Two Axis Solar Tracker Design and Implementation Salih FADIL1, Ahmet Can ÇAPAR2, Kerim ÇAĞLAR3 1
ESOGU, Eskisehir, Turkey,
[email protected], ESOGU, Eskisehir, Turkey,
[email protected], 3 ESOGU, Eskisehir, Turkey,
[email protected] 2
Abstract The energy extracted from a solar photovoltaic (PV) panel depends on solar insolation. For the extraction of maximum energy from the sun, the plane of the PV panel should always be normal to the incident solar ray. The seasonal movement of the earth affects the radiation intensity received on the PV panel. Sun trackers move the PV panel to follow the sun trajectories and keep the orientation of the solar panel at an optimal tilt angle. Energy efficiency of a solar PV panel can be substantially improved by using solar tracking systems. In this work, two axis solar tracking system has been designed and realized by using LDR sensors and DC motors with gear arrangements. The tracking (azimuth angle and altitude angle) has been implemented via microcontroller based control logic. Important points of this design are using minimum energy while tracking, stability of trajectory, maximum energy efficiency with gear arrangements and being cheaper than the other tracker systems.
1. Introduction The green energy, also called renewable energy, has gained much attention nowadays. Some renewable energy types are solar energy, hydro potential energy, wind energy, biomass energy, terrestrial heat, temperature difference of sea, sea waves, morning and evening tides, etc [1, 2]. Among these, solar energy is one of the most efficacious resources that can be used. However, so far the efficiency of generating electric energy from solar radiation is relatively low. Thus, increasing the efficiency of generating electric energy from the solar radiation becomes very important issue. Since PV systems were built at fixed position in the past, they cannot track the sun. Therefore their efficiency is low. The average solar energy intercepted by a fixed PV panel is constant. More energy can be extracted in a day, if the PV panel is installed on solar trackers. Different ways have been experimented for tracking the sun. One of these is freon gas system. This system tracks the sun in one direction (East-West), it is effected by weather conditions (especially on rainy days) and it is also expensive. Because of the above reasons, it has not preferred [3]. Another alternative is to have a database of the sun’s position according to the region and seasons where the tracker will be implemented. Annual positions of the sun are recorded to database of microcontroller. Recorded data sets the position of tracker round the clock. However, this system has to be put up in east-west direction. If there is any error in put up direction, the system will not function properly. Usually such systems are expensive and
complex based on the requirement for the database storage media and clock accuracy. The two axis solar tracker sense the direct solar radiations falling on a photo-sensors as a feedback signals to ensure that the PV panel is tracking the sun all the time, keep the PV panel at a right angle to the sun’s rays for getting the maximum solar insolation. In this work, two axis solar tracker system has been designed and implemented by using four LDRs and two DC motors with gear arrangements. The tracker’s control algorithm has been implemented via Atmega328p microcontroller on a simple and cheap mechanical structure.
2. Description of Two Axis Solar Tracker System 2.1. Schematic Arrangement Two-axis tracking system changes both azimuth (horizontal) and altitude (vertical) degrees of solar panel. Schematic block diagram of the proposed solar tracker is shown in Fig. 1.
LDR Sensors Sistem
PV panel
Trimpot
Gear Drive 2
Gear Drive 1
DC Motor 1
DC Motor 2
Micro controller Atmega328p
Motor Driver L298
Fig. 1. Block diagram of the solar tracker Four LDR sensors and a trimpot are used to feedback from DC motors. Trimpot has been connected to shaft of DC motor 1. LDR1 and LDR2, LDR3 and LDR4 are taken as pairs (please see Fig. 5). If one of the LDR in a pair gets more light intensity than the other, a difference will occur on node voltages sent to the respective ADC channels of the microcontroller. The microcontroller calculates those node voltage differences and compares them with the respective set values. After that it generates necessary logic signals to actuate the DC motors in
such a directioons that light inntensities on LD DRs in each paair are equal. The vooltage value com ming through Trimpot T is com mpared with predefineed value to deteermine the posittion of tracker. LDR pairs have beeen fixed to recipprocal positionss on the border of PV panel (see Figure 5). If LDR pairs are illuminated equally by b the sun, the analog voltage signaals received by the ADC channnel of the microconttroller will have equal values and microconttroller will not generaate any logic siignal to actuate the motors. L2298 IC having two chhannels has beeen used to drivee the DC motorrs. DC motors with geear arrangemennts have been seelected since thhey are cheaper than stepper s and serrvo motors. Mootors which drivve the PV panel in azimuth a and altitude positions (motor 2 and motor 1) are seen inn Fig. 2. D.C motors m with geaar arrangementss have been used to achieve a the dessired speed in moving m the PV panel in azimuth annd altitude posittions. The mosst important efffect of using DC mootors with geaar mechanism in two axis trracker system is gettting mechaniccal stability off PV panel without w spending mucch power for DC D motors. Whhen the panel is not desired to movve, the DC motors are not driiven and PV paanel is kept in stable position due too the mechanicaal lock mechaniism in the gear systems of DC mottors. So, the eleectrical efficienncy of solar panel sysstem has also been increased inn this manner.
Motor 1 1
uit respectivelyy to receive tthe voltage signals comingg circu throu ugh LDR1, LD DR2, LDR3 andd LDR4. The microcontroller m r calcu ulates the diffeerence of voltaage signals recceived at ADC C chann nels 0 and 1 for the altituude angle traccking and thee differrence of voltagge signals receivved at ADC ch hannels 2 and 3 for th he azimuth angle tracking. If tthe difference of o those signalss is greeater or less thhan a predefineed value, micro ocontroller willl send logic signal too the H-bridgee (IC L298) to o drive the DC C moto ors. The trimpott mounted on thhe shaft of moto or 1 feeds backk a volltage value thatt is used to deteermine the posiition of the DC C moto or 1. This volttage is also uused to determ mine the initiall position of the PV panel. If the value of the voltage v comingg ugh this trimpoot is outside off the permissiblle region, DC C throu moto or 1 is stopped for safety of thhe system and the t the panel iss put in nto initial posittion. Finding thhe initial positiion of our solarr track ker by itself is the t most imporrtant difference from the otherr track ker systems. Aft fter sunset whenn the weather turned t dark, alll LDR Rs sense night, trimpot reportss the position of o DC motor 1.. Microcontroller anaalyzes the data aand generates a logic signal too drivee the DC motorr 1 to turn bacck the PV paneel to the initiall position. The initiaal position of the PV panel is parallel too horizzontal plane. Puutting the PV panel into its initial positionn preveents it turning back b to sun’s raays in the morn ning. The ADC C chann nel 4 of the miicrocontroller iis connected to o adjustable legg of trimpot.
Motor 2
Fig. 2. 2 Motors drivinng the tracker mechanically m
2.2. Sensor and a Trimpot System Light dependdent resistor (L LDR) is a resistor whose resisstance decreases withh the increase of light intensiity falling ontoo it. If light falling on the devicee is of high frequency, phhotons t semiconducctor gives enouugh energy to bound b absorbed by the electrons to juump into the conduction bandd. The resulting free electron conduucts electricity, thereby loweriing the resistancce [4]. To track the suun an electro-opptical sensors are a needed. Usinng six LDRs and thheir algorithm for the sun trracking is baseed on utilization of four LDRs forr tracking the azimuth a and alltitude s the day and night [5]. In our angle and the other two for sensing T sensors aree used work, only foour LDRs havee been used. The both for trackiing on azimuthh and altitude angle a and sensinng the day and night. These sensorss are placed on the frame of thhe PV L is connected in series with w a panel by 90° apart. Each LDR resistor of 2200Ω and a Wheattstone bridge ciircuit is formedd using all four LDRs and four resisttors. Wheatstonne bridge and trrimpot circuit diagram m for the sensoor system is illuustrated in Fig. 3. A voltage divideer circuit is foormed at the node n 1, 2, 3 and a 4 between LDR R and a series resistor of 2220Ω. The voltaage is measured at thhe nodes as inpput to the microcontroller. Thee ADC channel 0, 1, 2 and 3 off ATmega328pp microcontrolller is t node 1, 2, 3 and 4 of thee Wheatstone bridge b connected to the
Fiig.3. Wheatstonne bridge circuitt for the sensor and trimpot system m
2.3. Two Axis Sollar Tracker C Controller Thee control circuitt is powered by a 12V battery and a this batteryy is chaarged by the PV V panel. Thus, tracker system m does not needd any external e power supply. Output voltage of PV V cells changess with sun’s radiatioon therefore; tthe output voltage has beenn regullated with LM317T IC to chargge the battery.
F 4. Regulatiion circuits Fig.
Microcontrolleer supply has been provided by the batteryy with help of LM7805 IC. Regulattion circuits aree illustrated in Fig. F 4. The DC motors can turn either in cloockwise or coounter clockwise direection dependinng upon the seequence of the logic signal sent to t L298 driveer IC. Two logic ports of o the microcontrolleer are used for each channel of L298 IC DC motor drive. The sequence s of thhe logic signnal depends onn the difference of intensity i light on o the LDR sennsors. DC motors can move togetherr in the system m. One of the motors m does noot wait other. They caan be driven in the t same time.
urned dark. It iss a predefined value, it means that thhe weather is tu therefore motor1 iss put into its initial position n (PV panel iss paralllel to horizontaal plane). In steep 4, the voltagee value comingg from the trimpot iss checked againnst the permisssible region. Iff this value v is outside of the permissible region, mo otor 1 is soppedd just not n to destroy PV panel mecchanically (oth herwise the PV V panell can run into thhe pole that suppports the PV panel p frame). Inn the other o steps, volltages coming from LDR paiirs (LDR1 andd LDR R2, LDR3 andd LDR4) are compared. Iff the absolutee differrence between the voltages coming from LDR L pairs aree biggeer than value VD ( a presset
VLDRR1 -VLDR2 >VD , VLDR3 -VLDR4 > >VD ) , the necessary n logicc 2.4. Softwarre Description n Arduino IDE E has been usedd to obtain the operation codee. The programmer card c for the same s IDE is used to uploaad the machine code into the microocontroller. Thee code has beenn also simulated in PROTEUS P Proffessional Simulaator to see if it works w properly. The algorithm of thhe written codee is given as steps in what follows. Step 1) Readd all analog voltages coming from all ADC channels. Step 2) If anyy voltage cominng from a LDR R is lower than 0.025 volt, then movve motor 1 into its initial posittion and go to step s 1, otherwise go to t step 3. Step 3) Check (VLDR1-VLDRR2)>VD. If it iss true, go to sttep 4, otherwise go to t step 13. Step 4) Checck the voltage coming from the trimpot. Iff it is outside of thee permissible reegion then stopp motor 1 and go to step 1, otherwise go to step 5. Step 5) Checkk (VLDR1-VLDR2)>VD again. Iff it is true, go to step 6, otherwise go to step 9. Step 6) Move motor 1 in backkward directionn. Step 7) Checkk (VLDR1-VLDR22)VD. If it is true, go to steep 10, otherwise go to t step 12. Step 10) Movee motor 1 in forrward directionn. Step 11) Checck (VLDR2-VLDRR1)VD. If it iss true, go to steep 14, otherwise go to t step 16 Step 14) Movee motor 2 in cloockwise directioon. Step 15) Checck (VLDR3-VLDRR4)VD. If it iss true, go to steep 17, otherwise go to t step 19. Step 17) Movee motor 2 in counterclockwisee direction. Step 18) Checck (VLDR4-VLDRR3)
