Solar Tracking system:There arethree main types of the solar tracker drives divided based on the type of thesensing, drive, and the positioning system that they incorporate. The threetypes are:· Passive Trackers. · Active Trackers. · Open Loop Trackers.· Passive Trackers:A compressed gas fluid is usedin the passive tracker in two canisters in the east and west of the tracker inorder to move it. The mechanismis depending on the direction of the sunlight that falls on the gas container.
If one side is heated other side piston rises and create a gas pressure,causing the panel to move and tilt over the sunny side until it gets toan equilibrium position. This system doesn’t require any controller, and needslittleActive trackers:Motors, actuators, and gears areused in the active tracking system to locate the solar tracker to beperpendicular to the sun. It use light sensors to track the sunlight andmeasure the light intensity to point the required position and use it as ainput data for the microcontroller to monitor the motors and actuators toadjust the location of the solar panel.
Open Loop Trackers:This type use the pre recordedinformation in a particular site to determine the sun’s position instead of thesensors. PROPOSEDMODEL: Themain components of the solar tracking system consist of three main parts:• Four LightDependent Resistor (LDR)• Servo Motors• Arduinoas main controller. Block diagram of Solar tracking system using LDR Light DependentResistor (LDR): LDRs are also named as photo resistors or photo conductors; it is alight controlled variable resistor which is made of a high resistancesemiconductor that applies the principle of photoconductivity. As the incidentlight intensity increase the resistance of the photo resistors decrease. It canbe applied in light and dark activated switching circuits, and light sensitivedetector circuits. LDRs are very effective and useful sensors especially in thedark, it has a very high resistance normally as high as thousands Mega ohms(M?), but it have a low resistance in the light.
The Light Dependent Resistor(LDR) is mainly used in this project to sense the sunlight and track the sun,and provides the arduino with the analog input. The table below shows the behavior of Light Dependent Resistor with thelight intensity change. LIGHT INTENSITY LDR OUTPUT (V)Dark 0.56Average 3.39Bright 4.6 Lightintensity measurement The LDR’s havea simple structure; whichis made of cadmium sulfide (CdS) and gallium arsenide (GaAs). Figure: LDR construction, and Electronic symbol the The LDR used with the Arduino: A0 DO Sensitivity Adjustor: · Clockwise to increase the sensitivity towards the light intensity.
· Anticlockwise to decrease the sensitivity towards the light intensity. Solar SensingDevice: We built a solar trackerusing four LDRs that have a cylindrical shade. The design of the solar sensingdevice is shown in figure (no. of fig). The sensing system is attached with thephotovoltaic panel, where the South- North LDRs and the East-West LDRs are usedto detect the azimuth motion and the elevation motion of the solar panel, themain principle of the light sensors is based on the shadow. As the sun changeits direction the solar sensing system track the movement of the sunlight, ifthe solar panel is not perpendicular to the sun, the shadow will cover one ortwo light sensors. As a result, a light intensity difference is created to bereceived by the solar sensing system. Solar tracking system with a four quadrant LDR sensor.
The concept of using four LDRs: Concept of using fourLDRs for sensing is illustrated in figure (no. of fig), which shows theinterconnection of the closed loop tracking system. The main aim of the solartracker is to arrange the solar panel location to track and follow the sunlocation as closely as possible. The system consists of LDR sensors,differential amplifier, and a comparator. In the tracking process, the lightsensors measure the intensity of the sunlight as an input signal. So, when thefour LDRs have the same light intensity, the system is said to be in the stableposition. But when the sun moves from south to north or from east to west, thelevel of the light intensity falling on each LDR is change, and a voltagedivider is used to calibrate this change into voltage. The unbalance in thevoltage levels are amplified and then create a feedback error voltage, which isproportional to the difference between the solar panel position and thesunlight position.
At this time a built in comparator of the microcontrollercompares the error voltage. If the output voltage goes high, the servo motor isactivated, so as to change the rotation angle of the solar panel to face thesun and track the sunlight. Servo motor Block diagram of the solar tracking system. The four LDRs measure the sunlight intensity from fourvarious locations, where the south, north, east, and west LDRs are produce thesensing voltages Vs, Vn, Ve, and Vw respectively. Figure (no.
of fig)represents the working algorithms of the system. CreatingFeedback Error Voltage: Theelectronic circuit for creating feedback error voltage is shown in figure(no.of fig). As it can beseen, when the corresponding LDR is shadowed the output voltage from thevoltage divider will be lower.
So, if one LDR sense the light more than theother which will be shadowed, the difference voltage between them will beamplified by the differential amplifier. The feedback error voltage can beexpressed as: Thiscan then be rearranged as: If the east LDR is shaded, Vw > Ve and Vwe >0, and the same for Vs and Vn.