Alternative Solar Energy...

University of Central Florida

Alternative Solar Energy Generation Fall 2011 – Spring 2012

Group 7: Andy Bryan, Beau Eason, Rob Giffin, Sean Rauchfuss

12/5/2011

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Table of Contents Executive Summary .......................................................................................................................... 1

Technical Content ............................................................................................................................ 2

Project Motivation ....................................................................................................................... 2

Project Significance ...................................................................................................................... 3

Goals and Technical Objectives ................................................................................................... 4

Specifications and Requirements ................................................................................................ 6

Related Projects ............................................................................................................................... 8

Relevant Technologies ..................................................................................................................... 9

Solar Tracking Research ............................................................................................................... 9

Active solar tracking research - Photo detecting ....................................................................... 12

Photo detecting array configurations ........................................................................................ 14

Solar tracking components ........................................................................................................ 16

PCB Research ............................................................................................................................. 20

Tracking Motor Control .............................................................................................................. 22

Rotational Motors ...................................................................................................................... 23

Communication with motor....................................................................................................... 27

Actuators .................................................................................................................................... 31

Batteries Researched ................................................................................................................. 32

Induction vs. Permanent Magnet motor Research .................................................................... 34

Direct coupling vs. Belt Driven Research ................................................................................... 35

Lithium Ion battery versus Lead-acid battery ............................................................................ 37

Wire Research ............................................................................................................................ 45

Fuses and Breakers .................................................................................................................... 46

Generators ................................................................................................................................. 47

Coupler ....................................................................................................................................... 56

Possible Hardware Architectures ............................................................................................... 58

Stirling Cycle Engine Research ................................................................................................... 61

Strategic Components .................................................................................................................... 66

MSP430 Family of devices ......................................................................................................... 69

Code Composer Studio .............................................................................................................. 71

Power modes ............................................................................................................................. 71

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Control Procedure ...................................................................................................................... 72

Fresnel Lens Possibilities ............................................................................................................ 74

Linear Actuators ......................................................................................................................... 77

Stepper Motors .......................................................................................................................... 78

Mounting Options ...................................................................................................................... 80

System Prototyping of light sensing array ................................................................................. 82

Circuitry going to the MSP430 ................................................................................................... 83

24 Volt DC Generator ................................................................................................................. 83

12 Volt output voltage regulator ............................................................................................... 84

12 Volt AGM Battery .................................................................................................................. 84

12 Volt charging controller ........................................................................................................ 85

Wires .......................................................................................................................................... 85

Miscellaneous Supplies .............................................................................................................. 85

Coupler ....................................................................................................................................... 86

Motor Types ............................................................................................................................... 86

Initial Design Draft ......................................................................................................................... 88

Final Design Draft ........................................................................................................................... 92

Safety Considerations .................................................................................................................... 98

Hardware Prototyping ................................................................................................................. 101

Testing .......................................................................................................................................... 106

Milestone discussion .................................................................................................................... 113

Budget .......................................................................................................................................... 115

Appendices ................................................................................................................................... 121

Copyright Permissions ............................................................................................................. 121

References ................................................................................................................................... 124

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Executive Summary In today’s world the desire for alternative forms of energy is ever growing, especially for those which do not harm the environment. This sparked the mindset for this project; to generate an alternative form of solar energy collection. This alternative form is to move away from the popular use of photovoltaic cells and to instead utilize a Fresnel lens and a Stirling cycle engine. Then the mechanical output of the Stirling cycle engine will be transformed into storable electrical energy. Further motivation to take on this project has come from the amount of potential solar energy available in Florida. The need for new, innovative methods of renewable energy is in high demand and is a major contributing factor in the motivation to seek out this solution. The project is graciously being funded by Progress Energy.

Completing this project will achieve a reliable source of sustainable energy with a minimal carbon foot print. The project is to be scaled as a proof of concept that this method can be reliable, efficient, cost effective, and safe. The function of the project begins by concentrating solar energy using a Fresnel lens. The converging solar rays will be used as a heat source to power a Stirling cycle engine. The mechanical output of the Stirling cycle engine will then be transformed into electrical energy using an electric generator. Because the Fresnel lens focal point is very small a feedback system is used to control precisely where the focal point sits and to adjust the position as the sun moves throughout the day. This will both greatly boost the efficiency of the product and also make it so that it can operate for an entire day without human interaction.

Further goals of the project are for it to be capable of working for an entire day. Meaning that it is able to sense the start of a day and begin producing energy, stay active for that entire day, and can then reset at the end of that day to prepare to work for multiple days in a row. Also the system shall be rugged enough to withstand the changing weather conditions of Florida. Additionally the system will be able to manage the charge of the batteries while also remaining self-sufficient. To add to the ease of operation for the user the charging system will include a charging status indicator. The cost of the project is to remain competitive with current technologies such as solar cells.

The input to the project is a bright and steady sun. This input will be going through a Fresnel lens no larger than 40 cm by 80 cm. This setup will output a focused beam of light about one cm in diameter and can reach up to 2000 degrees Fahrenheit. The required power output of the lens has to be in the range of 1-10 watts. This setup in combination with a Stirling engine will create the basic prototype. This prototype will be looking at a run time of about 10 hours per day every day from dawn until dusk. The footprint of the project will occupy an area of two square meters and have a height of one meter. The goal is for a total weight of less than 50 kilograms. This will guarantee that the project is portable enough for only two people to safely carry it.

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After the prototype has been created and the power requirements have been met, focus will be shifted to battery charging and solar tracking specifications. The battery portion will be required to have a controller and an indicator for when a battery has been charged. The required controller will be able to shift between different batteries to be charged, show which batteries are full, and work for 10 hours a day everyday with minimal power consumption. Solar tracking will greatly benefit the project. The objective is completed via a motor hooked up to an arm which is connected to the lens and controlled by a microcontroller. This microcontroller will be turned on about every 5 minutes from sleep mode for an interval of the time which the sun is visible to the system, sensed by the solar tracking system. Once this microcontroller has awoken it will adjust the Fresnel lens according to different sensors which will be supplying feedback to the system.

Finally, safety requirements must be made to insure the project. One thing that has to be considered is protection from harmful rays to the retinas and high temperatures that could potentially start a fire. A protectant shield around the focused beam would be ideal. This protectant shield will be of heat retardant material and also help absorb the reflected rays. In turn if the lens were to shift a little bit it would strike the heat retardant material instead of the surrounding area. Also the system operator will be fully aware of the potential dangers and provided necessary safety and protective equipment.

Technical Content Project Motivation The world we live in is one where Humans require energy to survive. Because of this we have developed many ways to produce this energy. In recent history however several ways we do this have been deemed both detrimental to the environment and unsustainable. Because the energy sources are being depleted while the need for it is not people are exploring new ways to generate energy. This is why this project is being done, to satisfy this energy need in an innovative way. New energy generation techniques must come from renewable sources. Along with coming from a renewable source the energy must be extracted and/or stored in a way that does not produce harmful byproducts. This project accomplishes both of these things. This project uses energy from the sun (renewable) and produces no emissions aside from heat and the material used for the apparatus. The result is an energy generation system that solves each of the above mentioned problems, sustainability and environmental impact.

There are other motivations for renewable energy sourced power generation. One of which, being practically the motivation for everything, is money. With this system the user will not have to purchase fuel to operate, sunlight being free. So, the system could generate enough power over its lifetime to pay for itself and

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eventually make the user money. Should the project be deemed scalable for industrial use the money making potential could be greater.

But wait, solar energy is already being captured using other methods, right? Yes, but the project will use sun energy in a very different way than the most common form (photovoltaic cells). We aren’t creating any new physical processes or materials for this project. We are taking things available already and assembling them to create this new power source. Specific specifications can be found later in this document concerning the power usage/generation. Though, the goal isn’t necessarily to be more efficient at creating energy. Rather, it is to create a new type of system to transform this underutilized solar energy. This will be completed using an intelligent solar tracking system utilizing a microcontroller to handle input data and perform appropriate corrective operations.

It should be added that the even though solar systems in place are quite efficient there are still negative environmental effect associated with them. The manufacturing process produces many toxic waste materials such as mercury and chromium. These materials must be handled and disposed of in a very careful manner to avoid serious health and safety problems. Solar panels are also very inefficient collecting only around 40% of energy taking in requiring large groups of them to be assembled to viable power generation. These large groups must then be maintained and repaired on a regular basis making the process even more expensive. This design may not address all of these problems (such as the problems with large scale production) but it offers an alternative and the more ideas out there the closer one can come to environmentally friendly, efficient energy production.

So this project is motivated by the energy needs of people today. These needs are driven by many things and have several requirements to be tangible. the project accomplishes all of these requirements; it is a solar-thermal power generation system that has almost no emissions and is relatively low cost to create and maintain. Through research and design it is hopeful to make this project a viable candidate for future power generation systems for private and/or cooperate entities through a fully functioning prototype.

Project Significance There are several sources being used to power these new renewable energy generation techniques. These phenomena are being utilized in a variety of ways such as windmills, photovoltaic cells, etc. These systems work well and do produce energy but like any system they are not perfect. Because of these imperfections people are diligently working to improve the systems by using new technologies and configurations. There are other ways to harness these energies not being utilized and this project examines one of these.

The systems that exist for capturing sun energy are already efficient so why would we try a new way? The hope is two things, one to show that there are still

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new ways to create energy and that new ideas are needed; and that this design can be scaled and refined to be a viable source of energy.

This project is being created using consumer grade products and it might be said that anyone could create this system with little to no engineering background. This is true; solar tracking isn’t that difficult and there are apparatuses out there to convert Stirling cycle motion directly to battery power. But, this project will focus on efficiency by using very low power components whenever possible. On top of this the control algorithm will be optimized for low power usage.

Doing these things requires a greater deal of skill than assembling a few components together. Instead, the goal is creating a process that each subsystem and the interface between these systems are optimized for low power usage. The reasoning behind this that if the goal of the project is to create electric power it should require as little power to operate as possible.

Finally it is hope that this project becomes an example of how innovation helps society’s energy problems. Every new way to create renewable energy brings attention to the energy problem and hopefully will inspire people to create more solutions. This awareness will be pivotal in solving these problems and this project is a step in that direction.

Goals and Technical Objectives The goal of this project is to design and implement an automated solar-thermal energy generation apparatus using optically concentrated light energy to charge an energy storage device using a thermal engine system for conversion. The project’s design decisions will be made with renewable and sustainable energy goals in mind. This means that there should be little to no emissions from the process. Also, all materials used must reusable for numerous operation periods. The only energy input to the system will be the sun. There will be no energy gained via combustion engines. There may need to be an available source of DC energy for power. This objective is to be achieved by concentrating a solar input, accomplished utilizing a Fresnel lens. The concentrated solar input will be used to heat a Stirling cycle engine which will in return output mechanical power in the form of a running flywheel. The flywheel will be connected to an electrical generator which will be used to charge an arrangement of batteries. It is important to note that this is only a scaled version of what it could potentially be therefore the goal is to prove the concept can be reliable, efficient and safe.

A full operation cycle will be the continuous period during a day that the sun is in the position that permits adequate energy production from the lens to the Stirling cycle engine. This time period is dependent on several factors including weather, season, and distance from the equator. During this time all subsystems should be fully functional. The systems will be designed to function in a range that is slightly longer than this to prevent malfunctions because of fatigue. The final design should also be robust enough for repeated daily use. This will require

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materials that are not sensitive to a range of temperatures and a way to weatherproof electrical systems.

Reliability requires that four guidelines be met. First is for the system to independently be capable of capturing useful sunlight for an extended amount of time by tracking the position of the sun as it changes location relative to the system throughout the day. Extended amount of time in this use is to be defined as from the sunrise of one day to the sunset of that same day. The second is for the system to automatically reset to a predefined initial position after sunset and to be in standby waiting for the following day’s sunrise and again begin capturing useful sunlight to be turned into energy by the system. For the system to be considered reliable the Stirling cycle engine and generator system need to also be able to operate for an extended period of time. At the start of each day the Stirling cycle engine requires a kick to begin running, similar to the need of a starter in a car engine. The system will need to be self-capable of providing this starter kick at the start of each day and also in the event of a stall of the Stirling cycle engine. Therefore the system will also need a sensor to identify and communicate to the starter if a stall does occur. The final requirement of reliability for the system is that the system can withstand changing weather conditions. That is, it will be able to either continue operation in the event of partial cloud cover or be able to self-recover after a period of complete shade. Also the system will be rugged enough to withstand moderate winds.

An automated control system will follow the sun’s movements during the earlier mentioned operation cycle. Once the system has been started there will be no need for monitoring or maintaining of the system by a technician. There should be procedures for problems with input, for instance if it starts raining or the sun is no longer out.

For efficiency the objective is that the system will be able to provide enough energy to charge a battery while also being self-sufficient to power the necessary control systems needed for continuous operation. The battery will need to reserve some initial charge to properly align the system at the beginning of each day and in case of complete shade. Also reserve charge will need to be kept on the battery for in the event that for any reason the engine stalls. The battery charging system will need to be capable of efficiently sensing that the Stirling engine has stalled and the system will then provide the necessary kick to restart the engine. For the system to successfully accomplish all of this a printed circuit board will be required to properly manage the battery charging system. This PCB will include indicators to show the user the current charge status of the batteries and the present charge stored on the batteries. The PCB must also be capable of safely charging the batteries to max capacity and reserving portions of battery power for system restarts. The final responsibility of the PCB is to sense if the Stirling cycle engine is running and determine if the system should be running. By checking that the system is properly aligned and communicating with the starter motor it can determine if it should to provide the necessary jump to restart the Stirling cycle engine.

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The power generated from this machine will be stored in a battery. The battery should be of a size that would allow it to be charged from empty to 100% during a full operation cycle. There is a possibility that the battery could become fully charged in less than an operation cycle. A discussion of this and possible methods of handling this situation will be had later in the design document. The power consumed by the tracking system must not exceed the power generated by the engine. The overall goal of this design is to generate energy from the sun via tracking. To do this a control system must be implemented which consumes less power than the generator outputs. The lowest power consuming option will yield the greatest energy production and will be selected for the design.

This project should be of a size that permits it to be transported by two adults. All construction, prototyping, and testing will be conducted with no special transportation equipment. This specification constrains both the volume of the apparatus as well as its weight. This limits the scale of the project to something that will be easy to move with no assistive tools. Parts of the system will be removable for maintenance reasons. The project may not be able to fit through the normal width of a door but the disassembled components may.

This project must not pose serious safety hazards. There are several safety risks associated with the operation of the device. Optical shielding will be employed because of the high intensity light that is at the focal point on the Stirling engine. Also at the engine contact there will be very high levels of heat. Temperatures of this magnitude pose a serious fire risk that must be addressed in the design of the housing of the engine. Finally construction, prototyping, and testing must to be done extremely carefully with protective equipment before all safety mechanisms are fully functional.

All materials used in this design will have to be available to the general public. In order to ensure the ability to implement this design all materials must be able to be purchased. Certain components could be efficient should they be manufactured specifically for this application. This design will use existing technologies to implement something new.

Specifications and Requirements The operation period will be the period during the day that the sun is strong enough to generate power from the Stirling cycle engine. This will put stress on several components and they will need to be selected with this requirement in mind. In order to guarantee this all components will have to be able to operate for at least a 12 hour period. This is longer than any place on Earth would receive the amount of sun required for device operation.

The power output of the system will depend on several factors. First it’s how efficiently the Fresnel lens focuses the light input. The light’s heat that is then concentrated on the stiling engine will not be 100% efficient. Then there will be additional efficiency loss during the engine cycle. With all of these energy losses

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it can be hard to predict exactly what sort of energy output will be gained. It is however safe to say that with the tremendous amount of heat energy produced from the lens the generator will output be at least two watts.

The weight of the entire device must be less than 75kg. The area that the device takes up should be less than two meters square and it should be less than one point five meters tall. As far as physical specifications of the system; the Fresnel lens shall be no larger than 40 centimeters by 80 centimeters. The focal output of the lens shall occupy a space of roughly ten centimeters on the heat element of the Stirling cycle engine. The total surface area footprint of the system will be less than two square meters with a max height of one meter. In the interest of portability the system as a whole shall weigh no more than 50 kilograms.

The Fresnel lens will need to be capable of generating at least the minimum required temperature input of the Stirling cycle engine. The actual degree which this will need to be depends on the size and type of Stirling cycle engine. The solar tracking system must be capable of maintaining proper alignment of the Fresnel lens focal point exactly on the heat element of the Stirling cycle engine. The level of acceptable inaccuracy is to be determined by the size of the heat element of the Stirling cycle engine. The power generation system needs to be capable of charging the chosen batteries in the course of a single day. Again the exact specifications will depend on the chosen Stirling cycle engine and battery system.

While it would be great to be able to achieve all of these goals a realistic set of minimum requirements should also be set. The size limits listed above stand as the system needs to be portable. Further the weight objective will be a maximum to avoid transportation logistical difficulties. The goal for solar tracking over a continuous day has several complications which can potentially disrupt this objective. Most notable is unpredictable weather. The prototype is not to be designed to be waterproof. This is acceptable for a proof of concept because during a rain storm there will not be adequate solar energy to heat the Stirling cycle engine anyways. Further it is an ambitious goal to have the system capable of restarting on its own at the start of each day. A realistic requirement is that without any complications from cloud cover the system will be able to track the sun from when the sun is directly visible to the system in the morning until when the sun is no longer visible to the system at the end of the day. An additional minimum requirement is that a printed circuit board must be used somewhere in the system. It should be treated as a customer request and is not to be disregarded. The figure below represents and overview of the project.

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Related Projects While doing research on other projects and products that use a solar input to be used with a Stirling engine many different and creative designs were encountered. There is a senior design team from Illinois that worked on a Stirling heat engine generator in the fall of 2008. In this design the students proposed a project to help preserve the natural resources of the world and create an effective method of converting thermal energy into electricity through a Stirling engine. In their project they also tested two different methods of their initial heat source. The first method was to create a heat source through solar thermal power which is similar to the way this project will operate, but then they also tested another way of creating a heat source through the burning of fuel. The fact that they tested two different types of heat sources but the method of burning fuel as a heat source is not a method that can be used in this application, because a focus system to use renewable sources. The burning of fuel disregards the need to make a system which preserves the world’s natural sources.

Sensor Array

PCB and Control System

Actuator/Motor

Sunlight Fresnel Lens

Stirling Cycle Engine

Heat Element

Generator to charge batteries

Battery charge

management system

Batteries

Figure 1: Block diagram of how each subsystem fits together

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The output of their design is totally different from the one being designed. In their design they have an output of 120 volts AC signal at 60 hertz. The project being designed now is a little different because it will have the system charging an array of 12 volts batteries. Their method for the readiness of the system is intriguing because of its ability to be applied to a load for most commercially sold products, but what happens when the sun goes down when they are using it as the thermal heat source? The system becomes useless because when the sun goes down the Stirling engine will stop running and there is no storage of energy in their system.

This design will be effectively charging batteries the whole time during the hours of operation of the Stirling engine. This approach is better because this provides the opportunity to have energy stored for use at any time until the storage devices have been completely depleted. Even at night time when there is no more solar heat input. One critical thing is that in the other team’s project proposal there is no information about any solar tracking or even if they used any type of solar tracking. It seems like in the end they stuck with a system that was made more for the burning of fuels which defies the need for a system that preserves natural resources.

There are many big companies experimenting and doing a lot of research on Stirling engines and different ways of how to use them. For example, the solar plant developer Tessera Solar has a solar Stirling farm where they strictly use big parabolic dishes to reflect the suns solar rays at a centered Stirling engine which is directly in front of the dish at its center collecting all of the reflected heat. The solar farm is huge and has 60 of these solar Stirling generators which all output a combined power of 1.5 megawatts. These Stirling engines are a little different from the ones used here because theirs are hydrogen gas-filled while the one used here uses air as a medium. This is a very ecofriendly design and is a great way to create power without harming the atmosphere.

Another big company called Infinia which is based in Kennewick, Washington has released a large Stirling solar dish about the size of a large satellite TV receiver. The output of these Stirling solar dishes are rated at 3 kilowatts and have a 24 percent efficiency. These Stirling solar dishes are designed for large organizations like city governments and other large facilities. This company has many other products and has even utilized the Stirling engine to be used in air conditioning applications.

Relevant Technologies Solar Tracking Research A major component in achieving the goal of sustainable power generation through an extended period of time relies on successfully tracking the sun. The purpose of any solar tracking system is to keep the payload correctly oriented

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towards the sun. The measure of success is to keep the focal point of the Fresnel lens consistently on the heating element of the Stirling cycle engine for an extended amount of time. To find the design that will work best for this system a comparison of the techniques that could potentially be used and determine which applications best suit the project’s needs.

There are several known methods of solar tracking. The most notable are chronological, passive, and active. Chronological solar tracking involves using a clock and a table of the angle of the sun at different dates and times. For this method to work the system needs to be aligned to a set direction corresponding to the data table. Second is passive, a passive system involves using thermodynamic fluids which change in volume as the sun warms them to align the system accurately with the sun. This method isn’t as precise as the others. Finally is the active tracking approach. Active trackers use photo sensor arrays to detect the direction of the most light and motors to adjust the system into that direction. For the purposes of the project active tracking is the only realistic option because it is the most accurate and will give the best method for guaranteeing that the Fresnel lens focal point stays on the Stirling cycle engine. This is important because if the focal point strays from components which are designed to withstand the extreme temperatures produced by the lens the system could damage itself or cause injury to the user.

Active solar tracking typically comes in two forms; single axis and dual axis. Single axis active solar tracking involves rotating across a single axis. The system is usually aligned north and then rotates the system face from east to west as the sun moves throughout the day. The advantage of single axis is that the system is far less complex the downside is the increased simplicity allows for only a certain level of precision. An example of a single axis tracking system can be seen in figure 2. Dual axis active solar tracking has two degrees of mobility. The additional axis of mobility in this system is much more accurate and therefor better meets the needs of the project to keep the focal point of the Fresnel lens on the Stirling cycle engine.

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There are two common dual axis trackers. The first is the tip-tilt dual axis tracker (TTDAT). The TTDAT has its primary axis horizontal to the ground with a secondary axis normal to the primary. As seen in figure 3 TTDAT systems have the advantage of having a minimal footprint. The disadvantage of a tip tilt tracker is that for the application the location of the focal point of the Fresnel lens will vary. Therefore it will be necessary to continue searching for other method of dual axis tracking.

The other common dual axis tracker is called an azimuth-altitude dual axis tracker (AADAT). This system has its primary axis vertical to the ground with a secondary axis normal to the primary system. The downside of this type of system is that they typically have a larger footprint and typically involve different types of motors for each direction of movement. The AADAT system better fits the application because as can be seen in figure 4 this system will allow us to

Axis of rotation

Figure 2: An example of a Single Axis solar tracker

Tip

Tilt

Figure 3: An example of a Tip Tilt Dual Axis Tracker

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achieve a central focal point. This is because the lens will rotate about the central focal point required on the Stirling cycle engine.

Active solar tracking research - Photo detecting Active solar trackers utilize photo detector arrays to take advantage of the short wavelength and vast distance from the source of sunlight to earth or in other words the fact that light waves are nearly parallel to one another. By doing so they are able to detect the direction of the sun compared to the direction in which the array is facing. Before discussing the different arrangements for the sensors of an active solar tracking system it is necessary to discuss what types of detectors are available for this application and research which will best fit the application of this project.

There is a wide variety of sensors available to detect the amount of light at the sensor. The key differences are how the sensor electrically outputs the amount of light it detects; either current or voltage. Also the sensitivity, or degree of accuracy, of the sensor is important to note because of the potential damage to the system or harm to the user if the high temperature Fresnel lens focal point is misaligned. Other details to pay attention to are if the sensor requires an input voltage to be in detection mode or if it can do so independently of a separate power source. Further considerations for the sensors will be the cost per unit of each type of sensor. Figure 5 below is a graphical representation of how the photo detector will communicate with the tracking system.

Altitude

Azimuth

Figure 4: An example of an Azimuth Altitude Dual Axis Tracker

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Perhaps the most basic option for detecting light involves taking a regular light emitting diode (LED) and using it with the positive anode terminal of the LED connected to ground and the negative cathode terminal inputting to the system. When using an LED as a sensor it is only sensitive to wavelengths equal to or shorter than the wavelength of the color it emits. Since the system is tracking the visible light of the sun the optimal LED color will be red since it has the highest wavelength of the visible spectrum and will therefore detect all visible light. An LED used as a light sensor will output a voltage corresponding to the amount of light it receives. In direct sunlight the output should be roughly between 1.3V and 1.5V. When shaded the output is expected to be between 0V and .05V. The final point of consideration for the LED is the cost per unit. For a high powered red LED the cost is $0.50 per unit. Using an LED as a light sensor has the benefit of not requiring any additional power for standard operation.

A second option would be to use a photocell. Photocells are small, inexpensive and low power. They are also referred to as photo-resistors or light dependent resistors (LDR). LDR’s cost approximately $1.50 per unit. The resistance of an LDR varies depending on the intensity of light which it is visible to. As the light intensity into the LDR is increased the resistance of the device drops. The opposite is also true; as light intensity decreases the resistance of the LDR nears its peak. To measure this value for the application of this project a voltage will need to be held across the LDR and communicated to the control system that way. A major downside with using LDR’s is that they are not very accurate and can vary by up to 50%. This type of inaccuracy is unacceptable for this system and therefor LDR’s will not be used for the solar tracking circuitry. Additionally LDR’s are typically constructed with cadmium sulfide, lead and other harmful chemicals. For a project promoting the development of green energy using these products would be a step backwards from the overall goal of the project.

There are also purpose built photodiodes available on the market. The basis of a photodiode uses a pn junction which when struck by a photon will produce a photocurrent. The advantage of using these sensors is that there are so many different forms of photodiodes produced it is easy to find one which fits the application need and allows for a greater degree of accuracy. The form of

Sunlight Photo detector To control

system

Figure 5: Block diagram of how sunlight is communicated to the control system

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photodiodes that everyone is probably the most familiar with would be when operating in photovoltaic mode, which is when the cathode is positive and the device is used in zero bias. Large area photodiodes operating in photovoltaic mode are what most people recognize as solar cells. A traditional solar cell could very easily be implemented as a photo detector and could also potentially generate enough power to operate the other solar tracking systems. A small 6 inch by 6 inch solar cell cost $5.65 dollars and would output roughly .55 Volts. However, one of the objectives of this project is to develop an alternative method of solar power and to use traditional solar cells would go against this objective. Another type of photodiode is known as a phototransistor, this type of photodiode is basically a bipolar transistor modified so that light can reach the base-collector junction and is thereby amplified by the transistors current gain. The advantage behind phototransistors is that they have a greater response to changes in levels of light. The downside is they are less accurate as light levels decrease. A second disadvantage of phototransistors is that they have longer response times compared to that of basic photodiodes. Overall photodiodes have great potential for this purpose however purchasing individual units of photodiodes can be difficult. The table below summarized the information discussed above.

Table 1: Comparison of various photo detectors

Cost Key Advantage Major disadvantage

LED $.50 No supply voltage needed Not Applicable

LDR $1.50 No supply voltage needed Inaccurate

Photodiode $.75-$3.00

Purpose built for light detection

Many require supply voltage

Small PV cell $5.65 No supply voltage needed Size and cost

Photo detecting array configurations While there are several ways to set up the sensor array, all setups utilize similar techniques of having the same amount of light hit both sensors if the system is properly aligned and if the system is misaligned then one of the sensors in the array will receive more light than the others. This difference in received light will be communicated to the control system that realignment will be necessary. There is no difference between a single axis sensor array and a dual axis sensor array. The dual axis would simply employ two single axis sensors, one for each axis of movement. Therefore it is only necessary to discuss the advantages and disadvantages of a single axis sensor array.

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The first shade-sensor setup to be considered is based on putting two sensors facing away from one another at a chosen angle. The advantage of this setup is that the angle between sensors can be set up to be adjustable so that the desired accuracy can be adjusted for further refinement of the system after initial construction. For this setup when the system is perfectly aligned neither sensor receives direct light. Instead both sensors will receive the same amount of light based on the angle between the two sensors. As the light source moves one of the sensors will receive more light than the other. As seen in figure 6a, sensor A is receiving more light so to realign the control system will need to adjust until both sensors return to receiving the same amount of light as seen in figure 6b.

Figure 7 shows a second shade-sensor setup. The setup is designed by placing two photo sensors next to each other and then setting up a perpendicular wall between the two. This works by casting a shadow onto one of the sensors if the direction of the sunlight is not parallel to the wall. If a shadow exists it will decrease the amount of light that is seen by the sensor and the control system will be able to sense that adjustments will be needed for proper alignment. As with the previous shade-sensor setup the accuracy of this array can be adjusted by the height of the wall which is between the two sensors. As wall height increases the sensitivity of the array will increase because for the same angle of offset the higher wall will cast a larger shadow onto the sensor array.

Figure 6: First example of light sensor array when out of alignment (6.a) and when properly aligned (6.b)

6.a 6.b

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Solar tracking components For the solar tracking components of this system to operate correctly a control system is needed to interface between the photo detectors and the motors which will adjust the Fresnel lens to be properly aligned. There are two categories to consider when determining what type of system to be the brains of the solar tracking system. The core of these two categories is the decision to either go analog or digital. The digital option is to create an embedded system by utilizing either a microprocessor or microcontroller. The difference between a microprocessor and a microcontroller is that a microprocessor is generally used to perform a wide set of general purpose functions. On the other hand a microcontroller is typically used to perform a small set of specific functions. Because the control system is being used to specifically control the direction which the Fresnel lens faces based on the input of the photo detector array a microcontroller will best fit the project’s needs. The advantage of all microcontrollers is that they are easily available for relatively cheap, typically under $50.00 for a development board, are able to perform essentially any task which the user programs the chip to, and also have programmable input and output peripherals. An additional advantage to using a microcontrollers is that if further refinement of the control system is needed after initial testing the adjustments are as simple as editing the program which runs the microcontroller. Any microcontroller which will be used will need to first be configured and tested

Sensor A Sensor B Sensor A Sensor B

Figure 7: Second example of light sensor array when out of alignment (7.a) and when properly aligned (7.b)

7.a 7.b

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using a development board. Then the microcontroller will be plugged into a custom printed circuit board (PCB). The second option would be to design a custom analog circuit which will utilize differential amplifiers and bipolar junction transistors to adjust the motors as necessary. This custom analog circuit will be implemented directly onto a PCB. The disadvantage behind the custom analog circuit is the complexity it will add to the PCB. Typical custom PCB’s cost around $50.00 and if any adjustments are needed a second PCB would need to be manufactured.

There are hundreds of microcontrollers available for purchase and each comes with its own set of advantages and disadvantages. To determine what potential processors are available and if any would make a suitable match for the project a few of the most popular microcontrollers are to be considered. To choose which microcontroller will best fit the needed application it is important to consider what the exact functions of the microcontroller will be and then compare these application needs with what each microcontroller is capable of performing. Since one of the goals of the system is to generate power the microcontroller to be selected should be as low power as possible in order to maximize the net power generated by the system. Because the position of the sun in the sky changes slowly throughout the day it is not necessary to continuously monitor the alignment of the system therefore the microcontroller needs to have an available standby mode during which minimal power is used. Transferring in and out of standby mode should also be as efficient as possible. All microcontrollers should be capable of taking in multiple inputs and controlling multiple outputs, it is however very important to make certain that the number of inputs and outputs matches the needs of this system. Also important to note is the form which the microcontrollers will be used. They all are available with development boards which are very useful for programming and testing of the microcontroller. For the purposes of solar tracking there will be four inputs in the form of voltages ranging from 0V to 1.5V. The output needs to be capable of controlling the speed, time to be on and the direction of rotation for each of the motors which will adjust the location of the Fresnel lens.

Arduino is a favorite microcontroller of many hobbyist and tinkerers. It has gained this reputation by being an easy, reliable and versatile product to use for system prototyping. Arduino boards, like most microcontrollers are used to develop interactive objects. They can take inputs from a variety of switches or sensors and control a variety of lights, motors and other physical outputs. Advantages of using an Arduino system are that they are relatively inexpensive; most cost under $50.00 dollars. Also Arduino products are based on open source and extensible software/hardware, meaning that the entire product line is completely customizable. Adruino’s are programmed using Arduino software which is compatible with mac and PC. The programming language is a spin of C++. For the purposes of this project the best Arduino board would be the Arduino Nano. Table 2 shows a comparative list of the features of the Arduino Nano.

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Texas Instruments also has a microcontroller which fits the needs of the system. The MSP 430 has an ultra-low supply voltage which matches the project needs perfectly. This leads to a further advantage of the MSP430 is that it can be setup to go into a low power mode to save power and wake itself up at a set time interval to check the status of the photo sensors and determine if any adjustments are needed. The wakeup from standby mode time for the MSP430 is less than one micro second. For comparison purposes the 2xx 16MHz series of MSP430’s will be researched. The MSP430 is significantly less expensive compared to the Arduino Nano, costing only $4.30 dollars for the development board. Texas Instruments provides the code composer studio, a C/C++ based software for programming the MSP430. Table 2 shows a comparative list of the features of Texas Instrument’s MSP430 2xx series.

Figure 8: Arduino Nano development board. Reprinted with pending permission from Arduino

Figure 9 Texas Instruments MSP430 Launchpad development board permission pending

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A final MCU to be compared is the 68HC11 originally designed by Motorola and now manufactured by Freescale Semiconductor. The advantage of the 68HC11 is that the group members are familiar with using it from previous classes. In today’s rapidly advancing technical world the 68HC11 is really outdated as it was originally designed in 1985. Due to its age the 68HC11 will not be capable of being the greatest, most efficient microcontroller. The 68HC11 is also now produced only as a legacy part and is unavailable for purchase directly from Freescale and would instead need to be purchased from third party sources. Table 2 shows a comparative list of the features of Motorola’s 68HC11.

A second option for the control system is to use an analog solar tracker circuit. The advantage of using a circuit such as the one below is that after the circuit is built correctly there are very few ways for the system to fail since it is purely hardware. The disadvantage of using a circuit to perform solar tracking is that making changes to the circuit can be significantly more difficult, often requiring an entirely new printed circuit board to be manufactured. Also with how the circuit above is configured it would not be very efficient since it will be continuously adjusting the system which is not necessary for this application given that the position of the sun moves slowly throughout the day. To create a sleep like mode for the circuit a 555 timer would need to be added which would further complicate the system and its initial setup. The addition of a 555 timer would also increase the complexity of debugging any problems that may be noted during the testing of the circuit.

Figure 10: Motorola 68HC11 development board

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Table 2: Comparison of different options for the brands of the control system

PCB Research A requirement for this project is to use a printed circuit board (PCB) which is to be designed by the group. There are several websites that sell PCB’s which are custom printed. It is first necessary to go over what the PCB is going to need and be capable of doing it. On the PCB will be the chosen microcontroller, pins for connecting the inputs and outputs of the microcontroller and a method for

Microcontroller

Cost Input Voltage

I/O Pins

Footprint Communicates with computer

Greatest advantage

Arduino Nano

$47.19 7-12 14 0.73”x1.70”

USB mini Common with lots of online support

TI MSP430 $4.30 1.8-3.6 10 0.25”x0.3”

USB Cheap, low input voltage

68HC11 unavailable

4.5-5.5 38 2.4”x0.5” USB Not applicable

Circuitry $50 ~5 Any 2.4”x2.4” n/a Meets technical objective

Figure 11: Example layout of solar tracking circuitry

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indicating the real time voltage stored in the battery. The PCB will be basic so only two layers will be necessary. Also silkscreen and solder masks are preferred for aesthetic and presentation reasons. Many of the details for what will be on the PCB are dependent on the other components which are selected. Therefore reference the strategic components section of this report to see further design specifications.

The website batchpcb.com has the potential of being one of the cheapest providers as they charge per square inch instead of a flat rate for up to a certain size. In total batchpcb.com charges a $10 dollar setup fee plus an additional $2.50 dollar per square inch. This price delivers a two layer board with solder mask and silkscreen on both sides. Batchpcb.com also accepts most formats of PCB design software however, no software is provided. The reason batchpcb.com is able to offer such a low price is because they offset the price with increased lead time, typically three to four weeks according to their website.

Expresspcb.com offers a special for their mini-board pro product. The mini-board pro is two layered and comes with set dimensions of a 3.8 inch by 2.5 inch rectangle. For $75 dollars expresspcb.com delivers three identical custom mini-board pros with silkscreen and solder mask. Also expresspcb.com offers a free CAD software for designing layout of the PCB.

The next website researched was custompcb.com; they offer a set price of $105 dollars for four identical custom PCB’s. The boards can be up to 6.3 inches by 4 inches and come with solder mask and silkscreen. The typical lead time for a two layer custompcb.com board is one week plus the time for shipping. Custompcb.com does not offer any CAD software; they are also limited in the file formats which they support.

Pcbexpress.com, yes it’s different from expresspcb.com is yet another website which offers services to deliver custom printed circuit boards to customers. For $139 dollars pcbexpress.com offers their E2-2 layer family of boards. They come with silkscreen and solder mask as well as an incomparable lead time of only two days. The price delivers to the customer a pair of two identical boards with dimensions up to nine inches squared. Pcbexpress.com also offers a free CAD file software for their customers.

The final website which was compared for ordering a PCB from is 4pcb.com. The great thing about 4pcb.com is they offer a student special for projects just like this one. The special is with the discount code “student” and a university shipping address students can get; there is a minimum order quantity of one $33 dollar custom PCB. The service includes free PCB layout software as well as a free design file report which checks for common errors from freeDFM.com. The PCB can be up to 60 inches squared and typically have a lead time of five business days.

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Table 3: A comparative feature list of each PCB manufacturer's websites

Website Solder mask and silkscreen?

Dimensions

Free CAD software?

Lead time

Min

quantity

Price ($)

Batchpcb Yes Up to 10”x15”

No 3-4 weeks

1 10

+2.50/in2

Expresspcb Yes 3.8”x2.5” Yes 1 week

3 75

Custompcb Yes Up to 6.3”x4”

No 1 week

4 105

Pcbexpress Yes Up to 9in2 Yes 2 days

2 139

4pcb Yes Up to 60in2

Yes, and free design check

5 days

1 33

There are several complications that can arise for a solar tracking system. The most notable is unpredictable weather. The system needs to be able to continue operation despite these weather complications. For the system to operate correctly there is a minimum threshold of light that needs to be reached in order for the Stirling cycle engine to get enough heat to run and actually generate power. For this system, in the case of clouds blocking direct sunlight the active tracking could potentially lose alignment with the sun moving. However, once direct sunlight is again visible the system will realign itself and continue normal operation. Another complication that can affect the performance of the solar tracking system would be if somehow one of the sensors was momentarily covered while the system is active, giving a false alignment calculation. To avoid this problem the system should continuously sample until the system is properly aligned. By doing so the momentarily covered sensor would be uncovered and the system could adjust to regain proper alignment.

Tracking Motor Control In order to track the sun’s movement certain components of the system must be able to move. There is also a need to have precise control over these movements. Since it has been determined that a microcontroller is the best

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option for handling input data from sensors it follows that the same controller can be used to communicate with the motors. Reasons for using the microcontroller here are the same as before, easy to make corrections or modifications to the movement algorithms and the reduced power consumption from utilization of low power modes. Since power generation is the overall goal of the project any time a design consumes less power than another is gains tremendous precedence over competing designs. However; it is still important to consider alternate circuit configurations during the design process. It is also important to remember that the motor control sequence must be reversible so the motor will be able to rotate in both directions. This is also true for the actuators used in the design because the lens will be required to extend and contract to adjust its angle as the day progresses.

Figure 12: Control flow diagram

Before these control decisions are made the motors being used must now be selected. The design calls for two such devices; one rotational motor and one linear actuator. The rotational motor will be used for rotating the base of the apparatus while the linear actuator will adjust the angle of the lens. The two motors will work in conjunction to achieve active solar tracking discussed elsewhere in this report. These movements will need to be small and precise to maintain adequate heat on the Stirling cycle engine and thus energy production. If the motors could be implemented and controlled without feedback from said motors the design of the control system would be much simpler, leaving less room for error, and thus preferred over ones that require feedback. Another criteria in selecting a motor how it is powered; AC or DC motors. DC would be preferred because then the motor could be directly run by the microcontroller’s output or with a straightforward amplification procedure. Keeping with the overall goal of power generation lower voltage motors would also be preferred in an effort to minimize power consumption by the control system.

Rotational Motors Let’s examine different types of rotational motors that could be applicable to this project’s design. The most popular type of motor used in control design is the servo motor. Servo Motors have several internal configurations, with alternating current or direct current inputs. The direct current configurations include

Microcontroller Motors Apparatus

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permanent magnet, shunt, series and compound wound, and finally stepper motors. Alternating current models are induction, synchronous, and asynchronous. AC motors are usually used in applications where a constant speed is required, and this speed is controlled by the frequency of the input signal. This project has no need for continuous motion and constant speed is of no concern, so AC motors will not be considered in the control design system. Next the different types of DC motors must be examined to determine the optimum choice for this application.

The first three DC motors to be considered will be shunt, series, and compound wound motors. The different names refer to the relation between the connections of the rotors and stators. In shunt wound motors the rotor is connected in parallel with the stator, in the series wound they are connect in series, and in compound windings two stators are used in both series and parallel. Different combinations of series and shunt turn ratios can result in a variety of speed vs. torque curves depending on application. Next there is the permanent magnet DC (PMDC) motor. Here the stator field is generated by the permanent magnet and is constant. This constant flux allows for a linear speed-torque curve. These motors are not a good fit for this project because there is no need for speed control. Instead the only concern is with the final position of the components. This is why none of these configurations will be considered in this design.

This leaves only one remaining DC motor configuration, the stepper motor. This type of motor is especially suited for control systems for several reasons. This type of motor is used extensively in open loop configurations (meaning no feedback is required). The operator has precise control over the rotational movement of the motor. The motor can be held at a constant speed or the speed can be modulated. These things are accomplished by special internal circuitry within the motor that only allow discrete angular movements of uniform magnitude. This precise control is exactly what this design calls for. With proper step size selection the correct rotational resolution for the apparatus could be achieved. This could be realized using the types of motors discussed previously but methods utilizing those would require a more precise output from the microcontroller and a feedback loop. The size of the steps is not the only concern related to step motor selection, there are also the power usage, internal configuration, and torque parameters. Because of this the different types of stepper motors will be examined below.

Stepper motors are divided into two main categories permanent magnet and variable reluctance. There are hybrid configurations that utilize both permanent magnet and variable reluctance together, though in application they work the same as permanent magnet designs. Permanent magnet stepper motors have unipolar and bipolar configurations. There also exists many more varieties of stepper motors, such as Lavet, bifilar, multiphase, but their applications are specialized and will not be considered in this discussion. There are common parameters to all of these configurations. All will, once one winding is energized, have the rotor moved to a fixed angle and hold this position until either a signal is

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applied or the maximum holding torque is exceeded. If this torque is exceeded the motor will rotate one step (slip) and again try to hold each subsequent step with equal force. This holding force will be used extensively in this application since the motor will only be required to move on broadly spaced intervals and otherwise hold its position. It is not expected that slipping during the non-movement periods will be a large concern because of the location of the motor. The static torque will be caused by the wind drag of the lens and shouldn’t have a magnitude of much significance.

In order to decide which stepper motor configuration will fit this application best both permanent magnet and variable reluctance motor characteristics will be examined. It is important to discuss the differences between the two types’ internal structures because this structure directly affects application procedures such as connection circuitry used and sequential signals sent. In variable reluctance stepper motors there exists a finite number of coil pairs that are energized in sequence to achieve rotation. By turning these coils on an off in a specific sequence the rotor will spin in that direction. This can be seen in the figure below.

Figure 13: Variable Reluctance Stepper motor. Permission pending

The leads labeled one, two, and three represent inputs to the motor on the right. When input one is energized the rotor (white cross in center of motor) will go to the position seen above. The next step would be to turn off input one and then turn on input two, resulting in a rotor rotation of thirty degrees. The procedure then continues by turning off input two and turning on input three for another rotation of thirty degrees. This procedure can be reversed by reversing the order of charging and discharging inputs (going one, three, and then two instead). In this example the step size is thirty degrees and the motor would be referred to as a 3 phase selective reluctance stepper motor. There are variable reluctance stepper motors with more phases and thus more inputs. The control procedure works the same but care must be taken to ensure proper ordering on inputs. More phases result in a smaller step (i.e. less than the thirty degree step that the figure uses).

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The next class of stepper motor to be examined is the permanent magnet configuration. The prevailing difference between permanent magnet motors and the one discusses previously should be obvious from the name, the existence of a permanent magnet. This magnet is in place of the cross shaped rotor seen in the figure above. It is a disk shaped magnet has a number of poles distributed around its circumference. The number of poles is directly related to the step size; more poles results in a smaller step and thus more control over small movements. An example of a unipolar permanent magnet stepper motor can be seen in the figure below.

Figure 14: Permanent Magnet Stepper motor Permission pending

This figure uses four inputs; 1a, 1b, 2a, and 2b. The procedure for rotation is similar to that of the variable reluctance motor but the wiring is different. This is why these different configurations are being analyzed so closely. In the figure above 1a is positively energized and this magnet is pulled to the position shown. Next 1a would be turned off then 2a would be energized for a thirty degree rotation clockwise. The sequence would then continue with 1b and 2b then back to 1a. These steps can be reversed. With this configuration there exists and alternative rotation algorithm that uses pairs of charged inputs. The sequence for this is 1a2b, 1a2a, 1b2a, 1b2b then back to 1a2b. Using this algorithm results in 1.4 times the torque but also uses twice the power. A final note is that half steps can be achieved using a conjunction of the two previously mentioned algorithms.

The final configuration to be considered is the bipolar permanent magnet configuration. These motors are constructed the same as the unipolar version except the wiring is different. There are no center taps between the a and b poles. This requires a different drive circuit (all three will be discussed below)

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from the unipolar configuration but the control signal sequence remains the same. Also the higher torque and half step rotations are also available in this configuration.

Communication with motor Now that a rotational motor type has been chosen it must be connected to the microcontroller. From here it must be determined what signals must be sent from the controller to be amplified to be sent to the motor to gain the desired rotation. This can be achieved by either directly connecting the motor to the output pins of the microcontroller, an intermediate protection circuit using discrete components, or by using a motor control module. This decision is based heavily on the sizes of the microcontroller and motor being used (not physical size but rather current and voltage ratings). Great care must be taken to ensure the correct voltage and current levels are being supplied to the motor from the controller. Additionally some sort of protective circuitry is necessary for the voltage spike which can occur when switching the motor on and off that could damage to the control mechanism (if there is a large mismatch between motor and microcontroller I/V characteristics). The simplest way to connect the motor would be directly connect the motor to the microcontroller and send appropriate signals via appropriate pins. This configuration could not be used in this application because of the mismatch between the power levels of the MSP430x2xx family and the high torque (and thus high current and voltage) required to rotate the apparatus. Because of this the discussion on intermediate circuitry will consist of a comparison between protective circuits that can be built using discrete components and prefabricated protection and driver circuits.

The type of stepper motor being used (selective reluctance, uni or bipolar) also determines the types of discrete protective circuitry that can be used. Let’s continue the same order as before and start with the variable reluctance stepper motor’s drive circuitry. The basic idea here is to have the windings wired where one side is the supply voltage and on the other the control signal. The control signal is held by a switch. When this switch is opened the large voltage spike occurs so there must be protection against this. There are two simple methods for controlling this voltage; either a capacitor or a diode can be connected around the motor’s winding. Each choice will pose additional design parameters such as choosing a diode that can handle the correct amount of current and the capacitor must be of a large enough size to prevent overvoltage of the switch. Also when using the capacitor the winding and the capacitor create a resonance circuit. Should the frequency of the control signal be similar to the resonance frequency of the capacitor/winding circuit the torque can be greatly reduced. To avoid this, experiments must be done because the inductance of the motor will change with shaft angle and this measure is rarely examined in the motor’s datasheet. Simple circuit diagrams of what was discussed can be seen below.

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Figure 15: General set up without protection for variable reluctance stepper motor Permission pending

Figure 16: These represent the two protection circuit options Permission pending

The unipolar permanent motors have a unique driving circuit. There are switches on each side of the stator windings connected to the control signals. The power is distributed through the center of the stator. The same voltage spike problems are experienced with this configuration. To account for this the same procedure from before is employed; capacitors and diodes. A single capacitor can be connected the stator’s winding in parallel. There are still resonance concerns associated with this approach but the torque response is very different. There is a spike in torque associated with the electrical resonance frequency and a severe drop in torque at the mechanical resonance frequency. The placement of the electrical resonance frequency can influence mechanical resonance is they exist close together. A similar testing procedure would have to be employed to

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find these resonance frequencies that were discussed in the selective reluctance driver circuits. The diode approach here requires 4 diodes for each stator winding and can be seen in the figure below. The challenge with this approach lies in the switching of the diodes on and off. At turn on/off transitions the voltage across the switch can be made negative and this can damage some switches. Again circuits discussed here can be seen in the diagrams below.

Figure 17: This is the driver circuit without protection. The white boxes represent switches as seen in previous figures. Permission pending

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z

Figure 18: Shown here are the two protection circuits Permission pending

The last discrete driver circuit to be discussed is for the bipolar permanent magnet stepper motor. The circuits employed here are the most complex because of the lack of a center tap on the stator winding to the supply voltage. The circuit used is referred to as an H-bridge. The circuit uses different combinations of having switches A, B, C, and D on and off. The diodes are connected to protect against the voltage spikes caused by the switches operation. The configuration has an inherit risk of short circuiting. To avoid this simple TTL gates are employed. Both configurations can be seen below. These logic gates also allow for the use of the two inputs per stator rotation algorithm discussed previously.

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Figure 19: Left: H Bridge with protective diodes. Right: H Bridge with protective logic gates. Permission pending

Now the switches used in these applications must be examined. There are many different switching circuits that can be used. They only need to have two parameters satisfied. First, the switch must be able to handle a high enough current level and secondly they must protect the controller sending the signal. The second parameter is very important for this design because of the low power characteristics of the MSP430x2xx family. Should it be determined that the motor used requires currents under a specific value a family of integrated circuits exists that have arrays of these switches. Some examples of these are the UDN2547B quad power driver made by Allegro Microsystems (<600mA), the ULN200x family of darlington arrays from Allegro Microsystems (<500mA), or the Texas Instruments SN754x line (<300mA).

The next thing to be discussed is a premade driver circuit. These greatly reduce the complexity of the circuitry required to operate these motors. The logic inputs to this device can be directly connected to the microcontroller. Also there is a separate voltage input for power amplification. The outputs of the device are connected directly to the stepper motor. There is an internal potentiometer which controls the current output of the device. Configurations of these drivers exist to fit any stepper motor configuration and for any current input. Notice the outputs on the right correspond directly with the four inputs discussed earlier when comparing different stepper motor configuration (selective reluctance, uni, and bipolar).

Actuators In order to control the angle of the Fresnel lens this design calls for a linear actuator. There are many types of linear actuators that employ a variety of mechanisms to achieve linear motion. These different types include mechanical, hydraulic, pneumatic, piezoelectric, electro-mechanical, and telescoping actuators. Mechanical linear actuators generally operate by converting some rotary motion into the linear displacement of the actuator. The three main types of mechanical actuators are screw, wheel and axel, and cam. In a screw actuator

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a nut is usually rotated that results in a linear motion in the screw shaft because of grooves carve into said shaft. Wheel and axel actuators involve spinning a wheel that results in another component in the system’s movement such as a pulley cable system, and finally a cam actuator works similarly to a wedge; as the oblong shape rotates the section with a large radius causes a linear displacement on an attached piston. Hydraulic and pneumatic actuators operate by a two chamber system filled with a material (air for pneumatic and some sort of liquid for hydraulic actuators). These materials in one chamber are pressurized in a way that in order to equalize the pressure between the two chambers precise linear motion results. Piezoelectric actuators use materials that expand when high voltages are applied. These actuators have a very limited range of movement but are very accurate except the material can be deformed easily making repeatable results hard to obtain. Telescoping actuators are ones that are used in applications that have space restrictions. These actuators extend beyond the length of the unextended version I.e. unextended the mechanism occupies ten inches but extended it has a length of fifty inches. Finally there are electro-mechanical actuators. These actuators are mechanical actuators whose movements are controlled by an electric signal. This application of a linear actuator will work best with an electro-mechanical actuator because of the ability for autonomous control again using the msp430x2xx microcontroller.

Now that a general class of actuators has been chosen different parameters associated with the actuators must be examined. Firstly, electro-mechanical actuators are typically screw actuators attached to a rotational electric motor. The types of motors used to control this actuator are the same as the motors discussed earlier in the report. The first thing that must be selected is the length of the actuator. In this application the actuator need to have a dynamic length of at least 22.5 inches. Next there are load capacity concerns. There are two such parameters, the force the actuator extends with, and the static load capacity. The static load capacity is especially important in this application because of the need to hold a precise position between periodic movements. Both of these parameters are going to be relatively small for actuators of the length required. Because the actuator can be controlled by a stepper motor it would be the best choice for the same reason as the stepper motor was chosen for the rotational motion; precise control over small movements with no concern for high speeds. The connection of the actuator to the microcontroller will be the same as the other stepper motor with its own driver circuit.

Batteries Researched For this project two 12 Volt batteries will be used for storing the energy generated by the engine. There are a wide variety of commercially available batteries comprised of different materials and designs. Out of all the battery types there are two main kinds that were considered for this project, lead-acid batteries and lithium-ion batteries. Alkaline and NiCad batteries have been discarded due to their inefficiency and will not be considered for the project. A starting or cranking

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battery is one that has been designed to deliver quick bursts of energy for a short period of time, draining relatively little of the charge. These will not be used because they are not typically suited for extended usage. The deep cycle battery does not have the large, quick, impulsive shots of energy, but instead has a greater long-term energy delivery and can last for many more discharges and recharges. This is attractive for the goals of this project.

Within the lead-acid batteries there are several different types. These types include standard flooded or "wet" batteries, gelled, and absorbed glass mat (AGM). The difference between these types is not the chemistry of them, but rather how they are constructed and put together. The wet batteries typically require maintenance by having to be replenished with electrolyte every so often. They are of the weakest and tend to leak. The Gel type lead-acid battery is better than the wet because it does not leak and it doesn't have to be maintained, but are being used less and less due to the much better AGM battery. This leaves two different battery types applicable to this design, AGM and lithium ion batteries.

The first of the two batteries is of the valve-regulated lead-acid battery class called AGM. This battery has the advantage of low internal resistance, which is good for charging and discharging rapidly, and usually last between four to seven years. It also has a good power density due to purer lead. There is also no spilling with this type of lead-acid battery because all the acid is absorbed into the glass fibers, so it can be oriented any way that is necessary. Another good thing about this type of lead-acid battery is that they are recombinant, which means water is conserved and water does not need to be added over time.

One of the most interesting things about this battery is that it's depth of discharge for optimal performance goes up to 80%. With this depth of discharge, the batteries can be discharged to low levels without causing damage to them. Some disadvantages of this battery are that it's more expensive than typical lead-acid batteries, they are heavy when compared to lithium ion, and they do not tolerate overcharging.

The second of the two batteries is the Lithium Ion battery. For starters, this type of battery has a very high power density for its weight, therefore they are really light. This is really good considering it will be mounted to the rotating base of the system. Another advantage about their small size and weight is that there will be a larger variety of places to put them because they would fit into smaller areas. Lithium Ion batteries also have a high open circuit voltage which allows more power to be transferred at a lower current. They also have a low capacity loss per year when stored at about half their charge capacity (4% loss per year at 50% charge level), but this is counteracted at higher ambient temperatures.

There are a few down sides to lithium ion batteries. First, the cell life of the batteries at higher temperatures increases by almost double from 77 degrees to 104 degrees Fahrenheit. Two, the internal resistance is high compared to other

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types of batteries and this resistance increases with the age of the battery. Finally, there is the danger at high temperatures that these batteries can cause an explosion. If these batteries are used there would have to be some safety concerns taken into account because of the high temperatures of the Fresnel lens output.

A motor attached to the Stirling engine will act as the generator. The best way to do this is to directly couple the shaft of the motor to the gear of the Stirling engine, but there is also the method of attaching it by a belt which should also be considered. The generator could either be 12 Volts DC attached to the batteries in parallel or 24 Volts DC attached in series. The reason for choosing DC instead of AC is because the system will be charging batteries, which requires DC, or an ACDC converter. Also all of the controllers were designed to operate on DC. There are many types of motors with different RPM and sizes. A permanent magnet motor is needed for the design in order for it to have the reverse generator action. The option exists of have a gear embedded generator or a regular generator.

Induction vs. Permanent Magnet motor Research The reason why a permanent magnet motor needs to be used for the generator instead of an induction motor is because an induction motor uses the flow of alternating current in a coiled wire to produce a rotating magnetic field and turn the rotor. In order for an induction motor to have generator action the shaft would have to spin the rotor at a faster angular velocity than required for motor action. This type of motor would also create AC power which is not desired, and the higher RPMs required for generator action is also a downside to using this type of motor due to the low torque of the Stirling engine. On the other hand, the permanent magnet motor can be used as a synchronous generator, which means the required RPMs would be the same for both generator and motor action. Also, the output power would be in DC as needed by the system.

The good thing about the gear generator is that it can work at low RPMs. With a load applied the Stirling engine RPM of the gear changes drastically because it doesn't have a lot of torque. The good thing about a DC gear motor is that it has a gearing mechanism already inside of it that can be used for attaching it to a low RPM and producing a higher RPM into the motor thus producing a higher voltage. A generator that does not have this feature can have negative effects on the overall voltage produced. After attaching this motor to the Stirling engine gear, the load from the motor will reduce the RPMs from the Stirling engine to less than the desired RPM range of the motor desired range of operation and the voltage produced by this motor will be hindered.

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Direct coupling vs. Belt Driven Research The interface of which the motor will be attached to the engine can be by belt or by a direct couple. If it is chosen to be attached by belt, an adjustment of the sizes of each gear ratio desired for a certain RPM. If the size of the motor gear is decreased when compared to the engine gear one can get a higher RPM and vice versa. Some disadvantages is that there is some loss due to friction and also the fact they will wear out and would need to be adjusted from time to time, especially at higher temperatures. By direct coupling, there would be no loss from slippage of the medium and also a greater resistance to thermal heat expansion. Using a coupler one can also have a better response when they are initially starting the system. When the system is started there is going to be an impulse that acts on the motor to get it going which will then start the Stirling engine. Due to the Stirling engine needing a rotational impulse in order to kick start it, the direct couple method is the way to go. While using the direct couple method one can look at various gear motors to get the required RPMs needed for the voltage output.

When picking out the coupler for the design certain considerations have to be made, specifically the size of the Stirling engine where it will be coupled to, and the size of the motor where it will be coupled to. Depending on the difference in the sizes a corresponding coupler with the needed reduction from one to the other will be used. The coupler also has to be ridged enough to withstand the applied torque and has to be able to be secured to the two shafts so that no slippage occurs while the engine is turning on or while it is running.

The way in which the batteries will be connecting to the generator is very important to the charging process. In order to have a constant charge flow without loss a means of giving the system the impulsive kick start is required. When in charging mode one needs to direct the charge flow directly to the batteries without letting any flow backwards. To do this a rectifying circuit will be implemented which will let current flow towards the battery and not back towards the motor. In this circuit it will also have a separate connection with a switch which does let current flow towards the motor. The reason for this is so that when the system is starting up it will be able to close the switch and send an impulsive kick start to the motor so that it gains the initial momentum needed to start the system. After the impulse is sent the circuit will then signal to open the switch and the charging cycle begins. This is a major feature of the connection between the generator and the batteries as this will allow the system to startup on its own and reduce standing current loss.

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Figure 20: This flowchart is the basic generator process

The flow chart above shows the basic outline of the charging system and the way it is connected to the power supply system. After the Stirling engine has been heated up by the sun through the Fresnel lens it will have the hot side ready to work. The Stirling engine cannot start on its own because it needs a force larger than its inertia and static friction in order to get it moving. For this the two 12 Volt batteries, assuming they are fully charged, will be set in series in order to get a total voltage of 24 volts. The two batteries in series along with a capacitor should be enough to overcome its inertia. Once the Stirling engines flywheel starts rotating the optical RPM sensor that is on the generator will send a signal to the processor. When the processor gets the signal from the optical RPM sensor that there is enough RPM to keep the Stirling engines momentum moving and able to rotate the motor on its own, the circuit will be switch back into charging mode. When back into charging mode the batteries will be back in series and the charging controller will begin sending power to each battery one at a time until they are full, then the circuit will change to the other battery and start charging that one.

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12v DC

12vBattery

(1)

12vBattery

(2)

Switch between

charging and starting

Kick Start Capacitor

ChargingController

Current Flow à

Figure 21: Basic circuit setup

In the diagram above is the basic circuit of how the generator will be connected to the batteries. While the switch in this circuit is connected to the bottom node the system is in charging mode and no current would flow out of the two 12 Volt batteries. During the system startup this circuit will switch to the top node along with some other switches being flipped for a very short time so that the 24 Volt motor gains the required momentum to start the generator. After this very short procedure the circuit will switch back to the bottom node and begin the charging process.

Attached to the batteries will be a circuit for rotating the base of the system. This is required for the solar tracking that will be used for the system. When the processor wakes up and analyses the orientation and position of the system in accordance to the sun a signal will be sent to turn on the motor that will then rotate the base at a very low speed until the desired position is reached. For this a high torque motor will be needed because of all the weight it will be displacing. This motor will be connected in parallel to the circuit above.

Lithium Ion battery versus Lead-acid battery There are certain things that need to be considered when charging batteries. For one thing the batteries need to have a source for measuring the voltage across it and the current. The voltage across a single lithium-ion cell should not exceed the standard 4.20 Volts. If overcharging were to occur there is the danger of the battery overheating and bursting into flames. Depending on the output voltage of the generator it would have to either raise the voltage or lower it before it gets to charge the batteries. This would require a system before the batteries with a

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constant feedback from the batteries which will be testing for charge capacity and threshold temperatures. Another danger to be considered with lithium-ion batteries is that at high temperatures there is a possibility of combustion. Considering how hot some parts of the project will be this is something that has to be taken seriously. The lithium-ion batteries would have to be protected from its surroundings and direct sunlight.

Based on the RPM output of the generator a certain output voltage would arise. One could create a function based on RPM versus Voltage to be used for the variable charging system. Once the RPM versus Voltage function has been created it can be implemented to be used for the controller that will be regulating the charging voltage/current towards the batteries. The optical sensor will be connected on the base that the motor is mounted to and will be pointed towards the Stirling engine. It will be aligned such that it will be reading the RPM off of the flywheel of the Stirling engine. This will then be fed to the microcontroller along with the open circuit voltage outputs of the batteries.

The open circuit voltage outputs will be needed for protection and the status of the batteries. The batteries have a certain minimum voltage at which they should not go below and a certain maximum voltage of which they should not surpass. If the batteries were to go below a certain voltage or discharge level this could cause permanent damage to them because they need some charge in order to work properly. Also, if they were to go beyond a certain maximum voltage level this can cause overcharging and meltdowns which would damage the batteries and could be potentially dangerous to the operator and the overall system. Therefore, when the batteries have reached a certain level of charge or discharge an indication will be obvious to the observer via a light emitting diode.

One indication would be a discharged light indicating that the battery is low on charge and needs to be charged or is already being charged. This indication light would most likely be red and if the charging process has already begun an accompanying yellow light would be seen along with the red light indicating that it is being charged. The yellow light indicates that there is current flow towards the batteries from the generator.

The red light would only be on during a low discharged range of about 30-50% of total charge. This is the optimum range of the depth of discharge in order to protect the battery from dyeing and also to prolong its life cycles. Above 50% charge level the red light would turn off and the yellow light would stay on indicating that the battery is being charged. Finally, when the battery has reached about 99% of the total charge level a green light will turn on indicating that the battery is fully charged and the yellow light will turn off. A blue LED would show that there is being current drained from the batteries. This would be a nice addition to have to the design so that an operator would be able to tell the status of each battery by just looking at the LED's. The following flow chart is a representation of the logical thinking that a processor would go through in order to display the LED's correctly according to the status of the batteries charge

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state. The charge state can be known from the open circuit voltage from the battery and the battery being used is known from current drain.

Figure 22: LED logic Diagram

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There will be a 24 Volt generator with a step down microprocessor controlled voltage regulator to bring the circuit down to the correct voltage. Once the voltage has been stepped down from the generator to what is needed for the batteries a charging controller will be implemented. The voltage regulator will be controlled by an alternate circuit and will be varied depending on the output voltage of the generator. This will step down the voltage to the desired level. The amount of RPM coming out of the system is going to be very important in the system, because from this one can find a pattern with the amount of RPM and the voltage output of the generator to make a successful equation for controlling the circuit. This will be in part of the testing phase once the initial generation process has been constructed. A series of tests would have to performed on the system in order to get the design working the way it is intended

The following circuits show the different isolated functions that the setup will be able to perform. This first one has to do with the first stage of charging the lead-acid AGM batteries. This first stage along with a second stage will complete the overall charging cycle and will be repeated over and over throughout the charging process.

12V Batteries 1 & 2Voltage Regulator

24V DCGenerator

BatteryChargingController

Z

Figure 23: Circuit for stage 1 of charging

In order to have the system working the way it is intended, there is going to be some isolating and combining of different components and batteries. The circuit above shows the first stage in charging. In this stage of charging, one of the batteries is connected to the generator, the voltage regulator, and the battery charging controller. The other battery on the other hand, will be giving power to the loads. There will be separate small loads that the battery that is not charging will be giving power to. The microprocessor will need power, along with the actuator for raising and lowering the Fresnel lens during solar tracking and the stepper motor that will be turning the system for solar tracking. Once the battery that is in the charging process has reached its full charge limit, then the circuit will make a switch to the other stage of charging.

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24V DCGenerator


Z

Figure 24: Circuit for stage 2 charging

After the first stage of charging is complete, it will go into the second stage of charging which is in the circuit depicted above. In this stage the two batteries have be switched from their position in the first stage. The second battery all the way on the right is now in the charging mode and is connected to the generator, the voltage regulator, and the charging controller. While in this mode the other battery is now connected to the same loads as stated above in the first charging process. Again, the loads will be receiving a steady power source from the battery that is not in the charging state. Once the battery that is connected to the charging components has been fully charged the circuit will change once again. The two batteries will switch states again and the first stage mentioned above will begin a new cycle. This is the cycle that the charging process will be following over and over again, until the system goes into the sleep mode at the beginning of the night or the input power from the sun is lost due to extreme weather conditions.

12v Battery 12v Battery

24v DCMotor

Figure 25 : Startup Circuit

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In the circuit above, the two batteries have combined in series. In this stage of the total circuit design the batteries along with a capacitor will provide and starting forces for the 24 Volt DC generator/motor. This stage is very important because when the system is off there is a large start up inertia that needs to be overcome in order to get the 24 Volt generating motor running fast enough to sustain its momentum with the attached Stirling engine. The two batteries in series will provide a stable 24 Volt potential. These two batteries will be of the lead-acid AGM type, so there internal resistance is low and they have a higher power output than other battery types. The power from the batteries will be able to charge up the capacitor quickly to the point of energy release. Once the energy that has been charged up in the capacitor has reached its accumulation limit, it will then be released towards the 24 Volt motor and provide a large enough electrical force in order to get the motor attached to the Stirling engine the required startup inertia needed to get it going. This is a prototype of what the startup circuit will be doing and this will need to be tested with all the loads to make sure that it has enough startup inertia power to provide rotation. If the way this startup circuit is connected doesn't give it the startup inertia needed a voltage step up transformer can be easily added to the system. If this is the case a small one to two step up transformer can be easily adapted in series to the circuit in order to double the voltage potential and give it sufficient startup power. The 24 Volt generator/motor would not be damaged in this process. It has been rated to be able to withstand this voltage as long as the current does not get higher than 10 amperes. At 10 Amperes the internal windings to the 24 Volt generator/motor can begin fusing and creating short circuits which could potentially damage the motor/generator as well as the electrical system.

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24V DCGenerator


Figure 26 : Combined startup and charging circuit in one

The circuit above is how the total charging and starting circuits are going to be connected as one. In the first stage of the charging process the battery on the left of the two batteries will be connected to the generator, voltage regulator, and charging controller. The short circuit across the voltage regulator and the battery charging will be open so that current flows through the charging system. The short circuit across the capacitor will be closed as this is not needed in the charging circuit. After the first battery is fully charged the switch towards the first battery will be opened and then the switch towards the second battery on the right will be closed. Once again the short circuit across the voltage regulator and the battery charging will be open so that current flows through the charging system. The short circuit across the capacitor will be closed as this is not needed in the charging circuit. For the starting process in this circuit the short circuit across the voltage regulator and the charging controller will be closed, the switch towards the first battery will be closed and the switch towards the second battery will be opened. The two pole switch after the first battery will be switched towards the second battery so that they can be combined in series. On the way out of the second battery the short circuit switch across the capacitor will be opened so that the capacitor can be implemented in the startup circuit. Once the startup inertia has been overcome and the motor/generators momentum has is being sustained

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by the Fresnel lens and the Stirling engine output, the circuit will switch back to the charging mode and the process of charging each battery one at a time will begin repeating itself over and over again. This startup process will be implemented every time there are no RPM coming out of the Stirling engine and there is sufficient heat from the Fresnel lens to get the Stirling engine in a stable oscillation.

Charging of a lithium-ion battery requires precision controlling because of the sensitivity of them. The voltage and currents into the battery have to be changed at different stages of the battery charging to obtain the utmost performance of the batteries. The reason for this is to provide a safe and secure way of charging the battery while preventing cell capacity loss. If a lithium ion battery is not charged to its highest limit the capacity of the battery will decrease rapidly. If it is over charged the battery could be damaged. Typical duration of charging is around two hours.

There are a total of four stages which are typically used to charge lithium ion batteries to the highest efficiency. The first stage requires a slowly increasing voltage with a constant current typically between one Amperes to one point five Amperes. The second stage requires a constant high voltage of about 4.20 volts per cell while the current slowly decreases. This stage is the saturation stage and by the time the battery reaches full charge the current should be zero. The third stage is a terminated state that shuts the charging off when the current has reached less than 3% of the rated current. Finally, the fourth stage is just a standby mode which periodically applies a topping charge to prevent cell loss. This can all be done with a very accurate charging controller and these stages of charging must be considered in order to provide ultimate charging and safety to the batteries.

One thing that must be looked at is the torque required to run the motor. A motor with higher torque requirements might not work with the design because of the low torque output of the Stirling engine. This can be looked at in two parts. The startup torque and the running torque. The startup torque is when the engine is first turning on and doesn't really matter because there is sufficient power going to the motor in order to break the inertia. The running torque is what is important because this is directly related to the generation of power. If the Stirling engine does not have the running torque needed the design could be a failure. Unfortunately the exact specifications about the Stirling engine cannot be acquired. The figure below shows the basic circuit required for the charging controller system.

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Figure 27 : Basic charging controller circuit

Wire Research There were a variety of different wire colors and prices found. The price range of wire is anywhere from $5.00 to $15.00 for the length and gauge is needed for the project. Some of the wires could withstand up to 194 degrees Fahrenheit and others a little less. The wires that were picked for the project are capable of withstanding up to 194 degrees Fahrenheit, as needed because of the high temperatures resulting from the Fresnel Lens. The average lengths found were anywhere between 10 feet and 24 feet. The pricing online wasn't too bad but compared to the local hardware store the cost is less and the length and type of wire is much more flexible at the local store. A chart of different prices and color wire are as follows. These include prices from the local hardware store as well. The brand that was found at the local hardware store is Cerrowire. The rest of the wires were found online from different manufacturers.

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Table 4: Chart of different prices for wires

Part number:

207-3402R17

207-1205R24 RP1210 64177 8125 8121DL

Make: Cerrowire Cerrowire Road pro Camco Delcity Delcity

Length 17 ft 24 ft 10 ft 10 ft 15 ft 15 ft

Color White Green Black White Black Red

Gauge 14 16 12 12 12 12

Type Stranded Stranded Stranded Stranded Stranded Stranded

Heat High High Medium Medium-High High High

Price $4.69 $4.69 $4.00 $3.00 $5.22 $5.22

Fuses and Breakers Another thing that must be considered for the project is circuit protection. Circuit protection is required for the system to protect any components from any damage due to over current flow or short circuit. A fuse is an adequate form of circuit protection and can be used in this project. Basically, when there is an overload of current or a short circuit that the fuse it connected to it will pop and have to be replaced before starting up the system again. There are many expensive and temperature sensitive components of the system and protection is important.

The fuse works well to protect from overload and short circuit but it has to be replaced when it burns out. There is another type of circuit protection device called a breaker. The breaker is similar to the fuse in that when there is a current overload or a short circuit it opens the circuit by a tripping mechanism. The breaker, unlike the fuse that has to be replaced every time an overload occurs, can be reset manually over and over again. This makes it easier to trouble shoot a system quickly without having to keep replacing fuses while still having protection. Even though the breaker doesn't have to be replaced like the fuse, the high heat that is going to be around the design might have some adverse effects on it and might cause it to trip. This is because the breaker will trip when there is a lot of heat involved. An ambient extremely hot temperature can cause the breaker to trip and this could become a problem.

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Although the breaker is the better component because of the ease of being able to reset it without making any replacements, there just weren't any breakers found for the low amperage needed for this design. Maybe if the system was giving out at least 10 amps then it would be better to go with the breaker, but this is not the case. The fuses came in a wide variety of amperages and there was one well suited for the design that holds up to 3 amps. The price of it is only one dollar but they also carry small fuses like it at the local hardware store.

Generators There are three different 24 Volt DC generators that were of interest. The first one is from windstreampower.com This generator is rated at 24 volts with a 1.5 Amp continuous duty. The price of it is $149.00 without tax. The stator consists of two high-energy saturated C8 ceramic magnets and the shaft diameter is 8mm. The armature is wound with AWG30 magnet wire capable of withstanding up to 10 Amps before fusing begins. The brushes are 6.3 x 4.7 x 8mm, and they have plenty of replacements in stock. The bearings are two double-sealed 26mm ball bearings. The stator can rotate in either direction and function as a generator or motor, which is what is needed. At about 400 RPM the output voyage is rated at 20 volts, which is sufficient. It can be mounted by the front or back through four holes, or by a hose clamp on the magnet drum. The weight is only 3.3 pounds. It has an internal resistance of 21 Ohms and an inductance of 40mH.

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Figure 28: Permission pending

There is also a more expensive one at $249.00, which generates more Amperage. The following graph is from the same manufacturer as above but is it a higher powered motor. In this graph you will notice that there is a higher amount of output amperage at the same RPM as above. The reason for this is because the more expensive motor has a higher number of slots and windings

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inside of it. Yes, the output ampere is higher at the same RPM but the extra wires will give it a greater inertia and heavy weight which will cause more load onto the system which cannot be afforded due to the nature of how delicate the Stirling engine is.

Figure 29: Permission pending

The second motor is from alibaba.com, and this is also a low RPM 24 Volt DC motor. This motor also has high density permanent magnets and works on brushes. The speed is at 21 RPM with a continuous current of 45 Amps. This motor is also small and light weight. It has a large torque and has a wide variety

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of uses. The nice thing about this motor is that is has an advanced short circuit protection function. It also has a veritable gear design that you can pick to your standards. Although this is a very nice motor/generator the price for it is not listed. The company has been contacted for current pricing but no a response has been received. Also, this product will be shipped from out of the U.S., so it would probably have high shipping costs which are undesired. They also don't provide spare parts and detailed graphs of their products performance like the one above from the first motor.

The third motor is a geared motor designed to work at about 450 RPM. It is being sold online at CMACMA technologies. This one is also permanent magnet, but it doesn't state the type of magnets. It has an 80 inch-ounce torque and an intermittent duty cycle. The diameter of the shaft is 1/4" and a 3/4" shaft with flat 2-tapped 10/32 mounting holes in motor face. This doesn't give much of a choice on how to strap it down, so that is a disadvantage. It is a fairly small motor at 2" X 3-3/4". It is also the lightest weighing, at 1.5 pounds. This motor is also very cheap, only $34.00, but the amperage is at 24 Volts and no load is pretty low, coming in at 0.38 amps. This is lower than the first motor, which is rated at 1.5 amps. The provider of this motor, like the previous provider, does not have an operating statistics graph like the first generator.

Table 5: Generator product details

Part number : 443540 130ZYT55CPX144A3 WBB236691 443541

Voltage 24VDC 24VDC 12-24VDC 24VDC

Current 1.5A 45A 14A 3A

RPM 0-5,000 21RPM 1800-3900 0-5,000

Width 150mm 110mm 3.16inch 150mm

Height 150mm n/a 3.16inch 150mm

Length 300mm n/a 7.38inch 300mm

Total volume 6.75mm3 small 73.69inch3 6.75mm3

Weight 3.3lb light 9lb 9.2lb

Price $149.00 Waiting Reply $193.95 $249.00

For the voltage regulator that will be outputting the correct voltage needed from the generator to the output, there are three that could work well with the system. The first of the three is from the same provider as the first of the 24 Volt DC

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generators that was looked at from Wind Stream Power. The input voltage to this regulator has a maximum of 80 Volts DC, which is sufficient. The output comes out to 13.8 Volts at no load and should not exceed 14 Volts for the safety of the batteries. The output current is capable of up to 10 Amperes DC maximum. It has an internal voltage drop of 0.5-3 volts depending on the load. The dimensions are 152mm long, 90mm wide, 48mm high, and weigh 380 grams. For mounting the device there are four holes on the base of the regulator that can be adapted practically anywhere. The connections of the regulator are terminated in a crimp and can be easily attached to a stripped wire. The cost of this regulator is a little pricey at $125.00.

The second of the regulators is from currentlogic.com. This regulator has an input range of 16-40VDC and steps down to an adjustable range of 1~12VDC. The rated maximum amperage is at six amperes. The size is 6.8 x 4.3 x 2.2cm. The no load current is rated at 10mA and is subject to change according to different loads. The typical efficiency is at 90% and is also subject to change according to different loads. The working ambient temperature is anywhere from -20~60 degrees Celsius. The typical ripple is about 100mV. It also has a very nice overload protection and a short circuit prevention that shuts down in the event of over current. The connection ports have slots that can be easily attached to wires and pinned in. The cost of this regulator is only $19.00

The third voltage regulator is from powerstream.com. They have four different model types, but the one that was good for the specifications is the PST-DC/2812-8. This has an input range of 10V-30V DC and has an output of 12V. The output voltage can be regulated from 11 Volts to 13.9 Volts by an internal port VR4. It can handle a continuous output current up to 8 Amperes and a continuous output power of up to 100 Watts. It has a line regulation of 1% and a load regulation of 3%. The efficiency is 75-85% less than the one above. It has a couple of protection types, which include input polarity protection, input low voltage drop out, input high voltage protection, output show circuit protection, output current limit, and over temperature protection. The dimensions are 300mm x 88mm x 42mm. Its weight is 3.3 pounds and has a temperature range of 0-55 degrees Celsius which is low for the project. The connection types are input and output binding posts. The cost is $144.76, which is the most expensive of the three.

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Table 6: Voltage Regulator details

Part number : 461400 AD2016 PST-DC/2812-8

Input Voltage 80VDC Max 16-40VDC 10-15VDC

Output Voltage 13.8V 1-12VDC 12V

Input Current low <1.8A low

Output Current 10A DC max 6A max 7.5A

Width 90mm 68mm 200mm

Height 48mm 43mm 164mm

Length 152mm 22mm 67mm

Total volume 0.655mm3 0.064mm3 2.1mm3

Weight 380g light 1.5kg

Price $125.00 $19.00 $154.00

For the project there is need for the batteries to have low resistance so that they don't affect the load as much towards the generator and are able to dump out a lot of power at once. This is why lead-acid batteries were selected for the project. There are a few AGM lead-acid batteries that are good to work with the design. They are all rated around 5aH. The first battery that was considered is made by Amstron power solutions. It is rated at 12 Volt and has a capacity of 5 Amp-hour. The power rating is 60 Watt-hour and is constructed with a total of six cells. The connector type is F2 and can be easily attach to plugs. It has a high power density and uses state of the art, heavy-duty, calcium-alloy. It is valve regulated and maintenance free. The dimensions are L = 9.04 cm, W = 7.04 cm, and H = 10.01 cm. It weighs 4 pounds and has a 1 year warranty. The color is black. Its price is at $17.99.

The second of the batteries is made by Leoch. It is also of the lead-acid chemistry and is 12 volts. The capacity is six Amp-hours and has a power rating of 72 Watt-hour which is higher than the first battery. It is made up of six cells and has F1 connector type that can be easily attached to plugs. They are maintenance free and have a wide operating temperature, long service life and deep discharge recovery. It is of the AGM technology and is valve regulated. No water has to be added. The dimensions are L = 8.99 cm, W = 7.01 cm, H = 10.11

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cm. It has a cool grey color and weighs four pounds also. They also provide a one year warranty. The price of this battery is $19.79 which is a little more than the previous battery but the higher power rating justifies the increase in price.

Finally, the last battery that was considered is from Universal Battery. This is also a 12 Volt AGM valve regulated battery. It is rated at five Amp-hours and is enclosed by ABS plastic. Its ambient temperature charge is from -4 to 122 degrees Fahrenheit. It is leak proof, maintenance free, valve regulated, and has multiple applications. It has F2 terminals which can be easily attached to plugs. It has a high discharge rate and temperature control formation. Its dimensions are L = 3.54 inches, W = 2.76 inches, H = 3.98 inches and It weighs 3.75 pounds. It's black and has a maximum charging current of 1.25 Amperes. Its cost is the cheapest of the three batteries at $15.10.

Table 7: AGM battery details

Part number : LP12-6-F1 AP-1250F2 UB1250-D5777

Make: Leoch Amstron Universal Power

Voltage 12VDC 12VDC 12VDC

Max Charge Current 1.25 A 1.25 A 1.25 A

Capacity 6 Ah 5 Ah 5 Ah

Power Rating 72 Whr 60 Whr 60 Whr

Terminal Type F1 F2 F2

Op. Temperature (-)4°to140°F (-)4°to140°F (-)4°to140°F

Ambient Temperature (-)4°to122°F (-)4°to122°F (-)4°to122°F

Class AGM AGM AGM

Width 2.76inch 3.56inch 2.76inch

Height 3.98inch 2.77inch 3.98inch

Length 3.54inch 3.94inch 3.54inch

Total volume 38.8inch3 38.8inch3 38.8inch3

Weight 4lb 4lb 4.4lb

Price $19.79 $17.99 $15.10

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A charge controller will be necessary for the system. There were four charge controllers that were of interest. The first charge controller is made by Harger. This charge controller accepts an input range of 10 Volt DC to 15 Volt DC and is good for charging a battery to 12 volts. It has a continuous charging current of 7.5 Amperes. The charging algorithm is 4 stage, 3 level adaptive microprocessor controlled. It can charge a battery range of 0.5 Amp-hours to 100 Amp-hours. Some protections that it has are low input voltage protection, high input voltage protection, over temperature protection, output short circuit protection, and battery polarity protection. The dimensions are 200 x 164 x 67 mm and the input has screw terminals for the connections and the output has binding posts. There is also an onboard controlled DC fan. The operating temperature is from 0 to 55 degrees Celsius. It weighs 3.3 pounds and costs $154.00. There are also LED lights at different stages of charging that work as follows.

Table 8: Harger charge controller LED display

Status Completion Red LED1

Red LED2

Yellow LED

Green LED

Standby

LEDs cycle while waiting

Trickle before bulk charge 0-10%

The two red LEDs cycle Off Off

Bulk charge 10-90% Off Red 2 and yellow cycle Off

Fill Charge (also known as "over charge") 90-99%

Yellow and green cycle

Float charge 100%

Green flash

Low Battery voltage alarm Flash Off Off Off

High Battery voltage alarm Off Flash Off Off

Low input voltage alarm Flash Off On Off

High input voltage alarm Off Flash On Off

Over temperature alarm Off Off Flash Off

The second charging controller is made by Blue Sky Energy. This charging

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controller works on 24 Volt/15 Amperes and on 12 Volt/20 Amperes. It has an optional display which provides charge control and full featured battery system monitoring. It works on the three stage charge control with filtered output which supposedly improves battery performance and life. It has a galvanized mounting box and coated electronics that resists corrosion. It features an automatic or manual equalization to periodically condition flooded lead-acid batteries. It also has an IPN network interface which can utilize multiple controllers and an optional battery temperature sensor and display for it. An auxiliary output provides 15 or 20 Ampere load control or a two Ampere auxiliary battery charge. There is also a lighting control which provides separate post-dusk and pre-dawn timers. Its power consumption is 0.20 Watts plus 0.40 Watts each for charge on and load on. The power conversion efficiency of the battery is 97% at an output of 28 Volts and 12 Amperes. The operating temperatures range from -40 to 50 degrees Celsius. This controller is supposed to be able to increase charge current by up to 30% or more. The bad thing about this charge controller is that it is very expensive, costing $249.00.

The next charging controller that was found is made by Atkinson. These charge controllers can be used with 12 Volt or 24 Volt batteries. This charge controller was made to be used with photo-voltaic panels but it looks like a good candidate for the project. It only weighs three ounces and its size is 0.875 x 3.2 x 1.2 inches. Its enclosure is epoxy potted in PVC pastil and it is easily mounted to anything with double stick tape. Its load capacity at 14 Volt DC is at 12 amperes. Its current draw is less than or equal to 6 milliAmperes continuous and 35 milliAmperes during charging. It has a red LED that indicates when it's in charging mode. The temperature is made to handle from -30 to 75 degrees Celsius. Its life time is said to last up to 100 million mechanical operations. This charging controller also has a relay which checks the battery status every four minutes. It can work with flooded or sealed batteries. It also has safety cutoff that disconnects the charging process once the battery has reached a certain high output voltage. The cost of this controller is $43.22.

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Table 9: Battery Charging Controller Details

Part number : PVCM10 SB1524iX PST-BC1212-

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Make: Atkinson Blue Sky Energy Power Stream

Input Voltage 12V or 24VDC 12V or 24V 10-15VDC

Output Voltage 13.8V 13.8V 12V

Input Current <35mA Minimal low

Output Current Controlled 20A maximum 1-7.5A

Width 0.875inch 13.5cm 200mm

Height 3.2inch 13.5cm 164mm

Length 1.2inch 11.9cm 67mm

Total volume 3.36Inch3 2.1mm3 2.1mm3

LED Indication Red LED charging

Charge Status and load Multiple Stage

Mounting Double stick tape Bracket Bracket

Weight 3 ounces light 1.5kg

Price $43.22 $249.00 $154.00

Coupler In order to connect the Stirling engine to the motor a coupler will be needed. The inner diameter of the flywheel of the Stirling engine is 1/2 inch. and the diameter of the 24 Volt DC generator is 5/16 inch. There are many different types of couplers available for a wide variety of applications. There were a total of four couplers that fit the description of the model available from different sources. The first product is made out of glass filled black nylon and is a 5 pack. It is from the Eldon James company and the model number is C8-5 GFBN-5. This little coupler can withstand up to 275 degrees Fahrenheit. It is capable of withstanding high forces and is very rigid. There is no warranty for the part and only a 60 day return policy after the invoice shipping date. The cost of the Eldon James coupler is only $3.50, and it comes with three units per package.

The next coupler is a silicone hose black coupler. This reducer coupler is made

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by HPS and the model number is HTSR-031-050-BLK. This coupler is made of four-ply reinforced silicone and can withstand high temperatures. Although this is a coupler, it is not of the type desired because it is not as ridged as what is needed in order to hold all the torque without slippage. This coupler looks like it will have a lot of slippage from the material that it's made of. One advantage though is that it can withstand over 350 degrees Fahrenheit. The price of this coupler is $14.00.

The third product to be considered is the Thogus - TAF10810N10G. This coupler is made out of heavy duty construction nylon. The contents of this product come with 10 of these couplers for a price of $18.04. The high temperature range tolerates up to 275 degrees Fahrenheit and it can withstand a lot of force. This coupler might be able to screw onto the Stirling engine because it has a female side, but insufficient data is available to determine if it will screw on until the Stirling engine is acquired and has been examined.

The last of the list of couplers that are considered are also made by Eldon James, like the first product that was considered. This product has a nice picture and it looks like it is the sturdiest out of the four couplers. It is made out of black nylon and offers good tensile strength. It has a single-bard design and is capable of withstanding temperatures up to 275 degrees Fahrenheit. This product can also handle a lot of force. The product number is 64282 and it only costs 33 cents. This product appears to have been manufactured to easily slide on and off. It is worth it to just buy this item and tests it out because it is so cheap. If it slides on it can be secured to the shaft with a hose clamp. If it doesn't slide on easily it looks like it can be stretched a little and forced onto the shaft, and if this is the case this product would work perfectly.

Table 10: Coupler selection matrix

Part number: C8-5 GFBN-5

HTSR-031-050-BLK TAF10810N10G 64177

Make: Eldon James HPS Thogus Camco

Input 1/2 inch 1/2 Inch 1/2 inch 1/2 inch

Output 5/16 inch 5/16 inch 5/16 inch 5/16 inch

Max Temp 275°F 350°F 275°F 275°F

Amount 5 1 10 1

Material Glass filled black nylon

Reinforced silicone

construction nylon

black nylon

Price $3.50 $14.00 $18.04 $0.33

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Possible Hardware Architectures The process of harnessing solar thermal energy first requires the concentration of solar radiation to reach sufficiently high temperatures to power an engine. The two main methods for concentrating light are mirror or lens based amplification. The largest modern solar thermal generators utilize arrays of mirrors spaced equally across an area to amplify the light. Reflecting the sun’s rays from numerous locations to one fixed point increases the intensity of the beam to the point of boiling water. This requires large amounts of open land and usually a tall tower to avoid interference from the environment, as well as large mirrors controlled by motors, a pumping system to provide continual water, and high precision pressure monitors to ensure the system is not overly stressed. Despite their high power output they are permanent, expensive, and require crews to maintain.

Another mirror based method uses a single parabolic mirror to focus the solar radiation to a heat engine located above it. Large parabolic mirrors are quite expensive to fabricate, so arrays of square mirrors can be arranged in a parabolic shape. The heat engine casts a shadow on the reflective surface reducing the total power efficiency. Such configurations can be produced practically on smaller scales however, making it the more favorable method. A diagram depicting its operation can be seen below.

Figure 30: Parabolic reflector based generator

The last method considered uses optical lenses to concentrate the light to a small area. Even relatively small lenses can reach high enough temperatures to achieve combustion. This method is more susceptible to interference from cloud coverage and precipitation than the mirror based approach because it is dependent upon a single surface rather than arrays. Lens amplification is more practical on a small scale because the focal point is a fraction of the lens size, whereas in mirror array amplification the focal point is the size of each individual mirror. Small mirrors could be employed, but the cost of machining that many

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precision mirrors would not justify their low power output. Lens amplification was selected because its offers the highest concentration of solar energy in the smallest area for the lowest cost.

The two main lens configurations are polished concave glass lenses and optical acrylic Fresnel lenses. Most industrial and civil applications use small glass lenses, but Fresnel lenses are used primarily in overhead projectors and lighthouses. Fresnel lenses are smooth on one side and have angled grooves on the other surface that alters the angle of incoming light. The grooves are concentric circles with the angle of the groove increasing as the distance from the center increases which causes the light to converge to a central point. The theory is that only the edge of the lens is actually refracting the light. By removing the non-refracting material in the middle the same effect can be achieved. The figure below shows both lens cross sections. Fresnel lenses are made of light weight and flexible acrylic, and are much cheaper than precision milled glass, but can suffer breakdown after prolonged exposure to ultraviolet radiation if not properly treated. They also have a limited transmission spectrum and allow around 80% of visible light to pass through.

Figure 31: Comparison of Fresnel and traditional lenses

Glass lenses are heavy, fragile, and considerably more expensive to fabricate. The advantage of using a glass lens is that they typically have a higher quality, lower reflection coefficient, and can operate for extended durations without deteriorating. The downside is that very large glass lenses are extremely rare and expensive, and therefor generally unavailable. Smaller glass lenses are commercially available up to nearly two feet in diameter and cost up to two hundred dollars. The size of these lenses limits the possible power output and supporting the added weight of the glass lens would require a more robust control system, consuming more power.

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The decision to use Fresnel lenses was made due to their availability in large sizes at relatively low prices. The two main focal patterns of Fresnel lenses are linear and spot. The former focuses the light into a thin beam about five inches long and an inch wide, while the latter focuses the light into a tiny circle. The largest commercially available lenses are around four feet by three feet in area, with linear lenses producing a beam around five by one inches and the spot lenses producing a circle .4 inches in radius. The spot lens can achieve higher temperatures than the linear due to the smaller focal area, but the linear lens can heat a surface safer. Linear lenses can be useful for applications which require heating tubing without any point getting too hot, and are ideal for powering steam engines. A large spot lens can easily melt many metals and damage critical system components, giving the linear lenses the advantage of safety. Linear lenses are also less expensive to fabricate due to their grooves running parallel rather than concentric circles in the spot lens. The Stirling cycles considered have relatively small heating points and would absorb energy more efficiently from a highly concentrated focal point rather than a distributed area, which makes the spot lenses more attractive. The second step is converting the concentrated solar energy into mechanical energy via a heat engine. The most common industrial heat engine is known as the rankine cycle and is a closed steam powered system. A heat source creates steam that is pressurized and turns turbines. The steam is cooled, condensed, and pumped back into the heat source. This process can reach thermodynamic efficiencies up to 60% theoretically but typically achieve less than 45%. It also requires cooling towers, pumps, sophisticated pressure monitoring mechanisms, and other subsystems making them large, complex, expensive, and immovable. This is clearly non-ideal for a small portable generator.

Other commercially available steam engines are small mechanical devices which have steam intake hoses that generate rotary motion. The power output is proportional to the pressure of the steam inputs and can be very large. The one pictured below can easily achieve five horsepower. In all of these cases the steam is released into the air after passing through the engine. Therefor they require a constant supply of steam, and will cease operating almost as soon as the pressure drops. Maintaining a steady steam rate depends on the rate of water delivery as well as rate of vaporization. It would be difficult to control the water flow rate to match the vaporization rate as the amount of solar radiation fluctuates. Despite their high power output and availability at fairly low prices, the steam based heat engines do not satisfy the goal of the project, which is to provide a zero emission, zero fuel required energy generation system, and are therefor ill-suited for this project. Additionally the released steam may cause the lens to become foggy and detriment the power output.

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Figure 32: Portable Steam engine. Copied with permission from Robert Green

The Stirling cycle is a closed system using expanding and contracting gas, usually alcohol vapor, as the driving agent. The thermodynamic efficiency of Stirling cycle engines can theoretically approach that of Carnot cycles, but in practice efficiencies around 50% are achievable. They can be fabricated from inexpensive material, are simple to operate, have relatively few moving parts, and can be made small enough for portability. They operate by heating one point and cooling another, causing the vapor to expand and push a piston, compressing the cool gas on the other side. The heated gas then cools due to the increased surface area of its chamber and contracts, pulling the piston back. The fact that these engines do not have any emissions and require no fuel other than heat makes them even more attractive for this application. Stirling cycles were selected due to their high efficiency, low complexity, and availability in portable sizes.

Stirling Cycle Engine Research The goal of this project is to identify an alternative form of capturing solar energy from conventional photovoltaic panels. The actual powerhouse of the system will be a heat engine where the heat source actually comes from the sun. To make the heat source more specific a Fresnel lens will be used to concentrate the solar power. The correct type of heat engine for this application is known as a Stirling cycle engine. Figure 33 is a block diagram showing how the Stirling cycle engine system will be integrated into the system.

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Stirling cycle engines are very different from conventional engines such as the ones found in cars. The Stirling cycle engine operates based on the principles of thermodynamics. The fundamental design of Stirling engines is that the gasses inside the engine never escape and are there for constant. The engine operates through a cycle of events which change the pressure of the gas inside the engine causing the engine to do work. Of course no work is free, Stirling engines rely on a heat source, typically a burning fuel however in this project it will be heat from the sun. The heat expands the gas on that side of the engine and causes pressure to build in the system. The opposite end of the engine from the heat element is typically a heat sink which cools the air inside the engine by radiation heat transfer. The cooled air drops in pressure creating a pull towards that end of the engine. The piston out of the engine can be connected to a flywheel which in turn powers a generator to create electrical energy. The internet is full of Stirling cycle engines for sale however most of them are novelties and toys, which are not built to withstand the heat that the Fresnel lens is capable of producing. This has made locating a practical Stirling cycle engine for the purpose of this project difficult. Luckily a few options were found for sale.

The first Stirling cycle engine for comparison is for sale on Ebay. It is a modern version of the original KYKO hot air engine. The engine is designed to be powered by natural gas and is specified to be very efficient, capable of running for up to 500 hours per kilogram of liquid propane gas. Another great aspect of this engine is that it requires very little initial movement to start the engine. The typical operating speed of the engine ranges from 450 – 500 RPMs. For safety concerns this engine comes with a built in instant stop button. Total weight of the engine is roughly ten kilograms with a height of 27 inches and a cylindrical diameter of roughly 14 inches. With shipping included, this unit cost $600 dollars. The cost of the engine is expensive however it is a key component of the total system and with only a few available may be worth the high cost for the extra features. Figure 34 below shows a picture of the Stirling cycle engine for sale.

Sunlight Fresnel Lens Stirling Cycle

Engine Heat Element

Generator to charge batteries

Figure 33: Block diagram of sunlight as it gets turned into mechanical energy to charge the batteries

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The only other Stirling engine which could be found for sale that meets the specific needs of this project is sold by a company called GreenPowerScience. They have a fully assembled small Stirling engine for sale. The major advantage of this Stirling cycle engine is that the GreenPowerScience website shows the engine being powered by a Fresnel lens. Knowing that this engine is capable of withstanding the intense heat from the Fresnel lens makes it favorable because it eliminates the risk of not knowing if the engine will fit the application. This is very important considering how expensive the item is. The cost of this Stirling cycle engine with shipping is $300 dollars. Figure 35 below shows a picture of the Stirling cycle engine from GreenPowerScience.

Figure 34: Stirling cycle engine. Printed with

pending permission from ebay user.

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All solar thermal generators must implement solar tracking in order to function optimally. This is especially true with the lens approach because the plane of the lens must be perpendicular to the sun or else the focal point will not be optimally shaped or located. The sun’s trajectory could be best modeled using a spherical coordinate system. Fresnel lenses have a fixed focal length, so optimal tracking can be accomplished by varying only the horizontal and vertical angles to keep the lens perpendicular to incident rays. To accomplish this, the system must be able to rotate three hundred sixty degrees horizontally and up to ninety degrees vertically. To match the horizontal angle the entire system will rest on top of a raised platform that can be rotated about a supporting axle fixed to a base plate. One method to control the rotation could be to use the motor as the supporting axle. The motor needs to be large enough to handle the total weight of the assembly, which increases the price immensely. This also creates complications in controlling the system accurately since rotary motors typically operate at hundreds of rpms while this application needs thousandths of rotations per minute. Another method for rotating the platform is to have a small motor connected a distance from the central axle with a fan-belt or gearing system. This allows the central axle to support most of the load and reduces the cost of the motor. This is also advantageous for the design because a small motor can be used which consumes very little power. Fan-belts are less temperature resilient and are typically utilized in applications demanding high rates of rotation. They are also susceptible to slipping, and therefore cannot be controlled with a high degree of precision. Connecting the motor to the pedestal with a gear allows the torque to be precisely controlled yielding the desired rotation. Alternatively motorized wheels could be attached to the base plate and provide some of the structural support.

Figure 35: Stirling cycle engine. Printed with pending permission from GreenPowerScience

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To track the suns vertical angle requires rotating an assembly containing the lens about a fixed axis. This can be accomplished by rotating the entire system to match the suns inclination. It is not feasible to rotate the whole system horizontally and vertically simultaneously, so a subsystem is required to track the vertical angle. Such a system consists of supporting arms the size of the focal length attached to hinges on one end and the lens on the other. Hollow tubing was selected to construct the lens support arms because of their reduced weight and price. Two methods for controlling the vertical rotation are with rotary motors or linear actuators. Either could be directly coupled to the supports to provide the force necessary for rotating the assembly, but the rotary motors would be less efficient. Balancing the lens assembly with a motor directly would constantly consume power to provide torque. A gearing mechanism could be employed to couple the rotor with the axle and prevent the lens assembly from rotating between adjustments, but such a system would add complexity and weight unnecessarily. A mechanical gearbox would also be susceptible to being over or under driven, as it would have no limiting switches, possibly damaging the hardware.

Figure 36: Linear actuator as modeled for the project

A linear actuator already has the gearing and contained internal structure for providing the type of motion required. An actuator pinned to the platform and lens support arm would provide a constant counter torque without consuming any excess energy. This is ideal for elevating the lens assembly because it is the most energy efficient method of support. Linear actuators can also be controlled to a high degree of precision. This is essential to successful solar tracking because the average required angular adjustment is very small, averaging one degree every four minutes. Actuators are available that can sustain loads that vastly exceed the requirements as well, and are available in a wide variety of sizes and operational configurations. The majority of actuators also have built-in limiting switches that prevent them from being over driven. Some even have position feedback system to control exactly where the extension point is. The low weight and simplicity of control interface make linear actuators more desirable than traditional motors,

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and although they are typically more expensive, their performance advantages justify the cost.

Strategic Components The first crucial component to be strategically selected is the solar tracking design. The system will need to be built as an azimuth-altitude dual axis tracker. The reason this specific method of following the sun will work best is because it will rotate the Fresnel lens about a central point which, in this case, will be the heat element of the Stirling cycle engine. Using an AADAT system is significantly improved over a single axis system because of the increased accuracy which can be achieved. When comparing azimuth-altitude and tip tilt dual axis trackers the AADAT system of rotation about a central point provides more use to achieving the system design objectives over the TTDAT advantage of having a smaller footprint. To achieve the chosen AADAT design a vertically mounted actuator will be used to raise and lower the altitude of the Fresnel lens. To adjust the azimuth angle the entire system will be designed to rotate. While prototyping the construction of the system to adjust each of these angles it will be crucial that as the angles change the Fresnel lens focal point remains on and never leaves the heat element of the Stirling cycle engine.

The next important component to be selected is which type of photo detecting device will be used by the system to locate the direction of the sun. The components which were researched were light emitting diodes, light dependent resistors, and photodiodes. For the purposes of this project the photo detectors will be used by comparing one to another therefore the sensors need to have minimal variance from one part to another. Because of this need, LDR’s won’t make a good selection as they can vary by up to 50% even between parts which come from the same production lot. Another goal of the project, which needs to not be forgotten, is maximum efficiency. Because many photodiodes require a supply voltage to be turned on they will not be the best selection for this project. This leaves only the LED’s, which are a great selection because they of their simplicity to use. No supply voltage will be needed since they can be connected by simply hooking the positive terminal to ground and the negative terminal feeds into the control system. Within the available types of LED’s the best to use will be high powered red as they are the best for sensing the entire visible spectrum of light.

There is no real advantage of using one layout of photo detectors over another for the design of the light sensor array. As a result the choice of which layout to use will be based on which will be easiest to build and also to later refine. The array which will be the easiest to build is the one with two sensors next to each other and a wall placed between the two to cast a shadow if alignment is not proper. This layout will also be easy to modify if the accuracy of how exactly aligned the system needs to be needs to be changed. Therefore it will make a perfect layout for the LED’s to be used in the system. When the actual sensor is

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built it will need to be modified into a four sensor array with two walls. This modification is important as it will allow a single sensor array to detect for both the altitude angle as well as the azimuth angle. This sensor will need to look like the one shown below in figure 37. The sensors will communicate in pairs to the control system. For example if the sun is casting a shadow onto sensors A and B then the control system will know that the altitude needs to be adjusted down until sensors A and B are no longer shaded. A second example would be if sensors A, B, and D are shaded then the system will need to adjust altitude down as well as azimuth left until the three sensors are no longer shaded. In the case of this situation the control system can make the adjustments in altitude first and then once only sensors B and D are shaded the control system will adjust the azimuth angle.

With the array design decided upon it is next necessary to consider how to actually construct the sensor array. Items to take under consideration are what materials will need to be used and also where the sensor array will be mounted. To construct the sensor array a nonconductive material will need to be used. Perhaps the easiest material to work with which is also an insulator is wood. Woods are often classified as either hardwood or softwood; the main difference between the two is the density of the wood. Based on the need for the array to be lightweight, balsa wood will be a perfect fit as it is a very lightweight and easy to work with type of wood. To be more specific the base of the array where the LED’s will sit will be made from half inch balsa wood and the walls will be placed perpendicular to the base as well as to each other and be made out of quarter

Sensor C

Sensor A Sensor B

Sensor D

Altitude Up

Altitude Down

Azimuth Right Azimuth Left

Figure 37: The finalized design of the solar tracking sensor array.

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inch balsa wood. The walls will be precisely placed and then held to the base permanently with hot glue. The sensor array will be placed on the frame of the Fresnel lens. When placing the sensor array it will be crucially important that the array is exactly aligned with the Fresnel Lens and also that it is oriented such that the correct sensors will trigger the correct change in either altitude or azimuth angle.

The best control system will be based utilizing a microcontroller. The most substantial reason for choosing the microcontroller route is that they have the lowest power consumption and ease of designing. Also a microcontroller will be the easiest option for continued refinement after the initial prototyping and testing of the system. Based on the research of microcontrollers the best option to go with will be TI’s MSP430. The ultra-low input voltage requirement of the MSP430 is its most attractive attribute. Also the price for the MSP430 was nowhere near rivaled by the Arduino or 68HC11 microcontrollers. Further research as to which MSP430 series part is to be used will be discussed further on in this paper.

In addition to the project objective which requires use of a printed circuit board (PCB) the MSP430 chip will need to be mounted to the PCB and linked to its power supply, ground, inputs and outputs. Several websites which offer manufacturing services of PCB’s were compared in the relevant technologies section. Of those the one which best fits the need of this project comes from 4pcb.com. The value of the student special offered by 4pcb.com goes above and beyond what is offered by competitors. The most attractive part is that there is no minimum quantity order so there will be no waste from having to order extra, unnecessary boards. Also 4pcb.com seems to have an understanding that students will need extra assistance while designing their first PCB’s, this shows with their complementary CAD software for designing the PCB and the free error checking design report. It is these additional features which lend to the favoritism to purchase from 4pcb.com.

Now that each component for the solar tracking system has been selected it is clearer to provide a block diagram of how the system will operate.

Sunlight Array of four LED’s

MSP430 Actuator/Motor

Figure 38:Block diagram of the solar tracking system with finalized component selections indicated

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The best Stirling cycle engine to use for this project will be the one available from GreenPowerScience. This is the best option because it is already proven to work in the exact environment it will be used in. The incredible temperatures produced by the Fresnel lens could easily damage a Stirling engine that is not built to withstand these conditions. Additionally the engine found on Ebay is a bit large for the scale of this project and could push the whole system to go over the weight limit listed in the technical objectives. A second disadvantage for relying on purchasing a part from Ebay is that even though there appears to be a trend of this type of engine always being available it is not guaranteed to remain that way. Thus GreenPowerScience is a more reliable source to go with. Further the system from GreenPowerScience is a better financial option as it cost half as much as the Stirling cycle engine that was found on Ebay.

MSP430 Family of devices The MSP430 was chosen for a variety of reasons. Firstly, using any microcontroller allows for adjustments to be made to the control system much easier than using static components. Also, and more importantly, this family of devices also has many low power modes that can be utilized during periods where motor control and signal sampling are not needed. This will use much less power than a circuit that is constantly running or some other microcontroller that does not have these special lower power modes. The microcontroller can switch to active mode, perform necessary operations, and then go back into the lower power mode; lowering energy needs of the control system tremendously.

The MSP430 has a large number of different configurations, over 200. With the large number of options available it will be necessary to determine which one will work best. All versions of the MSP430 are considered low voltage. They can all operate in a variety of low power modes depending on the model. The different models vary based on the size of memory, CPU speeds, the number of input and output pins, power usage, and a variety of other parameters. Each character describes a parameter of this MCU. Since this application of a microcontroller could be accomplished with almost any commercial controller the selection criteria should revolve around using the most stripped down version that will accomplish this project’s control needs.

First one of the most versatile families of the MSP430s was examined; the MSP430X2XX. These are 16-bit low power microcontrollers and operate on 1.8 to 3.6V. These controllers and the development hardware (called “Launch Pad”) are readily available. Launch Pad will play a pivotal part in the prototyping and testing of software and interfacing various subsystems with the controller. Using Launch Pad the MSP430 can be programmed, registers can be monitored real time using emulation software, and interfaces with the numerous I/O ports and LEDs already found on the board. To interface Launch pad with the MSP430 TI’s Code Composer Studio will be used. However, there are still over 40 devices

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within this 2xx family. It was decided that a general purpose configuration would be used for prototyping and testing (the MSP430G2231 has already been obtained) and a specific MCU would be chosen later based on other needs of the project. This is easily done because despite the numerous configurations of this family any code written on one will be compatible with any of the others. The table below shows all MSP430s compatible with the launch pad development board with versions not supporting analog to digital conversion omitted.

Table 11: Pricing, number of pins, and memory of different MSP430s

MSP430 Value Line Device Program (kB) SRAM (B) I/O ADC Ch/Res 1kU Price

MSP430G2131 1 128 10 8ch/ADC10 $0.49

MSP430G2231 2 128 10 8ch/ADC10 $0.52

MSP430G2112 1 256 16 Slope $0.49

MSP430G2212 2 256 16 Slope $0.55

MSP430G2312 4 256 16 Slope $0.60

MSP430G2412 8 256 16 Slope $0.65

MSP430G2132 1 256 16 8ch/ADC10 $0.55

MSP430G2232 2 256 16 8ch/ADC10 $0.55

MSP430G2332 4 256 16 8ch/ADC10 $0.60

MSP430G2432 8 256 16 8ch/ADC10 $0.70

MSP430G2152 1 256 16 8ch/ADC10 $0.55

MSP430G2252 2 256 16 8ch/ADC10 $0.60

MSP430G2352 4 256 16 8ch/ADC10 $0.65

MSP430G2452 8 256 16 8ch/ADC10 $0.70

MSP430G2153 1 256 24 8ch/ADC10 $0.65

MSP430G2233 2 256 24 8ch/ADC10 $0.65

MSP430G2253 2 256 24 8ch/ADC10 $0.65

MSP430G2333 4 256 24 8ch/ADC10 $0.70

MSP430G2353 4 256 24 8ch/ADC10 $0.75

MSP430G2433 8 512 24 8ch/ADC10 $0.80

http://focus.ti.com/docs/prod/folders/print/MSP430G2131.html




















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MSP430G2453 8 512 24 8ch/ADC10 $0.80

MSP430G2533 16 512 24 8ch/ADC10 $0.90

MSP430G2553 16 512 24 8ch/ADC10 $0.95

The next MSP430 under consideration was the MSP430L092 because it is the lowest power MCU in the MSP430 family of devices. This MCU only requires a .9V source to operate. There is no other microcontroller that can run on this low of a voltage. Keeping with the overall goal of power generation this microcontroller would be the best choice. The MSP430L092 comes in a package with fourteen pins, and eleven of which are input/output pins. The controller is capable of both digital to analog and analog to digital conversions (both with an eight bit resolution). Upon researching the part’s availability it was determined that it would not be a viable option. The controller IC itself is readily available however; the development board (MSP-FET430U092) was initially unobtainable. As of early December 2011 this development board and a USB programmer have become available. This complicates research conducted while this controller was not considered a viable option. This controller may become the ones used in the final construction of the device if, and only if, it can be accomplished with little alteration to other systems designed using the MSP430x2xx.

Code Composer Studio The interactive development environment that will be used to program and debug the microcontroller will be Texas Instruments’ Code Composer Studio. This IDE is based off of Eclipse’s open source framework. This studio supports all embedded processors. It has a C/C++ based compiler environment as well as support for editing assembly code. It also has support for a debugger and emulation tools. The software has already been obtained and several preliminary tests have been completed on it using the Launch Pad interface in conjunction with the MSP430G2231.

Power modes The MSP430X2XX family and the MSP430L092 have six different operating modes. First, there is the active mode which has all clocks and the CPU on. Next there are the five low power modes (LPMx) in which the CPU is off and different combinations of clocks and oscillators are on and off. LPM 0 -2 could have been used for this project but each one has extra components turned on that will not be used for a simple timer. The remaining mode LPM4 is even lower power than LPM3 because it has all clocks and oscillators off. This mode requires an external signal to be the interrupt that will “wake up” the MSP430 to enter active




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mode. Because the project requires only a definite delay between samples LMP3 works the best. Below is a table showing the differences between the modes.

Table 12: Explanation of different low power modes

Mode CPU Mclock SMclock Aux. Clock

Oscillators

Active Active Active Active Active Active

LMP0 Off Off Active Active Active

LMP1 Off Off Active Active Active (for LF oscillator and CLKIN as source, HF oscillator is mapped to LF

oscillator as source)

LMP2 Off Off Off Active Active

LMP3 Off Off Off Active Active (for LF oscillator and CLKIN as source, HF oscillator is mapped to LF

oscillator as source)

LMP4 Off Off Off Off Off

Due to the fact that the sun moves slow enough that constant adjustment isn’t necessary, the system will only be checked at certain intervals and decide if an adjustment must be made. A clock within the MSP430 will be used to determine when this time period has elapsed. Only one clock is needed in this implementation and this permits a low power mode to be used instead of the full active mode. The low power mode that will be used is LMP3 (low power mode 3). This power mode disables the CPU and all other clocks except the Auxiliary clock within the microcontroller.

Control Procedure The controller will wait in low power mode 3 until the timer interrupt has occurred. Once the interrupt is received, the MSP430 will go into active mode, where all clocks and the CPU are active. In this active mode the control routine will be completed. This control routine consists of a loop that has three steps. First, a

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sample and hold of the analog inputs from the sensor array, an adjustment to the position of the lens via motor movement, and lastly another sample to ensure the correct positioning has been achieved. Should correct the correct position not be achieved; the loop will repeat itself. Upon completion of the loop the MSP430 will then return to the low power mode 3 and wait another delay period before sampling sensor data again. This low power mode to active mode rotation will continue until the break condition is encountered. This condition is that the battery has been fully charged, though this will only be checked during the active mode. The following flowchart depicts this loop

.

Wake up to Active Mode

Sample Sensor Data

CPU Decision

Switch to LMP3

Delay CycleAdjust Position

Figure 39: Code flow diagram

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Fresnel Lens Possibilities Table 13: Available lenses capable of achieving 500 degrees Fahrenheit From greenpowerscience.com

To determine the ideal lens a number of lenses are compared in the table above. The size and power output must be maximized while keeping the weight and cost to a minimum. A basic analysis can be made by dividing the average temperatures by the cost including shipping and handling. The spot Fresnel lenses stand out immediately as being the most cost effective as well as the lightest. When the temperature is compared to the surface area the quality, and therefore reflectiveness, of the lenses can be estimated. It is apparent that the circular glass lenses have the highest quality and reflect the least light. The spot lenses have the second best quality, with the linear lenses having the lowest quality. Using glass lenses would maximize the efficiency of the output, but at the cost of supporting a much heavier load. Glass lenses would also last much longer during continuous operation than the acrylic Fresnel lenses without suffering any degradation of quality. They also produce a much cleaner focal point because they are a continuous surface. This projects a nearly perfect circle of light, unlike the Fresnel lenses which produce more of an oblique rectangle. The clarity of the glass lenses would ensure that more of the focal region falls on the heating point of the Stirling cycle. The shipping and handling of the glass lenses is also less expensive than the other varieties because they occupy a smaller area, despite weighing more. The larger lenses must be carefully packaged to avoid damage during the shipping process so they cost more to package. Although the surface is susceptible to scratches that would cause increased reflections, the acrylic Fresnel lenses are far softer than glass and so are more likely to get scratched. Fixing scratches on the glass lenses would be as easy as

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applying the right epoxy to the surface to fill in the removed material. The glass lenses may have the highest quality, but they are undesirable because of their limited availability in large sizes, and therefore power output. The weight listed for them does not include a wooden mounting frame, whereas the linear or spot lenses come with wooden frames. It can be seen that the glass lenses alone weigh about as much as the other lenses do with their wooden frames included. The linear lenses are significantly less expensive than the other options, seeing as how the most expensive one is less expensive than the smallest spot based lenses. They have much lower temperature ranges due to the wider distribution of the focal area. This makes them ideal for heating tubing uniformly and safely in applications such as steam engines. In the event that a Stirling cycle cannot be obtained at a reasonable price and with the desired power output, a steam based engine could be considered. In that case a linear lens would be optimal for boiling water to operate the engine. Such a steam engine requires a water supply which will add to operating cost and decrease safety if complications in providing a constant water supply arose. The spot lenses have the highest temperature to price ratio, and concentrate the majority of the light into a spot four tenths an inch in radius. The tight focal region of these lenses makes them ideal for heating a Stirling cycle engine because the heating point is not very large. Using glass lenses could accomplish a similar focal region, but the expensive nature of precision milled and polished glass combined with the increased load makes them non-ideal in this application. Although the glass lenses have a higher quality, their limitations in size would limit the potential power output while increasing the power consumed by the control system. The 40 inch by 28 inch spot lens was ultimately selected for the project because it had the second highest temperature to price ratio and second to least weight. It also had one of the higher temperatures to surface area ratios. The low weight and high temperature output makes it the most desirable to use in the project. The physical dimensions are not overly excessive, and the necessary support mechanism should exceed the specification for the maximum surface area occupied.

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Figure 40: Spectral transmission for .25 inch optical acrylic Fresnel lenses. Permission pending

The average peak intensity of sunlight in Florida is around one kilowatt per square meter. The lens considered measures .7112 by 1.016 meters with an area of .723 square meters. This yields a theoretical maximum of 723 watts. The actual power will be less due to light reflecting off the lens. The figure on the page above illustrates the transmission efficiency of Optical Acrylic Fresnel lenses and indicates that on average ninety percent of the light between 400 and 1100 nanometer wavelengths is transmitted. An average of eighty percent of light between 1100 and 1700 nanometers is transmitted through the lens. Taking that into consideration, the expected peak power output from the lens would be no more than .550 kilowatts. It should be noted that up to sixty percent of ultraviolet radiation is transmitted as well.

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Linear Actuators Table 14: Available linear actuators with forces over 100 lbs and stroke lengths

greater than six inches

Linear Actuators

stroke in

closed in

open in

push lbs

static lbs

price $

max I amps

closed/ stroke

FA-240-S-12-6

6 10.5 16.5 200 200 119 5 1.750

FA-200-L-12-8

8 14.88 22.88 200 200 119 3 1.860

FA-PO-150-12-8

8 13.9 21.9 150 300 138 3 1.738

FA-240-S-12-9

9 13.5 22.5 200 200 119 5 1.500

PA-02-9-400

9 15.89 24.89 200 400 129 4.5 1.766

FA-05-12-9 9 17.5 26.5 150 150 129 3 1.944

FA-240-S-12-12

12 16.5 28.5 200 200 119 5 1.375

To determine the optimal linear actuator to use the most important factor is reliability of support. Actuators with a static force of less than one hundred pounds were not considered because they might potentially fail under high stress situations. Actuators meant to sustain loads above five hundred pounds were also not considered because they far exceed the possible load requirements. Twelve Volt actuators were selected to match the voltage of the batteries and the above table was produced by searching for actuators within those criteria. Surprisingly the prices for many different size actuators are very similar, so the size of the components should only be decided considering the physical requirements of the system, rather than by cost. One feature that noticeably inflates the cost is a potentiometer positional feedback system. Although such a feedback system would be useful for controlling the position of the lens assembly it would add to the cost unnecessarily. Most of the actuators have built in limiting switches that do not allow them to be extended or contracted beyond their capabilities. The integrated potentiometer would facilitate the process of determining when the system has reached the end of its operating capacity for the day, which would be beneficial.

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To provide the maximum amount of force in the desired direction of motion, a midpoint of the lens support arms were selected as the interface point. To minimize the horizontal stress forces on the actuator’s bracket it must be attached to the pedestal fairly close to the axis of rotation. To meet these requirements an eight or nine inch stroke actuator fits the best. The closed length of the actuator determines the lowest possible angle of inclination of the lens assembly. However, a certain minimum length is required to fully extend the lens assembly to the ninety degree position. In order to achieve the full range of motion it is desirable for the actuator to have the lowest closed length to stroke length ratio. The FA-240-S-12-9 actuator is the most ideal because it’s closed to stroke length ratio is the lowest of the similarly sized actuators available. Although it draws more current at a full load than the other actuators this factor is not critical as the load applied will be significantly less than the maximum capacity. The current will likely be less than three amps by examining the actuator current curves located in the appendix. The average adjustment necessary is very small as well so the time it will be operating is nearly impulsive. The infrequent and minimal duration of adjustments means the actual power consumption will be very low. This actuator will provide the optimal support for the lens assembly when bracketed down eleven inches from the central axis of rotation. Stepper Motors The torque of the stepper motor is the most important factor for determining which one to use. The physical sizes are necessary to take into consideration, but as long as the motors are not longer than the height of the pedestal they should fit. The amount of current being drawn is worth taking into consideration but not of critical importance due to the small number of steps required for the average adjustment. The weight should be kept to a minimum to reduce the stress on the main support. The shaft diameter affects the gears required but is not of critical importance to the selection of components. Other factors not listed but still considered are the length of the shaft and the required voltage. Every motor listed runs at 12 volts or less

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Table 15: Available stepper motors with high torque and low weight

Stepper motors

Torque oz-in

Current amps

Price $

Weight lbs

Torque/ Price

Torque/ Weight

Shaft radius

HT23-180-8

180 2 29.95 1.54 6.010 116.88 .125

HT23-260-4

260 2.5 39.95 2.31 6.508 112.55 .125

HT23-280-8

280 4.2 49.95 2.2 5.606 127.27 .125

85BYGH 450A-08

582 3 48.95 3.2 11.887 181.83 .188

57BYG H405A

277 3 22.5 2.926 12.311 94.66 .158

57BYG H303

208 2.3 19.95 1.43 10.426 145.45 .125

11YPG1 02S-LW4

705 0.67 93 0.213 7.581 3300 .063

TGM25-075-26

55.5 0.467 35 0.045 1.586 1221 .58

By comparing the torque to the weight of the motors it is possible to obtain an idea of their relative power density of the different motors. This is important to consider, as the maximum torque for the minimum weight is ideal because the motor will be weighing down the system increasing the coefficient of friction and the required torque to overcome it. The accuracy of a stepper motor also is dependent on the load which it must move. If the weight is too high or the torque is too low the motor can lose steps, reducing the accuracy of the control system. Since the weight of the pedestal and assembly will be relatively large in comparison to the whole system, it is critical that the motor has sufficient torque to never misstep. High torque is also required to maintain stability in the presence of environmental factors because the motor is the only thing preventing the pedestal from rotating.

The HT23 series stepper motors are attractive because of their low power consumption, low weight, and fairly low cost. The 11YPG has an integrated gearbox which allows the torque to be increased to 705 ounce-inches and has a potential maximum of 2116 ounce-inches. This far exceeds the required applied torque to the system and is too expensive to realistically consider. The TGM25

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motor is extremely light weight and draws a very low amount of current making it very attractive for the design. The low amount of torque it provides limits its utility however and gives it the worst price to torque ratio. The BYGH series stands out for having the highest torque to price ratio by far. They also have some of the highest torque to weight ratios next to the 11YPG and TGM25 motors. Although the BYGH series consumes much more power than the two previously mentioned, the high torque and low price make the series ideal for this project. The 85BYGH450A-08 provides the most torque for the lowest cost, and despite the fact that it weighs the most it is the optimal stepper motor to use in the design. The motor is 2.2 inches wide and 2.98 inches tall with an axle length of 1.45 inches. The size of this is ideally situated for interacting with the lower axle assembly which is two inches below the mounting point on the pedestal.

Mounting Options Table 16: A small sample of large diameter needle, ball, and mounted bearings,

incomplete due to unavailable info

Type Outer dia

Inner dia

width weight Static load

Dynamic load

price

needle 1.5 1 1.181 0.26 2730 1428 9.95

1.5 1.142 1.181 0.2 2730 1428 9.95

2.06 1.5 1.25 0.437 14300 7100 17.34

ball 2 1 9300 17.97

2.25 1 11300 25.42

1.5 0.5 0.567 0.25 1900 830 31.15

1.5 0.63 0.44 0.151 11.21

mount na 1.378 1.748 3.53 5777 3462 14.95

na 1 2.2 3147 1764 18.1

na 1.5 1.031 4.37 6542 4001 39.06

In order to facilitate the horizontal rotation of the pedestal a bearing must be employed inside of the axle housing. There are a large variety of bearings available for industrial applications that far exceed the requirements for this

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project. The three main types of bearings considered are standard ball bearings found in skateboard wheels, needle or cylindrical roller bearings that are used in automotive applications, and square based mounted bearings.

The most important factors for determining the appropriate bearing is the physical size and the load capacity. Obviously the bearing has to fit the axle assembly correctly or else it fails to accomplish its objective of facilitating rotary motion. A small sample of available large diameter bearings was selected to populate the above table. Ball bearings consist of two small metal rings that have smaller metal spheres between them and grease sealed in by plastic or rubber typically. The number of different ball bearings available is staggering, and they are by far the most common bearings on the market. Their applications range from toys to heavy duty machinery. Cylindrical rollers have an outer ring with very thin metal cylinders embedded within it that contact the inner ring and allow it to rotate freely. Cylindrical roller bearings are capable of handling much higher loads than traditional ball bearings, but at a more expensive in price. They can also rotate at much faster speeds, typically operating safely at thousands of RPM. The 2.06x1.5 inch bearing would be ideal for implementation in the current design for the axle assembly.

The loads associated with supporting the rotating pedestal in the project are rather small, less than 100 lbs, so ball bearings could be used effectively. In the prior two cases a custom mounting configuration needs to be designed to interact with the axles. They are typically more expensive than ball bearings, but ball bearings of this size defy that generalization.

Figure 41: Square mounted UCF208 bearing permission pending (Dimensions: 5 1/8” x 5 1/8” for the square outer bracket)

The third type of bearings available come pre-mounted in a housing that has screw holes already bored through and can be seen in the image above. Mounted bearings such as these are commonly used in industrial applications like large roller drums or cam shafts. These would be the easiest to integrate into

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the design, as they require the least amount of assembly and custom machining. Should difficulties be encountered in obtaining the custom milled axle housing modeled, this type of bearing would be the most useful for redesigning the main support system.

The bearing considered is the 1.5 inch inner diameter square mounted bearing, which is the most expensive as well as the heaviest bearing in the selection. A 1.5 inch steel rod could be inserted into the bore and the tension screws on the side tightened to provide the main axle. The bearing would be mounted on the pedestal upside down. In this case the weight of the bearing does not negatively affect performance, as the added mass will only aid in keeping the system secure.

System Prototyping of light sensing array

Table 17: List of materials needed for building the LED sensor array

Item Quantity Needed Cost

Bright red LED 4 1.60

½” Balsa wood 3”x3” 2.00

¼” Balsa wood 2 3”x3” 4.00

Hot glue 1 Stick Acquired

Electrical Wire 4 4’ 16 gauge 10.00

The solar sensor array will be built by first taking the half inch thick piece of balsa wood to be used as the base and drilling holes into it for where the LED’s will be placed. It is important to do this step first as it will be difficult to drill into the baseboard later in the procedure. The holes to be drilled will need to be slightly slimmer than the width of an LED, typically about .4 inches. The holes are to be drilled in each of the four corners of the board exactly .75 inches perpendicularly from the two closest walls. It is very important that the LED’s all be placed in the exact same manner as to guarantee symmetry and make it simpler for the system to interpret the signals from each LED. The next step for the array assembly will be to take the half inch base piece of balsa wood and precisely hot glue the two quarter inch thick pieces of balsa wood to the base such that the angles between each of the pieces of quarter inch wood are exactly 90 degrees from one another and also that each quarter inch piece is placed exactly 90 degrees to the half inch base. Notice it will be necessary to trim the center of each of the quarter inch thick pieces so that they will properly fit together. Next the LEDs will need to be set into the base piece. This will be accomplished by

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pushing the LEDs through the predrilled holes such that the terminal wires are no longer visible. The LEDs will then be hot glued into place, while doing this it is obviously important that the hot glue in no way will block light from reaching the LEDs. It is also important to make certain that all of the LEDs are placed into the wood perpendicularly and that they each protrude out of the base board the same amount. The final product will look like the Solidworks model of the sensor array seen below in figure 42.

Circuitry going to the MSP430

For the solar tracking system to successfully track the sun for a whole day the sensor array will need to communicate with the selected MSP430. The expected output voltage of the LED’s in high light is between 1.3 Volts and 1.5 Volts. In low light or when shaded by the tracking fixture the output voltage is expected to be between 0 Volts and .05 Volts. The LED’s will communicate with the MSP-430 microcontroller by inputting to the input pin their voltage which corresponds to the amount of light being seen by the LED. The MSP430 will be mounted on the base of the entire system so a set of four wires will need to run from the negative terminal of each LED, along the Fresnel lens support arm, and to the MSP430.

24 Volt DC Generator The Generator to be used for the project is the Wind Stream Power 443540 Permanent Magnet 24 Volt DC Generator. This generator costs $149.00. The reason for choosing this over the others is because of its heavily saturated magnets and 12-slot armature. It is also the only company that has a

Figure 42: Solid works model of LED sensor array

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performance graph that compares its RPM to the open circuit voltage, short circuit current, and the overall power. Also, at about 400 RPM it can output at least 20 Volts DC, which is what is required by the system. The other generator that was considered didn't state the magnet types and also didn't produce as much short circuit current as this one, and the way to secure it wasn't as flexible as the generator that will be used. The Wind Stream Power 443540 PM 24 Volt DC Generator is overall the better choice and can be strapped down with a belt or also by four screws on the front, back, or both sides.

Figure 43: Dimensions of the 24VDC Generator; Permission pending

12 Volt output voltage regulator The voltage regulator that will be used is the Current Logic AD2016. This voltage regulator has the perfect voltage input range that will be needed for the system (16~40 Volts DC) and is less that 1.6 Amperes. The output can be varied all the way from 1 to 12 Volts DC. It also has a very low no load current at 10 milliAmperes and is very efficient at about 90%. This is also the only one out of the three voltage regulators that had a shut down for over current protection. Also, the price of the other available regulators is very high compared to the price of the AD2016 despite performing similarly. The other options were priced at $125.00 and $144.76 which is excessive compared to $19.00.

12 Volt AGM Battery For the 12 Volt batteries that will be needed for the system is the Leoch LP12-6-F1. These will be used for the system because of their overall greater power output. Almost all the 12 Volt AGM batteries that were researched were about the same. The size of the terminals varies from battery to battery but is not a major design consideration. The battery from Leoch has a higher power output rating of 72 Watt-hours compared to alternatives which only have 60 Watt-hours. The price is slightly higher than the rest but only by a few dollars which is worth the performance. It has a wide temperature operating range and is maintenance free. The Leoch LP12-6-F1 also has a one year warranty, long service life, and a deep

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discharge recovery.

12 Volt charging controller The ideal charging controller would be the Harger controller, because it has everything that is needed and it also has a lot of protective circuits. It has a very good four stage algorithm for charging a 12 Volt battery, but most of all it has indicator lights stating the status of the battery and charging built into it. It has two red LEDs, a yellow LED, and a green LED. With all these LEDs combined it is capable of displaying what stage of charge it's in, when the battery is full, when the battery has a low or high voltage danger, when there is a low input or output voltage, and an over temperature alarm. The only reason why this controller wasn't chosen is because it costs $154.00 plus a required cable to interface it with; the cost is not justified by the performance advantages. Therefore the cheaper alternative was chosen. The Atkinson PVCM10 acts sufficiently as the charging controller for the design. This one only costs $43.22 and only consumes 35 milliAmperes during charging. The last option was also a good choice but was way too expensive to consider at $249.00.

Wires

Out of all the wires that were researched the best ones can be found at the local hardware store and can be cut to the specific size that is needed. The ones that will be used are the Cerrowire 207-3402R17. These wires come in multiple sizes and compared to some other wires have a high temperature resistance. They are of the stranded wire type and are highly flexible and easy to work with. This particular model comes in white and is 14 gauge and 17 feet long, which is sufficient. They also carry every other color that will be needed for the same price at $4.69. The system will require buying them in white, red, and green. With the price of the three wires combined, the total price comes out to $14.07.

Miscellaneous Supplies Everything else that is required for the project can be found at the local hardware store. The 12 Volt AGM batteries that were chosen use an F1 terminal connector. These connectors can be bought from the local hardware store for fairly cheap. Also for the protection of the circuit there are very cheap series fuses that can also be bought from the local hardware store to be implemented in the system. There are also other types of protective circuit devices like breakers that can be bought from the local hardware store. The protection for the devices in the circuit is very important so one of these protective devices will be acquired. Most likely it is going to be the fuse because at such low amperage there aren't many breakers available. Other things required for the project such as wiring, nuts, and/or terminals can also be found at the local hardware store. These will be required in order to connect all of the wires together and the ground to a common node. Electrical tape will also be needed to wrap the wire nuts and to organize

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the wires to prevent them from relocating during operation.

Coupler From comparing and contrasting all of the different couplers, the last one to be analyzed is produced by Eldon James. The item #64282 was selected for the design. The first coupler was about the same and had a very similar rating. In fact, it is made by the same manufacturer, but the pricing on the first one was more expensive for practically the same thing. The one selected appears to fit the engine interface better. The second one was constructed out of silicon and although it has a very high resistance to heat the material that it is made out of makes it very likely to slip.

The third of the couplers was made out of heavy duty nylon and can withstand a temperature of 275 degrees Fahrenheit. This one comes with 10 units per pack and has a female jack. It initially believed that it would be able to screw onto the Stirling engine fly wheel, but upon further investigation it was realized to be impossible. The reduction coupler that was chosen is only 33 cents and withstands temperatures up to 275 degrees Fahrenheit, and can be fit to the axle using hose clamps in the event that it does not fit perfectly.

Motor Types The electric motor to be used in the projected will be one of the most important components in the design. There are electric motors that work on alternating current or direct current. An electric motor can be run in reverse in order, meaning its axle is manually rotated to generate electricity. An AC motor works with alternating current by producing a rotating magnetic field. Most widely used AC motors are made with inductors and usually don’t have permanent magnets as most as DC motors do.

There are quite a few AC motors that work by different methods. All AC motors utilize a polyphase system. There is the synchronous electric motor that is an AC motor which utilizes a spinning rotor with coils passing magnets at the same rate as the alternating current and resulting magnetic field which drives it. The term used for this type of motor is zero slip under usual operating conditions. Compared to the induction motor which uses slip to produce torque. The induction motor is one of the most widely used motors in the world today. This type of motor is an asynchronous AC motor that transfers power to the rotor by electromagnetic induction. This type of motor is sometimes thought of as a rotating transformer because it uses a primary and secondary side, also known as the stator part and the rotor part.

There are two types of induction motors, one called a squirrel-cage motor and another called a wound-rotor motor. The squirrel-cage motor has a heavy winding made up of solid bars of aluminum or copper. The shape of this motor’s bars is what determines the torque and speed characteristics. The wound-rotor

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motor consists of many turns of insulated wire in the rotor creating a coil. This is then connected to slip rings on the motor shaft. Both of these motors can have their speeds altered through an externally attached resistance controller. The good thing about the wound-rotor motor is that it is very good for starting a load that has a high inertia. The speed of this motor is directly proportional to the load torque required. This type of motor can also have variable speeds due to the resistors in the slip ring starter.

Finally, the last of the AC motors worth considering is the torque motor. This is a special type of induction motor which is capable of withstanding a load which totally stops it while not having any damage dealt to it. This type of motor applies a steady torque to the load, and is usually used with an electronic sub system attached to it that controls the current flow to it. One of the best things about this motor is that it eliminates a need for gears or clutches due to the control system and ability to withstand unlimited amounts of torque.

As for the DC motors, they seem like the better choice to be used for the power generation of the project. The type of DC motor that is most interesting is the permanent-magnet motor. These types of motors have permanent magnets on the stator or rotor and are widely used to generate electricity. The good thing about this is that there is not as much heat lost to the coils of the wires and the amount of energy created is related to the speed of the spinning rotor. There is the possibility of having a brushless DC motor or a brushed DC motor. These types of DC motors can have a wound or permanent magnet stator. The main difference is that in a brushed DC motor there is an armature with a split ring commutator which can change DC to AC or vice versa.

The bad thing about the brushed DC motor is that it actually uses brushes to extract the electrical energy generated. This creates a lot of unnecessary friction and also can have sparks at the interaction between the brushes and commutator. Also, the brushed DC motor requires maintenance in order to keep it working well. After a while the brushes get worn out and have to be replaced. This is bad, especially with this system and the heat that will be around it will cause the brushes to wear out even faster. There is also a lot of electrical noise associated with this type of DC motor which is undesired for this system. The brushless DC motor looks like a good candidate and is probably what will be used for the final design. This motor has eliminated the need for brushes and commutators with an electronic system. The efficiency of the DC brushless motor is somewhere between 85-90%. This is very good and provides a good supply of power to the system without excessive losses. Without the need of brushes and a commutator the life of this motor is greatly increased. Also, the chance of sparks and noise into the system is eliminated because of the elimination of friction. This is what is needed for good constant electricity into the system but are very expensive and not used as much in a smaller scale, so it was decided to use the brushed version.

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Initial Design Draft The system can be divided into three main sections: the base, pedestal, and lens assembly. The base provides all the support for the pedestal with the main axle and laterally spaced rollers. The pedestal can revolve about the axle and contains the engine, generator, actuator, battery, and supports for the lens assembly. The lens assembly can rotate about its supports and contains the sensor array for positioning feedback.

The base was designed as a solid circular platform, a quarter inch thick, with angled sections cut away to minimize the required materials while maintaining sufficient support. The radius of the base plate is two and a half feet and the struts are six inches thick. The main support consists of an upper and lower axle housing measuring four inches in height and four inches in diameter when the two pieces are joined.

The lower portion of axle housing is connected to the center of the baseplate, along with four roller support columns and the housing for the rotary motor. The upper portion of the main support interlocks with the lower and seals the bearing in, limiting contamination and evaporation of lubricant. The assembled baseplate design can be seen in the figure below with the top portion of the axle housing in place.

Figure 44: Preliminary Base Plate with rollers, motor, and upper and lower main support columns merged.

Although the main support bears most of the load, the smaller rollers offer a critical counter-torsional support. The rotational inertia of the system varies with the positioning of the lens assembly. The radially spaced wheels add enough support to ensure robustness during normal operations, and especially in the presence of unpredictable natural forces. Rubber skateboard wheels with metal ball bearings will act sufficiently as rollers because their design specifications demand reliability in handling sustained loads and intense impulses much greater than the weight of the assembly. The wheels are one inch in diameter and their supports are three and three fourths inches tall. A hole is drilled a quarter inch from the top, allowing the wheels to make constant contact with the underside of the pedestal.

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A stepping motor with a gear affixed to it provides all of the horizontal force for the system to rotate. The motor is located at the edge of the base plate to achieve a high torque on the system. The height of the motor with gear attached must be equal to or less than four inches to interact with the edge of the pedestal. If the motor is too short then it can be elevated to the correct height by its supporting architecture. The wiring for the motor runs along the base to the center and wraps around the lower axle before ascending through a bore hole in the upper platform. So long as the pedestal never experiences more than one complete revolution this configuration should not cause any complications.

The pedestal is fabricated out of a cylindrical plate and contains most of the project’s components. The battery, control box, Stirling cycle, generator, and lens assembly supports are all bolted down to the surface. The entire perimeter is geared to provide the most efficient interaction with the motor for rotating the assembly. Bore holes are drilled to fasten the actuators brackets to the pedestal, as well as the other main components. The bare pedestal is shown in the figure below.

Figure 45: Pedestal with gearing cut, actuator bracket holes drilled, and lens assembly supports welded into place with axle holes drilled.

Attaching the lens assembly directly to the pedestal would cause the focal point of lens to fall onto the platform itself rather than on the hot point of the Stirling engine. Elongating the lens support arms would cause the focal point to shift dramatically during the course of the day so it is not a viable option. To make room for the engine on the platform, the interface with the lens assembly must be raised up on supports, rather than fixed directly to the platform. This elevates the axis of rotation while keeping the focal point stationary, providing enough room to accommodate the Stirling engine and generator. The most efficient method for attaching the lens assembly to the supports would be a simple pin and latch. The lens assembly supports are solid metal blocks one foot tall and are welded into

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place after drilling out the axle holes and rounding the tops. The upper portion of the axle housing is welded to the bottom of the platform in the center.

The lens is housed in a wooden frame one inch thick which connects to six support arms. The arms are screwed into the frame, three on each side, and converge to a central bracket. The bracket is pinned to two supporting arms on the pedestal and is free to rotate. The two central support arms are twenty seven inches long while the outer four arms are thirty and a half inches long. The support arms are welded to the latch on each side and have holes drilled to interface with the actuator arm. The extended end simply pins to the lens support arms to provide the necessary force. Drilling multiple sets of holes allows for adjustments to be made later if testing indicates the current support mechanism is insufficient and also allows wiring to traverse the tube, reducing the need for adhesive.

The actuators interface with a simple bracket that’s bolted to the support arms. The optical sensor array is affixed to a corner of the top of the frame near one of the support arms with permanent adhesive and the wiring runs through the hollow tubing. The lens assembly can be viewed in the figure below which illustrates the fully assembled system set at the maximum angle of inclination. The actuators used in this model are nine inch stroke with a closed length of fourteen inches and are located four inches from the edge of the pivot support arms. They can support up to two hundred pounds each which is far more than necessary to maintain stability.

Figure 46: Fully assembled system at maximum vertical angle

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The battery and control box are located at a far end and the Stirling cycle engine is located directly in the center as shown in the image above. Having the battery and control box located at the far end keeps the circuitry out of the intense beam of light and safe from overheating. Locating the battery on the opposite side of the lens assembly will counteract some of the applied torque from the extended lens and help maintain stability. To provide an additional layer of protection an insulating cover could be designed to shield the sensitive components from expose to intense concentrations of light.

The generating motor is not shown but would couple directly with the engines flywheel and have connecting wires to the battery and control box. The generator would be bracketed down to the pedestal right next to the Stirling cycle so a common axle could connect them, but far enough away that it would not be susceptible to thermal damage from light scattered by the Stirling cycle.

Figure 47: Bare system at lowest vertical angle achievable.

The figure above shows the lens at its lowest possible position with the actuators fully contracted. It can be seen that the actuator limits the minimum angle but still allows the system to track the sun during its peak intensity. Locating the actuator further away from the central supports is not possible due to the circular configuration of the pedestal, and adjusting the interaction point with the lens assembly arms would further limit the range of motion in either way.

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Final Design Draft Upon considering the fabrication challenges associated with the initial design it became apparent that significant alterations needed to occur to meet the requirements. The most immediately obvious design flaws are the large circular sheets of metal. For adequate structural support a minimum thickness of one quarter inch was selected for the platform and base. Sheets of metal that thick and large are not widely available and are excessively expensive. Additionally, a large amount of time and effort would be spent cutting out the circular sections. Metal plates six inches wide are commercially available for relatively low prices so the system was redesigned to utilize them. Constructing the pedestal and base out of these pieces significantly reduces the cost and weight of the system compared to cutting circles out of a solid square sheet. The redesigned layout of the baseplate consists of a central four foot long plate with two twenty one inch plates welded perpendicularly to the center so that the system is symmetrical for uniform support. The effective area is then 16 square feet, or 1.448 square meters, which is well within the specified area of two square meters.

Figure 48 Aerial view of redesigned system, actuator fully extended.

The new layout of the pedestal system is similar to baseplate in that it is comprised of multiple pieces of the same metal plating in a similar configuration reduced in size by two inches on each side. Pairs of mounting holes are drilled

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two inches apart along the length of one side to bracket the actuator to. The figure above illustrates the new configuration of the baseplate and pedestal with the lens assembly fully extended. Originally a height of twelve inches was selected for the height of the lens assembly supports. It was determined that this was too tall because interfacing the required actuator length was excessive. By reducing the height of the lens assembly supports to six inches, a shorter actuator could be used.

The pedestal was redesigned with a one inch wide ring located fifteen inches from the center. This ring allows the pedestal to constantly make contact with the roller support system. If there are challenges associated with fabricating the four circular arcs of metal required for the support ring, or the price of custom ordering the cuts is too great, then the torsional support system needs to be redesigned.

An alternative to the currently employed method could be a system of wheels that are attached to the pedestal itself rather than the base. The four current wheel supports could be inverted and bolted to the four struts comprising the pedestal at the same distance the previous system used. The baseplate would then need to be a flat and continuously smooth surface to allow the rollers to make constant contact with it. Spring based suspension could also be used on the new roller support mechanism to allow for operations on uneven terrain.

The elevation control mechanism was also improperly designed initially, as it did not allow for a full range of motion of the lens assembly. Due to the restriction of the actuator’s closed length, the lens assembly could not achieve angles less than thirty degrees to the horizontal. This made the system fail to achieve the specification of tracking the suns position throughout the entire course of the day. Although the amount of energy reaching the system decreases as the sun nears the horizon, it was unacceptable to limit the range of motion so extensively. Another problem was that the initial vertical rotation control was that the design required two actuators to achieve adequate balance. The cost of actuators this length remains relatively the same even for variations in the supporting strength. The pull force of the actuators are not directly proportional to the price so two actuators would have been unnecessarily expensive and consumed more power than necessary.

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Figure 49 Horizontal view of system, actuator fully extended.

To compensate for this inefficiency a new system was designed to integrate a single centralized actuator with the supporting arms. The new design consists of an additional quarter inch diameter axle with four inch long lever arms attached such that the actuator couples directly with. The axle arms pin to the lens support arms, allowing it to rotate through a fixed range. This added degree of freedom allows the effective minimum and maximum length of the actuator to be modulated, allowing the design to track the suns lowest useable angle of inclination as shown in the figure on the page above. The configuration can be seen at its maximum angle of inclination in the figure below. The actuator is fully extended pushing the system down to its lowest possible angle. The functional range of rotation of the axle bar can be seen when comparing the figure above with the figure below. The axle bar is limited in the degree of freedom because it is pinned on the outside of the lens support arms, preventing the bar from ever entering or blocking the beam of light. The battery and control assembly are ideally situated as far away from the focal region as possible to maintain their temperatures within operable range. Shielding should be considered to ensure that excess heat does not reach the circuits, as it could damage the wiring or even the circuitry itself.

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Figure 50: Horizontal view of system, actuator fully contracted. Stirling cycle fixed to central plate.

The direction of operation for the actuator has been reversed from the previous design. Initially the actuators were on the same side of the pedestal that the lens would rotate towards, which is inherently limiting in the range of motion. It used the actuator to pull the assembly down and push it up. By locating the actuator on the opposite side of the lens assembly a wider range of motion can be achieved, and the actuators extensive pull strength is utilized to raise the lens instead of pushing the lens down as in the previous design. Because the axle bar is free to rotate, more than one angular location is possible for each extended length of the actuator. The weight of the lens assembly will keep it at its lowest possible angle; however wind could cause the lens to experience undesired rotation which the actuator would be unable to prevent. To counteract this possibility springs are mounted between the axle bar and the support arm, which provides a constant force keeping the lens in the lowest angular position possible. The springs must provide at least twenty pounds of force when extended maximally.

The horizontal rotational control system was also in need of redesign due to some invalid initial assumptions. Initially the motor was affixed to the baseplate and would interact with the geared edge of the circular pedestal. Constructing a gear of that radius would have required cutting the pattern out of a solid square

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metal plate. This would have been time consuming, expensive, and difficult to accomplish with a high degree of precision. Locating the motor on the base plate presented a problem because the battery is optimally located on the pedestal itself. The wiring to power and control the motor could become wound around the assembly or interfere with the roller supports as the system rotated.

Redesigning the pedestal from a circular configuration required the motor to be located away from the most extreme edge. Gears as large as the pedestal are not commercially available so the motor had to be relocated closer to the central axle. For optimal operation the motor is bolted directly to the underside of the pedestal near the center. The gear head of the motor interacts with a larger gear on the base axle to rotate the system as shown in the image below.

Figure 51: Close up view of gearing interaction

The smaller gear attached to the motor has 25 teeth and is two inches in diameter while the gear around the axle has 52 teeth and has an inner diameter of four inches. Both gears are one tenth an inch thick, but that value can be adjusted if the thin gears have problems maintaining alignment or there’s not enough contact area between them. The larger gear is fixed to the axle and cannot rotate, ensuring that the pedestal rotates as the motor turns with less applied torque than the previous iteration.

Some of the potential problems with this configuration are that although the Stirling cycle’s hot point will be located within focal region at all times, the angle of incident rays with respect to the engine will change throughout the day. At the highest angle, or the fully contracted position of the actuator, the beam is perpendicular to the surface of the Stirling cycle and a large percentage of the energy will be absorbed rather than be reflected. However, at the lowest angle, when the actuator is fully extended, the beam of light will be nearly parallel to the

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Stirling cycle and therefore will reflect more energy than will be absorbed. A portion of the light beam would also be blocked by the body of the Stirling cycle itself and would not reach the heating point, further decreasing the efficiency of the generator.

A method to compensate for this angle differential could be to mount the Stirling cycle in the center of the platform in such a way that it rotates along with the lens assembly. This would present a constant surface area perpendicular to the incident rays, greatly increasing the amount of energy absorbed. The lens support arms could be extended to allow for optimal placing of the focus on the heat point. Increasing the length of the lens assembly supports would increase the total rotational inertia of the assembly and increase the required force to achieve motion.

Such a design would require contacts with the lens support arm and additional bracketing, adding complexity and increasing the load the actuator must support and adjust. It would also lessen the rigidity of the supporting framework of the Stirling cycle, potentially causing destabilization during operation. The generator would be then located on the horizontal struts and still couple directly to the axle. Since the generating motor is sensitive to temperature variations, this design would keep the components farther away from the focal point of the light. This alignment is illustrated on the right side in the figure below.

Figure 52: Potential configurations of Stirling cycle with respect to lens assembly.

A less complex method to combat performance degrading reflections could be to adjust the position of the Stirling cycle such that it is parallel to the axis of rotation of the lens assembly. The figure above shows the three possible configurations, with the one described here on the left, and the current configuration in the center. This positioning would allow the beam to be distributed across a surface area that would remain constant as the system rotated throughout the day, as the

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profile would be circular. Doing so could complicate the generator-engine interface mechanism, as additional support platform would be required to mount the generator on. If testing indicates that the power output is suffering critically from this oversight then corrective measure can be enacted. If testing indicates satisfactory performance than it is unnecessary to alter the design further.

Safety Considerations The lens can easily ignite a variety of materials placed within the focal region. In order to adequately design the system to ensure against a meltdown an extensive material analysis must be performed. Testing can be achieved by setting up the lens in an elementary frame and placing different materials at different locations along the focus. It is suggested that no less than three materials be tested with three different thicknesses each at three different distances from the focal point. The materials considered are 6063 aluminum, 310 heat resistant steel alloys, and 625 nickel-based super alloy, all evaluated at 1/8th, 1/4th and ½ half inch thickness. Metal thicker than this will be too heavy to be used practically for the structural design. The aluminum is by far the cheapest material, so it would be ideal for construction if it performs comparably. To determine how effective each material is they will be placed directly at the focal point, one inch below, and three inches below. Each test must occur during the sun’s peak location in the sky, within the hours of eleven a.m. to one p.m. The testing duration for each sample will be decided upon once the effects of the lens have been observed. The minimum exposure duration should be between one and five minutes, and a maximum exposure should be fifteen minutes to an hour. The metal samples which display the highest levels of resistance to the extreme temperatures should be selected to construct the pedestal or a thermal shield protecting the more sensitive components. Another safety consideration is that reflections from the contact point can cause temporary or permanent impairment to vision. It is suggested that protective eyewear on the scale of welding goggles be used at all times when viewing the system, especially during maintenance. Handling of equipment must be accomplished using thermally insulated gloves to avoid injury from heated materials. The use of a reflective shielding fit around the cone of light could reduce the likelihood of accidental combustion or blinding. Such a reflector could be made out of polished aluminum or other light weight metals and might boost power efficiency by containing otherwise scattered energy. It could be attached to the lens assembly supports near their hinge and extend all the way down to the engine interface. Even an aluminum foil reflector would reduce the amount of harmful reflections without adding to the weight significantly. A flimsy reflector such as foil could easily become dislodged or disturbed, even by light atmospheric fluctuations, reducing the effectiveness as an added safety feature. More robust reflectors

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could be implemented by using solid aluminum sheets or even mirrors. These systems would add more weight to the lens assembly but would be worth considering for preventing damage to property and persons. It is also necessary that adequate fire retardant systems be immediately available. A fire extinguisher must be present at all test runs and during normal operations. A water based cooling system could be employed to prevent accidental overheating and meltdown, but such as system would add considerable weight to the pedestal though. Such a system could consist of tubing which pumps a continual flow across the underside surface. A standard garden hose could interface with the base and supply the necessary water. Another method would be to have a large volume of water present in containers that act as thermal dampers which prevent components from overheating. Both methods have their problems and complications though. The hose based approach will require a constant water supply which will add to the operating costs needlessly. The liquid ballast method will add even more weight to the system but would not require the need for a constant water supply. One of the primary concerns with the design is insuring the system is robust enough to avoid interference from atmospheric fluctuations. Strong gusts of wind could potentially destabilize the lens and increase the chance of damaging components. Sufficient testing is required to ensure stability in a variety of weather conditions. To ensure the system is capable of handling the forces involved, the prototype from should be tested extensively without the lens present in the assembly. A number of different loads should be applied at different positions on the lens assembly to simulate forces from sustained wind.

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Figure 53: Lens assembly with test force locations and values indicated

A one hundred, a fifty, and a twenty five newton weight could be tied to each of the corners of the supports independently to observe how the control system handles the added stresses. To simulate gusts of wind the lens assembly could be pushed by hand tangential to the direction of rotation. This would allow for the observation of any oscillatory behavior in the control system. If the lens assembly can withstand an impulse of up to one hundred newtons applied tangential to the range of motion without moving considerably then the design is robust enough to operate normally. If movements do result from the impulsive force then a more in depth analysis of the support system needs to be conducted to isolate the inefficiencies causing a lack of stability. It is of critical importance that the lens does not move to an undesired location. Should the lens become misaligned with the sun, the focal point could fall onto the controlling components and damage them and disable operations. An emergency control routine could be implemented which rapidly relocates the lens assembly away from the direction of the sun to limit damages. Such a response could rotate the pedestal away from aligning with the suns azimuth and then lower the lens assembly. This method would prevent the focus from damaging any components. Another safety concern is electrical insulation. There are numerous components in the design that draw multiple amps of current from the battery. The entire framework for the project is constructed from aluminum and is electrically

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conductive. Proper care must be taken to ensure that all wiring and contact points are adequately insulated, not only for the current rating but also for high ambient temperatures. By designing the wiring layout to avoid the focal region the risk of a melt down and potential shock can be limited. Corrosion due to salt in the air might also produce unsafe conditions, so the design needs to be resistant to rusting as well. A final safety consideration is due to Florida thunderstorms. The heavy rains could damage components by shorting them out if proper care is not taken to seal them sufficiently. Light plastic wrap and electrical tape can be used to water proof sensitive elements but would add combustible materials to the design, increasing the risk of fire.

During strong windstorms the lens assembly would be optimally located in the upright position, so that the lens is parallel to the wind direction. A small wind turbine could be purchased and integrated into the design to act as a sensor indicating when excessive winds were present and when to move the lens into the safest position. A rapidly deployable lens cap would also benefit the safety of the project, but it is unnecessary so long as emergency cessation routines are implemented.

Hardware Prototyping In order to construct the prototype system architecture first the parts must be acquired. The lens, Stirling cycle engine, and printed circuit board will all be shipped to the location. Local hobby shops and electronic part distributors will be checked to see if they have the actuator, stepper motor, bearing, battery, or generator required. If they cannot be located nearby they too will be shipped to the location. The wiring, bolts, screws, wheels, ball bearings, and other fasteners will be purchased from a local hardware store.

A local metal supplier would be ideal to purchase the raw materials, but in the event that none can accommodate the order an online one can be considered. For ease of calculating the prices online suppliers are considered as they have a large variety of products with a fixed price set on specific cuts. Although the actual cost of these components may vary, the websites are a good reference and backup plan.

To minimize the costs materials should be purchased in largest sections possible and cut personally in the fabrication lab. The metal plates required for the design are six inches wide and a quarter inch thick. Two twenty-one inch plates, two nineteen inch plates, one forty-eight inch and one forty-four inch plates are required to fabricate the base and pedestal for a total length of 172 inches. This much raw material should cost no more than $140.40 as calculated on

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onlinemetals.com. The tubing required to fabricate the lens support assembly is half inch wide and tall and one sixteenth inch thick. Four thirty-one inch long and two twenty seven inch long sections of tubing are needed, for a total length of one hundred seventy-eight inches which should cost no more than $22.00 according to metaldepot.com. Because the aluminum tubing is drastically cheaper than the solid plating, it is possible to construct the base frame out of tubing rather than plates. Each plate can be replaced by a pair of parallel tubes set six inches apart with perpendicular tubing welded every foot as shown in the figure below. At the center a small square plate can be welded into place to provide the floor for the axle assembly.

Figure 54: Alternative base support comprised of hollow tubing.

Once the base plates have been cut and welded together, the custom machined bottom axle must be welded to the center and the roller supports are welded to the frame. The wheels are placed in their supports and the bearing is inserted into the housing thus completing the base assembly. The pedestal is constructed in a similar manner, cutting the plates and welding them together, along with the ring. Holes are drilled through the surface to bracket the actuator and other components down. A row of two holes spaced two inches apart are drilled at two inch intervals to allow for readjustments to be made. Four holes are drilled three and a half inches from the center for the stepper motor. The upper axle housing is welded to the center of the underside of the pedestal.

The axle housing is shown below and is to be custom milled by an online manufacturer such as www.vivasd.com/cnc-machined-parts/. If difficulties arise in acquiring the axle components, or the cost is unreasonably high, an alternative configuration is required. Steel tubing two inches in diameter and a quarter inch thick could be used to construct the lower portion of the support axle which is

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welded to the base. A steel rod one and a quarter inch in diameter and four inches long could be used to construct the upper portion of the axle. In this case the square based mounted bearing would be used. The bearing would be bolted to the underside of the pedestal in the center and the thinner axle would be inserted in and secured with the built in tension screws. The upper portion of the axle would slide into the lower part and would not be permanently secured to the base. To perform maintenance or alter the layout of the layout the pedestal needs to be separable from the base plate. The large gear is welded to the bottom axle housing. The total price of steel tubing approach would be $45.92.

Figure 55: Lower axle housing section

The lens comes with a wooden frame already attached, ensuring that the lens assembly will be the easiest component to fabricate. The aluminum tubes for the support arms are cut to the desired lengths of four pieces at 31 and two pieces at 27 inches long. The outer support bars on one side have quarter inch diameter holes drilled for attaching to the axle bar. Additional holes are drilled spaced out one inch starting at 14 inches along the assembly, providing the option to reconfigure the position of the elevating mechanism. The support arms are then screwed loosely to the frame at the corners and midpoint using one inch long wood screws. The other ends of the support arms on each side of the lens are welded to the center. The screws are then fastened tightly and the bracket is welded to the end of the support arms.

The optical sensor array is glued down to one of the corners of the lens frame, and the wiring is soldered on and fed through the supporting arms. The axle bar is a solid aluminum rod a quarter inch in diameter and 44 inches long. The axle arms are four inch long, quarter inch thick, one inch wide plates with a quarter

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inch diameter holes drilled half and inch from the edge. The actuator’s end is locked between the arms, which are welded to ends of the bar

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Figure 56: Completed lens assembly without axle bar

The brackets can be easily milled by drilling the half inch axle holes at opposite ends of strips of metal two inches wide and six inches long. The strips can then be right angled or cut up and welded together to form the required shape. This process can be repeated with metal strips one inch wide and eight and a half inches long to fabricate the four roller support columns.

The lens assembly supports are cut from blocks six inches tall, four inches wide, and one inch thick. The tops are cut to be round with a two inch radius two inches from the top. This allows the lens assembly to be rotated about these supports smoothly. The half inch diameter axle holes are drilled two inches from the top then supports are welded on the horizontal struts 22 inches from the center of the pedestal. Although solid blocks were initially suggested because of the high levels of stress these supports will experience, hollow rectangular tubing would likely suffice and would reduce the weight and price of the system.

Once the pedestal, the base, and the lens assembly are constructed the electrical components can be integrated. The stepper motor first has its gear welded into place at the end of its axle, and is then bolted to the pedestal with four hex bolts. Then the pedestal assembly can be inserted into the lower axle of

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the base. A basic evaluation of the system can be performed to ensure the system is capable of withstanding the basic range of forces it will experience during operation. Rotating the pedestal and applying forces to the edge tests whether or not the supporting architecture is robust enough. If so, then the lens assembly is ready to be attached to the supports on the pedestal. The brackets are lined up with the holes in the supports and then are pinned into place with a half inch bolt.

The actuator will be purchased with its mounting bracket, which will be fastened eleven inches from the center point of the pedestal. The axle bar is pinned to the lens support arms, and a basic test of the actuators functionality can be observed by attaching its wires to the battery for a moment, and then reversing the polarity to open and close it. The system can be rotated with the lens assembly at different angles of inclination to ensure the base support system is robust enough to prevent tipping at every angle.

The battery is then bolted down to one end of the pedestal and the control box is installed directly on top of it. The wires for the sensors are soldered to the control box at the correct location, as are the wires for the actuator and the stepper motor. The generator is bolted down right next to the Stirling cycle and connects to it with a coupler. The wiring is soldered to the battery and control box at the generator input.

The total weight of the system should not exceed one hundred ten pounds, and the Solidworks model yielded a weight of 96.43 lbs. A view of the mostly completed model can be seen in the figure below with the notable absence of the generating motor.

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Figure 57: Completed prototype system

Testing As each subsystem of the overall project is built there needs to be a way to test each individual component. Each subsystem requires a different standard of testing procedures which relate back to the projects technical objectives. This insures that each of these requirements are met by the subsystem before it is approved to be used in the final system.

To independently testing the solar tracking system should prove to be relatively straight forward. First step is to prove that the LED’s will work correctly as a light sensor and that they have the same output voltage as what was originally expected. If this varies from what was researched it will be important to note because the microcontroller will need to be modified to the new output voltage to expect for various light conditions. Once the LED array has been assembled the developer will need to test that the system is sensitive enough. If the array looks in a direction not directly at a light source the LEDs will output different voltages corresponding correctly to the amount of light being received by each LED. Once the LED array has been confirmed as functional the system will need to be tested with the MSP430 development board to make certain that the two can communicate correctly. To test that the LEDs can communicate correctly to the MSP430 the sensor array will need to be hooked up to the inputs of the MSP430 development board. A simple control program will need to be written which will take the input of each LED and will turn on an LED hooked up to the output of the MSP430 if all four of the LEDs in the sensor array are receiving the same amount

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of light. This can be tested by aligning the sensor array with a light source and verifying that the output LED turns on. Then cover one of the sensor arrays LED’s and verify that the output LED then turns off.

The next system to be tested will be the MSP430 in the development board communicating to the actuator which will be responsible for adjusting the altitude angle of the Fresnel lens and the motor which will be responsible for adjusting the azimuth angle. To test this, a program will need to be run on the MSP430 in the development board which will output a signal first to the actuator which will first extend the actuator simulating increasing the altitude angle. After extending the actuator for two seconds the signal should be setup to then shorten the actuator and be run for another two seconds. It should be verified that the actuator is now at the same angle it was originally at. Next the program microcontroller should turn on the motor to rotate left for two seconds and then rotate right for two seconds simulating adjustments to the azimuth angle.

Once all four of these motions work correctly it will be time to set up the entire solar tracking system and begin testing it. Note that this test will be done without mounting anything to the frame of the Fresnel lens. The first step will be to set up the microcontroller with the finalized program, with the sole modification of removing the delays, allowing it to run continuously for quick testing. During a typical sunny day the array will be faced directly into the sun. Verify that no adjustments are being made. Next rotate the sensor array such that two of the sensors are shaded. Verify the appropriate actuator/motor begins to move in the correct direction. Realign the sensor array so that all four sensors are visible to direct light and verify no further adjustments are made. Repeat by rotating the LED array in a different direction and again verify that the correct adjustments are made by the actuator/motor. Finally cover all four LED sensors to simulate a clouds blocking direct sunlight. Verify that because all four LEDs are still receiving the same amount of light that no adjustments are made by the actuator/motor. Once this testing is complete and all objectives are verified, upload the final program to be run by the microcontroller with the sleep delays reinstated. Then verify that the system is capable of waking up, checking the sensors, making any necessary adjustments until the sensors signal proper alignment and then return properly to sleep mode for the correct time delay and repeat the process.

The PCB will be tested in two parts. First is to ensure that all traces correctly connect how they were designed to. Also it is necessary to check that there are no traces which connect anywhere that they shouldn’t. This test can be accomplished by using a multi-meter set to measure for resistance; some multi-meters have a feature to check for short circuits which would work as well. If the trace is proper it will show a very low resistance, typically around .002 Ohms. If the trace is broken the multi-meter will show that no resistance is identified, in other words the output of the multi-meter will look the same as before it is connected to the board. Once all traces of the PCB have been verified it will be safe to solder on all the necessary components of the PCB. This includes

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soldering the MSP430 to the PCB. After checking that all the solder connections are strong; the second phase of testing the PCB may begin. This testing will be based on testing the functionality of the PCB as a whole to ensure that it functions as designed. This will involve plugging the LED’s into the inputs of the PCB and also connecting the solar tracking motor/actuator to the appropriate outputs of the PCB. At this point the MSP430 should have the tested finalized program uploaded to it. What is to be tested here is that the MSP430 still functions properly once connected to the PCB. This will be accomplished by using the same testing procedures as were used to test the MSP430 in the development board. Verifying that the solar tracking system still functions properly will confirm that the PCB was designed and will continue working properly.

Two of the fundamental components of generating solar power for this system are the Stirling engine and Fresnel lens. They will also be the two largest purchases while acquiring materials. Before being installed into the system they will need to be tested independently and then together. The order of which to test isn’t important so for the sake of choosing one the Fresnel lens will be focused on first. The important characteristic to note from the testing is the location of the focal point of the Fresnel lens. Testing will be accomplished by simply taking the lens outside and verifying that the lens produces one central focal point. A measurement will need to be taken of how far the focal point is from the center of the Fresnel lens. This distance will decide the length of the mounting arm for the Fresnel lens and also the mount location of the Stirling engine. Next it will be necessary to test that the Stirling engine functions properly. What will be needed is a heat source capable of 500 degrees Fahrenheit. Once the heat source is on the heat element of the Stirling cycle engine it will be necessary to provide a kick start for the engine to start moving. Once the engine starts verify that it continues to operate and runs smoothly until the heat source is removed. Once each component has been tested independently the two will need to be tested together. The goal of this test is to verify that the Fresnel lens is capable of safely providing enough heat for the Stirling cycle engine to run continuously until the lens is no longer focused on the engine. Similar to the other test above it will now be appropriate to add the starter system to the Stirling cycle engine and test that it is able to sense if the Stirling cycle engine has stalled and to give the Stirling cycle engine the appropriate kick to start the engine. To test this it will be necessary to purposely stall the Stirling cycle engine and to then test and see if the system can recover from the stall.

The next subsystem which will need to be tested is the base on which the entire system will sit and the movable frame which will hold the Fresnel lens. The testing of this is rather straight forward, however, it is important because it is the first step in testing that the whole system will function for extended periods of time. It is crucial for the base to be able to rotate the azimuth angle and the Fresnel frame to be able to adjust the altitude angle up and down all while making certain that the focal point of the Fresnel lens never leaves the heat element of the Stirling cycle engine. Once the solar tracking subsystem and the

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base and frame subsystems have each been verified they can be combined. The actuator and motor will need to be mounted to the Fresnel frame and base respectfully. Once the two subsystems are together it will be necessary to verify that the solar tracking system keeps itself properly aligned with the sun as it moves across the sky. In this stage the solar tracking system can be tested as it will be in the final testing of the assembled prototype. To properly test the tracking system it will need to be verified that it is able to correctly follow the sun for an entire day. During this stage any problems with long term solar tracking will need to be identified and resolved as once the Fresnel lens is installed into the system it will be dangerous if the solar tracking system does not operate as expected.

Part of the testing will be how the clouds and climate affect the input source. Another part would be how the generator is working with the system. Another part would be how to correctly start the Stirling engine once the desired ambiance have been reached. Another important part would be to see if the status lights are working correctly. The batteries will have to be probed with an external voltage meter to check and see if the microprocessor switches on and off the generation and degeneration process at the desired set intervals. Tests would also have to be performed on how the motor that rotates the base is working and if it is going in the correct direction. If the motor is not going in the correct direction then it would have to be inverted so that it works properly. The actuator would also have to be tested that raises and lowers the Fresnel lens to the input of the Stirling engine.

A test to see if the system is changing properly from the starting mode to the charging mode would also be required. One would also have to test the design platform to make sure that it spins easily with everything loaded on it and that there are no places where it might get stuck. A test to ensure the base provides adequate support to prevent tipping over would also be required. The project has been designed to be balanced and not tip over but a large gust of wind might have an adverse effect. If so, then one would have to implement some kind of safety mechanism designed to make the base adhere to the ground better. A lot of testing would be done with the microprocessor to make sure that it is sending and receiving signals correctly. The batteries would have to be tested with a voltmeter to see if the circuit is switching correctly. When the voltmeter reached a low level of about 10.8 Volts the circuit should switch to charge mode and can be checked with an ammeter to see if there is current flowing. Also when the voltage across the battery is at max (about 13.8 Volts) the charging should stop and current flow should be shown at zero on the ammeter. The batteries can then be tested with different loads and the ammeter to make sure that the current coming out of the battery is steady and that there are no short circuits in the system.

When the batteries are charging the optimal configuration is in parallel so that they can both receive the same constant voltage, but when the system is starting the batteries would be connected in series so that they can supply a 24 Volt output to the motor and get its momentum going. In the starting mode the system

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doesn’t need the voltage regulator, so this will be taken off from the starting circuit, along with the battery charging controller. Once the motors' momentum is going the circuit would then be switched back to the generator process and start outputting power to the batteries.

Upon properly verifying that the solar tracking system is able to correctly align with the sun for an entire day it will be safe, to a certain level of confidence, to begin testing the system with the Fresnel lens and Stirling cycle engine installed into the system. The purpose of this testing is to confirm that without worrying about the battery charging system, the solar tracking system is able to keep the Fresnel lens exactly on the heat element of the Stirling cycle engine. Also that by successfully tracking the sun for an extended period of time, the system is capable of keeping the Stirling cycle engine running for the entire time. Once the system has been verified to this stage it will be appropriate to add the battery charging system to the other subsystems and begin actually testing the entire system.

Table 18: How each subsystem will be tested and what is checked to confirm the subsystem passes

Subsystem to be tested

Test How to qualify passing

LED’s Hook up to multimeter in different levels of light

Check what the output voltage is for each intensity of light

Light Sensor Array

Hook up each LED to multimeter. Set up array so not directly facing light source

Verify the appropriate LED’s show the difference in light received based on orientation of the array

MSP430 (in development board) - inputs

Hook up LED array to input ports and output port to LED which is set up in the microcontroller program to turn on if all LED’s in the array are equal

Orient the light source in and out of proper alignment and verify that only when misaligned the LED turns off. Also cover all LEDs and verify the output LED turns on.

MSP430 (in development board) – outputs

Write control program to extend actuator for 2 seconds then collapse for 2 seconds. Program should then rotate motor left for 2 seconds and then right for 2 seconds

Verify the actuator and motor each move appropriately to the program parameters. Also verify that each return to original position.

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PCB Use multimeter to check each trace on PCB. Checking for appropriate short and open circuits

Verify that the traces that are supposed to be in the board each work and that there are no unwanted traces in the board

PCB and MSP430

The MSP430 integrated into the PCB should be tested the same as the MSP430 in the development board for both inputs and outputs

Verification of the MSP430 integrated into the PCB should be the same as the specifications of the MSP430 in the development board for both inputs and outputs

Base and frame structure

To check if each axis of rotation functions properly. Also to check what happens to the Fresnel lens focal point as the structure rotates.

Verify the angles of altitude and azimuths are able to be appropriately adjusted. Verify as these angles change the location of the Fresnel lens focal point never changes from where the heat element of the Stirling cycle engine will be

Fresnel Lens To see where the focal point is located. Carefully operate Fresnel lens and align perpendicularly to sun. Raise/lower the lens until focal point is exactly on the ground below.

Measure distance from edge of lens perpendicularly to the ground. This will be the focal distance from the center of the lens to the ground.

Stirling cycle engine

Use separate heat source to heat Stirling cycle engine

Verify the engine runs smoothly until the heat source is removed

Stirling cycle engine starter

Enable sensor to on mode and see if it will attempt to start engine. Stall engine to see if able to detect stall and correctly restart the engine.

Verify the starter works appropriately for each situation

Stirling cycle engine and generator

Voltmeter across generator When Stirling cycle starts rotating

Voltage above 12 Volts

Solar tracking

Without the Fresnel lens test to see how well the mounted LED

Verify that for an extended length of time the MSP430

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system array can communicate to the MSP430 which will in turn communicate to the actuator/motor to adjust and keep the system properly aligned.

can adjust the system to keep the LED array perfectly aligned.

To properly test the system as a whole there needs to be a statement of the problem to be tested. The problem is to determine how accurately the system aligns itself to the sun at different times throughout the day and if the system is able to properly manage the charging of the batteries. For this particular system the accuracy within a defined range is very important for the solar tracking. So important is this accuracy that if off by even a couple of degrees it could cause catastrophic failure to the system. Because of this need for accuracy, several tests will need to be performed and statistical data will need to be collected and analyzed to guarantee to a specific degree of confidence that the system will function properly. The management of properly charging the batteries is equally important as improper charging of the batteries could result in failure as catastrophic as to cause the batteries to explode. Limitations of the study have to deal with unfavorable weather conditions or cloud cover.

The design of this experiment needs to be set up to ensure randomly sampled data. To achieve this, the tester will need a random number generator. This random number generator will need to output a random number between 1 and 30. The tester will then wait that number of minutes to collect the next set of data. After collecting that set of data the tester will draw a new random number. The data will be collected starting at sunrise and continue to be collected until sunset for three days in a one week period. An example of the data sheet to be completed by the data collector can be seen below in table 19, the information filled into the table are examples of the data in the format it shall be recorded in. Data will be collected by recording the time, weather condition, battery charge, battery charging status and degree of accuracy from the center target point of the Fresnel lens focal point. It is assumed that the experimenter knows how to setup the system.

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Table 19: Example of the data sheet to be completed while testing the final prototype

Time Weather condition

Battery charge

Battery charging status

Focal point accuracy

Sunrise – T:TTam

Clear 10% Active Within 3 inch

… Raining, no direct sunlight

20% Standby No visible focal point to measure

... Overcast, still direct sunlight

50% Active Within 1 inch

… Clear 100% Maintain Within1 inch

Sunset – T:TTpm

Overcast, no direct sunlight

90% Active Greater than 5 inches

The hypothesis to be tested is that the battery charging system will function properly and that the system will stay within the degrees of freedom which are to be determined as acceptable. Techniques used in analysis require a clear definition of different weather conditions, a way of measuring the current charge on the batteries, a way to tell the charge status of the batteries and a method for measuring angle of the system compared to that of the sun. For the focal point accuracy a ruler scale will be setup and a measurement will be taken to show how far off the focal point is from the target center. To analyze the data it will be input into an Excel data sheet by the data collector. Using the tools of Excel statistical analysis will be performed on the data. Correlations that are being looked for include if during certain times of day the system is less accurate. Also if certain weather conditions affect the system accuracy. Useful statics that can be taken of the data include determining the confidence interval for which the system functions properly and also the mean value collected for the entire experiment of the system accuracy to determine current system performance.

Milestone discussion To ensure a timely and stress free project completion team set milestones can be utilized as a great tool. As a whole the group meets when needed on Monday mornings, Tuesday and Thursday after the class lecture and also on Fridays as needed. At these meetings updated findings from research is discussed to make sure that as a group we are headed in the same direction. Self-checks to make certain that the entire team is on track are also taking place at these meetings.

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Within each semester there are certain milestones that need to be achieved in order to keep the project on track.

Fall semester begins with choosing and defining a project concept. Once an idea has been selected the remainder of the semester is focused on researching the chosen concept.

Table 20: Milestones for fall semester 2011

Task – Fall 2011 Completion Deadline

Research project concept September 20, 2011

Design parameters selected September 25, 2011

Initial Project and Group Identification September 27, 2011

Funding source(s) secured October 14, 2011

Begin researching/writing paper October 15, 2011

Table of contents/paper outline complete October 27, 2011

Complete paper for team review November 28, 2011

Turn in refined paper December 5, 2011

Acquire major components December 2011

Experimentation, finalized design December 2011

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Spring semester focuses on prototyping and testing the finalized system.

Table 21: Milestones for spring semester 2012

Task – Spring 2012 Completion Deadline

All parts acquired January 8, 2012

Solar tracking array built and tested January 2012

System base and frame built and tested January 2012

Printed circuit board designed January 2012

Stirling cycle engine and Fresnel lens tested together January 2012

Microcontroller system programmed and tested February 2012

Printed circuit board implemented and tested February 2012

Battery charging system implemented and tested February 2012

Preliminary entire system testing and Refinement March 2012

Assemble and practice final presentation March 2012

Final testing and recorded presentable data April 2012

Final presentation and judging April 2012

Progress Energy Conference April 2012

Budget The project is being funded by Progress Energy. To be approved for funding we submitted a report detailing the expected budget (this can be seen in the table below). Progress energy then approved us for the full amount of funding we requested below. It is important to remember this budget was done with minimal research completed. The purpose of this budget was to cover expected expenses for each subsystem.

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Table 22: Initial Budget Proposal

No Item Purpose Cost Quantity Total cost

1 MSP 430 processor 4.30 2 $8.60

2 PCB required 50.00 2 $100.00

3 Temp sensor feedback 3.99 12 $47.88

4 Display components

display 5.00 10 $50.00

5 Solar panel feedback 11.95 4 $47.80

6 Aluminum square tube/foot

frame 5.00 24 $120.00

7 Stirling cycle engine

power source 300.00 1 $300.00

8 Fresnel Lens heat source 216.00 1 $216.00

9 generator mech power to elec potential

9.95 2 $19.90

10 low speed high torque motor

tracking rotating horizontal motion

34.90 2 $69.80

11 linear actuator tracking vertical angle

169.56 1 $169.56

12 battery li+ 12V 99.67 1 $99.67

misc hardware nuts bolts wiring insulation fan belts replacements

$150.00

Misc electronics

capacitors resistors transformer $150.00

$1,545.21

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total cost + 20%

$1,859.05

Sources

1 TI

2 http://www.4pcb.com/index.php?load=content&page_id=134

3 http://search.digikey.com/us/en/products/604-00011/604-00011-ND/1774440

4 http://search.digikey.com/us/en/products/LTST-C150GKT/160-1169-1-ND/269241

5 http://www.amazon.com/dp/B002MAX0FS/?tag=bizmarketing-20

6 http://www.iplexmall.com/browse.ihtml?pid=844124&step=5& prodstoreid=9818&source=cashback

7 http://greenpowerscience.com/SHOPSTIRLINGENGINES.html

8 www.greenpowerscience.com/FRESNELSHOP/45INCHSPOT.html

9 www.goldmine-elec-products.com/prodinfo.asp?number=G15492

10 www.scientificsonline.com/high-torque-dc-electric-motor.html

11 http://www.northerntool.com/shop/tools/product_200333245_200333245

12 http://www.supercircuits.com/Power-Supplies/MVLBCS-7

Through the conducted research since this time we have encountered many issues with the original budget. We have altered on sensor choices, the number of motors needed, and the power system. There was also little attention paid to the creation of the housing system (listed under misc. hardware and aluminum tubing). As the research/design/assembly continues more changes will need to be made, though it is not expected that the total expenses will exceed the approved amount.

The most glaring mistake in the budget is forgetting to include safety equipment. There are several safety concerns related to this project. First, the light at the focal point can easily damage eyes so protective eyewear is a must for all members. The type of protective eyewear needed is of the welding variety which

http://search.digikey.com/us/en/products/604-00011/604-00011-ND/1774440

http://search.digikey.com/us/en/products/604-00011/604-00011-ND/1774440

http://greenpowerscience.com/SHOPSTIRLINGENGINES.html

http://www.greenpowerscience.com/FRESNELSHOP/45INCHSPOT.html

http://www.goldmine-elec-products.com/prodinfo.asp?number=G15492

http://www.scientificsonline.com/high-torque-dc-electric-motor.html

http://www.northerntool.com/shop/tools/product_200333245_200333245

http://www.supercircuits.com/Power-Supplies/MVLBCS-7

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shields against all wavelengths of lights, as opposed to laser safety goggles which are made to filter certain wavelengths. Also, the heat the focal point of the light is 1000’s of degrees Fahrenheit. To account for this a fire extinguisher should be on hand at all times as well as some insulated gloves (rated for very high temperatures). This equipment will not cost an excessive amount. The table below shows prices of the safety equipment required.

Table 23: Safety equipment

No. Item Purpose Cost ($)

Quantity Total

1 Jackson WA-600 Cutting Goggles

Eye Protection 34.25 4 137

2 Auto Darkening Helmet Powerweld® PWH9843

Eye Protection 59.9 4 239.6

3 Front & Back Heat Insulated, CRUSADER Flex Gloves

Heat safety 20.12 2 40.24

4 Aluminized Carbon Kevlar® Wool-Lined Gloves

Heat safety 48 2 96

5 Kidde 1-A:10-B:C Fire Extinguisher

Fire safety 17.97 2 35.94

Sources

1 http://www.safetyglassesusa.com/3002690.html

2 http://store.weldingdepot.com/cgi/weldingdepot/PWH9843.html

3 http://www.fastenal.com/web/products/detail.ex?sku=1006024&ucst=t

4 http://www.vorpahlfireandsafety.com/GroupInfo/GroupID/19967

5 http://tinyurl.com/7oc2jo8

For each of the personal protection equipment items two different intensity levels were included. One was chosen at a medium level of tolerance, and the other with the highest level that could be found as a non-industry consumer. For instance the aluminized carbon Kevlar gloves are rated for fire proximity suits whereas the CRUSADER gloves are only rates for temperatures of 400 degrees

http://www.safetyglassesusa.com/3002690.html

http://store.weldingdepot.com/cgi/weldingdepot/PWH9843.html

http://www.fastenal.com/web/products/detail.ex?sku=1006024&ucst=t

http://www.vorpahlfireandsafety.com/GroupInfo/GroupID/19967

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Fahrenheit. The most robust option will be chosen in each case due to the high importance of all members’ safety.

Next there are the components that have been deemed unnecessary through research and development. First there were funds set aside for temperature sensors. These were originally going to be used in the solar tracking subsystem but through research it was discovered that tracking can be achieve using different components. The actual sensors that will be used are red LEDs. The cost of these will be significantly less than that of the temperature sensors per individual sensor and the total number of LEDs will only be four which is much less than the 12 temperature sensors allotted for. The costs will be less and the performance will be much more efficient as a result of discoveries made during the research/design process.

Another subsystem that has undergone drastic revision is the power subsystem. It was originally envisioned that a solar panel could be used for powering the apparatus (microcontroller, motors actuators, etc.) and the battery would be used only as the recipient of the charge power created. The decision was made that this needlessly complicates the design’s goal of charging the battery. Though, should this product go into more development for consumer or industrial use the solar panel may have a strategic value associated with it. This project will use the 12 Volts Battery to power the subsystems and charge the battery at the same time. Because of this the battery being used must have some initial charge on it which is why a commercial 12 Volts battery charger has been added to the budget.

The motor choices in the original budget were done almost arbitrary. There was no knowledge of what torque would be required from the motors so one rated for “high torque” applications was selected. Also there was little research as to how to power these motors or which type would be used (DC, AC stepper, wound, etc.). These issues have obviously been addressed during the drafting of this design document.

Item Function Price Quantity Total PCB Connecting

subsystems $33.00 1 $33.00

Bright red LED Solar Tracking $1.60 4 $6.40 ½” Balsa wood Solar Tracking $2.00 1 $2.00 ¼” Balsa wood Solar Tracking $4.00 1 $4.00

Hot glue Solar Tracking $2.90 1 $2.90 Electrical Wire Solar Tracking $10.00 3 $30.00

MSP 430 Microcontroller $4.30 2 $8.60 Fresnel Lens Concentrating Light $189.00 1 $189.00 WBB236691

generator Converting

Engine output $193.95 1 $193.95

85BYGH450A- Rotational Motion $49.98 1 $49.98

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08 Stepper motor

FA-PO-150-12-8 Linear Actuator

Lens Angle Adjustment

$138.00 1 $138.00

LP12-6-F1 Leoch Battery

Energy Storage $19.79 2 $39.58

PST-DC/2812-8 Voltage

Regulator


TAF10810N10G Coupler


SB1524iX Charger controller


Auto Darkening Helmet

Powerweld PWH9843

Eye Protection $59.90 4 $239.60

Aluminized Carbon Kevlar®

Wool-Lined Gloves

Heat safety $48.00 2 $96.00

Kidde 1-A:10-B:C Fire

Extinguisher

Fire safety $17.97 2 $35.94

misc hardware $200.00 1 $200.00 misc electronics $200.00 1 $200.00

Total $ 1,890.90

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Appendices Copyright Permissions

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Hi, I am a senior Electrical Engineering student at UCF and am currently doing research for the Senior Design Project. Our project is a Solar Stirling Generator and will be implementing the use of a charging controller to charge 12 volt batteries. During my research I have stumbled upon your webpage about Analog Devices. I read the article by Joe Buxton about the new battery controller and tried to get in contact with him but I only found your email. I would like to ask for permission to use the Figure 1 on that page for our senior design report. Please let me know if I can or how to get into contact with Joe Buxton. Thank you, Robert Giffin Senior EE student at UCF I'll be out of the office until Tuesday, December 6. For any urgent business matters, please contact [email protected] (781-461-3479).

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