Monitoring of Solar Still Desalination System Using the Internet of Things Technique PDF

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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/367339912 Monitoring of Solar Still Desalination System Using the Internet of Things Technique Research · October 2021 CITATIONS READS 0 17 4 authors: Mohamed Benghanem Adel Mellit Islamic University of Madinah- KSA Abdus Salam International Centre for Theoretical Physics 98 PUBLICATIONS 4,573 CITATIONS 189 PUBLICATIONS 10,418 CITATIONS SEE PROFILE SEE PROFILE Mohammed Esam Emad Abdulaziz Aljohani Islamic University of Madinah Islamic University ksa 8 PUBLICATIONS 24 CITATIONS 7 PUBLICATIONS 89 CITATIONS SEE PROFILE SEE PROFILE All content following this page was uploaded by Mohammed Esam Emad on 23 January 2023. The user has requested enhancement of the downloaded file.  energies Article Monitoring of Solar Still Desalination System Using the Internet of Things Technique Mohamed Benghanem 1, *, Adel Mellit 2,3 , Mohammed Emad 4 and Abdulaziz Aljohani 1 1 Physics Department, Faculty of Science, Islamic University, P.O. Box 170, Madinah 42351, Saudi Arabia; [email protected] 2 Renewable Energy Laboratory, Faculty of Sciences and Technology, Jijel University, Ouled-Aissa P.O. Box 98, Jijel 18000, Algeria; [email protected] 3 The Abdus Salam International Centre of Theoretical Physics (ICTP), Strada Costiera, 11, 34151 Trieste, Italy 4 Chemistry Department, Faculty of Science, Islamic University, P.O. Box 170, Madinah 42351, Saudi Arabia; [email protected] * Correspondence: [email protected] Abstract: In this work, a smart solar still prototype for water desalination is designed. It consists of a basic solar still, a solar preheater and a remote monitoring system based on the Internet of Things (IoT) technique. The monitoring system is developed and integrated into the hybrid solar still in order to control its evolution online, as well the quality of the freshwater provided by checking measured parameters such as pH. Thanks to the IoT technique, parameters collected by the monitoring system (e.g., air temperatures, relative humidity, etc.) are uploaded to the cloud for online remote monitoring. The users are notified by an SMS about the status of the system (e.g., water level in the basin, water in the tank, etc.), using an GSM module. The whole system, including the preheater, water pump, valve, sensors and an electronic board, is powered by a photovoltaic module of 75 Wp. The results showed



 that by adding a solar preheater system, the evaporation process is accelerated and, consequently, the daily yield is improved and reaches the value of 12.165 L/m2 /day. The saline concentration of Citation: Benghanem, M.; Mellit, A.; the tested ground water is 3.9 g/Kg (0.39%), and, after desalination, the salinity is 0.1 g/Kg (0.01%). Emad, M.; Aljohani, A. Monitoring of Solar Still Desalination System Using the Internet of Things Technique. Keywords: Internet of Things; mobile application; photovoltaic system; remote monitoring; smart Energies 2021, 14, 6892. https:// water desalination system; solar still doi.org/10.3390/en14216892 Academic Editor: Manolis Souliotis 1. Introduction Received: 4 September 2021 Around the world, there are many regions of vast extent that have numerous favorable Accepted: 16 October 2021 features but whose progress is mainly inhibited by a lack of freshwater. This is the case Published: 21 October 2021 in arid and semi-arid areas, where large-scale (LS) development has already occurred—for example, in parts of the Middle East and North Africa (MENA). Publisher’s Note: MDPI stays neutral In , the authors improved the performance of solar still desalination via the hydro- with regard to jurisdictional claims in phobic condensation surface using cold plasma technology, and the calculations showed published maps and institutional affil- that the produced freshwater using a plasma coating increased by 25.7% compared to the iations. uncoated system. A novel renewable-energy-based multigenerational system integrated with desalination and molten salt storage subsystems is developed in. Different types of basins have been employed and shown in. The difference between types of basins is due to the nature of the materials used, the geometric form, the type of transparent cover Copyright: © 2021 by the authors. and the means of providing and driving output water. As reported in , the outdoor Licensee MDPI, Basel, Switzerland. conditions of remote areas allow the best use of solar desalination. By minimizing the heat This article is an open access article losses, the daily distilled water increases, which is due to the lower boiling point of saline distributed under the terms and water inside the solar still under vacuum conditions. conditions of the Creative Commons In , an experimental system was developed and tested on a new absorber plate. Attribution (CC BY) license (https:// A new active solar still was compared with a conventional system in terms of efficiency creativecommons.org/licenses/by/ 4.0/). and water produced by using a hot water storage tank. In , experimental data were Energies 2021, 14, 6892. https://doi.org/10.3390/en14216892 https://www.mdpi.com/journal/energies Energies 2021, 14, 6892 2 of 12 used to validate the simulated results. The authors studied the effect of different factors on the freshwater productivity and solar still efficiency. Recently, in , the authors developed a desalination dual membrane framework that was powered by solar energy for purifying saline water using ancient methods to produce clean water for drinking and irrigation. Moreover, a recent study was conducted using seawater as continuous input into a conventional single-slope solar still. In this work, three kinds of absorbers were tested experimentally. It was found that the results of the absorber with 15 fins were better than those using the flat absorber. Another recent research work was undertaken to enhance a solar still’s productivity using thermal process modeling. It was found that the lower mass of water gives the highest daily productivity independently of the incident solar irradiation. In this work, a mathematical model was proposed to predict the performance of solar stills. A new design of a double-slope solar still was elaborated in. In fact, a novel methodology has been established allowing the calculation of the yearly solar thermal energy that can be received by a double-slope still. It was found that this input energy is affected by many parameters, such as the inclination angle of the glass cover, basin length and surface azimuth angle. The results showed that the designed double-slope solar still will receive a yearly solar input energy of 97.67 GJ. Another study was conducted to analyze the performance of a tubular solar still with different configurations. Three kinds of solar stills were assessed using a water depth of 1 cm. It was found that the tubular solar still with nano phase change material gave the best performance and highest yield. The main objective of this work is to design a low-cost smart hybrid solar still water desalination prototype. In fact, there are many configurations of water desalination systems; in this work, we are motivated by the solar still due to its simplicity, ease of implementation and low cost with acceptable efficiency. A monitoring system has been developed for the online control of the desalination unit using IoT technique. The most important parameters controlled by the monitoring system is the quality and the amount of freshwater produced by the system. This paper is organized as follows: the materials and methods are given in Section 2. The results and discussion are presented in Section 3. The conclusion is presented in the last section, Section 4. 2. Materials and Methods Figure 1 shows a block diagram of the proposed hybrid solar still system; it consists mainly of: A basic solar still that was fabricated with inner dimensions of 1 m × 1 m (effective area of 1 m2 ) and the glass cover was tilted at 25◦ with respect to the horizontal; A solar heater for preheating water, which was designed with an area of 1 m2 × 10 cm formed by copper tubes, as shown in the following diagram; A monitoring system used for data acquisition and parameter control using the IoT technique; A PV system of 75 Wp capacity was used for supplying different components of the system. Figure 2 shows a photo of the designed hybrid solar heater–solar still prototype. The main steps of the control process, implemented in the microcontroller, are sum- marized as follows: Initially, the tank (containing salt water) is considered full (500 L) as well as the basin (100 L); The water position in the basin is checked, which should be between two levels (L1 = 2 cm and L2 = 10 cm); if the position sensor indicates that the measured level is less than L1, the microcontroller activates the relay and the valve will be opened till the water level L2 is reached; then, the relay is activated automatically by sending a signal from the microcontroller; Energies 2021, 14, 6892 3 of 12 The water level in the tank is verified; if the level is less than L3 = 500 L, the microcon- troller sends a signal to start the water pump, till the L3 is reached; The Wi-Fi module is programmed to send the measured parameters to the cloud every 5 min, via the IoT technique ; Energies 2021, 14, x FOR PEER REVIEW If the system stops, an anomaly occurs or no distiller water is produced, the user is 3 of 13 alerted by a simple SMS via a phone. Energies 2021, 14, x FOR PEER REVIEW 4 o Figure 1. Figure 1. Smart Smart hybrid solar heater–solar hybrid solar heater–solar still still desalination desalination system. system. Figure 2 shows a photo of the designed hybrid solar heater–solar still prototype. Figure 2. A photo of the designed smart hybrid solar heater–solar still system. 2.1.Figure 2. A photo Monitoring of the designed and Displaying smart Solar Still hybrid solar Desalination heater–solar still system. Parameters Figure 3 shows the scheme of the developed monitoring system. The different con- Figure 2. A photo of the designed smart hybrid solar heater–solar still system. The main stepsstituents of the control are asprocess, follows:implemented in the microcontroller, are summarized as follows: The main Sensors steps oftemperature, (ambient the control process, relativeimplemented in the humidity, inside microcontroller, temperature, water are sum- tempera- marized Initially, ture,aswater the follows: tank level (containing and amountsalt water) is considered of distilled full (500 L) as well as the basin (100 L); output water); Initially, Actuators  water The (valve the tank position and water (containing in the basin pump); which should be between two levels (L1 = 2 cm and L2 salt water) is considered full (500 L) as well as the basin is checked, Liquid crystal display (LCD) permits us to visualize the measured data; 10 cm);(100 L); position sensor indicates that the measured level is less than L1, the microcontroller if the A low-cost microcontroller (Arduino Mega 2560) is used to control and monitor  Thethe activates water position relay and theininside the basin valve will is opened be checked, which should be L2 between two levels (L1 relay is different parameters and outside thetill solarthestill water level desalination is reached; unit. then, the The parameters = 2 cm and L2 = 10 cm); if the position sensor indicates that the measured level is less monitored are Ta, by activated Tstill, RH, Tw, WL and Wd (daily amount of output distilled water). thanautomatically sending L1, the microcontroller a signal activates from the the relay microcontroller; and the valve will be opened till the waterlevel The water levelinL2 theistank reached; then, the is verified; relay if the is activated level automatically is less than L3 = 500 L,by thesending a sig- microcontroller send nal from the microcontroller; signal to start the water pump, till the L3 is reached;  The water level in the tank is verified; if the level is less than L3 = 500 L, the micro- The Wi-Fi module is programmed to send the measured parameters to the cloud every 5 min, via th controller sends a signal to start the water pump, till the L3 is reached; IoT  technique The Wi-Fi; module is programmed to send the measured parameters to the cloud every 5 stops, If the system min, via an the IoT technique anomaly occurs or; no distiller water is produced, the user is alerted by a sim  ature, water level and amount of distilled output water);  Actuators (valve and water pump);  Liquid crystal display (LCD) permits us to visualize the measured data;  A low-cost microcontroller (Arduino Mega 2560) is used to control and monitor dif- Energies 2021, 14, 6892 ferent parameters inside and outside the solar still desalination unit. The parameters 4 of 12 monitored are Ta, Tstill, RH, Tw, WL and Wd (daily amount of output distilled wa- ter). Figure 3. Basic structure of the monitoring system (solid line: power, dashed line: data). Figure 3. Basic structure of the monitoring system (solid line: power, dashed line: data). The different steps of the control process are as follows: The different steps of the control process are as follows: Step #1: Initialization and loading of reference parameters (Tref, RHref and WLref),  whichStep #1:areInitialization and loading based on experimental of reference parameters (Tref, RHref and WLref), thresholds. which are based on experimental thresholds. Step #2: Measuring real parameters (Ta, Tstill, RH, Tw, WL and Wd).  Step Step#3: #2: Sending Measuring realtoparameters signal (Ta,by the actioners Tstill, RH, Tw, activating theWL and Wd). relay: corresponding  Step #3: Sending signal to the actioners by activating the corresponding relay: - Water pump: start filling the tank. -- Valve: Waterstart pump: startthe filling filling solarthe tank. basin. - Valve: start filling the solar basin. 2.2. Webpage Development 2.2. Webpage Development In order to upload and collect measured data and images showing a drop of water on theInsurface order toof upload the still,and collect a Wi-Fi measured camera data and (e.g., ESP32) images and a Wi-Fishowing a drop of water (e.g., NodeMCU) have on the been surface used. The of the still,was webpage a Wi-Fi camera designed for(e.g. ESP32) and aof the visualization Wi-Fi (e.g. NodeMCU) the phenomenon have of water Energies 2021, 14,been x FORused. PEER REVIEW The webpage was designed 5 of 13 evaporation. Figure 4 presents a block for the visualization diagram of the for uploading thephenomenon of water measured data and evaporation. images onto theFigure 4 presents webpage usingathe block IoTdiagram technique for. uploading the measured data and im- ages onto the webpage using the IoT technique. Figure 4. Uploading measured data and images onto the webpage. Figure 4. Uploading measured data and images onto the webpage. The page configuration has been designed using Hyper Text Markup Language (HTML) and, for an adequate environment, a Cascading Style Sheet (CSS) was used. For creating a dynamic environment, JavaScript was used. The Firebase conceived by Google was used to host the webpage and database management. Energies 2021, 14, 6892 5 of 12 Figure 4. Uploading measured data and images onto the webpage. The page configuration has been designed using Hyper Text Markup Language The page configuration has been designed using Hyper Text Markup Language (HTML) and, for an adequate environment, a Cascading Style Sheet (CSS) was used. For (HTML) and, for an adequate environment, a Cascading Style Sheet (CSS) was used. For creating a dynamic environment, JavaScript was used. The Firebase conceived by Google creating a dynamic environment, JavaScript was used. The Firebase conceived by Google was used to host the webpage and database management. was used to host the webpage and database management. 2.3.Mobile 2.3. MobileApplication Application ByByusing usingthe theNodeMCU NodeMCUESP8266 ESP8266module moduleand andExpo ExpoReact-Native, React-Native,we wedeveloped developedanan application for a mobile phone that allows the visualization of different application for a mobile phone that allows the visualization of different data issued data issuedfrom from solar still desalination unit parameters remotely. The use of a GSM module solar still desalination unit parameters remotely. The use of a GSM module with Arduino with Arduino allowsnotification allows notificationfor forusers usersabout aboutthethestatus statusofofthe thesolar solarstill stilldesalination desalinationunit. unit.Figure Figure5 5 providesa ablock provides blockdiagram diagramofofthis thisapplication. application. Energies 2021, 14, x FOR PEER REVIEW 6 of 13 Figure5.5.Mobile Figure Mobileapplication applicationstructure structurefor forSMS SMSnotification. notification. 2.4. Stand-Alone Photovoltaic System 2.4. Stand-Alone Photovoltaic System An autonomous photovoltaic (PV) system has been used to supply the different sen- An autonomous sors of photovoltaic the desalination (PV) unit,system includinghasthebeen waterused pump toand supply the different the electronic board. It com- sensors of the desalination prised one PV unit, moduleincluding (75 Wp)the water pump connected and the12electronic to one battery V/200 Ah, aboard. It solar charge reg- comprised one PV ulator (12 V/20 module (75A), Wp) a voltage regulator connected and to one a DC-DC battery buck converter 12 V/200 (in =charge Ah, a solar 7–12 V and out = 5 or regulator (12 V/20 A),3.3 V). a voltage regulator and a DC-DC buck converter (in = 7–12 V and out = 5 or 3.3 V). Figure 6 presents the block diagram of the PV system used to supply the electronic board and Figure 6 presents themicrocontroller block diagramused for PV of the monitoring system the solar used to still supplydesalination unit. the electronic board and microcontroller used for monitoring the solar still desalination unit. Figure 6. Supplying the SSDU using a PV system. Figure 6. Supplying the SSDU using a PV system. Figure 7 shows a photo of the stand-alone PV system installed on the roof of the Fac- ulty of Science at Islamic University (IU) of Madinah, Saudi Arabia. Energies 2021, 14, 6892 6 of 12 Figure 6. Supplying the SSDU using a PV system. Figure 7 shows Figure a photo 7 shows a of the stand-alone photo PV systemPV of the stand-alone installed systemon installed the roof ofon thethe Fac-roof of the ultyFaculty of Science at IslamicatUniversity of Science (IU) of Madinah, Islamic University (IU) ofSaudi Arabia. Madinah, Saudi Arabia. Figure Figure7.7.AA photo of of photo thethe solar desalination solar unit unit desalination powered by stand-alone powered PV system by stand-alone (roof of(roof PV system the Faculty of the of Science Faculty ofbuild- Science building at IU, Madinah, KSA). ing at IU, Madinah, KSA). 3. Results and Discussion To study the performance of the designed solar still desalination prototype, different experiments were performed. 3.1. Designed Prototype Figure 8 shows a photo of the developed solar still desalination prototype, including Energies 2021, 14, x FOR PEER REVIEW 9 of 19 the microcontroller Arduino Mega Board. The whole prototype’s Capital cost (Cs) was around USD 250. Figure 8. A photo of the smart hybrid solar heater–solar still desalination unit. Figure 8. A photo of the smart hybrid solar heater–solar still desalination unit. 3.2. Data Visualization Monitoring  Energies 2021, 14, 6892 7 of 12 3.2. Data Visualization Monitoring A monitoring system was developed to visualize the measured parameters online. The graphic interface of the main webpage designed for the smart solar desalination unit is presented in Figure 9a. Figure 9b shows the data posted on the webpage, collected from Energies 2021, 14, x FOR PEER REVIEW 8 of 13 the solar desalination unit. The uploaded data are the real-time values of Ta, Tstill, Tw1 and Tw2 recorded on 18th February 2021. (a) Graphical interface Solar Desalination Unit (b) Measured parameters of SSDU 120 Measured Parameters 100 80 60 40 20 0 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 Time (Hours) Ta Tw1 Tstill Tw2 Figure 9. The mainFigure webpage9. The main of the webpage solar of the solar still desalination still unit desalination (SSDU). unit (SSDU). (a) Graphic (a)(b) interface, Graphic interface, measured (b) parameters, Ta, Tw1, Tstill and Tw2,measured parameters, on 18 February 2021. Ta, Tw1, Tstill and Tw2, on 18 February 2021 Energies 2021, 14, 6892 8 of 12 3.3. Warning SMS A phone application was developed to check the status of the desalination unit. Thus, users can be notified by an SMS if any problem arises. An example of a warning SMS Energies 2021, notification informing the user that the tank of salted water is empty is illustrated in Energies 2021, 14,14, x FOR x FOR PEER PEER REVIEW REVIEW 9 9ofof1313 Figure 10. Figure Figure 10.10. SMS SMS notification notification (e.g.,tank (e.g., tankofof salted salted water water is is empty). empty). Figure 10. SMS notification (e.g., tank of salted water is empty). 3.4.Mobile 3.4. 3.4. MobileApplication Mobile Application Application AA A photo photo photo ofofthe of thethemobile mobile mobile application application application isis is presented presented presented inin in Figure Figure Figure 11. 11. 11. This This This application application application can can can help help help usersto users users totocontrol control control thethe the collected collected collected parameters parameters parameters ofof of the the the desalination desalination desalination unit unit unit remotely. remotely. remotely. Figure Figure Figure 11.11. 11. TheThe The main main main Android Android Android app app app screen screen screen for for for the the the designed designed designed smart smart smart solar solar solar still still still desalination desalination desalination unit. unit. unit. 3.5.Effects 3.5. 3.5. Effectsof Effects ofofDifferent DifferentParameters Different Parameterson Parameters onon the the the Yields Yields Yields ofof of Distilled Distilled Distilled Output Output Output Water Water Water Figure Figure Figure 12a 12a 12a presents presents presents thethe the evolution evolution evolution ofof of the the the hourly hourly hourly output output output water water water versus versus versus time timetime for for for different different different waterdepths. water water depths.The depths. Themaximum The maximumyield maximum yieldofofdistilled yield of distilledwater distilled waterisisobtained water is obtainedfor obtained forfora awater a waterdepth water depthofof22 2cm. depth of cm. cm. Figure 12b displays the variation in the yield of the solar still for diverse depths. It can bebe Figure Figure 12b12b displays displays thethe variation variation inin the the yield yield ofof the the solar solar still still forfor diverse diverse depths. depths. It It can canbe notedfrom noted noted from from the thethe curve curve curve that that that the the the maximum maximum maximum yield yield yield isis is obtained obtained obtained atat at thethe the minimum minimum minimum depth, depth, depth, which which which is is due essentially to the fast evaporation process. The effect of is due essentially to the fast evaporation process. The effect of coupling a solar heater on due essentially to the fast evaporation process. The effect of coupling coupling a a solar solar heater heater onon thethe yield yield ofof thethe solar solar still still waswas analyzed, analyzed, asas shown shown in in Figure Figure 12c. the yield of the solar still was analyzed, as shown in Figure 12c. It can be observed from 12c.It It can canbe be observed observed from from thetheexperimental experimentalresult resultthat thatthe theyield yieldofofthe thehybrid hybridsolarsolarheater–solar heater–solarstill stillisisnotably notablybetter better than that of a simple solar than that of a simple solar still. still. ItItwas wasfound foundthatthatthetheefficiency efficiencyofofthe thedesigned designedprototype prototype(hybrid(hybridsolarsolarheater–solar heater–solar still) is higher than a conventional double-slope solar still for still) is higher than a conventional double-slope solar still for the same basin conditions. the same basin conditions.  The water sample analyzed has a pH within the safe limit of 6.5 to 8.5 standard values. The permissible limit for EC is 300 µS cm−1. The EC of the used sample before desal- ination is 7550 µS/cm, which is higher than the standard value, and, after desalination, the electrical conductivity is 384 µS/cm. This shows that the EC value of water sample, Energies 2021, 14, 6892 after desalination, is reduced considerably and is almost close to the ordinary home 9water of 12 at Madinah City. Concerning the TDS, before treatment, the TDS value is 3770 (mg/L), and after desalination, it is 210 (mg/L). This shows that the TDS value of water after desalina- tion is close to the permissible value, which is 350 mg/L [15,16]. The salinity of the tested the experimental result that the yield of the hybrid solar heater–solar still is notably better groundwater is 0.39%, corresponding to 3.9 g/kg. After desalination, the salinity is 0.01%, than that of a simple solar still. corresponding to 0.1 g/kg. Figure 12. Figure 12. (a) (a) Hourly Hourly yield yield for for different differentwater water depths, depths,(b) (b)evolution evolution of of the theyield yieldof ofstill stillfor fordifferent different water depths and (c) hourly yield of double-slope solar still and proposed hybrid solar still. water depths and (c) hourly yield of double-slope solar still and proposed hybrid solar still. It was found that the efficiency of the designed prototype (hybrid solar heater–solar still) is higher than a conventional double-slope solar still for the same basin conditions. The daily yield produced by the double-slope solar still is 9.73 L/m2 /day, while the hybrid solar heater–solar still produces around 12.165 L/m2 /day. To check the water quality, some physical–chemical parameters, such as the concentration of hydrogen ions (pH), electrical conductivity (EC), total dissolved solids (TDS) and salt in the groundwater (before and after desalination), are measured. The test results are listed in Table 1. Table 1. Comparison of groundwater (before and after desalination): physical–chemical parameters. Groundwater Groundwater after Mineral Water Ordinary Home Chemical Parameters before Desalination Desalination (Nestle) Water pH 7.68 7.18 7.15 8.13 Electrical conductivity (µS/cm) 7550 384 225 361 TDS (mg/L) 3770 210 114 178 Salt (%) 0.39 0.01 0.01 0.01 Bold highlights the results obtained after desalination. A comparison was made with mineral water (Nestle) and ordinary home drinking water. The results show that the groundwater after desalination has almost the same values of chemical parameters as mineral water (Nestle) and ordinary home drinking water. The water sample analyzed has a pH within the safe limit of 6.5 to 8.5 standard values. The permissible limit for EC is 300 µS cm−1. The EC of the used sample before desalination is 7550 µS/cm, which is higher than the standard value, and, after Energies 2021, 14, 6892 10 of 12 desalination, the electrical conductivity is 384 µS/cm. This shows that the EC value of water sample, after desalination, is reduced considerably and is almost close to the ordinary home water at Madinah City. Concerning the TDS, before treatment, the TDS value is 3770 (mg/L), and after desalination, it is 210 (mg/L). This shows that the TDS value of water after desalination is close to the permissible value, which is 350 mg/L [15,16]. The salinity of the tested groundwater is 0.39%, corresponding to 3.9 g/kg. After desalination, the salinity is 0.01%, corresponding to 0.1 g/kg. 3.6. Cost Calculation of Solar Stills The unit cost of the desalination of saline water (UCdw) is the ratio of the total annual cost (TAC) of the passive solar still per unit area and the average annual productivity in liters (Myearly ) of the solar still per unit area. The costs of different types of solar stills are given in Table 2. TAC UCdw = (1) Myearly where TAC depends principally on the present capital cost (Cs), on the number of clear days in a year and on the average daily distillate output per unit area. Table 2. The unit cost of desalination of saline water. Solar Stills References Cs (US$) Myearly (L) UCdw (US$/L) Double slope 106 1511 0.007 Hybrid solar heater–double slope (Present work) 250 1800 0.022 Single slope 179 1043 0.024 Pyramid shape 250 1533 0.026 Solar still with solar concentrator 300 990 0.050 Bold highlights the results obtained for the present work. In Table 2, we show that the double-slope solar still has the lowest cost of de- salination (0.007 US$/L). The proposed hybrid solar heater–solar still presents a cost that is slightly greater than that of the conventional double-slope solar still but a better cost compared to the other types of solar still and gives the best average annual productivity in liters (1800 L/m2 ). 4. Conclusions A smart solar still water desalination prototype has been designed and verified experi- mentally at Madinah City, Saudi Arabia. It has been demonstrated that the proposed hybrid solar heater–solar still water desalination system outperforms the solar still with two slopes. The evaporation process of saline water has been significantly accelerated, consequently improving the daily yield, which reached a maximum value of 12.165 L/m2 /day, and the quality of distilled water complies with World Health Organization standards. A low-cost monitoring system has been developed and integrated with the hybrid solar still system. Thanks to the IoT technique, measured data have been posted online for the real-time and remote monitoring of the considered system. The PV system incorporated into the proposed prototype is used to supply the components of the solar still unit, like as sensors, electronic boards and water pump. Users can monitor and check their system remotely from their offices or homes, if we suppose that such systems are installed in remote areas. The proposed prototype could be generalized for large-scale solar desalination plants. Author Contributions: Data curation, M.B., A.M. and A.A.; Formal analysis, M.B. and A.M.; Funding acquisition, M.B.; Investigation, M.B. and A.M.; Methodology, M.B., A.M. and M.E.; Supervision, M.B. and A.M.; Writing—original draft, M.B. and A.M. All authors have read and agreed to the published version of the manuscript. Energies 2021, 14, 6892 11 of 12 Funding: This research was funded by the Deputyship for Research & Innovation, Ministry of Education in Saudi Arabia, Research Project No. 20/1. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Acknowledgments: The authors extend their appreciation to the Deputyship for Research & Inno- vation, Ministry of Education in Saudi Arabia for funding this research work through the project number 20/1. Conflicts of Interest: The authors declare no conflict of interest. Abbreviations Cs Capital cost CSS Cascading Style Sheets DC Direct current EC Electrical conductivity GSM Global System for Mobile Communications IoT Internet of Things LED Light-emitting diode LCD Liquid crystal display MENA Middle East and North Africa Myearly Average annual productivity of distilled water NodeMCU Node microcontroller unit pH pH is a scale used to specify the acidity or basicity of an aqueous solution PV Photovoltaic RH Relative humidity RHref Reference value of relative humidity SAPV Stand-alone PV system SMS Short Message Service SSDU Solar still desalination unit Ta Air temperature (ambient) TAC Total annual cost TDS Total dissolved solids Tstill Temperature inside the still Tref Reference value of temperature Tw Water temperature UCdw Unit cost of desalination of saline water WL Water level WLref Reference value of water level Wd Distilled water (output water) Wp Watt pick (maximum power of PV panel) References 1. 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