Construction and Automation of a Microcontrolled Solar Tracker

processes

Article Construction and Automation of a Microcontrolled Solar Tracker

Juliano da Rocha Queiroz 1, Anacreone da Silva Souza 1, Maurício Klein Gussoli 2 , Júlio César Dainezi de Oliveira 2 and Cid Marcos Gonçalves Andrade 3,*

1 Federal Institute of Paraná, Ivaiporã 86870-000, Brazil; [email protected] (J.d.R.Q.); [email protected] (A.d.S.S.) 2 Department of Mechanical Engineering, State University of Maringá, Maringá 87020-900, Brazil; [email protected] (M.K.G.); [email protected] (J.C.D.d.O.) 3 Department of Chemical Engineering, State University of Maringá, Maringá 87020-900, Brazil * Correspondence: [email protected]

Received: 30 May 2020; Accepted: 7 July 2020; Published: 19 October 2020

Abstract: A solar tracker can be deﬁned as an electromechanical system capable of following the apparent path of the Sun, in order to orient an array of solar panels and/or collectors directly to the solar rays, maximizing the collected energy. Accordingly, the present work describes the process of building and automating a micro-controlled solar tracker. Two mobile structures were built, one equipped with high-precision step motors and four luminosity sensors separated in quadrants by a cross structure, and the other equipped with DC motors and the 275 Wp solar panel, allowing the design and evaluation of the behavior of each structure separately. The control and automation system is centralized in an Arduino MEGA2560 microcontroller, which runs the tracking and positioning algorithms. The built prototype allows us to carry out studies of solar tracking strategies based on sensor and control systems applied to DC motors.

Keywords: solar tracker; photovoltaic; renewable energy; microcontroller

1. Introduction About 86% of the world’s energy matrix is made up of non-renewable resources, such as coal, oil and natural gas, while renewable resources such as solar, wind and geothermal represent only 14%. The Brazilian energy matrix is constituted of 43% from renewable sources, especially from biomass cane (17%) and hydraulic energy (12%). When restricted to electricity, the share of renewable sources is extended to 23% in the world, while in Brazil it exceeds 80%, focusing on hydraulic (65.2%), biomass (8.2%) and wind energy (6.8%). Solar energy, however, accounts for only 0.13% of the Brazilian electricity matrix, being used more in micro and mini generation [1]. Despite its low participation in the Brazilian energy matrix, the installed capacity of solar energy increased from 24 MW in 2016 to 935 MW in 2017 [1]. Overall, the photovoltaic market grew from 76 to 98 GW in the same period, with more than 75% installed in Asia, particularly in China (53 GW) and India (9.1 GW). In Europe, the country with the largest installed capacity is Germany with 1.8 GW, while in America we highlight the United States with 10.6 GW, Brazil with 935 MW and Chile with 668 MW [2]. The Earth’s surface receives enough solar energy annually to supply 7500 times the world’s energy needs in the same period [3]. However, solar energy needs to be converted into electrical energy through the photovoltaic eﬀect, discovered in 1839 by Edmond Becquerel, which consists of the transfer of photon energy to electrons in the semiconductor valence band, creating an electron-gap pair associated with a potential diﬀerence [4]. Since the power generated by a photovoltaic system depends

Processes 2020, 8, 1309; doi:10.3390/pr8101309 www.mdpi.com/journal/processes Processes 2020, 8, 1309 2 of 17 on the amount of solar radiation received, new technologies are studied and developed to maximize the energy collected. Among them are the solar panel angular position optimization systems, known as the solar tracker [5]. The solar tracker can be defined as an electromechanical device that follows the apparent trajectory of the Sun by positioning an array of panels and/or concentrators in the direction of the Sun’s rays. The first solar trackers were developed in Chile in 1962 and 1963, the first being a completely mechanical system with little gain [6], while the second already had an automatic irradiation sensing control system [7]. The first patent filed for a commercial solar tracker dates back to 1980, which featured an analog control system with a pair of photo sensors [8]. In the last four decades, several types of solar trackers have been proposed and developed, which can be classified according to four main characteristics: number of movement axes, presence of electronic system, presence of feedback and tracking strategy [5]. Regarding the number of movement axes, tracking systems can be built with one or two axes. Single axis trackers are usually oriented in the north direction and can be in horizontal (HSAT), horizontal with tilt (HTSAT), vertical (VSAT), inclined (TSAT) and polar inclined (PSAT) modules [5]. Katrandzhiev and Karnobatev (2018) proposed control algorithms to control a single-axis solar tracker that can operate manually, using light sensors and with movements programmed by time [9]. Mehdi et al. (2019) reported the energy provided by a single axis tracker being 50% higher compared to a static system [10]. In general, this type of tracker has lower tracking accuracy, due to the limitations of movement, but has less construction and control complexity. In contrast, two-axis trackers have greater tracking accuracy, thanks to their greater constructive and control complexity [5]. Sawant et al. (2018) presented a two-axis solar tracker that uses light-dependent resistors (LDRs) and a microcontroller in the control system, obtaining a 25% greater efficiency compared to single-axis systems [11]. The complete mathematical model of a two-axis solar tracker was developed by Ikhwan et al. (2018), as well as the proposal of a predictive control, which presented absolute errors less than 0.8◦ and mean error of 0.027◦ [12]. The low-cost approaches usually use Arduino, as with the device presented by Kaur et al. (2016), which obtained average gain of 13.44%, compared to the static panel [13]. Regarding the presence of an electronic system, trackers without control system are called passive, in which the position of the module is changed by a mechanical arrangement due to the incidence of inhomogeneous solar radiation on the system. Mwithiga and Kigo (2006) proposed a passive axis solar tracker, in which an expansive gas unbalances the system seeking alignment with the Sun’s rays [14]. The main advantage of this system is the simplicity of construction associated with the non-consumption of electricity in its operation; however, its tracking capacity is limited [5]. In contrast, the active trackers that use electronics, usually based on a microcontroller associated with electrical sensors and motors, provides greater accuracy in tracking. Examples of such a system are the trackers described by Mehdi et al. [10], Sawant et al. [11] and Kaur et al. [13]. Control systems used in solar trackers can be open or closed loop. Closed loop controllers have as their main feature the feedback signal of the output variable. Sensors are used to determine appropriate Sun position parameters, which are manipulated by the controller through tracking and control algorithms and techniques, and then trigger the device’s reorientation mechanisms towards the Sun [15]. Conversely, open loop controllers do not use feedback and decision-making is based only on the current state of the system. Thus, open loop controllers are simpler and cheaper, but do not allow for correcting steady state errors, as well as compensating for disturbances during system operation [16]. The tracking strategy used can be of three types: chronological, sensor or hybrid. In the chronological tracking strategy, a set of astronomical equations is used to determine the system orientation from the date, time and geographic location of the site [5]. In systems that use sensors to track the position of the Sun, two pairs of light-dependent resistors (LDRs) are usually employed in a cross-shaped structure. The illumination difference between these sensors is converted into different Processes 2020, 8, 1309 3 of 17 voltage levels, which are used as input signals for the algorithm that will determine the positioning of the panels. The equal illumination of the four sensors indicates that the panel surface is exactly perpendicular to the Sun’s rays and thus receiving as much light energy as possible [17]. The hybrid strategy, on the other hand, combines both the use of sensors and positioning from the theoretical position of Sun. A direct comparison of the three strategies has been performed in [18], wherein the gains were 8.5 (chronological), 10 (for sensors) and 13 (hybrid) percent in relation to the fixed panel. Table1 summarizes the main characteristics of the surveyed solar trackers, in which references with a * symbol use Arduino as an electronic control unit.

Table 1. Characteristics of tracking systems.

Tracking System Advantage Disadvantage References Lower performance than the Constructive simplicity. Easy Single Axis system with two axes. Limited [5], [9] *, [10]* control system. Lower cost. placement. Higher efficiency (compared to Higher cost and constructive Two Axis single-axis systems). More [11] *, [12] complexity. accurate positioning. Low efficiency. Limited to single Simple construction. Do not axis devices. Do not operate Passive need a control system and [5,14] satisfactorily in regions with power supply. very low temperatures. Greater efficiency (compared to Needs an external control passive). Operate under any system electrically powered. Active climatic conditions and can be [10,11], [13]* Greater complexity (compared applied to systems with one or to passive). two axes. Allows error correction and Greater complexity of the Closed Loop disturbances compensation, [15]* control system. Higher costs. enabling precise orientation. Needs a detailed preliminary Constructive simplicity study for the initial calibration Open Loop (compared to closed-loop [11,16] and initial parameters of the systems). Lower cost. algorithm. Constructive simplicity. Low efficiency. Need for a The control system is not Chronological previous study designed for [5] affected by disturbances (like proper functioning. clouds for example). Algorithm more complex Greater efficiency. Accurate control. It needs an accurate Sensors [17] tracking of the Sun’s position. modeling of the sensors. Affected by clouds. Higher cost. Greater complexity Combine the two tracking of the control system. It needs Hybrid [18]* strategies, greater accuracy. good modeling of the sensors and an adequate prior study.

In this context, this paper aims to report the process of construction and automation of a two-axis micro-controlled solar tracker with a sensor tracking strategy. The electronics are based on an Arduino MEGA2560 and four LDR-type light sensors. The built prototype was able to track the Sun and position the solar panel with a tolerance of 1 degree, achieving 39.5% energy gain on a 13 summer-day period. The two-axis tracker was chosen due to the latitude where the prototype was installed ( 24.25 ). − ◦ Figure1 shows the Sun’s apparent position and the annual variation at latitude 24.25 , and Figure2 − ◦ presents this variation in a location with the same longitude but located on the equator line [19]. In locations further away from the equator line, the variation in the elevation angle throughout the year is considerably greater, which justiﬁes the use of a two-axis system due to its positioning capability, allowing us to keep the panel perpendicular to the Sun’s rays in every season. Processes 2020, 8, 1309 4 of 17

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Figure 1. Sun’s apparent position annual variation at latitude −24.25° [19]. FigureFigure 1. 1.Sun’s Sun’s apparentapparent positionposition annualannualvariation variation at at latitude latitude −24.24.2525◦° [[19]19].. −

Figure 2. Sun’s apparent position annual variation at equator line [19]. Figure 2. Sun’s apparent position annual variation at equator line [19]. Figure 2. Sun’s apparent position annual variation at equator line [19]. The main contributions of this work are: to separate the structure of the tracker from the The main contributions of this work are: to separate the structure of the tracker from the structureThe mainwith contributionsthe solar panel, of thisallowing work greater are: to separateaccuracy the in structuretracking with of the lower tracker power from consumption the structure structure with the solar panel, allowing greater accuracy in tracking with lower power consumption withdue to the the solar size panel, and allowingweight of greater the device; accuracy to use in tracking commercial with solar lower panels power with consumption power of due 275 to Wp the, due to the size and weight of the device; to use commercial solar panels with power of 275 Wp, sizesimulating and weight real applications; of the device; and to use to provide commercial a proposal solar panels to change with the power tracking of 275 algorithm Wp, simulating to consider real simulating real applications; and to provide a proposal to change the tracking algorithm to consider applications;periods of low and irradiation, to provide avoiding a proposal unnecessary to change device the tracking movement. algorithm to consider periods of low irradiation,periods of low avoiding irradiation, unnecessary avoiding device unnecessary movement. device movement. 2. Prototype Construction 2.2. PrototypePrototype ConstructionConstruction The proposed system (Figure 3) consists of two mechanical structures with two axes of freedom, TheThe proposedproposed systemsystem (Figure(Figure3 )3) consists consists of of two two mechanical mechanical structures structures with with two two axes axes of of freedom, freedom, which are able to rotate around the elevation (angle to the horizon) and azimuth (angle to the north) whichwhich areare ableable toto rotaterotate aroundaround thethe elevationelevation (angle(angle toto thethe horizon)horizon) andand azimuthazimuth (angle(angle toto thethe north)north) axes, and one fixed structure with a conventional photovoltaic system. The first structure is equipped axes,axes, andand oneone ﬁxedfixed structurestructure withwith aa conventionalconventional photovoltaicphotovoltaic system. system. TheThe ﬁrstfirst structurestructure isis equippedequipped with two stepper motors and four light sensors, being responsible for tracking the apparent position withwith two two stepper stepper motors motors and and four four light light sensors, sensors, being being responsible responsible for for tracking tracking the the apparent apparent position position of of the Sun. The second structure uses direct current motors to move the photovoltaic panel. theof the Sun. Sun. The The second second structure structure uses use directs direct current current motors motors to move to move the the photovoltaic photovoltaic panel. panel.

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FigureFigure 3. 3. PrototypePrototype of of two two-axistwo--axisaxis active active solar solar tracke tracker.tracker.r.

Control and automation are centralized in a microcontroller electronic system, which performs ControlControl andand automationautomation areare centralizedcentralized inin aa microcontrollermicrocontroller electronicelectronic system,system, whichwhich performsperforms analoganalog sensorsensorsensor readings, readings,readings, communicate communicatecommunicate with withwith digital digitaldigital sensors, sensors,sensors, run the run trackingrun thethe andtrackingtracking positioning andand positioningpositioning algorithms, algorithms,inalgorithms, addition toinin controllingadditionaddition toto actuators. controllingcontrolling actuators.actuators. TheThe solarsolar trackertrackertracker device devicedevice is isis constructed constructconstructeded in inin an anan aluminum aluminumaluminum frame, frame,frame, with withwith height heightheight adjustable adjustableadjustable by by screwby screwscrew on onaon tripod, aa tripod,tripod, equipped equippedequipped with withwith two twotwo stepper stepperstepper motors motorsmotors that thatthat provide provideprovide movement movementmovement in inin the thethe angles anglesangles of ofof elevation elevationelevation andand azimuth.azimuth. These These stepper stepper motors motors are are connected connected to to the the rotation rotation system system by by endlessendless scrscr screw,ew,ew, which which amplify amplify movementmovement accuracy, accuracy, enablingenabling fourfour stepssteps perper degree.degree.degree. In In addition, addition, the the endlessendless screwscrew systemsystem allowsallows motionmotion transmission transmission only only in in the the direction direction of of the the frame, frame, reducing reducing external external wind wind and and gravity gravity action.action. TheThe lightlight sensorsensor arrayarray isis positionedpositionpositioneded atat thethe toptop ofof thethe device,device, consistingconsisting ofof aa 2020 cmcm highhigh andand 66 cmcm widewide polyvinylpolyvinyl chloridechloride crosscross structurestructure andand 44 light-dependentlightlight--dependentdependent sensors.sensors. Figure Figure 4 44 shows showsshows the thethe trackingtrackingtracking device,device,device, withwith detailsdetails forfor thethe endlessendless screwscrew system.system.system.

((aa)) ((bb)) Figure 4. Constructive details of the tracking structure: (a) structure overview; (b) gear and engine Figure 4.4. ConstructiveConstructive details details of of the the tracking tracking structure: structure (a): structure(a) structure overview; overview; (b) gear (b) andgear engine and engine detail. detaildetail.. A steel structure with a ﬁxed chain system coupled to DC motors was built to support the movable solarAA panel steelsteel with structurestructure dimensions withwith aa of fixedfixed 1.5 m chainchain by 1 msystemsystem and 18 coupledcoupled kg, as shown toto DCDC in motorsmotors Figure 5waswas. Azimuth builtbuilt toto movement supportsupport thethe is movablemovable solarsolar panelpanel withwith dimensionsdimensions ofof 1.51.5 mm byby 11 mm andand 1818 kgkg,, asas shownshown inin FigureFigure 55.. AzimuthAzimuth movementmovement isis achievedachieved byby meansmeans ofof aa bearingbearing connectedconnected toto aa disc,disc, inin whichwhich aa chainchain waswas attachedattached toto

Processes 2020, 8, 1309 6 of 17 achievedProcesses by 20 means20, 8, x of a bearing connected to a disc, in which a chain was attached to the6 outputof 17 of Processes 2020, 8, x 6 of 17 a 37:1the relation output gearbox.of a 37:1 Forrelation the elevationgearbox. For axis, the the elevation chain was axis, welded the chain in awas metal welded semicircle, in a metal to which the samesemicircle, gearbox to which system the issame connected. gearbox system This chain is connec andted. gearbox This chain system and allowsgearbox for system greater allows movement for the output of a 37:1 relation gearbox. For the elevation axis, the chain was welded in a metal accuracygreater and movement limits wind accuracy and gravityand limits action, wind and but gravity the speed action, is reduced. but the speed is reduced. semicircle, to which the same gearbox system is connected. This chain and gearbox system allows for greater movement accuracy and limits wind and gravity action, but the speed is reduced.

(a) (b) FigureFigure 5. Constructive 5. Constructive(a) details details of of the the solar solar panel structure: structure: (a ()a structure) structure overview;(b overview;) (b) motor (b) motor,, reduction reduction box and chain detail. boxFigure and chain5. Constructive detail. details of the solar panel structure: (a) structure overview; (b) motor, reduction box and chain detail. TheThe electronics electronics can can be be divided divided into into ﬁvefive mainmain modules, modules, as as shown shown in inFigure Figure 6. 6Control. Control and and processing are centralized on an Arduino MEGA2560, whose purpose is to communicate with the processingThe electronics are centralized can be on divided an Arduino into five MEGA2560, main modules, whose as shown purpose in isFigure to communicate 6. Control and with the other blocks through analog, digital signals and communication protocols. The human machine otherprocessing blocks are through centralized analog, on an digital Arduino signals MEGA2560, and communication whose purpose protocols.is to communicate The human with the machine interface module contains status indicator LEDs, a 16 × 2 LCD display that shows the measured and interfaceother blocks module through contains analog, status digital indicator signals LEDs, and communication a 16 2 LCD displayprotocols. that The shows human the machine measured and calculated quantities, a Bluetooth wireless communicator for laptop connection and a SD storage interface module contains status indicator LEDs, a 16 × 2× LCD display that shows the measured and calculatedcard. The quantities, sensing amodule Bluetooth include wireless the luminosity communicator sensors for (LDR), laptop current connection sensor and ACS712 a SD storage and a card. calculated quantities, a Bluetooth wireless communicator for laptop connection and a SD storage The sensingSpektron module solar radiation include sensor the luminosity connected sensorsto an analog (LDR),-to-digital current integrate sensord ACS712 circuit ADS1115 and a Spektron with 16 solar card. The sensing module include the luminosity sensors (LDR), current sensor ACS712 and a radiationbits resolution, sensor connected potentiometers to an analog-to-digitalserving as an angle integrated sensor and circuit a DS3132 ADS1115 digital withwatch. 16 Finally, bits resolution, the Spektron solar radiation sensor connected to an analog-to-digital integrated circuit ADS1115 with 16 potentiometerspower module serving consists as of an a DC angle voltage sensor source and with a DS3132 a rated digitalvoltage watch.of 12 V and Finally, a maximum the power current module bits resolution, potentiometers serving as an angle sensor and a DS3132 digital watch. Finally, the of 10 A, together with the stepping motors and DC motors in the full bridge inverter configuration. consistspower ofmodule a DC voltageconsists of source a DC withvoltage a ratedsource voltage with a rated of 12 voltage V and aof maximum 12 V and a currentmaximum of current 10 A, together withof 10 the A, stepping together motorswith the andsteppin DCg motorsmotors and in the DC full motors bridge in the inverter full bridge conﬁguration. inverter configuration.

Figure 6. Electronic system block diagram. Processes 2020, 8, x 7 of 17 Processes 2020, 8, x 7 of 17 Processes 2020, 8, 1309 Figure 6. Electronic system block diagram. 7 of 17 Figure 6. Electronic system block diagram. Due to the sequential drive characteristic of stepper motors, it was necessary to design a full Due to the sequential drive characteristic of stepper motors, it was necessary to design a full bridgeDue inverter to the circuit sequential (Figure drive 7) characteristicthat offered the of possibility stepper motors, of controlling it was necessary the current to at design the output a full bridge inverter circuit (Figure 7) that offered the possibility of controlling the current at the output bridgeby means inverter of an circuitanalog (Figurecomponent,7) that in o contrastffered the to possibilitythe traditional of controlling method of the pulse current width at modulation the output by means of an analog component, in contrast to the traditional method of pulse width modulation by(PWM). means For of this an analog purpose, component, potentiometers in contrast were toconnected the traditional to the methodgate of the of pulsepower width transistors modulation on the (PWM). For this purpose, potentiometers were connected to the gate of the power transistors on the (PWM).low side For of the this bridge, purpose, since potentiometers they are field were effect connected and the drain to the-source gate of current the power is proportional transistors onto thethe low side of the bridge, since they are field effect and the drain-source current is proportional to the lowvoltage side at of the the gate. bridge, In this since way, they adjusting are field the e ffvoltageect and divider the drain-source in the potentiometers, current is proportional the output current to the voltage at the gate. In this way, adjusting the voltage divider in the potentiometers, the output current voltagewas adjusted at the gate.to 2.5 In A, this in way,order adjusting to reduce the energy voltage consumption divider in the and potentiometers, prevent damage the outputto motors current and was adjusted to 2.5 A, in order to reduce energy consumption and prevent damage to motors and wastransistors. adjusted There to 2.5 were A, in five order full to reducebridge energyinverters, consumption two for each and bipolar prevent stepper damage motor to motors, and and an transistors. There were five full bridge inverters, two for each bipolar stepper motor, and an transistors.additional one There to werecontrol five the full DC bridge motors. inverters, two for each bipolar stepper motor, and an additional oneadditional to control one the to control DC motors. the DC motors.

Figure 7. Designed full bridge inverter. Figure 7. Designed full bridge inverter inverter.. The sensing of the angular position of the two built structures was carried out by means of the The sensing of the angular positionposition of the two built structures was carried out by means of the analog reading of the central pin of linear rotational potentiometers with a total resistance of 1 kΩ. analog reading of the central pin of linear rotational potentiometers with a total resistance of of 1 kΩ. kΩ. The relationship between the voltage read by the Arduino and the corresponding angle was The relationshiprelationship between between the the voltage voltage read read by the by Arduino the Arduino and the and corresponding the corresponding angle was angle performed was performed in an experimental way, taking measurements at 5° increment. This dataset was used to inperformed an experimental in an experimental way, taking measurementsway, taking me atasurements 5◦ increment. at 5° This increment dataset. was This used data toset adjust was used a cubic to adjust a cubic curve, which, together with moving average filters, perform the transformation of the curve,adjust which,a cubic togethercurve, which, with moving together average with moving ﬁlters, performaverage thefilters transformation, perform the of transformation the read value of in the read value in the AD to angle. Figure 8 shows the potentiometers used in the two structures. ADread to value angle. in Figurethe AD8 showsto angle. the Figure potentiometers 8 shows the used potentiometers in the two structures. used in the two structures.

FigureFigure 8.8. Constructive details of angle sensors.sensors. Figure 8. Constructive details of angle sensors. TheThe usedused solar panels characteristics are 38 V, 88 AA andand 275275 WW peak.peak. ToTo dissipatedissipate thethe generatedgenerated The used solar panels characteristics are 38 V, 8 A and 275 W peak. To dissipate the generated power,power, shielded shielded resistances resistances of of 3.5 3.5Ω were Ω were used used in an in aqueous an aqueous bath. bath. The voltageThe voltage is monitored is monitored by means by ofpower, a voltage shielded divider resistances circuit with of 3.5 an Ω attenuation were used factor in an ofaqu 1 toeous 11, bath. connected The voltage directly is to monitored the Arduino by

Processes 2020, 8, x 8 of 17 ProcessesProcesses 20202020, 8,, 8x, 1309 8 of8 of17 17 meansmeans of of a avoltage voltage divider divider circuit circuit with with an an attenuation attenuation factor factor of of 1 1to to 11, 11, connected connected directly directly to to the the ArduinoADArduino converter AD AD converter converter (Figure 9(Figure). (Figure The current 9). 9 ).The The iscurrent current measured is ismeasured measured by and ACS712 by by and and ACS712 Hall ACS712 E ﬀ ectHall Hall sensor, Effect Effect whosesensor, sensor, output whose whose is outputconnectedoutput is isconnected connected to the ADS1115 to to the the ADS1115 ADS1115 AD converter, AD AD converter, converter, in order in to in order increase order to to increase measurement increase measurement measurement accuracy. accuracy. accuracy. The Arduino, The The Arduino,throughArduino, through the through direct the the multiplication direct direct multiplication multiplication of the voltage of of the the byvoltage voltage the current, by by the the calculatescurrent, current, calculates calculates the generated the the generated generated power in powereachpower panel.in in each each panel panel. .

Figure 9. Dissipation circuit and power measurement. FigureFigure 9. 9.DissipationDissipation circuit circuit and and power power measurement. measurement.

AA cup cup anemometer anemometer was was used used to to measure measure wind wind speed, speed, in in order order to to interrupt interrupt the the system’s system’s operation operation whenwhenwhen wind windwind speed speedspeed exceeds exceeds exceeds 13.9 13.9 13.9 m/s, m m/s,/s, positioning positioning thethe the panelpanel panel parallel parallel parallel to to theto the the ground, ground, ground, to to avoid to avoid avoid damage damage damage risk risktorisk theto to the prototype. the prototype. prototype. The The DS3132The DS3132 DS3132 digital digital digital clock clock clock was was usedwas used used in combination in in combination combination with with thewith the SD the memorySD SD memory memory card card tocard store to to storethestore mainthe the main quantitiesmain quantities quantities measured measured measured and calculated and and calculated calculated in an orderlyin in an an orderly orderly manner. manner. manner. The electronic The The electronic electronic system system was system installed was was installedinsideinstalled a inside recycled inside a recycleda electricalrecycled electrical panel,electrical in panel, whichpanel, in twoin which which cooling two two cooling fans cooling were fans fans installed. were were installed. installed.

3.3. System System Automation Automation SystemSystem automation automation was was developed developed in in the the official official official Arduino Arduino integrated integrated development development environment environment ininin processing processing language, language,language, which whichwhich is is isbased basedbased on onon C C/CC//C++.C++++. Fundamentally,. Fundamentally, Fundamentally, the the program program consists consists of of algorithms algorithms forforfor tracking trackingtracking the thethe Sun’s Sun’s apparent apparentapparent position positionposition and andand for forfor controlling controllingcontrolling the thethe p hotovoltaic photovoltaicphotovoltaic panel panelpanel position. position.position. The The first firstfirst algorithmalgorithm aims aimsaims to to find findfind the the relative relative position position of of the the Sun Sun in in the the form form of of the the azimuth azimuth azimuth and and and elevation elevation elevation angles, angles, usingusing the the stepper stepperstepper motors motors’motors’ ordered’ orderedordered movement movementmovement on onon the thethe tracker trackertracker structure. structure.structure. The The angle angle values values found found are areare usedused as as input inputinput ref referencereferenceerence for forfor the thethe second secondsecond algorithm, algorithm,algorithm, which which drives drives direct direct current current motors motorsmotors to to control controlcontrol the thethe solarsolar panel panelpanel angular angularangular position. position.position. Figure Figure 10 10 shows shows the the block block diagram diagramdiagram of ofof the thethe closed closedclosed loop looploop control controlcontrol system. system.system.

Figure 10. Block diagram of the closed loop control system. FigureFigure 10. 10. BlockBlock diagram diagram of ofthe the closed closed loop loop control control system. system. The Sun tracking method employed is based on using four light sensors in a cross structure. The TheThe Sun Sun tra trackingcking method method employed employed is based is based on using on using four fourlight lightsensors sensors in a cross in a structure. cross structure. The sensors are light-dependent resistors (LDR) whose resistance drops dramatically with the incidence sensorsThe sensors are light are- light-dependentdependent resistors resistors (LDR) (LDR) whose whose resistance resistance drops drops dramatically dramatically with with the the incidence incidence of light (from MΩ to a few hundred Ω). Each LDR is connected to a voltage divider circuit together ofof light light (from (from MΩ MΩ toto a afew few hundred hundred Ω).Ω ).Each Each LDR LDR is isconnected connected to to a avoltag voltagee divider divider circuit circuit together together with a resistor, so the light intensity can be measured indirectly through the analog to digital withwith a a resistor, resistor, soso thethe light light intensity intensity can can be measuredbe measured indirectly indirectly through through the analog the analog to digital to converter. digital converter. When the cross structure is aligned with the Sun’s rays, the four sensors are illuminated converter.When the When cross the structure cross structure is aligned is withaligned the with Sun’s the rays, Sun’ thes rays, four the sensors four sensors are illuminated are illuminated equally, equally, resulting in very close voltage readings. When misalignment occurs, LDRs receive light equally,resulting resulting in very in close very voltage close readings.voltage readings. When misalignment When misalignment occurs, LDRsoccurs, receive LDRs lightreceive unevenly, light unevenly,unevenly, causing causing an an imbalance imbalance in in sensors sensors readings. readings. Figure Figure 11 11 illustrates illustrates the the S unSun’s ’srays rays striking striking

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Processes 2020, 8, x 9 of 17 causing an imbalance in sensors readings. Figure 11 illustrates the Sun’s rays striking unevenly betweenunevenlyProcesses the 20 leftbetween20, 8 and, x rightthe left sensors, and right causing sensors, a readingcausing a di readingﬀerence difference that indicates that indicates the direction the direction of9 of rotation 17 of rotation in the azimuth angle. The same principle can be applied when there is an imbalance in the azimuth angle. The same principle can be applied when there is an imbalance between the lower betweenunevenly the between lower and the leftupper and sensors right sensors, whose voltagecausing differencea reading differencepoints to the that direction indicates of the rotation direction at and upper sensors whose voltage diﬀerence points to the direction of rotation at the elevation angle. theof elevationrotation in angle. the azimuth angle. The same principle can be applied when there is an imbalance between the lower and upper sensors whose voltage difference points to the direction of rotation at the elevation angle.

FigureFigure 11. 11.Azimuth Azimuth angle angle sensor sensor tracking tracking method. method.

FigureFigure 12 presents12 presents the the flowchart flowchartFigure 11. of ofAzimuth thethe sensor sensor-tracking angle-tracking sensor tracking algorithm, algorithm, method. divided divided into intothree three situations: situations: 2 nightfall,nightfall, daylight daylight with with irradiation irradiation lowerlower than 600 600 W/m W/m 2andand daylight daylight with with irradiation irradiation higher higher than than 600 W/mFigure2. During 12 presents nightfall, the both flowchart the tracker of the and sensor the- movabletracking algorithm,panel structure divided moves into towards three situations: the east 600 W/m2. During nightfall, both the tracker and the movable panel structure moves towards the east innightfall, an initial daylight position. with The irradiationtracking strategy lower thanbased 600 on W/mlight 2sensors and daylight depends with on irradiationhigh irradiation higher level; than in an initial position. The tracking strategy based on light sensors depends on high irradiation level; therefore,600 W/m 2when. During the nightfall, irradiation both is thbelowe tracker minimum and the, the movable tracker panel does structure not move, moves and iftowards this situation the east therefore,lastsin an more wheninitial than theposition. fifteen irradiation Theminutes, tracking is belowthe movablestrategy minimum, basedpanel on thestructure light tracker sensors moves does dependstowards not move, ona default high and irradiation if position this situation based level; lasts moreontherefore, than the current fifteen when hour minutes, the of irradiation the the day. movable When is below irradiation panel minimum structure levels, the exceed tracker moves the does towards minimum, not move, a defaultthe and algorithm if position this situationfollows based on the currentthelasts proposed more hour than methodology, of fifteen the day. minutes, When moving the irradiation movablethe step- motopanel levelsrs structure exceedbased on moves the the minimum, LDR towards reading a the default difference. algorithm position As follows basedsoon the proposedason the the methodology,LDR current difference hour of moving became the day. thewithin When step-motors airradiation tolerance, based levelsthe tracking on exceed the LDR algorithmthe minimum, reading converge di thefference. algorithm and output As follows soon the as the LDRelevation ditheff erenceproposed and became azimuth methodology, within angles amovingas tolerance, reference the stepto the the-moto tracking positioningrs based algorithm algorithmon the LDR converge. reading and difference. outputthe As elevationsoon and azimuthas the LDR angles difference as reference became to within the positioning a tolerance, algorithm.the tracking algorithm converge and output the elevation and azimuth angles as reference to the positioning algorithm.

Figure 12. Flowchart of the sensor-tracking algorithm.

FigureFigure 12. 12.Flowchart Flowchart ofof thethe sensor-trackingsensor-tracking algorithm. algorithm.

Processes 2020, 8, 1309 10 of 17 Processes 2020, 8, x 10 of 17 Processes 2020, 8, x 10 of 17 AA simple closed loop on-oon-offﬀ controllercontroller withwith hysteresishysteresis performsperforms thethe movablemovable solar panel angular A simple closed loop on-off controller with hysteresis performs the movable solar panel angular positionposition control, as as shown shown in in Figure Figure 1 313. The. The angular angular reference reference comes comes from from the thetracking tracking algorithm algorithm and position control, as shown in Figure 13. The angular reference comes from the tracking algorithm and andis used, is used, together together with withsensing, sensing, to determi to determinene the error the errorsignal. signal. This signal This signaldetermines determines the full the bridge full is used, together with sensing, to determine the error signal. This signal determines the full bridge bridgeinverter inverter direction direction of activation of activation to drive to the drive two the DC two motors. DC motors. In this type In this of typecontroller, of controller, hysteresis hysteresis allows inverter direction of activation to drive the two DC motors. In this type of controller, hysteresis allows allowsa balance a balance zone around zone around the reference the reference point, point,preventing preventing unnecessary unnecessary and continuous and continuous switchin switchingg of the a balance zone around the reference point, preventing unnecessary and continuous switching of the ofactuator. the actuator. actuator.

Figure 13. Block diagram of the on-off controller. FigureFigure 13. 13. BlockBlock diagram diagram of of the the on on-o-offff controller.controller. FigureFigure 1414 showsshows the solar panel control algorithmalgorithm flowchart.flowchart. The DC motor movement direction Figure 14 shows the solar panel control algorithm flowchart. The DC motor movement direction isis determineddetermined byby thethe calculatedcalculated error.error. AsAs soonsoon asas this error comescomes within aa 11° hysteresis, the algorithm is determined by the calculated error. As soon as this error comes within a 1°◦ hysteresis, the algorithm convergesconverges andand thethe motorsmotors areare turnedturned ooffff.. converges and the motors are turned off.

Figure 14. Flowchart of the solar panel positioning algorithm. Figure 14. Flowchart of the solar panel positioning algorithm. Figure 14. Flowchart of the solar panel positioning algorithm. As only one drive circuit was used for the two DC motors, it was necessary to control the angles As only one drive circuit was used for the two DC motors, it was necessary to control the angles separately.As only Thus, one drivethe algo circuitrithm was first used controls for the the two elevation DC motors, angle it until was necessaryit converges to controland then the controls angles separately. Thus, the algorithm first controls the elevation angle until it converges and then controls separately.the azimuth Thus, angle. the It algorithmwas installed ﬁrst with controls four theswitch elevationes, which angle prevent until its the converges passage and of current then controls to the the azimuth angle. It was installed with four switches, which prevents the passage of current to the themotor azimuth in case angle. of failures. It was installed with four switches, which prevents the passage of current to the motormotor in in case case of of failures. failures. 4. Results 4.4. Results Results The prototype construction was the most laborious and time-consuming stage of the project, TheThe prototype prototype construction construction was was the the most most laborious laborious and and time time-consuming-consuming stage stage of of the the project, project, requiring several cycles of conception, construction, tests and validations. The obtained result was requiringrequiring several several cycles cycles of of conception, conception, construction, construction, tests tests and and validations. validations. The The obtained obtained result result was was satisfactory, since the tracking device presented smooth and precise movements, and the movable satisfactory,satisfactory, since since the the tracking tracking device device presented presented smooth smooth and and precise precise movements, movements, and and the the movable movable panel structure was able to support the weight of the solar panel. The electronic system performed panel structure was able to support the weight of the solar panel. The electronic system performed its functions efficiently, despite employing simple and inexpensive materials. its functions efficiently, despite employing simple and inexpensive materials.

Processes 2020, 8, 1309 11 of 17

Processespanel 20 structure20, 8, x was able to support the weight of the solar panel. The electronic system performed11 of 17 its functions eﬃciently, despite employing simple and inexpensive materials. ToTo evaluate evaluate the the response response of of the the tracking tracking algorithm, algorithm, the the transition transition from from a aperiod period of of dense dense clouds clouds withwith low low irradiation irradiation to to open open skies skies with with high high irradiation irradiation was was recorded. recorded. Thus, Thus, the the algorithm algorithm started started withwith the the Sun’s Sun’s apparent apparent position position reference reference distant distant from from the the current current angles angles of of the the tracking tracking device. device. FigureFigure 15 15 shows shows the the tracking tracking algorithm algorithm respons response,e, with with the the elevation elevation angle angle and and reference reference in in blue blue andand the the azimuth azimuth angle angle and and reference reference in in red. red. It Itcan can be be observed observed that that the the variation variation in in azimuth azimuth an anglegle waswas approximately approximately 50 50 degree degrees,s, leading leading to to a aconvergence convergence time time of of 220 220 s. s.For For the the elevation elevation angle, angle, the the variatiovariationn was was 16 16 degree degrees,s, with with a convergence a convergence time time of of 158 158 s. s.Although Although long, long, the the convergence convergence times times are are compatiblecompatible with with solar solar move movement,ment, which which is isapproximately approximately 15 15 degree degreess per per hour. hour. It Itis isimportant important to tonote note thatthat the the two two angles angles are are actuated actuated simultaneously, simultaneously, seeking seeking the the apparent apparent position position of of the the S Sun.un.

FigureFigure 15. 15. ResponseResponse of ofthe the sensor sensor-tracking-tracking algorithm. algorithm.

FigureFiguress 16 16 and and 17 17 illustrate illustrate the the behavior behavior of of the the tracker’s tracker’s elevation elevation and and az azimuthimuth angle angle (in (in blue) blue) comparedcompared to toSunEarthTools SunEarthTools database database (in (in red) red) in in February February 1st 1st (summer) (summer) [19] [19. ].In In the the first first half half of of the the day,day, the the tracker tracker presents presents a asmall small difference difference from from the the values values provided provided by by the the database database,, in in contrast contrast to to thethe second second half half,, where where the the value valuess almost almost overlap. overlap. Relative Relative to tothe the elevation elevation angle, angle, the the tracker tracker presents presents somesome peaks peaks due due to to the the tracking tracking algorithm, algorithm, as as well well as as two two inoperative inoperative moments moments (between (between 16 16 h h30 30 min min andand 18 18 h) h) due due to to the the presence presence of of clouds clouds and and operates operates from from 10 10° ◦toto 90 90°.◦ The. The tracker tracker azimuth azimuth angle angle is is mechanicallymechanically restrict restricteded to to operate operate from from −108108° toto 108 108°. . − ◦ ◦ To evaluate the movable panel position control, a step and a ramp were inserted at the reference. Figure 18 shows the azimuth angle response, with a step from 70 to 20 degrees, followed by another step from 20 to 0 degrees, and a ramp from 0 to 45 degrees at a rate of 1 degree per second. The DC motor speed is slow due to the reduction gearbox, making the step response slow. Regarding stability, the on-off control system features overshoot, associated with wind incidence and a small gear backlash. For the angle of elevation (Figure 19), the overshoot is smaller because the mechanical system is heavier and better fitted, so that the influence of wind is smaller.

Processes 2020, 8, 1309 12 of 17 Processes 2020, 8, x 12 of 17 Processes 2020, 8, x 12 of 17

Figure 16. Tracker elevation angle compared to SunEarthTools database. FigureFigure 16. 16.Tracker Tracker elevation elevation angleangle compared to to SunEarthTools SunEarthTools datab database.ase.

Processes 2020, 8, Figurex Figure 17. 17.Tracker Tracker azimuth azimuth angle angle comparedcompared to to SunEarthTools SunEarthTools datab database.ase. 13 of 17 Figure 17. Tracker azimuth angle compared to SunEarthTools database. To evaluate the movable panel position control, a step and a ramp were inserted at the reference. To evaluate the movable panel position control, a step and a ramp were inserted at the reference. Figure 18 shows the azimuth angle response, with a step from 70 to 20 degrees, followed by another Figure 18 shows the azimuth angle response, with a step from 70 to 20 degrees, followed by another step from 20 to 0 degrees, and a ramp from 0 to 45 degrees at a rate of 1 degree per second. The DC step from 20 to 0 degrees, and a ramp from 0 to 45 degrees at a rate of 1 degree per second. The DC motor speed is slow due to the reduction gearbox, making the step response slow. Regarding motor speed is slow due to the reduction gearbox, making the step response slow. Regarding stability, the on-off control system features overshoot, associated with wind incidence and a small stability, the on-off control system features overshoot, associated with wind incidence and a small gear backlash. For the angle of elevation (Figure 19), the overshoot is smaller because the mechanical gear backlash. For the angle of elevation (Figure 19), the overshoot is smaller because the mechanical system is heavier and better fitted, so that the influence of wind is smaller. system is heavier and better fitted, so that the influence of wind is smaller.

FigureFigure 18. 18.Positioning Positioning algorithm algorithm responseresponse for for azimuth azimuth angle. angle.

Figure 19. Positioning algorithm response for elevation angle.

In order to observe the full functioning of the system, the power supplied by the fixed panel and the movable panel was recorded in a SD memory card, as well as the power supplied by the direct voltage source, with one input per second from 7:00 a.m. to 9:00 p.m. on a 13 summer-day period in the city of Ivaiporã-Paraná. Mathematical computing software was used to perform numerical integration on power data and determine the energy generated per panel and provided by the source to the tracking system. Figure 20 shows the power generated by the fixed panel in blue and by the movable panel in red on February 1st. It can be seen that the movable panel has an expressive power output at 8:00 a.m. reaching a maximum at 9:30 a.m., while the fixed panel starts to have a significant power only at 8:30 a.m. and reaches its maximum value at noon. In this period of about four hours, the power observed in the tracking system exceeds the power of conventional fixed systems. This phenomenon repeats at 3:30 p.m., but it is interrupted due to the presence of clouds between 4:30 p.m. and 5:30 p.m. In total, the fixed photovoltaic system generated 1300 Wh, while the solar tracking system generated 2115 Wh, indicating a total energy gain of 815 Wh on this day, equivalent to 62.58%. To power the tracking and positioning system, the direct voltage source provided 76.93 Wh, causing the net energy gain to

Processes 2020, 8, x 13 of 17

Processes 2020, 8, 1309 13 of 17 Figure 18. Positioning algorithm response for azimuth angle.

FigureFigure 19.19. PositioningPositioning algorithmalgorithm responseresponse forfor elevationelevation angle.angle.

InIn orderorder toto observeobserve thethe fullfull functioningfunctioning ofof thethe system,system, thethe powerpower suppliedsupplied byby thethe fixedfixed panelpanel andand thethe movablemovable panelpanel waswas recordedrecorded inin aa SDSD memorymemory card,card, asas wellwell asas thethe powerpower suppliedsupplied byby thethe directdirect voltagevoltage source,source, withwith one input per second from from 7:00 7:00 a a.m..m. to to 9:00 9:00 p p.m..m. on on a a13 13 summer summer-day-day period period in inthe the city city of of Ivaiporã Ivaipor-ãParaná.-Paraná .M Mathematicalathematical computing computing software software was was used used to performperform numericalnumerical integrationintegration onon powerpower datadata andand determinedetermine thethe energyenergy generatedgenerated perper panelpanel andand providedprovided byby thethe sourcesource toto thethe trackingtracking system.system. FigureFigure 20 20 showsshows thethe powerpower generatedgenerated byby thethe fixedfixed panelpanel inin blueblue andand byby thethe movablemovable panelpanel inin redred onon FebruaryFebruary 1st.1st. ItIt can be seenseen thatthat thethe movablemovable panel has anan expressive power output at 8:008:00 a.m.a.m. reachingreaching a maximum at at 9 9:30:30 a a.m.,.m., while while the the fixed fixed panel panel start startss to tohave have a significant a significant power power only only at 8: at30 8:30a.m. a.m.and reaches and reaches its maximum its maximum value valueat noon at. In noon. this period In this of period about of four about hours, four the hours, power the observed power observedin the tracking in the system tracking exceeds system the exceeds power the of powerconventio of conventionalnal fixed systems. fixed This systems. phenomenon This phenomenon repeats at repeats3:30 p.m at., 3:30but p.m.,it is interrupted but it is interrupted due to the due presence to the presenceof clouds of between clouds between4:30 p.m 4:30. and p.m. 5:30 andp.m 5:30. In total, p.m. Inthe total, fixed the photovoltaic fixed photovoltaic system systemgenerated generated 1300 Wh, 1300 while Wh, whilethe solar the solartracking tracking system system generated generated 2115 2115Wh, indic Wh, indicatingating a total a energy total energy gain of gain 815 ofWh 815 onWh this onday, this equivalent day, equivalent to 62.58%. to 62.58%.To power To the power tracking the trackingand positioning and positioning system, system,the direct the voltage direct voltagesource provided source provided 76.93 Wh 76.93, causing Wh, causing the net theenergy net energygain to gain to fall to 737 Wh, or 56.67%. Figure 21 shows the relation between the irradiation and power generated by the movable panel in the same day. The two curves follow the same pattern, with peaks and lows at the same time, except for the central period in which the high temperature affects the panel efficiency. The total irradiation received on this day was 13,712 Wh, leading to 15.42% panel efficiency. The system operated from February 1st to 16th, in which three days’ worth of data were corrupted (11th to 13th), six days were sunny (1st, 6th to 9th and 14th), six days were cloudy (2nd to 5th, 10th and 16th) and one day had heavy rain (15th). Figure 22 shows an energy comparison between the movable panel, fixed panel and the power source. February 7th is an example of a sunny day, wherein the movable panel generated 2332 Wh, the fixed panel generated 1394 Wh and the power source consumed 56 Wh, resulting in a total gain of 67.28% and net gain of 63.22%. For cloudy days, the systems total and mostly the net efficiency drops—ion February 3rd, the movable panel generated 1202 Wh, the fixed panel generated 872 Wh and the power source consumed 77.18 Wh, resulting in a total gain of 37.84% and net gain of 28.99%. The worst possible climate condition is heavy rain with small periods of high irradiation, like February 15th. On this day, the movable panel generated 336 Wh, the fixed panel generated 301 Wh and the power source consumed 94 Wh, resulting in a total gain of 11.71% and net gain of 19.47%. During the experimental period, the movable panel generated 19,784 Wh, the − Processes 2020, 8, x 14 of 17 Processes 2020, 8, 1309 14 of 17 fall to 737 Wh, or 56.67%. Figure 21 shows the relation between the irradiation and power generated by the movableProcesses 20 20panel, 8, x in the same day. The two curves follow the same pattern, with peaks and14 of lows17 fixed panel generated 14,182 Wh and the power source consumed 4562 Wh, leading to a total gain of at the samefall to 737time, W h,except or 56. 67%for. theFigure central 21 shows period the relation in which between the highthe irradiation temperature and power affects generated the panel efficiency.39.5%by and the The netmovable gaintotal ofpanelirr 32.16%.adiation in the Itsame received is worth day. The notingon twothis curves that day the followwas movable 13 the,712 same panel Wh, pattern, generatedleading with topeaks more 15 .and42 power% lows panel than efficiency.the fixedat the panel same on time, every except analyzed for the day. central In regard period toin thewhich system the high efficiency, temperature Figure affects 23 summarizes the panel the obtainedefficiency. values The for total the totalirradiation and net received gains, whichon this haveday was a strong 13,712 relationship Wh, leading with to 15 the.42 incidence% panel of cloudsefficiency. and rain.

FigureFigure Figure20. 20. ComparisonComparison 20. Comparison between between between fixed ﬁxed fixed (blue) (blue) (blue) and andand movable movable (red) (red) (red) panel panel panel power power on on onFebruary February February 1st 1. st 1st..

Figure 21. Irradiation and generated power comparison on the movable panel.

The system operated from February 1st to 16th, in which three days’ worth of data were FigureFigure 21. 21. IrradiationIrradiation and and generated generated power power comparison comparison on on the the movable movable panel panel.. corrupted (11th to 13th), six days were sunny (1st, 6th to 9th and 14th), six days were cloudy (2nd to The5th, system 10th and operated 16th) and from one Februaryday had heavy1st to rain 16th, (15th) in . whichFigure three22 shows days an’ worthenergy comparisonof data were corruptedbetween (11th the to movable13th), six panel, days fixed were panel sunny and (1st, the power6th to source.9th and February 14th), six 7th days is an examplewere cloudy of a sunny (2nd to 5th, 10thday, and wherein 16th) theand movable one day panel had generated heavy rain 2332 (15th) Wh, the. Figure fixed panel22 shows generated an energy 1394 Wh comparison and the power source consumed 56 Wh, resulting in a total gain of 67.28% and net gain of 63.22%. For cloudy between the movable panel, fixed panel and the power source. February 7th is an example of a sunny days, the systems total and mostly the net efficiency drops—ion February 3rd, the movable panel day, wherein the movable panel generated 2332 Wh, the fixed panel generated 1394 Wh and the generated 1202 Wh, the fixed panel generated 872 Wh and the power source consumed 77.18 Wh, power sourceresulting consumed in a total gain56 Wh, of 37resulting.84% and in net a total gain gainof 28 .of99%. 67 .28%The worstand net possible gain ofclimate 63.22%. condition For cloud is y days, theheavy systems rain with total small and periods mostly of the high net irradiation, efficiency like drops February—io 15n thFebruary. On this day,3rd, thethe movable movable panel panel generated 1202 Wh, the fixed panel generated 872 Wh and the power source consumed 77.18 Wh, resulting in a total gain of 37.84% and net gain of 28.99%. The worst possible climate condition is heavy rain with small periods of high irradiation, like February 15th. On this day, the movable panel

Processes 2020, 8, x 15 of 17 Processes 2020, 8, x 15 of 17 generated 336 Wh, the fixed panel generated 301 Wh and the power source consumed 94 Wh, generatedresulting 336in aWh, total the gain fixed of 11panel.71% generatedand net gain 301 ofWh −19 and.47%. the During power the source experiment consumedal period, 94 Wh, the resultingmovable in panel a total generated gain of 1119.,71%784 Wh,and thenet fixedgain ofpanel −19 .generated47%. During 14 ,182the experimentWh and theal powerperiod, source the movableconsumed panel 4562 generated Wh, leading 19,784 to a Wh, total the gain fixed of 39 panel.5% and generated net gain 14of ,32182.16%. Wh It and is worth the power noting source that the consumedmovable 4562panel Wh, generated leading more to a total power gain than of 39 the.5% fixed and panelnet gain on of every 32.16%. analyzed It is worth day. notingIn regard that to the the movablesystem panelefficiency, generated Figure more 23 summarizes power than the the obtained fixed panel values on forevery the analyzed total and day. net gains,In regard which to thehave systema strong efficiency, relationship Figure with 23 tsummarizeshe incidence the of cloudsobtained and values rain. for the total and net gains, which have Processes 2020, 8, 1309 15 of 17 a strong relationship with the incidence of clouds and rain.

Figure 22. Energy comparison between the movable panel (red), fixed panel (blue) and power source FigureFigure(green) 22. 22.. EnergyEnergy c comparisonomparison between between the the movable movable panel panel (red), (red), fixed ﬁxed panel panel (blue) (blue) and and power power source source (green)(green)..

FigureFigure 23. 23.Solar Solar tracker tracker system system e ﬃefficiencyciency on on the the experiment experiment period. period. Figure 23. Solar tracker system efficiency on the experiment period. 5.5. Conclusions Conclusions 5. Conclusions In this work, we report the process of the construction and automation of a two-axis microcontrolled solar tracker, in which the tracking process is performed in a separate structure, equipped with stepper

motors with precision of four steps per degree, applied to a photovoltaic system with commercial panels of 275 Wp. The mechanical structures manufactured were satisfactory, meeting the requirements of movement precision, load capacity and resistance. Although simple and inexpensive, the electronic system performed its function eﬃciently. In general, the developed prototype is applicable in studying tracking strategies and the control of DC motors, with potential to become a commercial product if the number of controlled panels is increased. Processes 2020, 8, 1309 16 of 17

The tracking algorithm used was able to find and follow the apparent position of the Sun in periods of high irradiation, with a proposal to handle exceptions for low irradiation intervals that seek or avoid unnecessary movements in the tracker. The on–off controller with hysteresis achieved its goal of positioning the moving panel on the reference obtained by the first algorithm. However, due to the overshoot presented in its answer, it is believed that this controller is not the most suitable for solar tracking systems, since some of the energy spent in moving the motors is wasted. An evaluation of the system efficiency was performed, comparing the energy generated in the mobile panel with that of a fixed panel on a 13 summer days period, taking into account days with high incidence of irradiation, cloudy and rainy days. The system total efficiency was 39.5% and the net efficiency was 32.16%, considering the energy used to operate the system in the same period. For future research, it is suggested to evaluate the prototype performance with tracking strategy based on astronomical equations, as well as to apply controllers that minimize energy consumption in the positioning of the moving panel.

Author Contributions: A.d.S.S. and J.d.R.Q. have designed the experiment and worked in the development of the prototype equally throughout the project, collecting and analyzing data, as well as writing the article. M.K.G. and J.C.D.d.O. worked on the writing, review and editing the article. C.M.G.A. was project manager and article reviewer. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Acknowledgments: The authors would like to express their gratitude to National Council for Scientific and Technological Development (CNPq) and to CAPES (Coordination for the Improvement of Higher Education Personnel). Conflicts of Interest: The authors declare no conflict of interest.

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