sustainability

Review A Review of Monitoring Technologies for Solar PV Systems Using Data Processing Modules and Transmission Protocols: Progress, Challenges and Prospects

Shaheer Ansari 1 , Afida Ayob 1,* , Molla S. Hossain Lipu 1,2,* , Mohamad Hanif Md Saad 3,4 and Aini Hussain 1

1 Department of Electrical, Electronic and Systems Engineering, Universiti Kebangsaan Malaysia, Bangi 43600, Malaysia; [email protected] (S.A.); [email protected] (A.H.) 2 Centre for Automotive Research (CAR), Universiti Kebangsaan Malaysia, Bangi 43600, Malaysia 3 Department of Mechanical & Manufacturing Engineering, Universiti Kebangsaan Malaysia, Bangi 43600, Malaysia; [email protected] 4 Institute of IR 4.0, Universiti Kebangsaan Malaysia, Bangi 43600, Malaysia * Correspondence: afi[email protected] (A.A.); [email protected] (M.S.H.L.)

Abstract: Solar photovoltaic (PV) is one of the prominent sustainable energy sources which shares a greater percentage of the energy generated from renewable resources. As the need for has risen tremendously in the last few decades, monitoring technologies have received considerable attention in relation to performance enhancement. Recently, the solar PV monitoring system has been  integrated with a wireless platform that comprises data acquisition from various sensors and nodes  through wireless data transmission. However, several issues could affect the performance of solar Citation: Ansari, S.; Ayob, A.; Lipu, PV monitoring, such as large data management, signal interference, long-range data transmission, M.S.H.; Saad, M.H.M.; Hussain, A. A and security. Therefore, this paper comprehensively reviews the progress of several solar PV- Review of Monitoring Technologies based monitoring technologies focusing on various data processing modules and data transmission for Solar PV Systems Using Data protocols. Each module and transmission protocol-based monitoring technology is investigated with Processing Modules and regard to type, design, implementations, specifications, and limitations. The critical discussion and Transmission Protocols: Progress, analysis are carried out with respect to configurations, parameters monitored, software, platform, Challenges and Prospects. achievements, and suggestions. Moreover, various key issues and challenges are explored to identify Sustainability 2021, 13, 8120. the existing research gaps. Finally, this review delivers selective proposals for future research https://doi.org/10.3390/su13158120 works. All the highlighted insights of this review will hopefully lead to increased efforts toward the

Academic Editor: Aritra Ghosh enhancement of the monitoring technologies in future sustainable solar PV applications.

Received: 10 June 2021 Keywords: solar PV; wireless monitoring system; sensors; data processing board; data transmission Accepted: 15 July 2021 protocols; data acquisition Published: 21 July 2021

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in 1. Introduction published maps and institutional affil- The depletion of fossil fuels and carbon emission issues have transformed power iations. systems from conventional systems to renewable systems [1–3]. Moreover, the need for energy security and economic stability has increased, and hence more and more emphasis is now being given to the generation of [4,5]. Among the renewable energy sources, solar energy is attractive and sustainable [6]. Solar Photovoltaic (PV) Copyright: © 2021 by the authors. energy is considered a clean, attractive, and secure source of electricity generation [7,8]. Licensee MDPI, Basel, Switzerland. The solar PV system promises a great future and is increasingly popular due to its simple This article is an open access article installation, low maintenance cost, robustness, and zero fuel cost [9,10]. is distributed under the terms and abundant; thus, it could play a crucial role in fulfilling global energy requirements including conditions of the Creative Commons heating, ventilation, and air-conditioning (HVAC) systems, domestic lighting, hot water Attribution (CC BY) license (https:// systems, and other key applications [11]. The cost reduction in solar PV installation is creativecommons.org/licenses/by/ due to several factors such as improved technology, economies of scale, supply chain 4.0/).

Sustainability 2021, 13, 8120. https://doi.org/10.3390/su13158120 https://www.mdpi.com/journal/sustainability Sustainability 2021, 13, 8120 2 of 34

competitiveness, and the growing experience of developers [12,13]. At present, solar PV energy is the third-largest renewable source of energy generation after wind and hydro [14]. In the last two decades, the solar PV system has become one of the main sources for power generation [15,16]. In 2018, a unique milestone in the field of solar PV systems was achieved i.e., the 100 GW threshold of annual installations was crossed [17]. According to the Renewable Energy Market Report 2018 by the International Energy Agency (IEA), there will be a comprehensive growth in the generating capacity of solar PV systems from 572 GW to 720 GW between 2018 and 2023 [18]. Further, the global solar PV power capacity is expected to increase to more than 2840 GW by 2030, and to 8519 GW by 2050 [12]. Since the need for solar energy has risen around the globe, the development of an ad- vanced monitoring method has become an urgent necessity. Due to various environmental factors such as soiling, temperature, irradiance etc., the operation and functionality of solar PV systems can be affected. Thus, the accuracy and performance of the solar PV system can be improved by employing an efficient solar PV monitoring system [19]. Monitoring is the process of observing and recording the parameters from the solar PV power plant in real-time. An efficient monitoring technology of the solar PV system improves the performance efficiency as it provides updated information and executes the preventive measures if any flaws are found. The monitoring method also notifies the users by an alert signal when unexpected events occur in a solar PV system [20]. The monitoring of the solar PV power plant is performed either at the module, string, or system level. The monitoring of the solar PV at the system level provides information about the system exclusively. The monitoring technology related to panels and strings helps in identifying the root cause of the problem precisely. Every panel and string needs to be monitored for the overall efficiency improvement of a solar PV power plant, as even a change in the output from a single panel can affect the efficiency of the entire system. Henceforth, numerous monitoring methods have been introduced in recent decades. There has been a change of trend from wired to wireless monitoring systems in the past decade [21]. In the past, the wired monitoring system was commonly used for transferring data through an RS232 cable or an RS485 cable [22,23] However, as the solar PV system has expanded, real-time monitoring using conventional wired cables has resulted in additional significant costs. Moreover, the cables carrying the data are exposed to environmental conditions such as rain, humidity, temperature, etc. In contrast, the wireless monitoring system is less prone to environmental conditions compared to the wired monitoring system and can deliver faster decision-making in real-time. This is due to the exposure of sensors and nodes to the open environment installed for data acquisition and transmission. Furthermore, wireless monitoring technologies not only increase mobility and network security by implementing associated security protocols, but they also have a longer range, a high response time, and low maintenance costs. Nevertheless, various factors can cause a change in the output of the system, including a change from a sunny sky to a cloudy sky, the temperature of the panel, humidity, irradiance, the mounting angle, and the mismatch between the specification from the manufacturers and the actual PV output [24]. Therefore, further exploration is required to design an effective solar PV monitoring technology before the system can be implemented, considering the number of anticipated challenges. Very few notable review articles have been published on solar PV monitoring technolo- gies. Shariff et al. [25] emphasized different designs and topologies of solar PV monitoring systems. The different monitoring characteristics such as sampling time, mechanisms for data transfer, associated software etc., were highlighted in the work but the works did not outline the current progress in the field of monitoring with regards to module-based technology. Madeti and Singh [26] focused on examining solar PV systems in terms of the sensors employed, the controllers used, and data transmission techniques. Rahman et al. [27] discussed the architecture and features of various monitoring systems for so- lar PV power plants. Triki-Lahiani et al. [28] explained the various monitoring systems and concentrated on addressing the major failures in solar PV systems. All the above- highlighted reviews do not consider the insights of the technological implementation of Sustainability 2021, 13, x FOR PEER REVIEW 3 of 36

data transmission and data processing modules in the field of solar PV wireless monitor- Sustainability 2021, 13, 8120 ing systems in a comprehensive manner. 3 of 34 To bridge the existing research gaps, this review unveils new contributions with a detailed investigation of the monitoring technologies of the solar PV system. The review offersdata the transmission following andcontributions: data processing modules in the field of solar PV wireless monitoring • systemsA comprehensive in a comprehensive explanation manner. of various data processing modules for solar PV mon- itoringTo bridge systems the existingis presented research in terms gaps, thisof ca reviewtegories, unveils specifications, new contributions design withimplemen- a detailedtation, investigationsoftware platforms, of the monitoring results, and technologies limitations. of the solar PV system. The review offers the following contributions: • The categories of the various data transmission modules for wireless communication • in solarA comprehensive PV monitoring explanation systems of variousare report dataed, processing highlighting modules topology, for solar data PV moni-transmis- toring systems is presented in terms of categories, specifications, design implementa- sion rage, sampling rate, power consumption, and range. • tion, software platforms, results, and limitations. • TheThe existing categories issues of the and various challenges data transmission for the monitoring modules technologies for wireless communication of solar PV appli- cationsin solar are PV covered, monitoring emphasizing systems are data reported, hand highlightingling, security, topology, signal data interference, transmission energy efficiency,rage, sampling etc. rate, power consumption, and range. • • SomeThe constructive existing issues future and challenges recommendations for the monitoring are presented technologies toward of solar the PVdevelopment appli- of ancations efficient are covered, and reliable emphasizing solar PV data monitoring handling, security,system. signal interference, energy efficiency, etc. • TheSome paper constructive is organized future into recommendations eight sections are. Section presented 2 presents toward thethe development survey methodol- of ogy of thisan efficient review andpaper. reliable Section solar 3 PV covers monitoring an overview system. of the solar PV monitoring system and theThe classification paper is organized of the modules into eight based sections. on Section the data2 presents transmission the survey and methodology data processing boards.of this Sections review paper.4 and 5 Section highlight3 covers the data an overview processing of the technology solar PV monitoring and data transmission system technologyand the classification for monitoring of the solar modules PV basedsystems, on the respectively. data transmission The current and data issues processing and chal- lengesboards. are Sectionsdiscussed4 and in5 Sectionhighlight 6. the Section data processing 7 presents technology the discussion and data and transmission future perspec- tives.technology The concluding for monitoring comments solar PV are systems, outlined respectively. in Section The 8. current issues and challenges are discussed in Section6. Section7 presents the discussion and future perspectives. The 2. Surveyconcluding Methodology comments are outlined in Section8. 2.There Survey has Methodology been a growing interest among researchers to enhance the performance of solar PVThere monitoring has been systems a growing using interest various among tec researchershnologies. to In enhance line with the this performance matter, various of datasolar processing PV monitoring modules systems and data using transmission various technologies. protocols In have line with been this introduced matter, various in the last decade.data processingFigure 1 denotes modules the and number data transmission of papers published protocols between have been 2010 introduced and 2020. in theA sharp upwardlast decade. trend is Figure visible1 denotes in the number the number of arti of paperscles accepted published from between 2010 to 2010 2020 and which 2020. implies A the sharpimportance upward and trend potential is visible deployment in the number of of various articles modules accepted fromand communication 2010 to 2020 which proto- colsimplies in solar the PV importance applications. and potentialA total of deployment 443 papers of were various published modules between and communication 2010 and 2020. protocols in solar PV applications. A total of 443 papers were published between 2010 and Among the total number of manuscripts, 43.57% of the articles were published in the first 2020. Among the total number of manuscripts, 43.57% of the articles were published in seventhe years first seven (2010–2016). years (2010–2016). However, However, the number the numberof articles of articlespublished published in the next in the four next years (2017–2020)four years increased (2017–2020) at increased a greater at rate. a greater In this rate. period, In this 56.43% period, of 56.43% the articles of the articles were published were whichpublished is 12.86% which higher is 12.86% than higher the previous than the seven previous years. seven years.

80 70 75 70 55 60 50 50 40 42 40 31 34 30 21 20 12 13

Number of articles 10 0 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Year

Figure 1. Research trend of solar PV monitoring systems from 2010 to 2020. Figure 1. Research trend of solar PV monitoring systems from 2010 to 2020. Sustainability 2021, 13, x FOR PEER REVIEW 4 of 36 Sustainability 2021, 13, 8120 4 of 34

The goal of this review is to gather all the recent information, conduct an analysis, and provideThe goal a of critical this review discussion is to gather of the all monitoring the recent information, technologies conduct for solar an analysis,PV systems. and Firstly,provide Google a critical scholar, discussion IEEEXplore, of the monitoring MDPI, and technologies ScienceDirect for databases solar PV were systems. utilized Firstly, to exploreGoogle the scholar, related IEEEXplore, work for this MDPI, paper. and Seco ScienceDirectndly, keywords, databases abstract, were paper utilized content, to explore nov- elty,the related and the work main for topic this of paper. interest Secondly, of the keywords,journal were abstract, applied paper to search content, for novelty,the relevant and publicationsthe main topic within of interest the scope of the of journal this paper were including applied to solar search PV, for wireless the relevant monitoring publications sys- tems,within sensors, the scope data of processing this paper board, including and solar data PV,transmission wireless monitoring protocols. The systems, final suitable sensors, worksdata processing were investigated board, and by assessing data transmission the impact protocols. factors, the The review final process, suitable and works the werecita- tions.investigated by assessing the impact factors, the review process, and the citations. TheThe outcome ofof thethe screeningscreening process process can can be be categorized categorized into into four four sections. sections. Firstly, Firstly, the thereview review of solar of solar PV monitoring PV monitoring systems systems based based on data on processingdata processing modules modules with its with design its designfeatures, features, implementation, implementation, comments comments or suggestions, or suggestions, and limitations and limitations is presented. is presented. Secondly, Secondly,various data various transmission data transmission protocols are protocol studieds are for solarstudied PV for monitoring solar PV systems.monitoring Thirdly, sys- tems.the review Thirdly, investigates the review various investigates issues variou and shortcomingss issues and shortcomings of the monitoring of the monitoring technology technologyfor solar PV for systems. solar PV Finally, systems. the reviewFinally,delivers the review some delivers selective some future selective prospects future for pro- the spectsfurther for enhancement the further ofenhancement solar PV monitoring of solar PV systems. monitoring The review systems. process The review can be dividedprocess caninto be two divided phases into as showntwo phases in Figure as shown2 and summarizedin Figure 2 and as follows:summarized as follows:

(a) Screening Method Final Selection 148 references were selected and analyzed based on the impact factor, review process, and citation.

148 Initial Screening and Evaluation Second Screening Google Scholar, Scopus databases, 443 Relevant 228 articles were Web of Science, ScienceDirect, IEEE 228 identified based on keywords, Xplore, MDPI were chosen and title, abstract, article content, accordingly 443 papers were selected novelty and journal's main subject of interest

(b) Review Results

Solar PV monitoring Solar PV monitoring technologies based on data technologies based on data Progress of solar processing modules transmission protocols PV monitoring - Types - Range technologies - specifications - Power Consumption - Design and Implementations - Topology - Software/ Language used - Data transmission rate - Monitoring Platform - Sampling rate - Achievements - Limitations

Future Prospects Issues and challenges Selective and important suggestions for further - Data handling and security enhancement of solar PV monitoring technologies - Signal interference towards su stainable operation and management. - Energy efficiency - Data transmission range

Figure 2. SchematicSchematic diagram diagram of the survey methodology. Sustainability 2021, 13, x FOR PEER REVIEW 5 of 36

Sustainability 2021, 13, 8120 5 of 34

2.1. Selection Process • 2.1. SelectionIn the first Process search results, a total of 443 articles were found using various platforms including Google scholar, IEEEXplore, MDPI, and the ScienceDirect databases. • In the first search results, a total of 443 articles were found using various platforms • In the second screening results, a total of 228 articles were selected based on the including Google scholar, IEEEXplore, MDPI, and the ScienceDirect databases. appropriate title, keywords, abstract, and content of the paper. • In the second screening results, a total of 228 articles were selected based on the • In the third assessment results, the articles were analyzed based on impact factor, appropriate title, keywords, abstract, and content of the paper. review process, and citation. Accordingly, a total of 148 references were finalized for • In the third assessment results, the articles were analyzed based on impact factor, the review paper consisting of journals, conferences proceedings, and recognized review process, and citation. Accordingly, a total of 148 references were finalized forwebpages. the review paper consisting of journals, conferences proceedings, and recog- nized webpages. 2.2. Review Results •2.2. ReviewMonitoring Results technologies for solar PV systems based on data processing modules • Monitoringwere explained. technologies for solar PV systems based on data processing modules • wereFurther, explained. the monitoring technologies considering various data transmission proto- • Further,cols for solar the monitoring PV application technologies were discussed. considering various data transmission protocols • forKey solar issues PV and application limitations were of the discussed. solar PV monitoring system based on the presented • Keytechnology issues andwere limitations explored. of the solar PV monitoring system based on the presented • technologyRecommendations were explored. and future directions for the further improvement of the monitor- • Recommendationsing technology for solar and future PV systems directions were for presented. the further improvement of the monitor- ing technology for solar PV systems were presented. 3. Overview and Taxonomy of Solar PV Monitoring System 3. Overview and Taxonomy of Solar PV Monitoring System The architecture of the solar PV monitoring system can be divided into three levels, namely,The the architecture data acquisition of the solar level, PV the monitoring data processing system level, can be and divided the data into display three levels, and storagenamely, level, the data as illustrated acquisition in level, Figure the 3 data [27]. processing In the data level, acquisition and the level, data displaythe data and are stor-col- lectedage level, from as the illustrated various in sensors Figure 3such[ 27 ].as In theage, data current, acquisition temperature, level, the datahumidity, are collected irradi- ance,from theetc., various and are sensors then sent such to the as voltage,next stage current, using temperature,either the wired humidity, or the wireless irradiance, system. etc., Inand the are next then level, sent tothe the data next are stage stored using temporarily either the wiredin auxiliary or the wirelessdevices system.such data In theloggers, next processed,level, the data and are sent stored to the temporarily last stage for in auxiliarythe display devices of the such results. data In loggers, the last processed, level, the data and aresent received to the last by stagethe workstation for the display and ofthen the the results. required In the actions last level, are taken the data by the are system received to by the workstation and then the required actions are taken by the system to be configured be configured accordingly. These data can be accessed from anywhere at any time via the accordingly. These data can be accessed from anywhere at any time via the internet. internet.

wireless Wireless Router module Data logger

Panel Solar Wired Work station ; wired and Sensors Operating systems wireless

Figure 3. The basic architecture of a solar PV monitoring system.system.

A comprehensive review of solar PV monito monitoringring system-based data processing processing mod- ules and data transmission protocols has been carried out. The data transmission modules allow the acquisition, control, and management of connected devices and networks in a real-time environment. Furthermore, they act as middleware that connects with different devices through cloud computing technology. The solar-based monitoring system is com- prised ofof aa four-layerfour-layer structure structure which which consists consists of of sensors sensors (electrical (electrical and and environmental) environmental) for forgathering gathering data data such such as panelas panel voltage, voltage, current, current, temperature, temperature, humidity humidity (small (small scale) scale) etc., etc., a network layer for the transmission of the data by utilizing various transmission protocols Sustainability 2021, 13, x FOR PEER REVIEW 6 of 36