Date received: 23 of june 2021 - Date approved: 30 of november 2021
How to cite:
R. Jacob, B. Ghanishtha, J. Swaminathan, W. H. Vincent, E. Belwin, R. Sitharthan “A contemporary outlook on wireless sensor networks for solar power harvesting” , Revista Ingenio, 19(1), pp.16-21, 2022
While solar energy has been an emerging source of renewable energy for many years now with various studies delving into building more robust and compact solar cells, their use as a power source for mobile and small machinery such as Wireless Sensor Networks (WSN) is less discussed. However, with increasing global efforts in subsidizing more sustainable technology and energy, many studies have emerged in the past decade on building solar power based wireless sensor networks.The combination of novel harvesting circuits, mechanisms to obtain maximum possible power, smart power management algorithms and improving energy technology has provided the necessary framework for self-powered WSN nodes that have much longer lifetime.This paper reviews the newer proposed technology that aids the development of Solar Energy Harvesting Wireless Sensor Networks.
Keywords:Embedded Systems, Internet of Things, Renewable Energy, Solar Power Harvesting, Wireless Sensor Networks
Aunque la energía solar es una fuente emergente de energía renovable desde hace muchos años, con varios estudios que profundizan en la construcción de células solares más robustas y compactas, su uso como fuente de energía para maquinaria móvil y pequeña, como las redes de sensores inalámbricos (WSN), es menos discutido. Sin embargo, con el aumento de los esfuerzos mundiales para subvencionar tecnologías y energías más sostenibles, en la última década han surgido muchos estudios sobre la construcción de redes de sensores inalámbricas basadas en la energía solar. La combinación de novedosos circuitos de recolección, mecanismos para obtener la máxima potencia posible, algoritmos inteligentes de gestión de la energía y la mejora de la tecnología energética ha proporcionado el marco necesario para que los nodos de las WSN se autoalimenten y tengan una vida útil mucho más larga. En este artículo se revisa la nueva tecnología propuesta que ayuda al desarrollo de las redes de sensores inalámbricos con captación de energía solar.
Palabras clave:Sistemas embebidos,Internet de las cosas,energías renovables, captación de energía solar,redes de sensores inalámbricos.
At their core, ever wireless sensor node is characterized by its size, stand-alone power supply, its transmission latency and its sensory accuracy. Over the recent years,sensors have become increasingly accurate at miniscule sizes,therefore it can be deduced that the primary bottleneck in the size of a wireless sensor node is its powering mechanism or the size of the battery.It is observed that a significant correlation exists between the useful life of the individual nodes and their duty cycle as well as the volume of data flow within the system.While there are IoT objects that use high power per unit time, these tend to be less sustainable,therefore it is a standard practice to maintain a design constraint of being powered by a readily available source such as 1.5V IEC 60086 size R6 batteries .Though WSNs are mainly low power systems that do not need large batteries,Inherently the use of batteries applies a limit on the operational time of the network after which the system will have to be taken out of service to recharge or replace the batteries.This process interrupts the operation where the wireless sensor is being used and in cases where the network is spread over several kilometers the replacement can be time intensive and impractical.Therefore, a source of energy is needed that provides energy at the place of operation itself without the need for interrupting service,human intervention, or connection to grid. Some such viable technologies are stated in the Table 1.
From Table 1 it can be noted that solar power demonstrates the optimal trade-off between efficiency and power density amongst other comparable sources of energy.Furthermore,it should be noted that the size of harvesters of solar energy are becoming smaller by the day,recent cells using nanotechnology have been manufactured in the order of nanometers.The growing market for solar panel manufacturers also provides ample investment and resources for its integration with WSNs.Maurya et al.have stated that near about 15 mW/cm3 of photovoltaic power can be harvested from solar energy for wireless sensors.Converters are used to transform this energy to the DC that drives the internal circuitry of the WSNs. Additionally,advancements in storage technology allows the system to function in conditions that are not favorable for harvesting solar energy.The advantages of solar energy that make them optimal for powering WSN nodes, which are given as follows :• From a theoretical perspective the output from harvesting solar energy is inexhaustible.
The major objective of this critical review is to extensively encompass the features of a Solar Energy Harvesting based Wireless Sensor Node,to illustrate the known and potential shortcomings faced by such systems,and review in detail the solutions proposed in various recent studies to improve this technology or extend its application.The remaining portion of this paper is organized as follows:Section II aids in a more comprehensive overview of Solar Energy Harvesting Wireless Sensor Networks and provides an outline of the components involved in such a system.Section III provides the problem description or major considerations in designing an optimal system.Section IV reviews literature which proposes new technology to optimize the designs with respect to the considerations in the previous section.Section V provides some simulation platforms developed to aid in analyzing performance of the Photovoltaic Harvester.Section VI gives the overall summary of the review along with the author’s insight into the most efficient technologies in every domain.2. Major components of solar energy harvesting wireless sensor network
The sensor unit performs as the central instrumentation platform which detects physical quantities like temperature,light, humidity,or pressure, see Figure 1.The computational unit then processes this data to useful markers that would provide the system with decision making feedback.As per the mesh architecture these data packets of useful information are relayed to nearby nodes until it reaches the central database or gateway node.The end user can then access this information or it can be used to autonomously drive a control system.The energy harvesting unit, which is a unique feature of this build of WSNs,supply stable power at the operating voltage (3V) to the WSN node to allow continuous supply of energy and uninterrupted service.3. Modern Wireless sensor mechanisms for solar power harvesting
b. Maximum Power Point Tracking
Maximum power point tracking (MPPT) has often been availed in solar energy harvesting in order to ensure the maximum amount of power that can be harnessed through the solar panels may be collected.The maximum power point refers to the to the constant voltage level that provides peak power levels being produced in the photovoltaic cell.In most new designs of solar power systems and charge controllers,some version of the MPPT technique is employed.At its core, MPPT technique aims to make the solar module’s resistance equal to that of the load of the circuit or the battery. Generally, MPPT can boost energy generation by 20%–30% [9-.All MPPT algorithms fall into the following wide classifications:
- Perturbation and observation (P&O):
This method alters the operational parameters directly to try to achieve the MPP.This algorithm can be very complex and has been modelled to have optimal performance in various studies but essentially it boils down to the sequence shown in Figure 2a.
- Incremental conductance:This algorithm has been visualized in Figure 2b.Essentially it operates by comparing the incremental conductance of solar energy harvester to the instantaneous conductance.Depending on the feedback, which is either a positive or a negative value,it varies the voltage until a stopping condition (MPP) is reached. Unlike the first method once the stopping condition is met there are no further alterations in the voltage.
c. Solar Tracking for Wireless Sensors
As mentioned in the earlier sections of this paper,the main constraint with respect to WSN nodes is their size.Therefore,until recent times tracking,which is common in many commercial PV systems,was not used as the energy used by the tracker would be more than the energy harvested by the system overall.This would put the design into an energy debt and therefore was mostly deemed infeasible.However,many studies in recent literature have proposed trackers that ensures minimal energy is lost with low power consumption which are ideal for WSN nodes.Some of these studies are highlighted in Table 4.
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