AUTOMATIC SOLAR TRACKING SYSTEM
One of the most popular renewable energy sources is solar energy. Solar energy is rapidly gaining notoriety as an important means of expanding renewable energy resources. As such, it is vital that those in engineering fields understand the technologies associated with this area. My project will include the design and construction of a solar panel tracking system. The main purpose of the project is to achieve optimum energy efficiency by PV cell. We are using a PV solar cell to generate energy from Sun. But in the practical scenario of solar energy generation, conventionally we use static PV cell. So the efficiency of the total system is reduced. To achieve higher efficiency we track down the Sun. We are using LDR to sense the light. Then the sensed signals go to the comparator to compare and generate the control signal. This control signal goes to the driver circuit. This driver circuit drives the stepper motor. Stepper motor set position of the PV cell always to the perpendicular to solar beam radiation. Solar tracking allows more energy to be produced because the solar array is able to remain aligned to the sun.
The Project, Solar Tracking System, has been done as the final year project by the students of Electrical Department under the guidance and supervision of our Electrical Department Lecturers for many helpful discussions and comments accordingly which allowed us to complete this project smoothly.
Table of Contents:
- Need of a Tracker System
- Project Details
- Solar Tracker System
- Background Theory
- Circuit Diagram or Block Diagram
- Functional Part or Programming (optional)
- Material Estimating & Costing
- Result or Conclusion
- Future Developments
Renewable energy solutions are becoming increasingly popular day by day. Photovoltaic (solar) systems are but one example. Conventional fuels are becoming scare day by day & its increasing cost is affecting the cost of power generation. Solar Energy is one of the greatest Renewable Sources of Energy. And to harness this, various methods are being applied & out of all those methods one of them is the Solar Tracker which will track the Sun, harness its energy & convert it into electricity.
A Solar Tracker System maximizing power output from a solar system is desirable to increase efficiency. In order to maximize power output from the solar panels, one needs to keep the panels aligned with the sun. As such, a means of tracking the sun is required. This is a far more cost effective solution than purchasing additional solar panels. It has been estimated that the yield from solar panels can be increased by 30 to 60 percent by utilizing a tracking system instead of a stationary array. This project develops an automatic tracking system which will keep the solar panels aligned with the sun in order to maximize efficiency.
Need of a Tracker System:
Different power applications require different tracking systems. For certain applications a tracking system is too costly and will decrease the max power that is gained from the solar panel. Due to the fact that the earth rotates on its axis and orbits around the sun, if a PV cell/panel is immobile, the absorption efficiency will be significantly less at certain times of the day and year. The use of a tracking system to keep the PV cell/panel perpendicular to the sun can boost the collected energy by 10 – 100% depending on the circumstances.
If a tracking system is not used, the solar panel should still be oriented in the optimum position. The panel needs to be placed where no shadow will fall on it at any time of the day. However this needs continuous observation which is not possible all the time. Additionally, the best tilt angle should be determined based on the geographical location of the panel. It is generally taken to be 5°.
Solar Tracker System:
A solar tracker is a device that orients various payloads toward the sun. Payloads can be photo-voltaic panels, reflectors, lenses or other optical devices.
In flat-panel photo-voltaic (PV) applications, trackers are used to minimize the angle of incidence between the incoming light and a photo-voltaic panel. This increases the amount of energy produced from a fixed amount of installed power generating capacity. In standard photo-voltaic applications, it is estimated that trackers are used in at least 85% of commercial installations greater than 1MW from 2009 to 2012.
In concentrated photo-voltaic (CPV) and concentrated solar thermal (CPS) applications trackers are used to enable the optical components in the CPV and CSP systems. The optics in concentrated solar applications accepts the direct component of sunlight and therefore must be oriented appropriately to collect energy. Tracking systems are found in all concentrator applications because such systems do not produce energy unless oriented closely toward the sun.
To build An AUTOMATIC SOLAR TRACKER SYSTEM, made up of simple, cheap and inexpensive components that starts following the sun right from the dawn, throughout the day, till evening, and starts all over again from the dawn the next day and on cloudy weathers, it remains still and catches the sun again as it slips out of clouds.
This paper begins with presenting background theory in light sensors and stepper motors for better understanding as they apply to the project.
Light Sensors (LDR):
Light sensors are among the most common sensor type. The simplest optical sensor is a photoresistor which may be a cadmium sulfide (CdS) type or a gallium arsenide (GaAs) type.
The sun tracker uses a cadmium sulfide (CdS) photocell for light sensing. This is the least expensive and least complex type of light sensor. The CdS photocell is a passive-component whose resistance in inversely proportional to the amount of light intensity directed toward it. The resistance of the photo-conductive cell decreases with the increase in the level of light and the resistance increases as the level of light decreases. As long as no light is incident upon the device, the bulk photo-conductor has a certain high resistance called the Dark Resistance.
A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical movements.Stepper motors are commonly used for precision positioning control applications. All-stepper motors possess five common characteristics which make them ideal for this application. Namely, they are brush-less, load independent; have open loop positioning capability, good holding torque, and excellent response characteristics.
There are three types of stepper motors: permanent magnet, variable reluctance, and-hybrid. The arrangement of winding on the stator is the main distinguishing factor between the three types. Permanent magnet motors may be wound either with uni-polar or bipolar winding.
The sun tracker uses a unipolar step motor. As such, discussion will be limited to this type of stepper motor. Unipolar motors have two windings with each having a center tap as shown in below Figure..
The centre taps are connected to a positive voltage while the coil ends are alternatelygrounded to cause a reversal of the field direction in that winding Figure 2 shows a4-phase motor. The number of phases is equal to two times the number of coils. Themotor is rotated by applying power to the windings in a sequence as shown in Figure..CLICK HERE TO KNOW MORE ABOUT STEPPER MOTOR
For solar tracking strategies analysis, the need of an advanced solar tracking device arose. This device had to be robust, economical, easily producible and more than anything, adaptable.The requirement for robustness was justified by the fact that the system had to be able to withstand mechanical wear and loads. It had to be built, so that it was easy to assemble/disassemble, calibrate and put to work.
The system had to be economical due to the financial restrictions upon the project. In fact, economic constraints played a vital role in system evolution, as they do in any development process. For example, the initial plan for the tracking system was to use normal D.C. Motors combined with drive gearboxes. But superiority of this motor-gearbox pair is very well demonstrated by their price, which was around ten times more expensive, than the elements that were used in the final assembly.
Ease of production was aimed throughout all the design stages. The final assembly was to be consisting of simple, inexpensive discrete components by which a driver circuit was designed to drive a 1.8° step unipolar stepper motor.
Light Sensing Circuit:
Light sensing ckt. Is nothing but a voltage divider ckt., which is incorporated with comparator. Here we use three LDR to sense the light. We use IC LM324 as comparator. IC LM324 is a quad comparator IC. Here we use two comparator. Then the comparable voltage value is set by a voltage divider network.
Here is the pin diagram of LM324. The resistance values are likely to be 39 kΩ, 22kΩ, 15 kΩ, 100kΩ. The whole ckt. looks like bellow fir..
The outputs of the comparators are changed when the light fall upon the LDR. The sequence of the light is –
|LDR 1||LDR 2||Output 1||Output 2|
The resistance of the LDR varies from 10Ω to ∞.
One LDR is placed in parallel to the LDR 2, to track the sun rise after previous sun set.
The final output of the comparator goes to the stepper motor driver IC LM293D.
Generation of Drive or Control Sequence of Unipolar Stepper Motor:-
First of all we use IC NE555 to generate the clock pulse. We run this timer as an astable multivibrator to generate continuously clock pulse. The circuit diagram shows in fig
In astable mode we use 1Hz frequency of the square wave. We know that, we can change the frequency of timer by changing the RC constant of the ckt. The general formula of Frequency is- f=1.44/(R1+2R2)C
Here R1=810Ω, R2=25Ω, C=470µF
The output of timer goes to Decoded up counter CD4017. CD4017 is a 16 pin dual line in package IC. It has 10 decoded output pins. The general pin diagram of CD4017 looks like fig
When one clock pulse goes to the IC it energies one output pin. The output characteristic timing diagram is shown in fig
Stepper Motor Driving Circuit:
L293D is a dual H-bridge motor driver integrated circuit (IC). Motor drivers act as current amplifiers since they take a low-current control signal and provide a higher-current signal. This higher current signal is used to drive the motors.
L293D contains two inbuilt H-bridge driver circuits. In its common mode of operation, two DC Motors can be driven simultaneously or four DC Motors in the same direction or can drive a Stepper Motor or even a Servo Motor, both in forward and reverse direction. The motor operations of two motors can be controlled by input logic at pins 2 & 7 and 10 & 15. Input logic 00 or 11 will stop the corresponding motor. Logic 01 and 10 will rotate it in clockwise and anticlockwise directions, respectively.
Enable pins 1 and 9 (corresponding to the two motors) must be high for motors to start operating. When an enable input is high, the associated driver gets enabled. As a result, the outputs become active and work in phase with their inputs. Similarly, when the enable input is low, that driver is disabled, and their outputs are off and in the high-impedance state.Pin diagram of L293d is shown in fig.
Internal logic diagram shown in fig.
Here is the truth table I/O of L293d.
In our project we use two L293d IC. In both ic input is given from the decade counter ic. But the sequence is changed in both ics. We are just enble the chip all time by giving the supply of +9V to 1st& 9th pin. But we control the signal sequence by energizing or dEnergizng the 16th pin of the IC by the output of comparator.We are giving supply +18V to the 8th pin of the IC. This voltage drive the stepper motor. The ckt. diagram of motor driver is given on fig-
In this project we use two wooden column to give the support the PV cell. Length of both column are same. But the cross section area of the column are not same. On larger cross section area we make a grove to place the stepper motor.
We use a ball pen to make the extention of shaft. Then we fix the PV cell to the shaft extention by gum with clip.
The cross section diameter of the ball pen is 9mm. Then we make a hole of 10mm dia on other column. In this hole the shaft rotates freely. There is bushing or bearing arrangement is neglected.
On the solar cell we make two extension of link clip on two opposite side. On this link clip we fix LDR to scene light. On east side PV cell extention, we use one LDR. But on the west side extension one LDR placed on the front side and another placed on back side. This arrangement is made to track the
sun rise after previous sun set.
Circuit Diagram/Block Diagram:
In the project, Automatic Solar Tracking System, a 6-wire, 4-phase Permanent Magnet Type Unipolar Stepper Motor is used to drive the solar panel. Out of 6-wires, four wires is for the control sequence & the other two wires is to be connected to the +VCC. For the operation of Stepper Motor, proper control sequence/pulses are to be generated which is already being described in the Design Section. The control sequence is generated with the help of 555 timer operated in Astable Mode & a MOD 10 Decade Counter (CD 4017). The timer generates the continuous Square Pulse which goes as I/P to the CD 4017 counter. The logic of the counter is so designed that it generates proper control sequence to drive a stepper motor. However the O/P coming out of the counter is of low magnitude & hence to drive a motor it is to be amplified. This circuit remains in operation all day for 24 hrs.
To increase the magnitude of the counter O/P & to drive the motor an H-Bridge Driver I.C. (L293D) is being used. The O/P of the counter goes to the I/P of driving I.C. (say L293D 1) & whose O/P is connected to the motor I/P terminals/windings & thus drives the motor in one direction (say clockwise). But according to our project requirement, the stepper motor is to be rotated in both directions. So to obtain this control, another H-Bridge Driver I.C. (say L293D 2) is being used in the circuit. The connection of the two driver I.C. with the counter will be such that, one driver I.C. (say L293D 1) will rotate the motor in clockwise direction & the other driving I.C. (say L293D 2) will rotate the motor in counter-clockwise direction as already discussed in the Design Section. The driving I.C. used is a 16-pin I.C., containing, four I/Ps, four O/Ps, two Enable pins, four GND & two VCC already discussed in the Design section. The two VCC of the I.C. are pin-8 & pin-16. Pin-8 of the I.C. is for the motor voltage which helps the I.C. to drive the motor & pin-16 of the I.C. is the VCC (supply pin) of the I.C. If no supply voltage is given to this pin, the driver I.C. will remain in the OFF State & will not drive the motor. Up till now, the control sequence & the bidirectional control circuit of stepper motor are ready. But according to our project title Automatic Solar Tracker, i.e. to drive the motor in both directions automatically with respect to the intensity of light (i.e. sunlight).
So, to obtain this control, a Light Sensor Circuit is incorporated within the system which is already discussed in the Design Section. The Light Sensor Circuit consists of a simple Comparator (LM 324) circuit used in combination with LDRs. The LDRs senses the intensity of light, compares it & make the comparators O/P high according to the logic of the I.C. The working of Light Sensor Circuit is already discussed in the Design Section.
As already mentioned, that if pin-6 of the driving I.C. does not get supply; the I.C. will remain in the OFF State. So, instead of giving the supply to pin-16 directly, the O/P of the comparators is connected to the pin-16 of both driving I.C.s (say comparator 1 O/P is connected to pin-16 of L293D 1 & comparator 2 O/P is connected to pin-16 of L293D 2). When LDR 1 receives the light (LDR 2 is in dark), the comparator 1 goes high (comparator 2 remains low) & the comparator 1 O/P goes to the pin-16 of L293D 1 & thereby triggering the I.C. to ON State from OFF State & thus drives the Stepper Motor in Clockwise Direction & the solar Panel connected to motor shaft also rotates from east to west (single axis) thus following the Sun till sunset. Now, when LDR 2 receives the light (LDR 1 is in dark), the comparator 2 gets high (comparator 1 remains low) & its O/P is connected to the pin-16 of L293D 2 & thus triggers it to ON State (L293D 1 remains OFF at this time) & drives the motor & the Solar Panel in Counter-Clockwise Direction & the panel moves from west to east & thus faces the Sun again & tracks it. This is how, the Automatic Solar Tracker System works.
Material Estimating & Costing:-
Result or Conclusion:
In this project the LDRs are so positioned that LDR 1 helps to drive the motor in Clockwise direction & LDR 2 in Counter-Clockwise direction. Initially the panel is facing east. When the sun rises LDR 1 receives the light and will rotate the motor from east to west. The sun changes its position by 1° at every 4mins interval. So the LDRs will sense the position of the sun & will rotate the motor and will set the panel in such a position that it will always face and remain perpendicular to it so that maximum solar radiation can be captured by the solar panel & thus the O/P power & the efficiency of the panel can be increased. The panel searches for & tracks the sun till sunset and resets itself to the initial position i.e. east each new day. Next day when the sun rises the LDR 2 receives the light and rotates the motor & panel in opposite direction & thus the panel faces the sun again.
In cloudy days, when there is no sun, the tracker stops & searches for the sun. At this time equal amount of light is falling on the LDRs hence the motor is in the OFF State. Whenever the sun comes out of the clouds, the LDR senses it & rotates the motor and set the panel perpendicular to it.
Solar trackers are devices used to orient photovoltaic panels, reflectors, lenses or other optical devices toward the sun. Since the sun’s position in the sky changes with the seasons and the time of day, trackers are used to align the collection system to maximize energy production.
Several factors must be considered when determining the use of trackers. Some of these include: the solar technology being used, the amount of direct solar irradiation, feed-in tariffs in the region where the system is deployed, and the cost to install and maintain the trackers.
Concentrated applications like concentrated photovoltaic panels (CPV) or concentrated solar power (CSP) require a high degree of accuracy to ensure the sunlight is directed precisely at the focal point of the reflector or lens. Non-concentrating applications don’t require tracking but using a tracker can improve the total power produced by the system. Photovoltaic systems using high efficiency panels with trackers can be very effective.
There are many types of solar trackers, of varying costs, sophistication, and performance. The two basic categories of trackers are single axis and dual axis.
Single axis Solar trackers can either have a horizontal or a vertical axis. The horizontal type is used in tropical regions where the sun gets very high at noon, but the days are short. The vertical type is used in high latitudes where the sun does not get very high, but summer days can be very long. In concentrated solar power applications, single axis trackers are used with parabolic and linear Fresnel mirror designs.
Dual axis Solar trackers have both a horizontal and a vertical axis and thus they can track the sun’s apparent motion virtually anywhere in the world. CSP applications using dual axis tracking include solar power towers and dish (Stirling engine) systems. Dual axis tracking is extremely important in solar tower applications due to the angle errors resulting from longer distances between the mirror and the central receiver located in the tower structure.
Many traditional solar PV applications employ two axis trackers to position the solar panels perpendicular to the sun’s rays. This maximizes the total power output by keeping the panels in direct sunlight for the maximum number of hours per day.
Solar Tracker increases the amount of energy produced from a fixed amount of installed power generating capacity. In standard photovoltaic applications, it is estimated that trackers are used in at least 85% of commercial installations greater than 1MW from 2009 to 2012.
The goals of this project were purposely kept within what was believed to be attainted within the allotted timeline. This design is built by keeping in mind of using simple, inexpensive & cheap discrete components. As such, many improvements can be made upon this initial design. That being said, it is felt that this design represents a functioning miniature scale model which could be replicated to a much larger scale. The following recommendations are provided as ideas for future expansion of this project:
- Remedy the motor binding problems due to the photo sensor leads. This could be done with some sort of slip ring mechanism, smaller gauge wire, a larger motor with more torque, or a combination of some or all of these ideas.
- For better precision and accuracy, the stepper motor used can be half-stepped.
- Power supply improvements can also be done by using a lead acid or car batteries i.e., recharging batteries. This battery could be used twofold as a power source for the tracker and to store the power from the solar panels connected to the tracker. The use of battery to store energy would require the design of a robust charging system.
- Increase the sensitivity and accuracy of tracking by using a different light sensor. A phototransistor with an amplification circuit would provide improved resolution and better tracking accuracy/precision. Photodiodes can also be used.
- Utilize a dual-axis design versus a single-axis to increase tracking accuracy.
- For better & more precise control microprocessor or microcontrollers can be used. However, it will increase the complexity and cost of the system.
This paper has presented a means of controlling a sun tracking array with simple, cheap and inexpensive discrete components. It demonstrates the working of a tracker system for maximizing solar cell output by positioning a solar array accurately at the point of maximum light intensity. The light sensors sensethe sun and it drives the stepper motor with a step angle of 1.8° each time.This project presents a method of searching for and tracking the sun and resetting itself for a new day and thereby increase the efficiency of the solar cell.
In this project the purpose of using discrete components is to omit the complexity of using microprocessor or microcontroller and of making it simpler, understandable and cost effective. However this project has some limitations whichprovidean opportunity for expansion of the current project in future years.
i) Non-conventional Energy Sources by G.D.Rai, Khanna Publishers.
ii) Industrial Electronics and Control by Biswanath Paul, PHI Learning Pvt. Ltd.
iii) Digital Circuits and Design by S. Salivahanan & S. Arivazhagan.
iv) Electric Machines by Ashfaq Husain, Dhanpat Rai & Co.
v) Datasheet of CD4017 Decade counter- “Fairchild semiconductor”
vi) Datasheet of L293D H-Bridge Driving I.C. – “Texas Instruments”
vii) Datasheet of LM 324 Quad Comparator I.C. – “National Semiconductor”