Effect of Sunlight on Photovoltaics as Optical Wireless Communication Receivers

Abstract

This paper explores the effects of sunlight on using a low-cost off-the-shelf silicon solar panel as an optical wireless communication (OWC) receiver. A receiver circuit structure has been proposed to maximize simultaneous energy harvesting and data communication performance. An equivalent circuit model of the solar panel for simultaneous energy harvesting and wireless optical communication is discussed. By using the solar panel model, the effects of varying sunlight conditions on the performance of the model as an OWC receiver are estimated. Furthermore, an experimental setup is developed to study the effects and verify the simulated estimations. The experimental setup consists of a 3.5 m wireless optical link with a full Transmission Control Protocol and Internet Protocol (TCP/IP) network stack. The system uses DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) to use the available communication bandwidth efficiently. A 940 nm low-cost off-theshelf laser device along with an off-the-shelf off-axis-parabolic mirror is used as the transmitter. The maximum user throughput achieved over the air is 28.3 Mb/s while simultaneously harvesting energy using the maximum power point tracking (MPPT) technique. The peak power harvested with simultaneous communication is 4.5 W. The harvested energy is stored in a 38 Wh lithium-ion (Li-ion) battery. Index Terms-Optical Wireless Communication (OWC), photovoltaics, LiFi, solar cell, energy harvesting, orthogonal frequency division multiplexing (OFDM) types of PD used in LiFi technology are positive-intrinsicnegative (PIN) PDs and avalanche photodiodes (APDs).However, PDs can require additional power to generate the sometimes high bias voltage. Therefore, solar cells can be a good energy-neutral alternative to photodiodes (PDs) as they can convert variations in the intensity of the light to electrical signals without the application of reverse bias voltage. Furthermore, solar panels are by default manufactured with multiple solar cells connected in series and parallel configuration. This results in a large active area as a communication receiver and increases the energy harvesting capability. The optical energy harvested by a solar panel can be used to offset the energy consumed by the rest of the components of the communication system. Also, the large active area of the solar panel relaxes the process of alignment between transmitter and receiver (at long distances). Conventional PDs have a small area and can be very difficult to align when used for long-distance communication. This paper discusses the effects and trade-offs when a solar panel is used simultaneously for energy harvesting and communication. The simultaneous energy harvesting and communication performance of a solar panel has been maximized using the proposed solar panel receiver circuit structure. The effect of sunlight on the communication performance of a solar panel as an OWC receiver is studied and estimated using an equivalent circuit model of a solar panel. The variation in frequency re...

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