有关太阳能跟踪器中英文翻译资料.doc

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Solar Tracker
The Solar Tracker team was formed in the fall of 2005 from five students in an ME design team, and a Smart House 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 course of the day. The implementation of such a system dramatically increases the efficiency of solar panels used to power the Smart House. This report examines the process of designing and constructing the prototype, the experiences and problems encountered, and suggestions for continuing the project.
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 increase the efficiency of a solar power system by up to 50%. Given those 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 maximum increase in efficiency. The ultimate goal is that the project will be cost effective – that is, the gains received by increased efficiency will more than offset the one time cost of developing the rig over time. In addition to the functional goals, the Smart House set forth the other following goals for our project: it must not draw external power (self-sustaining), it must be aesthetically pleasing, and it must be weatherproof.
The design of our solar tracker consists of three components: the frame, the sensor, 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 house the main solar collecting panels. The frame itself 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 sensor design for the system uses two small solar panels that lie on the same plane as the collecting panels. These sensor 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 sensor 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 seeing any sunlight, at which point both solar panels on the sensor receive equal sunlight and no power difference is seen.
After evaluation of the previous direct drive system for the tracker, we designed a belt system that would be easier to maintain in the case 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 disassembled. It is easy to
interchange motors as needed for further testing and also allows for optimization of the final gear ratio for response of the tracker.
As with any design process there were several setbacks to our progress. The first and foremost was inclement weather which denied us of valuable testing time. Despite the setbacks, 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 able 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 set forth to us by the Smart House so we believe our sensed motion prototype for solar tracking will be the foundation as they move forward in the future development and implementation of this technology to the house.
2. Defining the Problem
The project was to complete the “REV 2” design phase of the solar tracker to be used on the Smart House. While the team was comprised of members from the ME160 senior design course, the customer for this project was to be the Smart House organization. Jeff Schwane, a representative from the Smart House, was our liaison and communicated to our group the direction Smart House leadership wished us to proceed.
At our first meeting with Jeff and Tom Rose, the following needs were identified:
1. Track the sun during the day
2. Use no external power source
3. Weather proof
4. Cost effective power gain
5. Must look good
6. Solar panel versatile i.e. can fit different types of panels
With these needs in hand, we constructed a Quality Function Deployment chart. This chart can be found in Appendix A. The QFD showed the major areas of concern might have been: number of panels/size of panels, internal power requirements, motor torque required.
At our first meeting we were also able to set up our goals for the semester. Having a working prototype capable of tracking the sun was to be the main goal for the end of the semester, but we soon found that in order to accomplish this, we would be forced to omit portions of the design criteria in hopes they would be worked out later. This would result in the optimization of platform space on the roof to be irrelevant, with our goal being to have one platform track. It also led to the assumption that our base would not need to be tested for stability or required to be fastened to the roof. With an idea of where we were to begin, from scratch with the possibility of using the frame from the “REV 1” design, and an idea of where we were to finish, with a moving prototype, we constructed the Gantt chart that can be found in Appendix B. Our group planned to meet with Jeff once a week to make sure we were on track with the needs of the Smart House. Jeff would also meet with Tom Rose, the director of Smart House, at least once a week in order to keep everyone on the same page. With our goals in mind we embarked on the process of idea generation.
3. Concepts and Research
3.1 Tracking Type
Our group used 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 presented to us by Smart House. Other concepts were generated through research 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 House. 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 course of a day and return at the end of the day. This concept presented the advantage of simplicity and presented us with the option to use materials from the previous structure (which was also intended 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 seasons. The advantage of this concept was a more efficient harvesting of solar energy. The third concept was to only track throughout the seasons. 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.
3.2 Structure
Once the method of motion was chosen, 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 House solar tracker group or through the use of columns which would support the axis on either side. While the prismatic structure presented the advantage of mobility and an existing frame, the columns would have provided us with ease of construction, simple geometric considerations, and ease of prospective mounting on the roof. Due to the heightened intensity of time considerations, the previous financial commitment to the prismatic structure by Smart House, and our limited budget, the presence of the pre-existing frame proved to be the most important factor in deciding on a structure. Due to these factors we decided to work within the frame which was provided to us from the previous Solar Tracker group.
3.2 Tracking Motion
Once the structural support was finalized we needed to decide on a means to actualize this motion. We decided between sensed motion, which would sense the sun’s position and move to follow it, and continuous clock type motion, which would track the sun based on its pre-determined position in the sky. We chose the concept of continuous motion based 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 sensing 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 these considerations, the implementation of a timing circuit and location sensing device seemed daunting. After consulting Dr. Rhett George, we decided on a device using two panels and shading for sensed motion.
4. Analysis and Embodiment
4.1 Structure Geometry
The geometry of the frame was created in order to allow the solar panels to absorb light efficiently. This was done by allowing rotation in the east-west direction for tracking the sun daily and a 36° inclination (Durham’s latitude) towards the south. Because this frame was designed to be placed on a roof with a slope of 25°, the actual incline of the frame was made to be 11°.
The geometry of the existing platform structure was modified. This was done in order to incorporate the results from the Clear Day Model supplied to us by Dr. Knight. This model led to the conclusion that the platform should track to up to 60° in both directions of horizontal. Thus, the angle range of the frame had to be increased. The sides of the frame were brought in to increase the allowable angle of rotation, and they were brought in proportionally to maintain the inclination angle of 11°. Also, crosspieces were moved to the inside of the frame to allow greater rotation of the platform before it came into contact with the support structure.
The panels used for sensing and powering rotation were placed on the plane of the platform. Mirrors were placed perpendicular to and in between the panels to shade one and amplify the other in order to produce a difference to power the motor. The sensing panels were placed outside the platform area to maintain the largest area possible for collecting panels. A third sensing panel was mounted nearly vertical and facing east to aid rotation back towards the sun in the morning. This panel was attached to the frame under the platform, so that during most of the day, it’s shaded with minimal effects on sensed rotation.
Minimizing the torques on the motor was a main concern in order to minimize the motor power needed. The platform designed for the placement of the collecting solar panels was placed under the rotational shaft so that the panels would be aligned with it the rotational axis. Since the main panels comprise the majority of the weight putting these in the plane of the rotational axis reduces torque on the shaft. The sensing panels were placed symmetrically about the axis of rotation in order to prevent additional torque on the motor. The third panel was attached to the frame instead of the platform or rotational shaft so as to also avoid any torque.
4.2 Materials
Materials selection for most of the frame was simple because it had already been constructed. The mirrors used for the amplification and shading of the sensing panels were also already purchased and available for use. Additional parts for attachment of the panels and mirrors to the frame were taken from the scrap pieces available in the machine shop. In our selection of sensing panels, size and power needed to be balanced effectively. The panels were to be as small as possible in order to add minimal stress and weight to the frame but also needed to be powerful enough to power the rotation of the platform. Therefore, the most powerful of the intermediate sized panels available were selected. The panels purchased also appeared to be the most reliable of our options.
4.3 Drive Mechanism
After designing a prototype and testing it, the motor purchased and used by the previous solar tracker group was slipping. It was removed, and the installation of a gear system with another simple motor was suggested and attempted. Professor Knight supplied some gears as well as some belts and pulleys. One end of the shaft was lathed so that one of the pulleys could be set on it, and spacers were bought so that a 6V motor we had available could power another pulley. These pulleys were to be connected by a belt. This motor demonstrated insufficient strength to turn the rotational shaft. The original motor, once detached, was taken apart and examined. Itappeared to be working again so a new pulley was purchased to fit it and was attached in the place of the 6V motor.
5. Detailed Design
5.1 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 base 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 base and folding the structure.
5.2 Sensor
Our sensing panels are bolted to the bottom of the main solar panel frame and braced underneath with half inch L-brackets. The mirrors are attached to the inside of the sensing panels and braced by L-brackets as well. The w