英文原文

The Design Of Phtovoltaic (PV) Electric Systems And Solar Tracker
1 Introduction
Photovoltaic systems use solar cells to capture the sun rays and convert that energy into electricity. Such systems allow homeowners to generate electricity in a clean, reliable, and quiet way that can offset the cost of future electricity costs and decrease their dependence on the energy grid.
Photovoltaic cells are generally made from modified silicon, or other semi conductive materials, that absorb and convert sunlight into electricity. Photovoltaic cells are long lasting (the first PV system ever installed in the USA – in 1954 – is still operating today). Most manufacturers warranty their products power output for a minimum of 20 years. But most solar professionals agree that a system should last at least 25 – 30 years.
1.1 Types of Solar Cells
There are three basic types of PV modules: monocrystalline, polycrystalline, and thin-film. All modules work well though monocrystalline cells often yield the greatest efficiencies. Thin-film technology typically costs less and its efficiency is ever improving as demand for solar panels grow. A growing variety of manufacturers and models are available in the marketplace today. A solar pro can walk you through the advantages and disadvantages of each system so that you find a design that performs optimally over its multi-decade long lifespan for your application.
1.2 How solar electric systems work
Photovoltaic panels are often mounted on a roof and wired into a building via an inverter. The inverter converts the direct current (DC) energy generated through the solar panels into alternating current (AC), the most common type of current used to power buildings in the USA. Orienting solar panels to the south maximizes the effectiveness of energy collection, and most roofs –from flat to 60-degrees –can accommodate photovoltaic cells. For more detailed information on how PV cells generate electricity, check out Cooler Planet's How Photovoltaic Cells Work page. Orienting solar panels to the south maximizes the effectiveness of energy collection, and most roofs – from flat to 60-degrees – can accommodate photovoltaic cells.
1.3 Solar Panels vs Building Integrated Photovoltaic Products (BIPV)
Solar panels are flat panels of photovoltaic arrays mounted on a roof or a pole to capture the sun's rays. They are the traditional arrays used to catch energy from the
sun. Because of their standalone design, solar panels are well suited for home retrofits or remodels.
Solar photovoltaic cells, however, are increasingly incorporated into building components such as windows, walls, or roof tiles. The effect provides a seamless integration into a building's design since the BIPV components essentially disappear into the skin of your home. BIPV products work particularly well for new home construction or a significant remodel. And because BIPV panels are made for both photovoltaic and thermal collection systems, designers often place both technologies side-by-side to further maximize efficiencies.
For more information about solar electric costs, visit our Solar Power Cost page or visit our Solar Power Financing Options page for information on how to pay for your system.
1.4 The Advantages of Mitsubishi Solar Panels
Solar panels are made to respond to three of the most basic concerns people have about electricity use such are cost-efficiency, environmental protection, and lower electric bills. While most solar panels of today generally answer these concerns, Mitsubishi Electric tries to go a little further through their continuing research for innovative use of materials and technology to maximize solar energy for home or office electric use.
Early this year, Mitsubishi made a solar cell that is able to produce the highest conversion efficiency rate of 18.6 percent using new technology based on serious research on photovoltaic technology. Removing lead and allowing expanded light reflection goes for improved efficiency as well as environmental preservation with the solder-coatingless cells.
Fine grid electrodes to expand the light-receiving area were also developed by Mitsubishi for their solar panels while their back surface field structure was improved. To lessen the reflection of sunlight from the module, anti-reflective coating was also used as well as a unique bus bar design was integrated to reduce resistance. The solar panels also used high transmittance glass that are cerium-free, and a high reflectance back film which accelerates reflection power to 90 percent.
Mitsubishi solar panels were also developed and mostly relied on by many users for their reliability and durability. Requiring little or no maintenance, these solar modules have guaranteed use of twenty years or more. Many owners of houses and buildings
have reported to still use them as efficiently as they still had them the first time over twenty years ago. Solar panels as alternative sources of electricity for common house or building facilities or appliances contribute to over 80 percent of overall electric use, making it more popular for energy-conscious home or building owners.
Mitsubishi solar panels are also known for their durability and reliability because of the use of special materials and built-in features that enhance their use as well as providing the most reliable convertible energy sources to people. To reduce the stress on tab wiring, straight tabs are used; while to avoid reduction of electric when dust begins to thicken on the module corners, increased between the module framed and the bus bar is observed; and to prevent corrosion, anodized aluminum frames are used with clear coating.
With the continuing research and technology innovation being made to improve and develop better solar panels, more and more people are turning to solar panel as their alternative energy source. With the flexibility, low maintenance, reliability, and cost-efficiency that these solar energy tools afford people, it is expected that more will resort to using these in their homes, offices, and other buildings. Building owners who are looking for ways to cut down on their electrical expenses have adopted this alternative energy approach with some even integrating the panels‟ design with their own building, rather enhancing or making the building more attractive. Other manufacturers are also accommodating homeowners who wish to use these as well by following the contour or roofing designs of the houses with their roof-mounted solar panels.
Mitsubishi solar panels are not far behind with these modern innovations and design adaptation. With the proper consultation and choice among their line of flexible solar panels, having these PV modules in more homes and buildings at a greater number should not be impossible.
2 Photovoltaic System Design
2.1 Introduction
After PV workers unremitting efforts, solar cell production technology constantly improve, and increasingly widely used in various fields. Posts and telecommunications in particular, the telecommunications industry in recent years
because of the rapid development of communication power requirements have become more sophisticated, so stable and reliable power Solar energy is widely used in communications. And how the various regions of solar radiation conditions, to the design of both economic and reliable photovoltaic power system, which is one of the many experts and scholars study the long-standing issue, but there are many excellent research results, for the development of China's photovoltaic laid a solid foundation. The author of the study at the design methodology of experts found that the design has only considered the self-maintenance of battery time (that is, the longest consecutive rainy days), without taking into account the loss of electric batteries as soon as possible after the recovery time (ie, two sets of the longest continuous rain days, the shortest interval between the days). This problem particularly in the southern China region should pay great attention to the southern region because of our rainy day is long too, and for the convenience of independent photovoltaic power system, because there is no other emergency backup power protection, so this problem should be included in the design considered together.
In this paper, an integrated design method of the previous advantages, combined with the author over the years actually engaged in the design of photovoltaic power systems experience, the introduction of two sets of the longest consecutive rainy days, the shortest interval between the number of days as the basis for the design of one, and comprehensive consideration of the the impact of solar radiation conditions of the factors that made solar cells, the formula for calculating battery capacity, and related design methods.
2.2 Many factors affect the design
Sun solar cells on the ground square on the radiation of light spectrum, light intensity by the thickness of the atmosphere (ie air quality), geographic location, the location of the climate and weather, terrain and surface features such as the impact of its energy in one day, January and a year of great change, or even years between the total annual amount of radiation There were also large differences.
Square solar photoelectric conversion efficiency, by the battery itself, temperature, sunlight intensity and battery voltage fluctuations, which is three in one day will change, so square photovoltaic solar cell conversion efficiency is also variable.
Battery is charging in the float state, with the square of its voltage output and load power consumption changes. Batteries to provide energy is also affected by environmental temperature.
Solar energy battery charge and discharge controller made by the electronic components manufacturer, it is also necessary energy, while the use of components of performance, quality, etc. is also related to the size of energy consumption, thus affecting the efficiency of charge.
Load of electricity, but also as determined by uses, such as communications relay stations, unmanned weather stations and so on, have a fixed power equipment. Some equipment such as a lighthouse, beacon lights, civilian power consumption such as lighting and equipment power consumption are often changing.
Therefore, the solar power system design, the need to consider many factors and complex. Characteristics are: the data used in most previous statistical data, the statistical data measurement and data selection are important.
Designers of the mission are: In the solar cell matrix under the conditions of the environment (that is, the scene of the geographical location, solar radiation, climate, weather, terrain and surface features, etc.), the design of solar cell and battery power system matrix is We should pay attention to economic efficiency, but also to ensure system reliability.
Location of a particular energy of solar radiation data to meteorological information provided the basis for the design of solar cells used phalanx. These meteorological data required to check the accumulation of several years or even decades on average.
Various regions on the Earth by sunlight and radiation changes in the cycle for the day, 24h. In a square area of solar cells also have the power output 24h of the cyclical changes in its laws and sun radiation in the region, the changes of the same. However, changes in weather will affect the square of the generating capacity. If you have a few days consecutive rain days, almost square on the power generation should not rely on batteries to power, and battery depth of discharge and then need to be added as soon as possible good. Most designers in order to weather the sun to provide a daily total of radiation energy or the annual average sunshine hours as the design of the main data. Each year because of a regional data is not the same as for the sake of reliability
should be taken within the last decade of the minimum data. Under the load of electricity consumption, in sunshine and no sunshine when battery power is required. Weather provided by solar power or the total amount of radiation the total sunshine hours on the battery capacity of the size of the decision is indispensable data.
Phalanx of the solar cell, the load should include all power system devices (except for use but also have a battery and electrical circuits, controllers, etc.) consumption. Matrix components of the output power and the number of series-parallel, and series are required in order to obtain the operating voltage, in parallel are necessary in order to obtain the current work, an appropriate number of components through which the composition of series-parallel connection of solar cells required phalanx.
2.3 Designed capacity of batteries
Solar cell power supply system is the battery energy storage devices. And solar cell batteries are usually square matching job at Floating state, with the square of its voltage output and load power consumption changes. Its load capacity than the power required is much greater. Batteries to provide energy is also affected by environmental temperature. And solar cells in order to match the job requirements of long life battery and easy maintenance.
2.3.1Battery Selection
And be able to support the use of solar cells, many different types of batteries, widely used at present have lead-acid maintenance-free batteries, ordinary lead-acid batteries and alkaline nickel-cadmium batteries of three. Domestic use are mainly maintenance-free lead-acid batteries, because of its inherent "free" maintenance of properties and less polluting to the environment characteristics, it is suitable for the performance of reliable power systems solar power, especially in unattended workstations. Ordinary lead-acid batteries require regular maintenance because of its larger environmental pollution, so the main suitable for the maintenance of the ability or have the use of low-grade occasions. Although alkaline nickel-cadmium batteries have better low-temperature, over-charge, take-off performance, but because of their higher prices, only applies to more special occasions.
2.3.2 Calculation of battery capacity
Battery capacity to ensure continuous power supply is very important. At one year,
the month of matrix generation has very different. Phalanx at the generating capacity can not meet the electricity needs of the month, to rely on battery power give supplement; electricity required in more than month, are relying on batteries to store excess energy.
Phalanx so inadequate generating capacity and surplus value, is to determine the basis for one of the battery capacity. Similarly, the continuous overcast and rainy days during the load of electricity must also be obtained from the battery. Therefore, the power consumption during this period to determine the battery capacity is also one of the factors.
3 Solar Tracke
3.1 Introduction
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.
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 s un 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.
3.2 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
e 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.
3.3 Concepts and Research
3.3.1Tracking 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.
3.3.2 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.
3.3.3 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. 3.4 Analysis and Embodiment
3.4.1 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.
3.4.2 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.
3.4.3 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.。