Telemetry Applications Optimized for Low Illumination Levels

Abstract

This paper reports the design of a photovoltaic energy harvesting device used as telemetry node in wireless sensor networks. The device draws power from the small solar cell, stores it into the primary energy buffer and backup supercapacitor, collects measured data from various sensors and transmits them over low power radio link at 868 MHz. Its design ensures reliable cold booting under very poor illumination conditions (down to 20 lx). The solar cell also enables indirect illumination level detection for the subcircuit that manages stored energy (day/night detector). The device is allowed to draw power from the backup supercapacitor only when it is not possible to gather enough energy from the solar cell during the sleep period. Short lasting and sudden drops of the illumination do not activate the backup power supply. A wireless sensor node design is adjusted to the proposed photovoltaic harvesting circuitry, so the overall power consumption in the sleep mode is less than 25 µW. Also, due to adaptive power consumption, proposed device topology ensures its autonomy time in the total darkness of 81 h. The device has been produced using commercially available components enabling versatile telemetric functionality by the implementation of different sensors.

Limitations and Characterization of Energy Storage Devices for Harvesting Applications

“…SCs can be used for applications with operation cycles on the order of seconds or minutes; they are widely employed in wireless sensor network (WSN) applications as an alternative to classic capacitors given their higher energy density [7,8]. For instance, in [9] the authors developed a photovoltaic energy harvesting device, conceived as a telemetry node with non-perpetual operation in the indoor environment. The node is equipped with a suitable power management system, also employing the solar panel for the indirect illumination level detection in order to draw power from the backup super-capacitor only during the sleep time intervals during which the system power consumption is less than 25 µW.…”

Energy Income Estimation for Solar Cell Powered Wireless Sensor Nodes

“…The disadvantage of using a separate sensor for energy income is the negligence of the electrical losses in the system. The second option, i.e., measuring the input current [3], also causes some problems. First, to measure the current a serial resistor has to be included, which is generating losses.…”

A Pulsed Coding Technique Based on Optical UWB Modulation for High Data Rate Low Power Wireless Implantable Biotelemetry

“…These systems require wireless biotelemetry links with high data rate, reduced power consumption, small Bit Error Rate (BER) and good electromagnetic compliance [3][4][5][6][7]. Solutions that make use of carrier-based narrow-band and Ultra-wideband (UWB) Radio Frequency (RF) links, employing Impulse Radio (IR) signal modulation, pose significant challenges when requiring high data rates due to their low power efficiency and electromagnetic compatibility [8][9][10][11][12][13].…”