Difference between revisions of "APSC 100 213B Solar Powered Laptop"
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Revision as of 17:59, 7 June 2010
- Jacqueline Pageau
- Cole De Sa
- Brad Jordan
- Kieran Potter
- Jake Garvey
Design of a Solar Powered Laptop
APSC-100 Project Proposal
Group Number: 213B
Jacqueline Pageau 5998198
Cole De Sa
Report Prepared For
Faculty Sponsor: Julie Boudreau
Project Manager: Nabeil Alazzam
Community Sponsor: Dr. Pearse
Date Submitted: October 16, 2009
“We do hereby verify that this written report is our own individual work and contains our own original ideas, concepts, and designs. No portion of this report has been copied in whole or in part from another source, with the possible exception of properly referenced material.”
One Laptop per Child is a non-profit organization that provides children in some of the most remote areas on earth with opportunities to meet their potentials by exposing them to a world of ideas. The organization has produced a laptop known as the XO laptop to be distributed to children in developing countries. Unfortunately the majority of these children have no access to electricity in order to power the laptops. Solar energy has thus
been proposed as a convenient alternative to energy that requires a great deal of infrastructure. The problem remains as to how to effectively and inexpensively power the laptops using solar energy.
The proposal requires a solution to the stated problem. The project requires that a successful prototype be constructed and presented for evaluation.
A general understanding of the XO laptop itself and the science of solar panels is needed in order to find an optimal design for presentation. Through research, various necessary criteria for the solar system accompanying the XO laptop are evident. The criteria for the solar panels are portability, durability, low cost, and sufficient energy output.
The prototype is still to be determined, although much research has gone into the decision of what solar panels will be used and the connection of the panel to the laptop.
Table of Contents
2.0 Problem Formulation…………………………………………………….……... 2
3.0 Design Considerations…………….……………..……….…………………….. 3
5.0 How Solar Panels Work…………………………..….………….……………… 5
6.0 Future Considerations…………………………..………….…………...………..6
7.0 Economic Analysis……………………………………………………………….8
Table of Figures
Figure 1: XO Solar Laptop Group 213B Project Plan ……………………………….7
Figure 2: Solar Panel Cost Comparison………………………………………………9
The XO laptop is an educational tool built to be distributed to poor children in underdeveloped nations around the world. As a result, it incorporates low cost, durable, and user friendly design elements in order serve as a practical tool for educating people in remote areas with little infrastructure and little money. One of its key design features is its low power draw: the XO laptop consumes less than 2 Watts of power (1). Despite this, it can be difficult for children to power the laptop due limited access to electricity.
One of the possible solutions to the problem of charging the XO laptop in areas with limited access to electricity is solar charging option. Any design for a solar panel to charge the XO laptop must take into account the same criteria that the XO laptop itself does: it must be very inexpensive, durable, easy to use, and still fulfill the function of charging the XO laptop in a reasonable amount of time.
Previous designs planning to power the XO laptop with solar panels are generally too expensive, not durable enough for the conditions, or do not provide enough power to charge the XO laptop quickly enough. Despite being impractical, many of these designs contained potentially useful elements. For example, one 10 watt at 21 volt photovoltaic cell design, despite being far too expensive for the XO laptop, incorporated a folding design in order to improve durability and practicality(2).
The design for the XO laptop solar charging option will be developed through further analysis of previous designs as well as research and analysis into the advantages and disadvantages of various types of solar panels and designs. A design will be chosen which is able to charge the XO laptop in a reasonable amount of time while minimizing cost and being durable enough to withstand the elements and use by children. The design will also be easy to assemble with instructions that must be understood by people all over the world.
2.0 Problem Formulation
The problem of finding a solar power solution for the XO laptop considers the most effective way to power the laptop using solar energy while minimizing cost, and maximizing practicality. The task involves the consideration of the materials to be used, the simplicity of the design, the practicality and cost, and the development of user-friendly instructions to accompany the product. The main purpose is to design a system that outperforms previous prototypes while keeping the organization’s main principles in mind.
There are numerous issues to be addressed when deciding on the design of the solar panel system. To begin, the XO is a durable, kid-friendly product, and as such, the solar panel accompanying it must also be a durable learning tool. Due to the fact that the product’s targeted audience is youth in developing countries, the laptop must be able to withstand any accidental abuse, such as being dropped. Since solar cells can be very fragile, finding a suitable way to protect the solar panels is an important task and may be difficult with the given budget. Next, the solar system must be compact and portable, similarly to the laptop itself. This is once again in response to the known targeted audience. Small children are unable to carry heavy loads and thus a lightweight product is necessary. Furthermore, the XO laptop contains an unusual plug. A suitable plug must therefore be found or fabricated. If a supplier for the plug can be found, the plug must be inexpensive and readily available. Finally, the instructions, which will accompany the XO laptop and its counterparts, will be presented along with the prototype and should be simple and universally understood. People from various backgrounds will read these instructions and they must therefore be communicable to people who speak a wide range of languages. The problems outlined above are to be solved with a budget of $80 and within a period of 12 weeks. The low budget and short time period will make the completion of the task challenging, although the formulation of this problem will help in the development of a timeline and the purchase of an inexpensive solar system. The formulation of the issues to be faced is thus a necessary step in finding a suitable solar solution for the XO laptop.
3.0 Design Plan
There are a large number of factors to be considered when deciding upon a design for the solar panel to accompany the XO laptop. Such considerations include the portability of the laptop, its durability, the cost of the solar system, the style and creative aspect of the system, the XO’s energy needs and thus the power output of the solar panel, and finally the XO’s unusual plug.
To begin, many designs involving a case were considered for the solar panels themselves since this would keep the panel safe from harm, such as being dropped. An alternative to this option is the choice of a thin-film, flexible solar panel to be used to power the laptop. These panels can be rolled and are also very lightweight. Thin film panels are not rigid, and a case is therefore unnecessary. Furthermore, the overall appearance of the prototype should be taken into consideration. Many people associate certain objects with various brands. The XO laptop itself has a specific appearance and in turn the solar system accompanying the laptop should follow suit. A simple and clean design will be chosen for the prototype, and as such will mimic the XO laptop. Finally, the XO plug is a non-standard plug. Finding the proper plug for the laptop and a supplier that offers the plugs at a low cost is fairly difficult. For this reason, constructing the plug becomes an option worth considering.
In keeping these considerations in mind, and once a solar panel is selected, the group plans on finalizing the design of a case to hold the panel and the corresponding plug.
5.0 How Solar Panels Work
Each solar panel, or photovoltaic cell, is composed silicon wafers that are precisely cut to less than a centimeter in diameter. Silicon is used because of the fact that it has four of a possible eight valence electrons and so when two silicon atoms bond, the result has no charge. There are also more atomic reasons for the use of silicon but this is the main reason. The top of the wafer, which will be exposed to sunlight, is coated in phosphorus and then heated so as to diffuse the phosphorus into the silicon. As a result, when the elements bond, they complete the valence shell of eight electrons and they have one left over; therefore the side is negatively charged. Next, the wafer is covered with a very thin conductive grid. Following that, the bottom of the wafer is treated similarly to the top but with boron, which has three valence electrons. As a result, when the elements bond, there is one space remaining in the valence shell and so the bottom is considered positively charged. Next, the top of the wafer is exposed to sunlight and the photons from the sun give the extra electron enough energy to detach from the plate. As soon as the electron is detached, it is attracted to the positively charged molecules below. As the electron is drawn downwards, it must first cross the wires which produces an electrical current.
During the design and construction of the project, it is crucial to remember that any protective material that is used to cover the panel must enable photons to reach the cells. That being said, the nature of non-amorphous solar panels is to be quite brittle and fragile therefore the protection offered by the covering material can not be compromised.
Another characteristic of solar panels that must be considered during the design of the model is that there is a high possibility of over-heating. As a result, it could be beneficial for the design to include either a fan underneath the solar panel or an open channel for fresh air to pass through.
6.0 Future Considerations
The main consideration for this project is the selection of the optimum solar panel that meets the specification requirements for the XO-1 Laptop with regard to compatibility. Additionally, the selected solar panel must be economically viable, to maintain the affordability, and consequently, the vision of the One Laptop Per Child project
The project plan outline is identified in Figure 1, with the main focus being the selection of the optimum solar panel for this project. It is intended that a commercial product be selected to interface with the XO Laptop, whereby all tolerances and specification requirements with respect to power, voltage, and amperage are adhered to.
Additional research is to be conducted to acquire basic electronics knowledge, which is necessary to facilitate the build phase. Research will also be carried out to identify possible solutions for effective connection of the solar panel to the laptop. Upon completion of the build phase of the prototype, testing is to be conducted to determine the efficiency of the power and solar performance, and if required re-design may then be addressed. Final design improvements will then be implemented to produce the optimum project design, including project documentation.
It is imperative that the final design allow for ease of manufacturing, as the intent is that documentation be provided to developing countries so as to facilitate local manufacturing of the solar solution. It has been identified that the documentation will utilize graphics rather than verbal communication, for ease of communicating assembly details in regions where the English language may not be utilized extensively.
7.0 Economic Analysis
One of the most important factors to be considered in the project is the identifying of a solar panel that meets the financial limitations identified in the problem. In order to meet our limited budget, a solar panel costing under $50 would be ideal. This would provide the group with an additional $30 remaining for extra materials needed for the project. In reality, a solar panel that would meet the specifications of this project and provide a workable solution is well above this price range. This is unrealistic for various reasons. First of all, the fact that the group is attempting to purchase a single solar panel as oppose to doing so in mass production results in a larger cost per unit. As seen in figure 2, costs are significantly reduced when purchasing a higher wattage panel as well as when purchasing in large quantities (3). Shipping costs are also an issue since many of the inexpensive panels are found outside of Canada and incur high shipping costs. It is evidently not economically viable to purchase a solar panel in which the shipping costs account for up to 30% of the cost of the panel itself. Moreover, the group is in need of a 10-20 watt panel. The cost per watt such a solar panel is larger than that of larger models. Clearly, one of the greater challenges will be finding a solar panel that meets the limiting requirements of the project.
The cost of construction and mass production of the final product could be significantly less expensive than the cost of the group’s prototype. The cost of each solar panel, when in mass production, will be much lower than that of the single panel purchased by the group. Ideally, any additional costs will be limited by the assembly of the product locally. This will decrease total construction and shipping costs as well as bolster the local economy by creating jobs and income.
Brand Watt Min.
Quantity* US$/Unit US$/
EPV Solar 50 368 $92.50 $1.85
REC 220 30 $533.97 $2.43
BP Solar 175 60 $424.97 $2.43
BP Solar 190 60 $460.97 $2.43
REC 210 30 $512.48 $2.44
BP Solar 175 40 $447.97 $2.56
BrightWatts 140 20 $378.00 $2.70
BP Solar 190 20 $568.00 $2.99
Evergreen 205 28 $738.00 $3.60
Sharp 198 1 $777.06 $3.92
Kyocera 135 2 $625.00 $4.63
Mitsubishi 125 1 $595.00 $4.76
Figure 2: Solar Panel Cost Comparison
In order to solve the problem of providing a solar charging option for the XO laptop, a photovoltaic system will be designed to provide power for the XO laptop while being durable, easy to assemble, and inexpensive.
In order to select the optimal design, further research will be done on previous designs and specific types of solar panels in order to find the most effective and inexpensive option. The solar panel will be selected approximately by the end of week six, and will then be ordered. Once all of the parts have arrived, a prototype will be developed and improved upon before a final design is obtained.
(1) “XO Solar: OLPC”. The OLPC Wiki. February 2009.
(2) “Product News: OLPC”. The OLPC Wiki. February 2009.
(3) “Solar Panels”. EcoBusiness Links. November 13th 2008. <http://www.ecobusinesslinks.com/solar_panels.htm>
10.0 Individual Contributions
In terms of individual contribution, Kieran completed the introduction and conclusion in this report, carried out research mostly concerning previous designs and produced the slide entitled “Previous Designs” in the oral presentation. Kieran also presented the slide “Design Considerations”.
Jacqueline completed the design plan and problem formulation sections in this report as well as carried out research concerning various solar panel options for the prototype. She also completed and presented the research slide as well as the XO specifications slide. Jacqueline also completed many progress reports for the group.
Cole De Sa
Cole completed the future considerations section including the Gantt chart in this report. Cole also carried out research concerning the current specifications of the XO laptop. As for the oral presentation, Cole completed and presented the slides entitled “Next Steps” and “How You Can Help”. She also assembled and submitted Team Assignment 1 for the group.
Jake completed the sections on materials and how solar panels work in this report. Jake also carried out research concerning different types of panels, specifically mono- and poly-crystalline panels. HE completed and presented the slides entitled “How Solar Panels Work” and “Our Goal”. Jake also assembled and submitted Team Assignment 2.
Brad assembled and submitted the initial submission of the written proposal report. He completed the slide on design considerations for the oral presentation and carried out research concerning the wiring of the XO laptop.
The XO Solar Solution
“We do hereby verify that this written report is our own individual work and contains our own original ideas, concepts, and designs. No portion of this report has been copied in whole or in part from another source, with the possible exception of properly referenced material.”
One Laptop per Child (OLPC) is a non-profit organization that has provided children in some of the most remote areas on earth with the opportunity to meet their true educational potential. The OLPC organization has addressed the critical educational crisis facing developing countries with the development of the XO Laptop. Unfortunately, the majority children in these countries have no access to electricity, and consequently, no possibility of powering the laptops. Solar energy has thus been proposed as a convenient alternative to electrical energy, which requires a great deal of infrastructure. Although previous attempts have been made to find a solar solution to the XO, they have been unsuccessful at identifying an inexpensive and effective solution to this problem.
The scope of the research for this project involved, initially, understanding the science of solar panels as well as identifying the technical specifications and limitations of the XO, to eventually select an optimum solar panel for this project. After selecting several possible solar panels for the solution, it was immediately identified that the limiting factor in this project was the limited budget. After several unsuccessful attempts to purchase a solar panel due to cost, delivery issues, and being limited to products available in Canada, a solar panel was selected that met the technical requirements of the XO.
The final prototype was comprised of a solar panel with a compatible connector encased in a wood enclosure consisting of a padded interior of weather stripping and soft foam, and a hinged lid with Velcro fasteners and carrying handle. It also included a retractable leg to allow the panel to be inclined at angles up to 45°, which would accommodate required angles based on geographical and latitudinal locations of the target countries, for the optimum collection of the sun’s rays. A shadow stick was included to manually adjust the case to the required angle.
Minimal testing was conducted, due to the resulting limited timeframe due to associated purchase issues, and consequently, limited accessibility of the XO and uncooperative weather conditions once the panel was received. Recommendations regarding testing include testing the power efficiency of the panel, as well as strength tests to assess the durability of the casing, and testing the complementary power outputs dependant on angle of inclination and geographic location. Additional testing should be conducted to assess the effectiveness of the solar panels’ capability of powering the XO, as well as possibly charging its battery.
Although the scope of the project was to provide a prototype design that was portable, durable, and inexpensive, the final prototype was not the optimum solution. The optimal solution to this problem can correspondingly be found once additional funds are allocated for the purchase of the best solar panel. It is unrealistic to find the optimum solution when the one-off cost of the solar panel equates to the proposed mass production costs for the final product when millions of units would be purchased. With the decreasing cost of solar panels and the correspondingly reduced cost associated with large purchase orders, the prospect of selecting a thin-filmed flexible solar panel that could be rolled is within reach. The flexible panel could be protected with a waterproof sleeve, similar to those housing camping gear, and include an external pocket to accommodate a foldable stand for acquiring the appropriate angle of inclination depending on geographic location. The result would be a durable, portable, lightweight, technically effective solar panel, which would be inexpensive once purchased in mass quantities, and could be assembled locally to reduce costs and provide financial stimulus to the targeted countries.
Table of Contents
EXECUTIVE SUMMARY III
TABLE OF CONTENTS IV
LIST OF FIGURES AND TABLES V
1.0 INTRODUCTION 1
2.0 PROBLEM FORMULATION 2
2.1 PROJECT OBJECTIVES 2
2.2 SOLAR PANEL TECHNOLOGY 2
2.3 ELECTRONICS TECHNOLOGY 3
2.4 FUNCTIONAL REQUIREMENTS 4
2.5 DESIGN SPECIFICATIONS 4
3.0 DESIGN CONSIDERATIONS 5
3.1 SOLAR PANEL SELECTION 5
3.2 MATERIAL CONSIDERATIONS 6
3.3 CASING DESIGN 7
4.0 DESIGN IMPLEMENTATION 11
4.1 SOLAR PANEL 11
4.2 ELECTRICAL CONNECTOR PLUG 11
4.3 SOLAR PANEL CASING 12
4.4 RETRACTABLE CASING STAND 13
5.0 EXPERIMENTAL TESTING 14
5.1 RESULTS 14
5.2 DISCUSSION 14
6.0 ECONOMIC ANALYSIS 15
7.0 RECOMMENDATIONS AND FURTHER CONSIDERATIONS 17
8.0 CONCLUSIONS 19
10.0 INDIVIDUAL CONTRIBUTIONS 21
APPENDIX A - MATERIAL SPECIFICATIONS 23
APPENDIX B - DGE SP 15-W SOLAR PANEL SPECIFICATIONS 25
APPENDIX C – SOLID EDGE MODEL - THE APOLLO PROTOTYPE CASE 27
The XO laptop is an inexpensive subnotebook computer developed by the One Laptop per Child (OLPC) organization. These subnotebooks, previously known as the $100 Laptop, was developed to be distributed to children in developing countries around the world, to offer an innovative solution to addressing the critical shortage of teachers in developing countries. The XO, provides the opportunity for these children to have access to knowledge via a modern, user-centered approach to education. Through the OLPC program, governments of developing countries have the opportunity to place an XO in the hands of each primary school child, and ultimately solve their educational crisis.
The XO has continued to evolve with the introduction of a mobile network with advanced mesh networking protocol, and a Linux based operating system. The XO 2, which has yet to be launched, will also have additional advanced features such as touch screens. Although the XO has advanced hardware and software features, it still remains impractical for most of the developing countries that this product is being developed for, because of lack of access to electricity. Attempts have been made to solve this problem through the use of photovoltaic (PV) solar cells, which would utilize the sun’s resources to power the XO in remote areas. Previous designs were unable to provide an inexpensive solution, or provide the benefits of solar power in an efficient and effective way.
This report will outline the design details of a solar power solution to the XO laptop. This design provides an inexpensive solution to powering the XO, by harnessing the power of the sun and converting the power into electricity through the medium of solar photovoltaic cells. Additionally, the selected solar panel must be economically viable, to maintain the affordability of the XO, and consequently, the vision of the One Laptop Per Child project. The design will address this issue through the use of a solar panel that is inexpensive, but meets the specifications with respect to power output requirements.
Secondly, the solar design will be durable to compensate for the rugged environments in which they will operate. The solar design will address this issue with the implementation of a protective case to house the solar panel.
The solar design also addresses the requirement that the final product be portable. The portability of the product will ensure that children are able to manage the movement of the solar design, which allows them to effectively charge the solar panel, that will ultimately power their learning,
Once a solar solution is identified, the intent is to provide open source documentation to enable developing countries the opportunity to manufacture the solar solution, ultimately providing education to their children, and financial benefits to their communities.
2.0 Problem Formulation
2.1 Project Objectives
A solar solution has yet to be found for the XO Laptop. The objective of this project was to provide a solar power solution, which would be effective at powering the laptop, as well as ultimately charging the laptop. Additionally, it was identified that the solution would be portable, durable, and inexpensive. Due to the fact that the original XO was $100, and the XO-2, which has yet to be released, is predicted to be $200, the budgetary goal of the solar solution was to identify a solution that would be within range of $50. In selecting an appropriate and effective solar panel for this project it was vital to obtain necessary background information on solar panel technology and basic electronics theory.
2.2 Solar Panel Technology
Each solar panel, or photovoltaic cell, is composed of silicon wafers that are precisely cut to less than a centimeter in diameter. Silicon is used in solar technology because of the fact that it has four valence electrons and so when two silicon atoms bond, the result has no charge. The top of the solar wafer, which will be exposed to sunlight, is coated with phosphorus and then heated so as to diffuse the phosphorus into the silicon. As a result, when the elements bond, they complete the valence shell of eight electrons and they have one electron left over, producing a negative charge. The wafer is then covered with a very thin conductive grid. The bottom of the wafer is treated comparably to the top, but with boron, which has three valence electrons. As a result, when the elements bond, there is one space remaining in the valence shell and thus the bottom is considered positively charged. When the top of the wafer is exposed to sunlight, the photons from the sun give the extra electron enough energy to detach from the plate. As soon as the electron is detached, it is attracted to the positively charged molecules below. Doping is used in solar panel technology to allow the transfer of electrons, and ultimately, the transfer of electricity.
2.3 Electronics Technology
Electronics technology associated with solar panels follow the basic premise of electrical theory, consisting of relationships of voltage (Volts), current (Amperes), resistance (Ohms) and power (Watts). Basic arrangements of series and parallel circuits are shown below in Figures 1 and 2.
Typically, solar panels have solar cells that are placed in an array. This means that the array will have both parallel and series properties. Since each cells’ voltage properties is based on the construction material, the effect that the series combination will have is that it increases the voltage to an optimum level. Conversely, the combination where cells are placed in parallel will result in the current created by one cell, will correspondingly, be multiplied by two. Additionally, the current is proportional to the load, and each branch/series current will theoretically have the same current flowing through it, since each cell is identical. It is important to note that the total current generated is directly related to the amount the load requires. The total current output affects the power output, which is one of the specification requirements for the project. Power is directly proportional to voltage and current, as identified by equation (1).
P = VI (1)
2.4 Functional Requirements
In identifying the solar solution to the XO, the specification requirements for the XO were researched to determine the electrical requirements for the solar panel to be selected. The following specification requirements (Table 1)  were identified to be vital in selecting solar panel(s) that would meet the operational requirements for the XO. The power conversion specifications  are as follows:
• DC power input, from 11V to 18V, internally limited to 15W draw
• Integrated charger for Ni-MH/LiFePO4 batteries
• High efficiency LED Backlight control circuit
• 6mm power input connector (1.65 mm centre pin)
2.5 Design Specifications
It was determined that the design specifications of the prototype must not only meet the functional specifications as outlined above, but must be durable, inexpensive, and portable.
The prototype should be durable, as the target population/user is primary age children, and the solar panel would be operated in rugged environments. Solar cells are delicate, and improper usage could render the cell ineffective at transmitting power or reduce efficiency. Additionally, rigid solar panels are susceptible to damage if not treated properly, thus the solar solution should include a casing so that the solar panel is protected from the dusty environmental conditions, but also withstand the forces associated with an accidental drop.
Correspondingly, the solar solution should be lightweight and portable, as the children would be transporting the XO and solar solution in a position to collect the sun’s rays. The degree of portability and weight, correspond directly with the budget allocated to this project, whereby with most engineering endeavours, a reduction in the weight or size of a product usually directly corresponds to an increase in cost.
The prototype should also provide a simple solution, as the product will ultimately be manufactured locally in developing countries, where English might not be a language that is prevalent. It was identified that the documentation sent to manufacturing facilities be in the form of step-by-step assembly diagrams with minimal written word.
It has been determined that the design specifications for the prototype include providing an inexpensive, durable, portable solar solution that meets the technical specifications and limitations of the XO Laptop. A protective case should compose part of the solar solution, and the level of protection should be in direct correlation between the specific panel chosen and the degree of protection required. All of these design considerations would be driven by the financial limitations of the project.
3.0 Design Considerations
3.1 Solar Panel Selection
It was identified that the critical decision with respect to this project would be the solar panel selection. Based on the functional requirements and the design specifications of the XO Laptop, extensive research was conducted to determine whether the approach would be to encapsulate multiple solar cells or select one single solar panel.
Methods of encapsulation were researched, including utilizing EVA (a vinyl acetate) and UV-transparent epoxy encapsulation. EVA is the most common encapsulating material. It is constructed on a glass front with the cells embedded in the EVA, between the glass and Teflon sheet behind. The disadvantage of this method is that extreme caution must be taken when handling the cells. The second encapsulating method involves UV-transparent epoxy, which although the modules are quite rugged and lightweight, the risks of encapsulating the cells are high.
The factors affecting encapsulating multiple solar cells and selecting a single solar panel are compared and summarized in Table 2.
It was determined that it would be exceedingly more advantageous to select a single solar panel composed of multiple arrays, vice to purchase multiple solar cells and having to deal with the risks associated with encapsulating them. Although the option of encapsulating solar cells manually was an option due to the group’s limited budget, the lowered overall cost was not believed to be worth the high risk of improperly encapsulating the cells. The only advantage to encapsulating the solar cells was cost, and this factor became minimized once the cost of single solar panels purchased in mass quantities was analyzed.
3.2 Material Considerations
In identifying the necessary materials for the construction of the solar panels’ casing, there were many aspects that had to be considered. Firstly, the materials had to be durable, so as to withstand the conditions under which the solar panel would be placed, Conditions in the target countries include extensive exposure to light and heat, potential dust, dirt and water exposure. Additionally, the materials must withstand the forces associated with an accidental dropping. The materials must also be inexpensive, due to a limited budget, and the goal of making the panel affordable to developing countries. It was also considered that the chosen materials be readily available to entrepreneurs in the less industrialized countries that are using the XO laptops. Finally, the case material must be lightweight, so as to make the casing portable, and to make it possible for the case to be carried by primary age children.
Regarding the criterion of durability, there are further considerations into which this was broken down. Considering the physical abuse the product would handle at the hands of the children using it, the elasticity modulus of the exterior material must be low, as it must be able to withstand and reduce the forces associated with an accidental dropping. This elastic material cannot however be the only material used, as it would reduce jarring, but would transfer any force it was unable to absorb right into the solar panel. For that reason, a more rigid material must be used to create a frame that would absorb the remaining force as well as prevent cracking from twisting of the case. The elasticity modulus of various materials is provided in Appendix A . The prices of various materials are dependent upon fluctuating markets as well as the quantity purchased and the location where they are purchased. As a result, the financial aspect of this prototype with regard to casing materials depends upon their price in Kingston, Ontario when purchased in a small quantity at retail stores. The availability of certain resources varies from country to country however the majority of the South American and North African countries to which the XO laptop has been distributed, have access to lumber. Finally, in considering the lightweight aspect of the case, it was decided that softwoods such as pine would make a much more logical material for the frame as it is significantly lighter than metals such as steel.
When mass-produced, the case could ideally be composed of a durable pine, aluminum or hard plastic frame covered in temper-treated rubber on the outside with a tight-fitting foam interior. For economical reasons, the materials used for the prototype will instead be a mix of materials that were readily available at no cost or purchased at a store for very little.
3.3 Casing Design
Many design plans were considered when attempting to find a suitable method to power the XO laptop with solar energy. The following sketch (Figure 3) is that of the first design solution formulated by the group.
The design is that of a rigid case into which the solar panel is placed. This model included a hinged top that may be locked into place, and a handle for easy portability.
Furthermore, the image below is that of another design concept formulated to accommodate a larger panel. The second design also included a handle and an additional feature of a hinged top that could act as a stand against which the bottom of the case could rest. This concept was added to the proposed product in order to provide the ability to adjust the angle at which the sun’s rays reach the solar module.
A design involving an amorphous solar module (Figure 4) was also considered due to the lightweight and compact nature of such a panel, thus making it extremely portable. The high cost of this solar solution was a main criterion that led to the dismissal of this prototype design.
Further designs were considered including cases capable of folding in half in order to make the product more compact. When considering various designs, a large number of criteria were used to differentiate between certain solutions. First of all, a casing that would be able to adjust the angle at which the solar panel is positioned relative to the sun was desired. This feature presents the ability to position the panel so as to gain optimal rays from the sun at varying times of day, and in turn, generate maximum efficiency from the solar panel. Research into the most favorable angle at which to place the solar module at different times of day was done with respect to areas of the globe where the majority of XO laptops are sold. With approximately 23,000 laptops sold in North Africa, and over 400,000 in South America, the group chose to focus on the sun’s rays along the equatorial line. The angle at which the sun strikes the equator changes as the day progresses, but the sun passes more directly overhead in the middle of the day at the equatorial line that in any other locations outside the Tropics of Cancer and Capricorn, and around the world.
The concept of a simple stand along the bottom of the casing, against which the product could rest, was furthermore developed. The group determined that the angle at which the panel should tilt must range between 0o and 45o in order to achieve optimal power output from the solar module. This was determined due to the fact that the sun spends the majority of its time during the day between -450 and 45o relative to its position perpendicularly overhead. This is particularly true for regions near the equator. Trigonometry was thus used in order to find the length the stand should measure. Equation (2) was utilized for the calculation to find the required length of the stand as follows:
cos (45o) = a/L (2)
Where a, is the length of the case, and L is the length the stand should measure, as shown below.
The length of the case, which was approximated to be 300 mm, was utilized in Equation (2), and correspondingly, the length of the stand was calculated to be 212 mm (Figure 5).
Multiple ideas for indicators that would help children know at which angle to position the module were also developed. The group’s initial idea was that of a plum bob that would hang from the side of the casing. When the module was placed at different angles, the plumb bob would indicate to the user the angle of the panel relative to the direction of gravitational force. A gauge, resembling a protractor and clearly labeled with different hours of the day, would be placed on the side of the casing, thus indicating where the plumb bob should hang at any given hour. It would then be simple to place the panel at the desired angle relative to the time of day in order to achieve optimal performance from the solar module.
An additional idea for an indicator of the panel’s angle was that of a short stick placed on top of the casing and extending perpendicular to the panel. The user would thus simply need to assure the panel was placed at an angle at which the shadow cast by the stick was no longer visible. This would essentially indicate that the panel was pointed in the direction of the sun’s rays.
By keeping many of these design considerations in mind, the group was able to implement an appropriate prototype for the outlined project.
4.0 Design Implementation
4.1 Solar Panel
The design chosen as the final model was a combined result of the research done regarding materials, as well as the availability of certain solar panels. After many failed attempts at purchasing selected solar panels, a 15W monocrystalline photovoltaic module was ordered for $89.00 from a Toronto company called A1 Parts.
4.2 Electrical Connector Plug
The connector that was selected to connect the solar panel to the XO Laptop was the Digi-Key DC power plug connector (Part Number CP-014-ND), as this connector was identified as being compatible to the XO Laptop by previous developmental teams (Figure 6).
4.3 Solar Panel Casing
Using the dimensions of the panel from the company’s website (Appendix B), a final case design was chosen and constructed (Figure 6). The case frame was designed
to be approximately ½ to ¾ inches thick and made of wood. The four sides were screwed and wood glued together for added strength. Although the initial intent was to have two grooves cut into all four sides so as to hold the base and the lid of case and allow them to slide in and out, this design was altered to a simpler version. The lid was hinged on top and notched to allow for a flat fit. The material for the lid and base was chosen based on availability of wood in the Queen’s University workshop. Although this
design was not ideal, and the result was a casing that was heavier than expected, this was the result of the budget being consumed by the purchase of the solar panel. Inside the wood frame, the panel rests on a half inch of Styrofoam, and an additional ¼” layer of soft foam was affixed to the lid to protect the solar panel surface. The utilization of the Styrofoam and soft foam was to avoid movement within the casing, and ultimately protect the panel. Weather stripping was applied to the interior of the casing so as to provide some cushioning and minimize movement of the panel if dropped. Additionally, a lifting tab was inserted on the inside bottom of the case, with the tab accessible at the top of the case below the handle, as shown in Figures 7 and 8. The lifting tab was designed to assist the user in removing the panel from the casing, as the casing was designed to provide a snug fit for the panel, to allow for maximum protection. To finish the case, a soft handle of cloth was attached to the side of the case with hot glue and wood staples to allow for easy portability. The material used in the construction of the case was dependent upon the available resources.
4.4 Retractable Casing Stand
Underneath the base plate a hollow was created to house the retractable casing leg. The stand design was a C shape beam made of wood, that was connected to the left and right sides of the case at the tips of the C as shown in Figure 7. The connection was made with two dowels sticking out of the sides of the case, through holes in the tips of the stand. At the end of the case where the stand is attached, are two cutouts in the end piece of wood to allow the stand to swing at a greater angle. Additionally, a toggle and string structure
was built to secure the stand, once placed in the proper position for optimum solar ray collection. A shadow stick was also connected to the case with a wooden dowel. The shadow stick was designed as a feature that would be utilized to indicate the location of the sun relative to the module. A notch was scribed in the case to indicate 90°, to assist the user when rotating the shadow stick to the appropriate angle for maximum ray collection. The appropriate angle would be obtained once the shadow on the ground is at a minimum. If this product were to be mass-produced with the identified solar panel, all of the wooden components could be substituted with plastic parts and the outside material could be weather-resistant rubber. A photo of the final prototype is provided above in Figure 9, and a Solid Edge assembly model of the prototype case is provided at Appendix C.
5.0 Experimental Testing
The testing of the solar solution prototype consisted of confirming that the wiring was correct for the connection to the XO, with the appropriate orientation of voltages at the panel and correspondingly, at the interface to the laptop. Unfortunately, this was due to the late stage at which the solar panel was received, compounded with the fact that the weather was inclement with cloudy skies and rain for the period from the receipt of the solar panel to the end of the project timeline. The specifications (Appendix B) identified on the company website for the solar panel indicate that the panel would have provided 15 Watts, which if maximum efficiency was obtained would have been sufficient to power the XO, and possibly charge it as well. Additionally, it has been shown that the charging time for a 15W solar panel is 1 hour 45 minutes . Due to the limited timeframe, inclement weather, and the limited accessibility of the XO laptop, the efficiency of this solar solution could not be evaluated.
Although no testing was conducted to determine the efficiency of the solar panel that was selected for this project design, the latitude of Kingston, Ontario is not indicative of the countries that have been identified to benefit from this project. The reduced amount of sunlight during the available time for testing, due to the season in which the testing was conducted, would have greatly affected the performance of the panel. Additional testing should be conducted in varying light conditions, and at varying latitudes to determine an accurate assessment of the performance of the solar panel. This testing could be conducted in concert with the evaluation of the portable stand and shadow stick, to determine the effectiveness of the stand, and the effects of errors in inclination on the efficiency of the panel. Additionally, it would have been beneficial to conduct a vibration and strength test of the casing to determine the allowable limits of force the case could withstand without damaging the solar panel.
6.0 Economic Analysis
One of the most important factors considered in the project was identifying a solar panel design that met the financial limitations identified in the problem, as well as the limited budget of $83. In order to meet our limited budget, a solar panel costing under $50 would have been ideal. However, in order to provide enough power to charge the XO laptop in under three hours, considering that rated output would not always be maintained, it was determined that a solar panel of 15 Watts was required . The cost of individual 15 Watt solar panels proved to be too expensive considering our budget  . Less expensive options were available from countries such as the United States and China , however these options were not viable due to shipping costs and time constraints associated with shipping and customs. As a result of these limitations, a monocrystalline panel costing $89 was selected in order to meet the design specifications, while maintaining the lowest possible cost. The cost of other materials needed for the prototype casing and electrical connection was limited through borrowing materials and using materials that were already available. The lack of funds available after the purchase of the solar panel affected the overall quality of the casing. Given a larger budget a different design for the casing may have been chosen which would have met the design specifications (specifically durability and portability) more closely.
The costs to produce the prototype in large quantities would be significantly less per unit than the cost of the original prototype since most materials are less expensive in bulk. As seen in Table 3, the bulk of the cost associated with the XO laptop comes from the solar panel. This cost will be minimized though mass production. Table 4 demonstrates the cost of purchasing solar panels in large quantities. Especially if thin film solar panels were used, the cost per watt of the solar panel could be greatly reduced from
$6 per watt to as low as $2 per watt considering the large volume of panels to be ordered.
Through bulk purchases and mass production, the total material cost of the XO Laptop solar charger could be decreased from about $90 to about $30 dollars.
Once the product is produced there are many opportunities for it to be adopted. As of July 2009, 900 000 XO laptops have been distributed in developing countries, 230 000 are being shipped, and 600 000 more have been ordered . Additionally, many countries have committed to ordering more XO laptops. For example, Peru plans to order 1.85 million more XO laptops . As well as these large government orders, OLPC has many pilot schools in the Americas, Asia, Africa and the Middle East which represent a possible growth in the market for the XO Laptop . Many of these pilot schools are located in remote rural towns , therefore they are a growing market for the product to be sold.
7.0 Recommendations and Further Considerations
Although the solar solution presented in this report met the specification requirements of the project with regard to the provision of adequate power to operate the XO laptop, there are several areas that require improvement.
The project budget severely limited the prospect of selecting the optimum solar panel for this design. Although the intent of the project was to find an inexpensive solution, it was difficult to select a panel that would have provided the most effective solution at a one-off cost. The developing countries will be purchasing these solar panels at an extremely reduced cost, due to the fact that they will be purchased in quantities of 100’s of thousands. With solar panels becoming increasingly more inexpensive, the prospect of selecting a thin-filmed photovoltaic panel that would fit within the confines of the fiscal limitations of the project would be accessible once the panels are purchased in mass quantities. It is unrealistic to provide an optimum solution to this problem when the funds allocated for the purchase of the solar panel are similar in amount, to the resulting production cost of the panel, when millions are being purchased. Developers that are poised to provide a workable solution to this problem should consider budgeting additional funds initially, to purchase an optimum solar panel for this project. In fact, with the decreasing cost of solar panels and with the massive quantities to be purchased, it would not be unrealistic to purchase a rolled thin-filled PV solar panel that would provide the best solution to the problem, and be economically viable within the fiscal goal of the project.
A thin-filmed panel that could be rolled would be an ideal solution to this problem, as it would be durable and portable. These panels are currently being used by the U.S. Forces in extremely rugged conditions. Rigid panels can be extremely fragile and can limit portability, whereas the durability of the flexible panels does not limit performance of the power output and can weather the rugged and extreme environments of the target countries. The flexible panels can also withstand forces associated with the accidental dropping of the product, whereas rigid panels would require an elaborate case to cushion and protect it.
The rolled panels would allow children to easily transport the product, and allow them to quickly and easily prepare the panel for absorption of the sun’s rays. An accessory that would be useful would be a waterproof nylon sleeve similar to those utilized for camping gear, whereby the panel can slide into the sleeve, which could be cinched at the end with a toggled cord. As with a sleeping bag or tent, the sleeve could contain the panel, and protect it from the elements. An additional feature would be a sling attached to the sleeve so that children can easily transport the panel. This would result in minimal biomechanical stress on the children’s bodies as it is slung over their shoulder. The sleeve would add minimal weight to the design, but would provide crucial protection from particulate matter that could harm the solar cells. Since the flexible panel is also rolled, this would also add a secondary layer of protection.
Additionally, another accessory would be to provide a foldable stand that could be used to hold the solar panel at a specific inclination with respect to the surface of the Earth. This would allow for optimum collection of solar rays based on the geographical and latitudinal location of the target country. The stand should allow for the adjustment of inclination to enable the user to adjust the angle depending on the time of year, the time of day, and the country they are located in. This stand could easily fit in the sleeve identified above since it is foldable, and a separate pocket on the sleeve could be created for the stand so that it would not come in contact with the solar panel. This would reduce any damage that could result from accidental collision of the stand and the panel.
It has been identified that the intent is to have the design manufactured locally in the identified countries, as to reduce cost, and to provide economic stimulus to the targeted areas. The flexible thin-filmed solar panel would be ideal with regard to manufacturing, as it would require minimal manufacturing processes with respect to the panel itself. Conversely, if multiple cells were assembled on location at these manufacturing plants, the possibility of damaging the cells increases, resulting in reduced efficiency, and dependability. It is imperative that the final design allow for ease of manufacturing, as the intent is that documentation be provided to developing countries utilizing graphics rather than verbal communication. This allows for ease of communicating assembly details, in regions where the English language may not be utilized extensively.
Although a solution was obtained for this project, it is recommended that modifications be made to the design as outlined above, with the main issue being selection of an optimum solar panel. It is highly recommended that a flexible thin-film solar panel that could be rolled be selected, as this would provide a durable and portable solution, which could be inexpensive, due to the large purchase quantities and the trend in solar panel pricing, and allow for ease of manufacturing.
Due to the lack of electricity in remote areas of the globe, solar energy is an ideal power source to be used in underdeveloped countries. In order to solve the problem of providing a solar charging option for the XO laptop, a durable, easily assembled, and inexpensive photovoltaic system has been designed.
Many criteria were considered when developing an optimal design solution, and it was quickly identified that budget would be a limiting factor in the design. Although the prototype met the specification requirements to operate the XO laptop, with additional funding for a superior solar panel, an optimal solution could be identified to solve this problem. It was recommended to further developmental teams for this project, that a thin-film flexible solar panel would be the best solution. Not only would the panel be durable, portable, and lightweight, but when purchased in mass quantities, could fit within the budgetary guidelines of this project. With future improvements in the manufacturing of the product, the photovoltaic solution created to power the XO laptop will inexpensively and effectively provide education to children around the world.
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10.0 Individual Contributions
In terms of individual contribution, Kieran completed the introduction and conclusion in the proposal report, carried out research mostly concerning previous designs and produced the slide entitled “Previous Designs” in the oral presentation. Kieran also presented the slide “Design Considerations”. He helped act in the promotional video. He was responsible for producing the Economics section of the final report as well as compiling the different sections. Kieran also assisted with the design, build and testing of the prototype.
Jacqueline completed the Executive Summary, Design Considerations, and Conclusion sections in this report as well as carried out research concerning various solar panel options for the prototype. She also completed and presented the research slide as well as the XO specifications slide for the proposal presentation. Jacqueline additionally completed many progress reports for the group as well as assisted in the editing and resubmission of the proposal report. Furthermore, Jacqueline took part in the building and testing of the prototype as well as assembled the group movie. Finally, Jacqueline helped put together the final oral presentation and presented the slides
Cole De Sa
Cole completed the Future Considerations section including the Gantt chart in the proposal report. Cole also carried out research concerning the current specifications of the XO laptop. As for the oral presentation, Cole completed and presented the slides entitled “Next Steps” and “How You Can Help”. She also assembled and submitted Team Assignment 1 for the group and conducted research concerning solar panel options. Cole assisted with the resubmission of the Project Written Proposal, and collaborated with other members of the team on the video, and in the design, and build of the prototype. She completed the Introduction, and Recommendations and Further Considerations sections of the report and assembled and submitted the final written report. Additionally, she assisted with design of the final oral presentation, and completed and presented the slide entitled “Recommendations “.
Jake completed the sections on materials and how solar panels work in the proposal report as well as the material considerations and design implementation sections of the final report. Jake also carried out research concerning different types of panels, specifically mono- and poly-crystalline panels. He completed and presented the slides entitled "How Solar Panels Work" and "Our Goal" in the proposal report as well as the "Our Goal" and "Material Considerations" slides in the final report. Jake also assembled and submitted Team Assignment 2 as well as occasionally submitting progress reports. Furthermore, Jake contributed to the design process with the other group members and worked a great deal on the construction of the final casing for the solar panel.
Brad assembled and submitted the initial submission of the written proposal report and completed the Economic Analysis section in this report. He completed the slide on design considerations for the proposal presentation and carried out research concerning the wiring of the XO laptop. Brad assisted with the design and build of the prototype and was instrumental in the selection of the prototype name. Additionally, Brad completed and presented the problem formulation for the final presentation.