Bill Lane* Department of Electrical and Computer Engineering Cleveland State University Cleveland, Ohio 44115 EEC 517 April 30, 2008
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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 microcontroller-based solar panel tracking system. Solar tracking allows more energy to be produced because the solar array is able to remain aligned to the sun. This system builds upon topics learned in this course. A working system will ultimately be demonstrated to validate the design. Problems and possible improvements will also be presented.
Renewable energy solutions are becoming increasingly popular. Photovoltaic (solar) systems are but one example. 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. This paper begins with presenting background theory in light sensors and stepper motors as they apply to the project. The paper continues with specific design methodologies pertaining to photocells, stepper motors and drivers, microcontroller selection, voltage regulation, physical construction, and a software/system operation explanation. The paper concludes with a discussion of design results and future work.
2. Background Information
This section presents background information on the main subsystems of the project. Specifically, this section discusses photocell and stepper motor theory in order to provide a better understanding as to how they relate to the solar tracker.
2.1. Light Sensor Theory
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 next step up in complexity is the photodiode followed by the phototransistor .
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. To utilize the photocell, it is placed in series with a resistor. A voltage divider is thus formed and the output at the junction is determined by the two resistances. Figure 1 illustrates the photocell circuit. In this project, it was desired for the output voltage to increase as the light intensity increases, so the photocell was placed in the top position.
R2 Output 2 R1 10 K 1 Photocell
Figure 1 – CdS Photocell Circuit
2.2. Stepper Motor and Driver Theory
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 brushless, 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 windings on the stator is the main distinguishing factor between the three types . Permanent magnet motors may be wound either with unipolar or bipolar windings . The sun tracker uses a...