Indoor Light Energy Harvesting Research Articles

Low light illumination study on commercially available homojunction photovoltaic cells

Low illumination (10−4suns) and indoor light energy harvesting is needed to meet the demands of zero net energy (ZNE) building, Internet of Things (IoT), and beta-photovoltaic energy harvesting systems to power remote sensors. Photovoltaic (PV) solar cells under low intensity and narrow (±40nm) light spectrum conditions are not well characterized nor developed, especially for commercially available devices and scalable systems. PV operating characteristics under 1 sun illumination decrease at lower light intensity and narrow spectrum conditions (efficiency drops from ∼25% at 100mWopt/cm2 to 2% at 1μWopt/cm2). By choosing a PV with a bandgap that matches the light source operating wavelength, the total system efficiency can be improved. By quantifying losses on homojunction photovoltaics (thermalization and leakage current), we have determined the theoretical optimized efficiency for a set of PV material and a selected set of light sources. We measure single-junction solar cells’ parameters under three different light sources (indoor light and narrow spectrum LED sources) with light intensities ranging from 0.5 to 100μWopt/cm2. Measurements show that indium gallium phosphide (InGaP) PV has the highest surface power density and conversion efficiency (29% under ≈1μWopt/cm2 from a 523nm central peak LED). A beta-photovoltaic experimental study identifies InGaP to be optimized for use with the ZnS:Cu, Al and tritium at STP. The results have guided the selection of PV material for scalable isotope batteries and other low-light energy harvesting systems.

Wireless sensor node demonstrating indoor-light energy harvesting and voltage-triggered duty cycling

We demonstrate a wireless sensor node (WSN) that operates purely on harvested ambient indoor light energy and regulates its duty cycle via voltage-triggered sensing and transmission. The extremely low-power light found in indoor environments can be considered at first sight as unsuitable for high-power load demands characteristic of radios [1], but by leveraging spectrum-tailored solar cells, trickle charging a high-power energy reservoir, and implementing triggered duty cycling, we show that these power demands can be consistently met. All energy harvesting and storage components are fabricated in our labs.

Organic solar cells and fully printed super-capacitors optimized for indoor light energy harvesting

Flexibility, lightness and printability make organic solar cells (OSC) strong candidates to power low consumption devices such as envisioned for the Internet of Things. Such devices may be placed indoors, where light levels are well below typical outdoors level. Here, we demonstrate that maximizing the efficiency of OSC for indoor operation requires specific device optimization. In particular, minimizing the dark current of the solar cells is critical to enhance their efficiency under indoor light. Cells optimized for sunlight reach 6.2% power conversion efficiency (PCE). However when measured under simulated indoor light conditions, the PCE is to 5.2%. Cells optimized for indoor operation yield 7.6% of PCE under indoor conditions. As a proof-of-concept, the solar cells are combined with fully printed super-capacitors to form a photo-rechargeable system. Such a system with a 0.475cm2 indoor-optimized solar cell achieved a total energy conversion and storage efficiency (ECSE) of 1.57% under 1-sun, providing 26mJ of energy and 4.1mW of maximum power. Under simulated indoor light the system yielded an ECSE of 2.9%, while delivering 13.3mJ and 2.8mW. Those energy and power levels would be sufficient to power low-consumption electronic devices with low duty cycles.

On the Feasibility of Indoor Light Energy Harvesting for Wireless Sensor Networks

This paper presents the important issues about the design of a low cost, micro power, indoor light energy harvesting system to supply a node of a wireless sensor network (WSN). Possible technology options, available for the photovoltaic (PV) cells, are discussed. Light power and irradiance measurements, in a real indoor environment, are performed and results are presented. From these results, a possible solution for cell sizing is described.

A CMOS micro power switched-capacitor DC–DC step-up converter for indoor light energy harvesting applications

This paper presents a micro power light energy harvesting system for indoor environments. Light energy is collected by amorphous silicon photovoltaic (a-Si:H PV) cells, processed by a switched capa...

Start‐up circuit for low‐power indoor light energy harvesting applications

A start-up circuit, used in a micro-power indoor light energy harvesting system, is described. This start-up circuit achieves two goals: first, to produce a reset signal, power-on-reset (POR), for the energy harvesting system, and secondly, to temporarily shunt the output of the photovoltaic (PV) cells, to the output node of the system, which is connected to a capacitor. This capacitor is charged to a suitable value, so that a voltage step-up converter starts operating, thus increasing the output voltage to a larger value than the one provided by the PV cells. A prototype of the circuit was manufactured in a 130 nm CMOS technology, occupying an area of only 0.019 mm2. Experimental results demonstrate the correct operation of the circuit, being able to correctly start-up the system, even when having an input as low as 390 mV using, in this case, an estimated energy of only 5.3 pJ to produce the start-up.

Indoor Light Energy Harvesting System for Energy-aware Wireless Sensor Node

This paper proposes a novel energy harvesting and power management circuit that includes maximum power point tracking (MPPT) circuit, energy storage circuit, energy instantaneous discharging circuit, and DC-DC boost converter. It harvests energy from indoor faint light by imposing the harvester to work close to its maximum power point and supply power for sensor node. The measured result shows that the prototype circuit can harvest energy from indoor light condition with input power of 72.74μW and successfully drive a smart wireless temperature and humidity sensor node with power consumption of 105mW per operating cycle.

Design considerations of sub-mW indoor light energy harvesting for wireless sensor systems

For most wireless sensor networks, one common and major bottleneck is the limited battery lifetime. The frequent maintenance efforts associated with battery replacement significantly increase the system operational and logistics cost. Unnoticed power failures on nodes will degrade the system reliability and may lead to system failure. In building management applications, to solve this problem, small energy sources such as indoor light energy are promising to provide long-term power to these distributed wireless sensor nodes. This article provides comprehensive design considerations for an indoor light energy harvesting system for building management applications. Photovoltaic cells characteristics, energy storage units, power management circuit design, and power consumption pattern of the target mote are presented. Maximum power point tracking circuits are proposed which significantly increase the power obtained from the solar cells. The novel fast charge circuit reduces the charging time. A prototype was then successfully built and tested in various indoor light conditions to discover the practical issues of the design. The evaluation results show that the proposed prototype increases the power harvested from the PV cells by 30% and also accelerates the charging rate by 34% in a typical indoor lighting condition. By entirely eliminating the rechargeable battery as energy storage, the proposed system would expect an operational lifetime 10--20 years instead of the current less than 6 months battery lifetime.