The objective of this project is to generate maximum power by tracking the Sun throughout the day. The solar tracker tracks the sun from East to West throughout the day. More energy is collected by monitoring the solar panel to track the sun like a sunflower. The solar tracking system is a mechatronic system that integrates electrical and mechanical systems, and computer hardware and software. The main components in the solar tracking system are standard photovoltaic solar panels (PV), light dependent resistors (LDR) a deep cycle rechargeable battery, stepper motor and Atmega32 microcontroller.
CHAPTER 1
THE PROBLEM AND ITS SETTING
Introduction
There are numerous ways to convert solar energy into electricity, be it on an industrial or commercial scale. One common method is through the use of photovoltaic cells (solar panel). The power output of solar panel depends on a number of factors. These include the operating temperature, irradiance and incident angle of the solar radiation. The daily average output of solar panel can be enhanced by a solar tracker, which forces sunlight to be incident normally to solar panel at all times, mimicking the behavior of certain flowers which follow the sun during the day. The presence of a solar tracker is not essential for the operation of a solar panel, but without it, performance is reduced. Tests have shown that up to 40% extra power can be produced per annum using a variable elevation solar tracker. Some current devices change the orientation of the solar panel, but this need not necessarily be the only method (McCluney, 1983).
An ideal tracker would allow the solar panel to accurately point towards the sun, compensating for both changes in the altitude angle of the sun (throughout the day) latitudinal offset of the sun (during seasonal changes) and changes in azimuth angle. The slow movement of the sun requires a damped system that will also respond slowly and avoid oscillatory movement. Other desirable aspects would include the nocturnal repositioning of the solar tracker to anticipate the alignment of sunrise, opposite to that of the previous day's sunset, reducing energy losses in the morning (Jha, 2010).
System description
The purpose of the tracking system is to constantly monitor the sun's position in order to maximize solar energy that is fed to solar cells. This system has a number of parts and is best installed by a expert in a field. The main part consists of solar panel that has solar panel that collects solar energy. A servo motor or stepper motor drives the system. Finally, electric components and control units allow panels to angle toward the sun.
General Statement of the Problem
In order to generate solar power in an optimal fashion, solar panels that are used to capture sun's rays need to be continuously repositioned based upon the movement of the sun.
Objectives
This project seeks to explore a simple, cost effective, robust solution to adjust the solar panels using sensors, microcontroller and stepper motors. The idea behind this proposal consists of three photo transducers that collect light from three different positions on the solar panel. The microcontroller can take inputs from three sensors and decide in which direction the solar panel needs to change position.
Limitations
The limitations of this implementation include the proposed system is not able to sense light in a cloudy environment. This should not be a major limitation since light collection during a cloudy day is at minimum. There might be some maintenance needed to make sure that sensors are not covered by dust and block the light.
Definition of Terms
Azimuth: An arc of the horizon measured between a fixed point (as true north) and the vertical circle passing through the center of an object usually in astronomy and navigation clockwise from the north point through 360 degree (Merriam-Webster, 2010).
Light dependent resistor: A device whose resistance decreases with exposure to light (Answers.com, 2001).
Microcontroller: A highly integrated chip that contains all the components comprising a controller. Typically this includes a CPU, RAM, some form of ROM, I/O ports, and timers (Webopedia, 2002).
Stepper Motor: A stepper motor is a special type of electric motor that moves in increments or steps, rather than turning smoothly as a conventional motor does (whatis.com, 2008).
Solar panel: A panel designed to absorb the sun's rays as a source of energy for generating electricity or heating (Go Solar Power For Homes, 2009).
CHAPTER 2
A REVIEW OF RELATED LITERATURE
Overview
This chapter presents an overview of history of solar trackers, different applications that need passive or active tracking with the direction of sun, various architectures implemented to optimize each the solutions that are unique to each of the application. This chapter further expands of the particular problem this project is trying to resolve i.e. moving solar panels adaptively based on direction of sun's movement. A literature review of solar tracking systems is followed by a brief review of micro controllers since micro controller is at the heart of the proposed solar tracking system.
History of Solar Trackers
The first ever automatic solar tracking system was presented in 1975 by Mcfee, who developed an algorithm to compute total received power and flux density distribution in a central receiver solar power system. The effect of mirror's wavy curvature and also the determination of tracking error of plane mirror heliostats in a rectangular array around a central receiver of the solar power system can be obtained by dividing the single mirror into 484 parts, and then summing the contribution of all the mirrors. Flux density and total power received from the sun for a given location were calculated, including the shading effects and blockage of adjacent mirrors. The heliostats were assumed to be mounted according to altitude-azimuth values (McFee, 1975).
Maish developed a control system called Solar Track, which provided sun tracking, communication, night and emergency storage and control functions to drive one and two axis trackers manually. It has comparatively better system reliability and accuracy as its control algorithm has self-alignment routine and self-adjusting motor actuation time. Its full day experimental results showed accuracy of better than +0.1 (Manish, 1990).
Kalogriou proposed a solar tracking system that used single axis solar concentrating systems and was mainly suitable for parabolic collectors with good concentration ratios. This system was made up of Light dependent resistors (LDRs). The LDRs detected the position and status of the sun. Kalogriou used three LDRs: ï¬rst to detect the focus of the collector, the second to detect the cloud cover and the third to sense day or night. The LDRs generated an electrical signal that was fed to a D.C. motor (12V), which operated at a very low speed. A speed reduction gear box was used, which helped in rotating the collector (Kalogriou 1996).
Abdallah and Nijmeh designed an electromechanical, two axes sun tracking system with an open-loop algorithm and enhanced it by using Programmable Logic Controller (PLC) for controlling the tilt, motion and position of solar panels. This system used two separate motors: one was used to drive the solar panels to adjust to the slope of the surface (horizontal north-south axis) and the other was used to drive the solar panels to adjust the azimuth angle of the surface (vertical axis). By using the two moving axes, the surface of the solar panels showed an increase in total capturing of solar energy as compared to single ï¬xed tilted surface. The experimental study showed that the increase in the collected energy is increased by 41.34% (Abdallah & Nijmeh, 2004).
In the same year, Reda and Andreas worked on a new procedure to implement a step-by-step solar position algorithm. The algorithm derived the solar zenith, azimuth and incidence angles based on parameters as ecliptic longitude and latitude for mean Equinox of date, apparent right ascension and apparent declination. The algorithm also included some correction parameters as mutation in longitude, mutation in obliquity, obliquity of ecliptic and true geometric distance (Reda & Andreas, 2004).
In 2007, Chen and Feng developed a solar tracking system on the principle of analogue optical nonlinear compensation. The traditional analogue sensor is consisted of a thin mask with a square aperture that was placed above a quadrant detector. The square aperture is consisted of four slits of equal width. A projective image is formed on the detector's plane by the illumination of incident sunlight in different positions of the detector, depending on the relative angle of the sensor axis. As a result, in a traditional analogue solar sensor the azimuth and elevation angles are obtained by the basic geometrical principles by processing the signals. The output signals vary non-linearly with the azimuth and elevation angles, i.e., sensor sensitivity depends on the incident angle of the sunlight. As a solution to this problem, the authors modiï¬ed the aperture area per unit length in accordance with speciï¬c laws. Thus, the nonlinear displacement of the projective image on the detector's plane caused by linear changes in the incident angle of the sunlight was compensated by the nonlinear aperture area per unit length such that the output of the sensor varied linearly with the input (Chen & Feng, 2007).
Summary
A summary of solar trackers literature can be subdivided into three fundamental areas:
1. Various techniques that were developed over time to capture the maximum amount of sunlight not just for solar panels but also for light fixtures, window coverings (block the sunlight), solar cookers and similar systems.
2. Open loop systems that use mechanical elements to maximize the sun light captured or sun light blocked in the case of window awnings. The term open loop signifies the fact that mechanical motion is pre-programmed based on various inputs. The complexity of such systems varies from simple direction changing from east to west based on the time of the day to very complex systems that use global positioning systems (GPS) to determine latitude and longitude and move the system accordingly based on seasons.
3. Closed loop systems that has an element of feedback to determine the position of the panel. These systems are conceptually elegant, far more accurate than open loop and sometimes easier to implement. However, various conditions have to be considered by the system designer to make sure closed loop feedback is active for all the conditions thus making the system stable and functional for all the possible operating conditions.
CHAPTER 3
METHOD OF INVESTIGATION
Introduction
In order to realize solar tracker control system, an appropriate design of the architecture needs to be developed. The methodology of research work was defined to assure accurate procedures. This section describes the methods and the equipment necessary for accomplishing the proposed project.
Overview
This project seeks to explore a simple, cost effective and robust solution to adjust solar panels using sensors (photo transducer), microcontroller, buffer and stepper motors. The idea behind this proposal consists of three photo transducers that collect light from three different positions on the solar panel and converts this light to analog voltage. The microprocessor can take inputs from three sensors and rotates the solar panel in desired direction and the whole process is shown in Figure 1.
Figure 1. Block Diagram of solar tracker.
There are two very clear advantages to this solution. First: since this solution is closed loop i.e. take light input as a variable, adjustments are made until an optimal point is reached. Second advantage is that all the parts of this system are off the shelf electronic components that bring down cost of implementation for mass production.
Methodology
The objective of this project is to control the position of a solar panel in accordance with the motion of sun and make sure that solar panel captures maximum amount of solar energy possible. The angle at which sun rays fall on the surface of the solar panel determined the amount of energy captured by the solar panel. As described in the statement of purpose for this project explores the ways to automatically adjust position of solar panel to capture maximum sunlight.
The LDR varies the resistance depending upon the light fall, so the resistance of these sensors is converted into a voltage by giving a bias current to LDRs. The microcontroller receives the three signals from the sensor circuit and compares them. Unless the solar panel is in optimal position where this project gets maximum solar energy, the LDR signals are not equal. When there is a difference between LDR voltage levels, the microcontroller program drives the stepper motor towards optimal position or normal incidence of sunlight. This is a feedback system as explained above since this correction mechanism keeps happening until solar panels are in optimal position.
Phase 1: Research and review of literature
In this phase, the necessary criteria such as system inputs, outputs and housing size for electronics and motor were identified and established.
Phase 2: Configuration
In this phase, all the hardware components were configured for proper operation. An interface was created between the sensors, microcontroller and dc motor.
Phase 3: Design
In this phase, an electronic circuit were designed and a micro controller programmed with the software required running the solar tracker system.
Figure 2. Investigation Sequence
Phase 4: Testing
In this phase, the complete circuit were verified and the digital output of the microcontroller is made to drive DC motor that turns solar panels.
Phase 5: Evaluation
In this phase, the obtained results was collected and observed.
Design of the system
Initial activities involved deciding the system architecture, reviewing the data sheet and specifications of microcontroller, drive power and voltage requirements of DC motor. The detail study for each of these steps corresponds with system complexity and system needs at each of these stages. The following topics will be studied in depth:
Fundamentals of microcontroller architecture and programming.
Required Hardware and software
DC motor operational requirements.
The required hardware includes a Solar panel, three light dependent resistors(LDR), Atmega 32 (Microcontroller), two buffers(ULN 2003), rechargeable battery, two stepper motors and a two-axis mechanical structure (Solar panel Mount) and a Codevisionavr software for microcontroller programming.
AVR (Advanced virtual risc) microcontroller is an improved Harvard architecture 8-bit RISC single chip microcontroller, it was developed by Atmel. The AVR was one of the first microcontroller families to use on-chip flash memory for program storage (Atmel Corporation, 2009).
A stepper motor is an electromagnetic device which converts the electrical signals to mechanical rotation. There are several types of stepper motors these cannot be driven in the same way. In this application note, a unipolar stepper motor has chosen to drive the solar panel (Condit, 2004).
The microcontroller chosen is codevision AVR which belongs to Atmel AVR family of micro-controllers. The complier that is needed to program this microcontroller is based in "C" programing language and it has support for Windows 2000, XP, Vista and Windows7 and also several 64-bit operating systems. Since C is commonly used programming language, choice of this microcontroller makes it easier and user friendly to program. There are some added features in this family of micro processes to help with embedded programming.
Testing of System
After the dualâ€axis solar tracker is successfully installed, a preliminary experiment to test the operation of the tracker needs to be performed. The data will be collected from the stationary, single axis and dual axis solar trackers every hour from 8AM to 7PM on three different days respectively, but with same environmental conditions(Sunny days in fall season with no cloud cover. Southern sun in fall will give a better idea of performance than mod summer sun).
The voltage from the solar panel will be measured every hour as well as the resistance of the solar panel will be measured at the same time with multi-meter. Current will be calculated from the voltage and resistance values as Voltage divided by the resistance gives current as per Ohm's law. Power output of solar panel is calculated as a product of Voltage and Current. The assumption here is that power output stays constant in the one hour period where readings are taken.
On the first day the data will be collected using the stationary solar tracker, i.e. without the microcontroller kit and dc motor required to turn the solar panel. Since the solar panel cannot turn, the panel is placed such that it catches maximum afternoon sun. On the second day data will be collected using single axis solar tracker, i.e. solar tracker will be operated with one stepper motor to detect the sunrays from East to West. Note that the experiment is done on a fall day when sun is low in the sky towards southern side. On the third day data will collected using dual axis solar tracker, i.e. the solar tracker will be operated with two stepper motors. One of the motors takes care of east to west rotation and the other tracker makes sure that solar panel is turned sufficiently southward direction such that optimal amount of light is captured.
Power output (in watts) is a measure of the rate of energy performance. The data collected in the experiments will be measured voltage and current. Power output (in watts) is a function of voltage and current Results of the preliminary testing are showed in Chapter 4.
With a designed experiment being chosen as the procedure leading to the analysis, the three main factors will be selected. The first analysis of advantages of dualâ€axis tracking versus single axis tracking. The next, emphasis is placed on different times of day. Though, the power output for three approaches might be same in the afternoon, dual and single axis trackers should show significant improvement in the morning and afternoon. Last, different weather conditions, fair and cloudy will be observed.
Some the noise factors in the discussion are: Cloud cover reduces the solar irradiance reaching the solar panel and restrict the power output. In the case of turbidity, the lower the quantity of aerosols in the air, the better for the solar panels efficiency. Precipital water vapor influences the total intensity and spectral distribution of sunlight. It is also one of the atmospheric variations that is related to the efficiency of solar cells. Temperature negatively affects the efficiency of PV conversion.
Evaluation of the system
Evaluation will collect the obtained results. For the purpose of this project, only voltage and current will be collected by multiâ€meter and other parameters required are calculated based on voltage and current measurements made. The information about weather conditions is available in website 'The Weather Channel". The results of the evaluation will be discussed in Chapter 4.
CHAPTER 4
FINDINGS
Introduction
This chapter presents a comprehensive summary of evaluation of solar tracking system. In this chapter, the presented data shows comparative results of the proposed solar tracking system with single axis tracking system and also stationary solar panel. The Experimental setup is used to prove advantages of the presented solar panel tracker versus other methods of implementation mentioned. And performance assessment is shown as a power output tables for different times of the day and average power for the whole day for each of the systems.
Description of the components
Light Dependent resistors (LDRs): The sensor functions of the solar tracker system is fulfilled by LDRs that are represented by A,B and C in the schematic diagram that is shown in Figure 3. This component can be modeled as a resistor whose value is controlled by the light that falls on it. The actual function of LDR is determined by the photo sensitive diodes that make up this system. To sense the LDR resistance value, compare it with a known resistor. To achieve this LDR is connected in series with 10K resistor thus forming an effective resistive divider. The resistance value of LDR is inversely proportional to the light that falls on it. When light falls on the LDRs, its resistance will be low and voltage at pins of microcontroller will be close to supply voltage (VDD). When there is no light on LDR, the voltage at same pins will be close to ground at 0V. Thus it can show the amount of light falling on LDR by looking at voltage on pins of micro controller.
Micro-controller: Micro controller is the heard of the proposed tracking system. After choosing the appropriate microcontroller, next step is to make sure that it is hooked up properly with right external components supplied to ensure proper functionality. All microcontrollers need a master clock frequency to run their operation. This clock frequency is generated by and internal real time clock circuit that uses an external accurate quartz crystal. In Figure 3, XTAL1 is the quartz crystal and C2, C3 represent the required capacitances that adjust the frequency of master clock.
Buffer Amplifier (ULN2003): It should also be noted that micro controller outputs cannot typically drive large current that is needed by the DC motor that moves solar panel in the right direction. We need to have buffer amplifier for this purpose. The buffer chosen is ULN 2003 and it takes digital signals of microprocessor and converts them into a format that can supply large amounts of currents needed by stepper motor. This circuit is not required from a logical diagram of the circuit, but, is inserted to take care of practical necessities of driving a stepper motor.
As discussed above, microcontroller outputs might not have enough drive strength to provide required current to stepper motor. Digital systems and microcontroller pins lack sufficient current to drive the relay. While the stepper motor's coil needs around 10ma to be energized, the microcontroller's pin can provide a maximum of 1-2mA current. For this reason, we place a buffer driver between microcontroller and relays.
Stepper Motor: Stepper motor is a simple DC motor that runs based on amount of voltage applied to its inputs and will be used to turn solar panels. Uni-polar stepper motors with center tapped winding are ideally suited for our application since we have a single power supply that is needed to power both the stepper motor and rest of the electronics. Having a center tapped stepper motor lets us utilize the low voltage most effectively since we are effectively doubling the voltage in a center tapped transformer.
Figure 3: Schematic Diagram of Solar tracker.
Implementation of System
Once all the main components are selected, the next phase is to choose other components to build printed circuit board like capacitors resistors and ultimately proper power supplies to supply requires voltage and current to the electronics. All the connections between the various components have to to be decided and physical placement of the components on the PCB(printed circuit board) is done with computer aided software.
The first step in physical placement is to place the three LDRs on the solar panel at three different positions in triangular shape as per proposal is shown in figure 4. These three sensors are placed equidistant from each other and it is made sure that entire area of exposure of the solar panel is equally covered with this placement.
Figure 4: Solar panel with three sensors, Two-axis Solar panel mount, Circuitry with
Rechargeable battery.
It is important to make sure solar panel is supported mechanically to be able to move based on the feedback from LDRs. To archive this, a two-axis mechanical structure with two stepper motors is designed to hold the solar panel at two distinct points is shown in Figure 4. In the next step micro controller is placed align with quartz crystal, frequency adjust capacitors, resistors and proper power supply connections. The buffers (ULN 2003) are placed at the output of the microcontroller. ULN 1 is connected to port C, ULN 2 to port C, sensor port is connected to port A of Atmega 32 microcontroller. There are various ways to power all this electronics some of the choices being use power transformer, computer power supply or a rechargeable battery. Rechargeable battery is hooked as this provided cleanest power.
Second phase of the project deals with required embedded software as hardware is now taken care of. In the second phase, Atmega 32 microcontroller needs to be programmed according to the requirements of the project. For this Codevisionavr software is used. The choice of this software enables easy higher level programming as complier takes care of translation to assembly code. Download the Codevisionavr software from Hp-Infosys website and generate code by selecting the proper chip and port selection. Dump the code on to the microcontroller by using the parallel port USB cable.
Once all the electronic and mechanical components are ready the final phase is to fix the solar panel on the two-axis mechanical structure. A proper Interface of the mechanical structure with printed circuit board that contains all the electronics is needed. After this sensors are connected to sensor port and stepper motors to stepper motor port. Final system is shown in Figure 5.
Figure 5: Complete system of Automatic Solar tracker.
Protecting the electronics from various weather conditions is important as this sytem has to work in various environmental conditions all around the year. A weather proof insulated box is chosen to host electronic kit and battery and to protect from environmental conditions.
Placement of the two-axis solar panel mount is in East-West facing to detect the daily changes of Sun. Microcontroller Coding will be explained in appendix A and the code will be explained with comments in Appendix B.
Data Analysis
Preliminary data was collected before the start of main experiment. Table 1 show the variation of power output (Watts) for three systems, i.e., Dualâ€Axis Tracker, Singleâ€Axis Tracker and Stationary solar panels. Figure 6 shows the combination of the power curves of Table1. In the Figure 6, three power curves increase from the morning to the afternoon.
.
Figure 6: The power curves for 3 systems on a clear Sunny Day
The peak power output exists at 14:00. The three power curves show a general bell shape. The preliminary experiment was conducted outdoors. As a result, a number of environmental conditions were taken into consideration. The cloud cover or the rising of the operation temperature will all decrease the solar panel energy conversion efficiency.
In summary, the dualâ€axis tracker shows better energy conversion efficiency most times during the day. This finding shows that the dualâ€axis tracker works properly and orients the solar panel perpendicularly to the sun.
Table 1: The Variation of Power Output (Watts) for 3 Systems on a Clear Sunny Day.
Performance Evaluation
Final experiment was setup to determine the percentage difference in power output between in stationary position, on singleâ€axis tracker and dualâ€axis tracker. Table 2 shows the calculations and difference of power output based on the comparisons of three systems, stationary, singleâ€axis tracker and dualâ€axis tracker. Even with minor fluctuations in the power output due to climatic changes, the average power output was greater in favor of the dualâ€axis tracker than singâ€axis tracker and stationary one. Regardless the time periods of linear increasing and decreasing of power output, the monotonic power output region, the period of time chosen was between 10:00 and 17:00.
Table 2: Power Output Values of 3 Systems and Percentage Difference Between Dual-Axis
Tracker and Other 2 Systems.
The average power increase by employing dualâ€axis tracker was calculated to be 21.99% and 56.33% over the singleâ€axis tracker and stationary one respectively. The difference of power out is shown in Figure 7.
Power increase in Morning &Afternoon time over stationary& Single-axis Solar trackers
Figure 7: Performance Evaluation
CHAPTER 5
SUMMARY AND RECOMMENDATIONS
Summary and Conclusions
Analysis of data in this work showed that the factors that are significant to the power output are tracking system, and weather condition. This research also confirmed that the dualâ€axis tracking system oriented solar panel perpendicularly to the sun and had a tremendous performance improvement. The results reveled that the employment of the Dualâ€Axis Tracking System produced 22% gain of power output, compared with a Singleâ€Axis Tracking System. The gain of output power with the Dualâ€Axis Tracking System was much higher (56%) when compared with a stationary system.
From the Figures 6, time of the day versus power output, a phenomenon was observed which showed a decrease in power output between 14.00 and 16.00 Hrs. This phenomenon was also been found in previous researcher. This behavior may be due to meteorological factors, such as temperature and cloud cover.
Recommendations
Dualâ€Axis tracker which takes advantage of two degree of freedom while tracking can contribute more accurate data and show the different power output since the change of the seasons. Perform longâ€term experiments to test the effect of seasons to the power output. Investigate the effect of temperature with particular attention to the unusual decrease in power output observed between 14.00 and 17.00 Hrs. Pay attentions to the influence of temperature.
