Solar Tracker
December 15, 2005
Duke University Smart Hou Pratt School of Engineering The Solar Tracker team was formed in the fall of 2005 from five students in an ME design team, and a Smart Hou liaison. We continued the work of a previous solar tracker group. The task was to design a prototype tracking device to align solar panels optimally to the sun as it moves over the cour of the day. The implementation of such a system dramatically increas the efficiency of solar panels ud to power the Smart Hou. This report examines the process of designing and constructing the prototype, the experiences and problems encountered, and suggestions for continuing the project剑桥英语培训班
1.Introduction
Solar tracking is the process of varying the angle of solar panels and collectors to take advantage of the full amount of the sun’s energy. This is done by rotating panels to be perpendicular to the sun’s angle of incidence. Initial tests in industry suggest that this process can increa the efficiency of a solar power system by up to 50%. Given tho gains, it is an attractive way to enhance an existing solar power system. The goal is to build a rig that will accomplish the solar tracking and realize the max
imum increa in efficiency. The ultimate goal is that the project will be cost effective – that is, the gains received by incread efficiency will more than offt the one time cost of developing the rig over time. In addition to the functional goals, the Smart Hou t forth the other following goals for our project: it must not draw external power (lf-sustaining), it must be aesthetically pleasing, and it must be weatherproof.
The design of our solar tracker consists of three components: the frame, the nsor, and the drive system. Each was carefully reviewed and tested, instituting changes and improvements along the design process. The frame for the tracker is an aluminum prismatic frame supplied by the previous solar tracking group. It utilizes an ‘A-frame’ design with the rotating axle in the middle. Attached to the bottom of this square channel axle is the platform which will hou the main solar collecting panels. The frame itlf is at an angle to direct the panels toward the sun (along with the inclination of the roof). Its rotation tracks the sun from east to west during the day.
The nsor design for the system us two small solar panels that lie on the same plane asups是什么东西
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the collecting panels. The nsor panels have mirrors vertically attached between them so that, unless the mirror faces do not receive any sun, they are shading one of the panels, while the other is
receiving full sunlight. Our nsor relies on this difference in light, which results in a large impedance difference across the panels, to drive the motor in the proper direction until again, the mirrors are not eing any sunlight, at which point both solar panels on the nsor receive equal sunlight and no power difference is en.
After evaluation of the previous direct drive system for the tracker, we designed a belt system that would be easier to maintain in the ca of a failure. On one end of the frame is a motor that has the drive pulley attached to its output shaft. The motor rotates the drive belt which then rotates the pulley on the axle. This system is simple and easily disasmbled. It is easy to
interchange motors as needed for further testing and also allows for optimization of the final gear ratio for respon of the tracker.
As with any design process there were veral tbacks to our progress. The first and foremost was inclement weather which denied us of valuable testing time. Despite the tbacks, we believe this design and prototype to be a very valuable proof-of-principle. During our testing we have eliminated many of the repetitive problems with the motor and wiring so that future work on the project will go more smoothly. We also have achieved our goal of tracking the sun in a ‘hands-off’ demo. We were a
ble to have the tracker rotate under its own power to the angle of the sun and stop without any assistance. This was the main goal t forth to us by the Smart Hou so we believe our nd motion prototype for solar tracking will be the foundation as they move forward in the future development and implementation of this technology to the hou.
2. Concepts and Rearch杀戮开关
2.1 Tracking Type
Our group ud a brainstorming approach to concept generation. We thought of ideas for different solar tracking devices, which proved difficult at times due to the existing frame and concept prented to us by Smart Hou. Other concepts were generated through rearch of pre-existing solar tracking devices. Originally our concept generation was geared towards creating a completely new solar tracker outside of the constraints of the previous structure given to us by Smart Hou. This initial brainstorming generated many concepts. The first one was a uni-axial tracking system that would track the sun east to west across the sky during the
cour of a day and return at the end of the day. This concept prented the advantage of simplicity and prented us with the option to u materials from the previous structure (which was also intendbreach
ed to be a uni-axial tracker) in construction. Another more complex concept was to track the sun bi-axially which would involve tracking the sun both east to west and throughout the asons. The advantage of this concept was a more efficient harvesting of solar energy. The third concept was to only track throughout the asons. This would provide small efficiency gains but nowhere near the gain provided by tracking east to west.
The different structures we came up with to accomplish tracking motion included a rotating center axle with attached panels, hydraulic or motorized lifts which would move the main panel in the direction of the sun, and a robotic arm which would turn to face the sun. The clear efficiency gains coupled with the simplicity of design of the uni-axial tracking system and the existence of usable parts (i.e. motor and axle) for the rotating center axle structure, led us to the choice of the East to West tracking, rotating center axle concept.demand的用法
2.2 Structure
Once the method of motion was chon, it was necessary to generate concepts for the structural support of the axle. Support could be provided by the triangular prismatic structure which was attempted by the previous Smart Hou solar tracker group or through the u of columns which wo
wellcomeuld support the axis on either side. While the prismatic structure prented the advantage of mobility and an existing frame, the columns would have provided us with ea of construction, simple geometric considerations, and ea of prospective mounting on the roof. Due to the heightened intensity of time considerations, the previous financial commitment to the prismatic structure by Smart Hou, and our limited budget, the prence of the pre-existing frame proved to be the most important factor in deciding on a structure. Due to the factors we decided to work within the frame which was provided to us from the previous Solar Tracker group.
2.2 Tracking Motion
Once the structural support was finalized we needed to decide on a means to actualize this motion. We decided between nd motion, which would n the sun’s position and move to follow it, and continuous clock type motion, which would track the sun bad on its pre-determined position in the sky. We cho the concept of continuous motion bad on its perceived accuracy and the existence of known timing technology. During the evaluation stage, however, we realized that continuous motion would prove difficult. One reason was the
inability to draw constant voltage and current from the solar panels necessary to sustain consistent
motion, resulting in the necessity for nsing the rotation position to compensate. Continuous motion also required nearly constant power throughout the day, which would require a mechanism to store power. Aside from the considerations, the implementation of a timing circuit and location nsing device emed daunting. After consulting Dr. Rhett George, we decided on a device using two panels and shading for nd motion.
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3. Detailed Design
3.1 Frame
The frame was designed from one inch square aluminum tubing, and a five foot long, two inch square tube for the axle. It is constructed with a rigid ba and triangular prismatic frame with side supporting bars that provide stability. The end of the axle is attached to a system of pulleys which are driven by the motor. It is easily transported by removing the sides of the ba and folding the structure.
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3.2 Sensor
Our nsing panels are bolted to the bottom of the main solar panel frame and braced underneath wi
th half inch L-brackets. The mirrors are attached to the inside of the nsing panels and braced by L-brackets as well. The whole structure attaches easily to the main panel frame which is attached to the main axle using four 2-inch U-bolts. A third panel is bolted to the structure to return the main panels direction towards the horizon of sunri.
3.3 How the Sensor Works
Our nsor creates movement of the motor by shading one of the panels and amplifying the other when the system is not directly facing the sun. The two nsing panels are mounted parallel to the main panels symmetrically about the center axle with two mirrors in between them. The shading on one of the panels creates high impedance, while the amplified panel powers the motor. This happens until the panels receive the same amount of sunlight and balance each other out (i.e. when the nsing panels and main panels are facing the sun.). We initially attempted using a ries configuration to take advantage of the voltage difference when one of the panels was shaded (Appendix C). This difference, however, was not large enough to drive the motor. We subquently attempted a parallel configuration which would take advantage of the impedance of the shaded panel (Appendix C) and provide the current needed to drive the motor. Once the nsing mechanism has rotated from sunri to sunt, the third panel, which is usually shaded, us sunlight from the s
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unri of the next day to power the
motor to return the panels towards the direction of the sun.
4. Conclusion
Throughout this project we enlisted the support of multiple resources (i.e. ME and EE professors, previous Smart Hou teams). We learned early on that a clear problem definition was esntial to efficient design and progress. We struggled initially as we tried to design a tracking device that was different from the previous solar tracker group’s attempt, without fully weighing the size of their investment and the advantages of using the existing frame for our purpos. As we worked with the fixed frame construction from the previous group we learned that variability of design is key, especially when in the initial phas of prototyping. After many tbacks in testing of the solar panels, we learned that when working with solar panels, much time needs to be t aside for testing due to the unpredictability of the weather.
The actual implementation of using the prototype in its intended location on the Smart Hou roof requires weather-proofing to protect the wiring and electrical connections from the elements, housing for the motor, a bracing system to attach the structure to the roof, and possible redesign to eliminate
excess height and simplify overall geometry. The efficiency of the nsor system could be improved by widening the mirrors or by placing blinders along the sides of the panels to decrea the effects of reflected and refracted light incident on the shaded nsing panel.
