This paper describes the design and implementation of an energy efficient solar tracking system from a normal mechanical single axis to a hybrid dual axis. For optimizing the solar tracking mechanism electromechanical systems were evolved through implementation of different evolutional algorithms and methodologies. To present the tracker, a hybrid dual-axis solar tracking system is designed, built, and tested based on both the solar map and light sensor based continuous tracking mechanism. These light sensors also compare the darkness and cloudy and sunny conditions assisting daily tracking. The designed tracker can track sun’s apparent position at different months and seasons; thereby the electrical controlling device requires a real time clock device for guiding the tracking system in seeking solar position for the seasonal motion. So the combination of both of these tracking mechanisms made the designed tracker a hybrid one. The power gain and system power consumption are compared with a static and continuous dual axis solar tracking system. It is found that power gain of hybrid dual axis solar tracking system is almost equal to continuous dual axis solar tracking system, whereas the power saved in system operation by the hybrid tracker is 44.44% compared to the continuous tracking system.
During the last few years the renewable energy sources like solar energy have gained much importance in all over the world. Different types of renewable or green energy resources like hydropower, wind power, and biomass energy are currently being utilized for the supply of energy demand. Among the conventional renewable energy sources, solar energy is the most essential and prerequisite resource of sustainable energy [
Solar energy refers to the conversion of the sun’s rays into useful forms of energy, such as electricity or heat. A photovoltaic cell, commonly called a solar cell or PV, is the technology used to convert solar energy directly into electrical power. The physics of the PV cell (solar cell) is very similar to the classical p-n junction diode. Sunlight is composed of photons or particles of solar energy. Semiconductor materials within the PV cell absorb sunlight which knocks electrons from their atoms, allowing electrons to flow through the material to produce electricity [
Different researches estimate that covering 0.16% of the land on earth with 10% efficient solar conversion systems would provide 20 TW of power, nearly twice the world’s consumption rate of fossil energy [
Over the years, researchers have developed smart solar trackers for maximizing the amount of energy generation. Before the introduction of solar tracking methods, static solar panels were positioned with a reasonable tilted angle based on the latitude of the location. In this competitive world of advanced scientific discoveries, the introductions of automated systems improve existing power generation by 50% [
There are mainly two types of solar trackers on the basis of their movement degrees of freedoms. These are single axis solar tracker and dual axis solar tracker. Again these two systems are further classified on the basis of their tracking technologies. Active, passive, and chronological trackers are three of them [
Previous researchers used single axis tracking system which follows only the sun’s daily motion [
Figure
Illustration of the solar angles: (a) altitude angle,
Solar tracking is best achieved when the tilt angle of the solar tracking systems is synchronized with the seasonal changes of the sun’s altitude. An ideal tracker would allow the solar modules to point towards the sun, compensating for both changes in the altitude angle of the sun (throughout the day) and latitudinal offset of the sun (during seasonal changes). So the maximum efficiency of the solar panel is not being used by single axis tracking system whereas double axis tracking would ensure a cosine effectiveness of one.
In active tracking or continuous tracking, the position of the sun in the sky during the day is continuously determined by sensors. The sensors will trigger the motor or actuator to move the mounting system so that the solar panels will always face the sun throughout the day. If the sunlight is not perpendicular to the tracker, then there will be a difference in light intensity on one light sensor compared to another. This difference can be used to determine in which direction the tracker has to be tilted in order to be perpendicular to the sun. This method of sun tracking is reasonably accurate except on very cloudy days when it is hard for the sensors to determine the position of the sun in the sky [
Passive tracker, unlike an active tracker which determines the position of the sun in the sky, moves in response to an imbalance in pressure between two points at both ends of the tracker. The imbalance is caused by solar heat creating gas pressure on a “low boiling point compressed gas fluid, that is, driven to one side or the other” which then moves the structure. However, this method of sun tracking is not accurate [
A chronological tracker is a time-based tracking system where the structure is moved at a fixed rate throughout the day as well for different months. Thus the motor or actuator is controlled to rotate at a slow average rate of one revolution per day (15° per hour). This method of sun tracking is more energy efficient [
To track the sun’s movement accurately dual axis tracking system is necessary. The active/continuous tracking system tracks the sun for light intensity variation with precision. Hence, the power gain from this system is very high [
A simple energy efficient and rugged tracking model is presented in this paper in order to build a hybrid dual axis solar tracker. To track the sun’s daily motion, that is, from east to west direction, a pair of light sensors are used and to track the seasonal motion of the sun real time clock (RTC) is used to create the accurate azimuth angle from some predetermined parameters. The light intensity is compared by microcontroller and it generates the suitable control signals to move the motors in proper direction. So a driver circuit is used to increase the voltage and current level for the operation of the motors. Two full geared stepper motors are used for rotating the solar module in two different axes.
A versatile mechanical system is introduced as a linear actuator to create proper tilt angle. In addition, this linear actuator has high weight lifting capability which is observed experimentally. It is found that energy efficient hybrid dual axis tracking yields almost same energy as continuous dual axis solar tracking system. It is also observed that in hybrid tracking system one motor can remain idle for one month and thus reduces more than 44% of power consumption as compared with continuous dual axis solar tracking system. This mechanism proved significant benefit of reducing energy consumption by hybrid tracker sacrificing a very little tracking loss. This paper also represents the comparative study between the continuous/active and hybrid solar tracking system.
The whole work involves the reading of different sensor values and then comparing them digitally to determine the exact position of the sun in east-west direction. Again the system is also given some predefined values based on the sun’s geographical location in the north-south direction. Overall the entire system can intelligently track the sun’s movement both in horizontal and vertical axis. In order to simplify the design and implementation process the whole system is divided into two parts.
These are as follows: mechanical system design; electrical circuit design.
linear actuator; panel carrier; panel carrier rotator.
Design and implementation of linear actuator: (a) implementation and placement of linear actuator with the aluminium body of panel carrier; (b) hardware design of linear actuator in computer aided drafting tool.
Linear actuator gives the linear motion in vertical axis (upward and downward) and is connected to one end of panel carrier through a straight single rod hook. The rod hook is attached to the wooden frame. There are some bolts and these are tied with seven 15-inch long circular rods of 2 mm diameter. There is also a 13-inch long screw thread and its diameter is 6 mm. A bolt is attached in the middle of the wooden frame and this bolt is also tied with the screw thread. Four circular rods are also mortised through the wooden frame.
The wooden frame moves up and down along with the bolt and the single rod hook. It works in such a way that the wooden frame does not let the bolt move along with the thread screw rather when the thread screw moves then the four circular rods mortised into the wooden frame cause the bolt to move up or down. Now when the single rod hook moves upward or downward it moves along with the panel carrier. The two ends of screw thread are placed in two bearings which helps it to rotate smoothly. These bearings are mortised into the roof and floor. One gear is also placed at the bottom of the screw thread and this gear is connected to the stepper motor gear which is placed on the floor of the linear actuator body. The floor and roof of the linear actuator are made of wood which holds all the linear actuator instruments.
Design and implementation of panel carrier: (a) implementation and placement of panel carrier with the linear actuator and panel carrier rotator; (b) hardware design of Panel carrier in computer aided drafting tool.
The light sensors are placed at the two ends of solar panel. Again the rectangular aluminium frame has a rectangular mortise in its horizontal base. Single circular rod hook from linear actuator goes through this mortise. Thus it helps to lift the panel carrier in a semi-circular path to get sun’s tilt angle caused by seasonal/annual motion. While the linear actuator lifts one end of panel carrier the other end needs to be fixed with a panel carrier rotator to get the perfect circular motion.
Design and implementation of panel carrier rotator: (a) implementation and placement of panel carrier rotator with the panel carrier and a wooden base; (b) hardware design of panel carrier rotator in computer aided drafting tool.
Experimental setup of the Hybrid dual axis solar tracker.
Block diagram of the electrical circuit.
light sensor; real time clock; position sensor.
A light dependent resistor (LDR) is a resistor whose resistance decreases with increasing incident light intensity. Figure
Specification of LDR.
Dark resistance |
Illuminated resistance |
Sensitivity |
Spectral application range |
Rise time |
Fall time |
---|---|---|---|---|---|
20 | 5–20 | 0.9 | 400–700 | 70 | 15 |
Basic LDR circuit.
This device is suitable for data logging, clock-building, time stamping, timers, alarms, and so forth. Microcontroller takes the month and hour values from the RTC device to track the sun’s annual motion and the darkness of night to take the solar panel at its initial position. Figure
Real time clock circuit.
Position sensor circuit.
Position sensor is placed in the panel carrier rotator. When linear actuator moves linearly then panel carrier rotator rotates a semicircular path which causes the position sensor to change its voltage level. The panel carrier rotator rotates 50° degree in a semicircular path with respect to the horizontal axis as in the experimental location sun’s latitude angle changes in between this 50°. The panel carrier rotator can rotate 75° in both sides which may also be applicable in other locations. In that case the sensor has to be calibrated accurately. For 12 months different 12 values of sun’s latitude angle are predetermined and set in the microcontroller and with respect to these values microcontroller decides how much to move the linear actuator. Panel carrier rotator rotates due to the linear actuator’s linearly upward and downward motion with the panel carrier. A gear is placed with the panel carrier rotator which also rotates with it. This gear rotation causes the variable resistor’s gear to rotate and this is how the resistivity of the variable resistor changes. Thus the signal is changing from the position sensor.
Main flowchart of microcontroller programming.
Continuation of main flowchart of microcontroller programming.
Movement adjustment unit: (a) the unipolar stepper motor and motor driver device (ULN2803) and (b) Darlington pair.
The two full geared stepper motors are used here for the accurate tracking of the sun. For our experimental purpose a small scale system was implemented for 3-watt solar panel. The specifications of solar panel and gear and stepper motors are listed as follows.
Specifications of solar panel as load of the motor: mass of solar panel, length of solar panel, width of solar panel, height of solar panel, volume of solar panel, density,
Specifications of gears: number of gear teeth, mass of gear, diameter of gear,
Specifications of motor: inertia of motor, pull-out torque pull-out frequency, friction coefficient, step angle, angle coefficient,
For the pull-out frequency of 100 Hz the required motor torque to rotate the panel is calculated as follows [
Calculation of moment of inertia is given as follows:
Inertia of the load is
Now, acceleration torque is
Now, load torque is
Calculation of required motor torque is given as follows.
Total calculated torque is
So from the above comparison it is clear that pull-out torque of 0.147 N
Current and voltage values of static and tracking panel at different times in a day.
Time |
Static panel | Hybrid tracking system | Continuous tracking system | |||
---|---|---|---|---|---|---|
Current |
Voltage |
Current |
Voltage |
Current |
Voltage | |
7:30 | 0.11 | 7.82 | 0.17 | 7.82 | 0.19 | 7.92 |
8:00 | 0.14 | 7.82 | 0.21 | 7.82 | 0.23 | 7.92 |
8:30 | 0.22 | 7.83 | 0.24 | 7.83 | 0.24 | 7.9 |
9:00 | 0.27 | 7.9 | 0.34 | 8 | 0.35 | 8 |
9:30 | 0.35 | 7.93 | 0.39 | 7.98 | 0.39 | 7.98 |
10:00 | 0.39 | 7.92 | 0.41 | 7.92 | 0.41 | 7.92 |
10:30 | 0.41 | 7.88 | 0.43 | 7.92 | 0.43 | 7.92 |
11:00 | 0.45 | 7.88 | 0.45 | 7.88 | 0.45 | 7.88 |
11:30 | 0.46 | 7.88 | 0.46 | 7.88 | 0.46 | 7.88 |
12:00 | 0.46 | 7.88 | 0.48 | 7.88 | 0.48 | 7.88 |
12:30 | 0.47 | 7.88 | 0.48 | 7.88 | 0.5 | 7.88 |
13:00 | 0.43 | 7.88 | 0.48 | 7.88 | 0.49 | 7.88 |
13:30 | 0.4 | 7.77 | 0.47 | 7.81 | 0.48 | 7.81 |
14:00 | 0.33 | 7.79 | 0.45 | 7.83 | 0.46 | 7.93 |
14:30 | 0.26 | 7.71 | 0.44 | 7.71 | 0.44 | 7.83 |
15:00 | 0.18 | 7.63 | 0.37 | 7.76 | 0.37 | 7.9 |
15:30 | 0.14 | 7.54 | 0.31 | 7.7 | 0.31 | 7.86 |
16:00 | 0.11 | 7.52 | 0.25 | 7.73 | 0.26 | 7.86 |
16:30 | 0.09 | 7.41 | 0.19 | 7.71 | 0.2 | 7.71 |
17:00 | 0.07 | 7.39 | 0.13 | 7.65 | 0.15 | 7.71 |
17:30 | 0.04 | 7.33 | 0.08 | 7.5 | 0.1 | 7.64 |
Comparison curve: comparison of current versus time curve for the static panel, hybrid tracking system, and continuous tracking system.
Table
Power values of static and tracking panel and the corresponding power gain by tracking panel over static panel at different times in a day.
Time |
Static panel | Hybrid |
Continuous |
Power gain by |
Power gain by |
Power gain by |
---|---|---|---|---|---|---|
Power |
Power |
Power |
% | % | % | |
7:30 | 0.8602 | 1.3294 | 1.5048 | 35.29412 | 42.83626 | 11.65603 |
8:00 | 1.0948 | 1.6422 | 1.8216 | 33.33333 | 39.89899 | 11.65603 |
8:30 | 1.7226 | 1.8792 | 1.896 | 8.333333 | 9.14557 | 9.848485 |
9:00 | 2.133 | 2.72 | 2.8 | 21.58088 | 23.82143 | 0.886076 |
9:30 | 2.7755 | 3.1122 | 3.1122 | 10.81871 | 10.81871 | 2.857143 |
10:00 | 3.0888 | 3.2472 | 3.2472 | 4.878049 | 4.878049 | 0 |
10:30 | 3.2308 | 3.4056 | 3.4056 | 5.132723 | 5.132723 | 0 |
11:00 | 3.546 | 3.546 | 3.546 | 0 | 0 | 0 |
11:30 | 3.6248 | 3.6248 | 3.6248 | 0 | 0 | 0 |
12:00 | 3.6248 | 3.7824 | 3.7824 | 4.166667 | 4.166667 | 0 |
12:30 | 3.7036 | 3.7824 | 3.94 | 2.083333 | 12.2449 | 0 |
13:00 | 3.3884 | 3.7824 | 3.8612 | 10.41667 | 12.2449 | 4 |
13:30 | 3.108 | 3.6707 | 3.7488 | 15.3295 | 17.09347 | 2.040816 |
14:00 | 2.5707 | 3.5235 | 3.6478 | 27.04129 | 29.52739 | 2.083333 |
14:30 | 2.0046 | 3.3924 | 3.4452 | 40.90909 | 41.8147 | 3.407533 |
15:00 | 1.3734 | 2.8712 | 2.923 | 52.16634 | 53.01403 | 1.532567 |
15:30 | 1.0556 | 2.387 | 2.4366 | 55.77713 | 56.67734 | 1.772152 |
16:00 | 0.8272 | 1.9325 | 2.0436 | 57.19534 | 59.52241 | 2.035623 |
16:30 | 0.6669 | 1.4649 | 1.542 | 54.47471 | 56.75097 | 5.436485 |
17:00 | 0.5173 | 0.9945 | 1.1565 | 47.98391 | 55.27021 | 5 |
17:30 | 0.2932 | 0.6 | 0.764 | 51.13333 | 61.62304 | 14.00778 |
The total power of static panel, hybrid tracking system, and the continuous tracking system throughout the day is 45.21 watt, 56.69 watt, and 58.24 watt, respectively. So the average power gain of hybrid tracking system over the static panel is 25.62%. Similarly the average power gain of continuous tracking system over the static panel is 28.10% and over the hybrid tracking system is 4.19%.
Comparison of stepper motor power consumption.
Hybrid tracking system | Continuous tracking system | ||
---|---|---|---|
Power consumption |
Power consumption |
Power consumption |
Power consumption |
0.6 watt | Almost zero ≈ 0 | 0.6 watt | 0.48 watt |
|
|||
Total = 0.6 watt | Total = 1.08 watt | ||
|
|||
|
So power saved by hybrid tracking system over continuous tracking system is 44.44%.
The design, implementation, and testing of a hybrid dual axis solar tracking system is presented in the study. The Performance of the developed system was experimented and compared with both the static and continuous dual axis solar tracking system. This work demonstrates that hybrid dual axis solar tracking system can assure higher power generation compared to static panel as well as less power consumption compared to continuous dual axis solar tracking system. The result shows that the hybrid dual axis tracking system has 25.62% more average power gain over static system while it has 4.2% less average power gain compared to continuous tracking system. In hybrid dual axis solar tracking system one motor runs continuously to track continuous movement of sun due to daily motion and another motor runs once in a month to track suns seasonal motion. But in other trackers like in continuous solar tracker it needs to move both the motors continuously. Thus the hybrid system is saving motor power consumption while the power gain compared to other technology is almost marginal. So further comparative study about stepper motor power consumption shows that hybrid tracking system can save 44.44% power compared to continuous tracking system. This amount of power saving will have a significant effect in large systems like heliostat power plants where a lot of trackers are required and power saved by all the systems will show a big amount of power. Other than this the designed tracking system can also be implemented for the solar thermal systems. Finally the proposed design is achieved with low power consumption, high accuracy, and low cost.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors thank M.D. Ahasanul Kabir of American International University, Bangladesh (AIUB), for his help with the mechanical system implementation.