Students Create Low-Cost, Energy-Saving Solar Tracker

Author(s):
Alex See, PhD - Monash University Malaysia School of Engineering and Science

Industry:
University/Education

Products:
LabVIEW, Data Acquisition, Motion Control

The Challenge:
Completing a mechatronic project to design, develop, and test a prototype solar tracker.

The Solution:
Using LabVIEW and Measurement & Automation Explorer (MAX) software to construct a system with stepper motor motion control, analog I/O, and data acquisition.

Designing an Efficient Solar Energy Solution
Satellite and space travel technology has resulted in solar cells converting solar radiation into electrical energy. Solar panels are useful in practical applications, such as thermal energy storage systems, electric power generating systems, and the aerospace industry. But the average solar energy intercepted by a conventional stationary solar panel is not fully optimized during the day due to static position and placement, which can hide it from sun exposure.

Although sun tracker systems are available commercially, they can be quite costly, depending on their tracking sophistication level. To create a less-costly alternative, a group of students designed and developed a prototype real-time solar tracking system comprised of two plane-parallel solar panels.

Flexible, Easy-to-Use Products Offer Short Learning Curve
For this project, we chose to use NI LabVIEW software with FlexMotion functions and the NI PCI-7334 motion controller card to control a two-axis stepper motor system.

There are many reasons why we chose LabVIEW for this experiment, mainly because LabVIEW is easy to use, and the LabVIEW learning period is substantially short for someone who has already had basic programming experience. Also, LabVIEW comes with extensive documentation and a large number of preconfigured VIs.

The students spent about four weeks designing the prototype solar tracker using AutoCAD software, and about two weeks designing and constructing the photodiode sensing circuits. They spent the remaining time programming, debugging, and testing.

Students Optimize Resources to Create Highly Capable System
NI MAX software configured the motion controller used for this project. A low-cost PCI-7334 motion controller card supported stepper motor control applications with as many as four axes. For this project, the students used only two axes and programmed the stepper motor motion using LabVIEW. A UMI-7764 interconnected to third-party stepper motor power drivers provides a comprehensive wiring and connection point for motion control and feedback signals. A single cable from the motion controller to the UMI-7764 carried all the input and output signals for all four axes. The UMI-7764 four-quadrature analog inputs (i.e., 0 to 5 VDC) accept the four current-to-voltage sensing circuit outputs.

The prototype solar tracker system structure included two solar panels and two VEXTA CSK series two-phase stepper motors and drivers for horizontal and vertical movement. The students configured the clockwise stepper motor outputs with an angular resolution of 1.8 degrees, requiring 200 steps to complete a revolution. Students placed photodiodes, which are used as light sensors, in a special pyramid shape mounted onto a flat perspex sheet. The photodiodes were positioned such that the opposite pairs tracked both the horizontal and vertical light source positions. The photodiodes produced a current proportional to the light intensity received from an external source (a table lamp), and the voltage from the sensing circuit increased or decreased accordingly. The four-voltage signals from the four sensing circuit outputs connected to the four-quadrature UMI-7764 inputs.

The light-sensing circuit was an I-to-V converter using a low-power LM158 operational amplifier. The different voltages became feedback signals LabVIEW used to command the stepper motor movement.

Successfully Tracking the Light Source Position
By developing a simple LabVIEW program, the students turned the stepper motor and later reset the target stepper motor position. For exploring target position, velocity, and acceleration, they wrote a program for acquiring analog voltage values from the I-to-V photodiode/op-amp sensing circuits. After testing, the program successfully demonstrated that the solar tracker was able to track the maximum light source intensity. The tracking resolution was actually the stepper motor resolution, which, in this case, was 1.8 degrees for both the horizontal and vertical positions.

The students designed their software flow chart based on the following information:

• This LabVIEW program read in four analog voltage values from the four individual photodiode-operational amplifier sensing circuit outputs via the four UMI-7764 analog input channels.
  
• The software compared voltage readings for the two pairs of sensors. The vertical opposite sensors performed vertical plane tracking, and the horizontal opposite sensors performed horizontal plane tracking.
  
• If the pair values differed from one another, the LabVIEW program generated commands to turn the stepper motor one step (i.e., 1.8 degrees) at a time, until voltage readings were the same in each pair. After achieving equilibrium, the solar panels aligned toward the direction of maximum light intensity.
  
  

Using a separate PCI-6036E DAQ board and a simple LabVIEW program, the students acquired the connected solar panels series open-circuit voltages. Until 8 s had passed, the solar tracker was at rest, as the light was turned off. But after 9 s, the students turned on the table lamp, which was positioned about 50 cm away from the system. The solar tracker started to respond due to the sudden strong light intensity, resulting from the increasing open-circuit solar panel voltage. The tracker continued to track both the vertical and horizontal stationary light source positions and maintained a steady condition after about 25 s.

Design, Test, and Development in a Short Amount of Time
Students appreciated LabVIEW functionality, particularly the motion control FlexMotion VIs. The students commented that the LabVIEW documentation and examples were clear and easy to follow.

Using LabVIEW, students designed, developed, and tested their prototype two-axis solar tracker system in a short span of time – 13 weeks. This project helped the students gain knowledge in different disciplines of engineering by actively engaging them in mechanical, electrical, and electronics circuit and software designs.

Author Information:
For more information on this Case Study, contact:
Alex See, PhD
Monash University Malaysia School of Engineering and Science
No. 2 Jalan Kolej, Bandar Sunway, 46150, PJ
Selangor Darul Ehsan
Malaysia
Tel: (60) 03 5636 0600 Ext. 3202
Fax: (60) 03 5632 9314
alex.see@engsci.monash.edu.my

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