Portable Solar Tracker Critical Design Review Group 1

Portable Solar Tracker Critical Design Review Group 1 Summer 2010 Stephen Holman Tri Bui Christopher Davis Tuyen Bui

Project Overview • Design and optimize a solar energy collection, storage, and distribution device • The device will track the path of the sun • Panel will be orthogonal to sun’s rays • The device will have a user interface displaying useful information

Goals and Objectives • High efficiency • Sustains on its own energy • Reliable operation • The best quality for the lowest cost • Durable • A user-friendly interface • Portable

Specifications Dimensions: Weight: Avg. Collected Voltage: Voltage Output: Current Output: Power Output: Temperature Rating: Efficiency (Output/Input) Life Expectancy Accuracy S. I. Units 0. 37 m long x 0. 203 m wide x . 508 m high 2. 7 kg max 10. 5 -13 Volts DC Imperial Units 14. 5 in long x 8 in wide x 20 in high ≈ 6 lbs. max - 5 - 6 Volts DC - 50 -100 m. A - . 25 -. 6 Watts -10 °C to 50 °C 14 °F to 122 °F 10% minimum (of the panel rating) 500 full charge/discharge cycles ± 3° of the sun’s position - - -

Components Part Name Battery Nickel Metal Hydride LCD HD 44780 Motor Hitec HS-322 HD Compass HMC 6352 Optics Parabolic mirror Solar panel 8 V with 44 m. A Battery Monitor IC DS 2438 Switch Pololu Switch Reasons • 7. 2 V • Inexpensive • Low power usage • Minimal connections • Fixed rotation servo • Draws 7. 4 m. A at 4. 8 V sitting idle • Operation at 2. 7 V idle • Easy Programmed and operated by MCU with I 2 C protocol • Better concentration • Good voltage • Efficient battery management • Reduce power consumption • Interrupts to display

Solar Panel Since the main specification for this project is the optimization of output power of a photovoltaic systems. What the aim of the solar tracker is to try to increase the output power at least by 10%. The solar panel that is used in this project is: • 8 V 44 m. A, . 352 W solar panel • The current solar panel array in which we will build is it is to have two of these panel connect in series. • There will be another configuration that will be used is to have 4 in parallel. The first configuration will provide 16 V with 88 m. A, providing 1. 408 W. As for the second configuration, it will provide 8 V with. 176 m. A and provides 1. 408 W.

Solar Panel Cont’d Since the main specification for this project is the optimization of output power of a photovoltaic systems. What the aim of the solar tracker is to try to increase the output power at least by 10%. The solar panel that will be used in this project will This be: is the current and voltage equation for a standard photovoltaic cell along with the simple photovoltaic circuit model. • . 5 V 3. 6 A, 1. 8 W solar panel • Optional panel is a 8 V 44 m. A, . 352 W R 1 = Series Resistor The current solar panel array in which R 2 = Shunt Resistor we will build is it is to have two of D 1 = Diode these panel connect in series. This array will have 1 V with 3. 6 A. Using the power equation P = VI, we have In this equation, I is the output current. IL is the current produced by the photovoltaic cell. 3. 6 W. This will be plenty to supply the That current is the short circuit current given by the manufacturer specification. ID is the battery. 6” diode current and ISH is the shunt resistance. Also another option we are looking into is have two types of panel. Each ID can be array describewill by the equation of the have their above, own the Schottkey diode equation. function.

Solar Panel Cont’d This is the energy conversion efficiency of the photovoltaic cells. Pm is the power produced by the cell =. 352 W E is the irradiance = 1000 W/m 2 Ac is the area of the cell =. 0381 X. . 0762 m =. 0029 m 2 So the efficiency for our single cell is =. 1214 Which is approximately 12. 14% ≈ 12% = This is the fill factor equation, which determines the ratio of the actual maximum power to theoretical power. Pm is the power produced by the cell =. 352 W Voc is the open circuit voltage = 8 V Isc is the short circuit current = 44 m. A (Values varies under certain conditions) Our FF = 1, a typical commercial cell is >. 7

Results Time Voltage (V) Current (m. A) Power (W) 8 6. 15 6. 75 8: 15 6. 33 6. 76 8: 30 6. 48 27. 16 0. 175997 6. 8 74. 8 0. 50864 8: 50 6. 52 33. 4 0. 217768 6. 77 78 0. 52806 9: 10 6. 58 40. 8 0. 268464 6. 66 82. 6 0. 550116 9: 30 6. 6 40. 6 0. 26796 6. 7 81. 3 0. 54471 9: 50 6. 7 53. 5 0. 35845 6. 76 83. 4 0. 563784 10: 10 6. 59 65. 2 0. 429668 6. 67 88 0. 58696 10: 30 6. 68 75. 1 0. 501668 6. 62 93. 6 0. 619632 10: 50 6. 6 76. 2 0. 50292 6. 63 93. 4 0. 619242 11: 10 6. 67 79. 6 0. 530932 6. 58 93. 6 0. 615888 11: 30 6. 62 80. 8 0. 534896 6. 6 91 0. 6006 12: 50 6. 64 100. 5 0. 66732 6. 63 102. 6 0. 680238 1: 50 6. 78 92 0. 62376 6. 65 93 0. 61845 Fixed Power (W) Voltage (V) Tracking

Results

Results In the morning, there is a 12% increase in efficiency. At mid-morning, there is a 6% increase in efficiency. Since, the sun’s rays is starting to become orthogonal to the panel As for noon, the efficiency are roughly the same. At this time both fixed and tracking panel are orthogonal to the sun’s rays.

Solar Panel Cont’d The following figure describes the effects of temperature on a photovoltaic cells. Provided by Squirmymchphee

Solar Panel Cont’d Other ways to improve the optimization of photovoltaic cells is to account for the rise in temperature of the cells. Possible Solution: • Usage of a heat sink • Usage of water • Either submerge the panel in a water solution. • Another method is the use a water system • Then there is the use of fan(s), the solar panel or the battery will help in powering the fan so that it can help reduce the temperature across the panel.

Optical Configuration Perhaps the most important aspect of the Portable Solar Tracker is the optical configuration. The purpose of the optical configuration is to increase the performance of the photovoltaic cells by increasing the amount of light that is received. Factors taken into consideration: • Size • Shape • Weight • Material Reflectivity • Durability • Heat Concentration

Mirrors

Mirrors Plane Parabolic Trough Simple Available Simple Easy to control Single or Dual-Axis Bulky/Less portable Foldable for a more compact frame Bulky/ Less Portable Single –Axis Less reflected light rays received Complicated frame/Motor System Simple Motor System Least amount of Heat Higher Heat concentration on Cells Not easily Available

Reflectivity The reflectivity of material is the amount of incident radiation reflected by a particular surface. Different materials are being considered including mirrors and aluminum foil among others. To maximize reflectivity the material has to exhibit specular reflection. Specular reflection is best explained by the law of reflection which states that the incoming light and the reflected light have the same angle with respect to the normal of the surface.

Optical Configuration The optical configuration that was chosen was a trough shape reflective material called Mylar placed onto a lightweight wire mesh. The trough shape was chosen because it could be made relatively cheap and efficient because it was easily modifiable to adjust the focal point to the location needed.

Optical Configuration Why A Trough Mirror? • No clear cut difference in Parabolic mirror over Trough or Plane mirror design • Easy to fabricate/purchase • Allows for more incident light to be reflected • Cheap • Lightweight Why not use a Lens? Two different lens types were tested while investigating optical configurations. Both magnifying and Fresnel lenses reduced or had no effect on power output of the solar panels. In addition the lenses focused too much light onto the photovoltaic cells which thus began to damage the panels and reduce their efficiency.

Battery Options The battery will be a critical element of the device and will need to satisfy the established goals. Type Pros Cons Lithium-ion High energy capacity, lightweight, low self-discharge, handles overcharge well Expensive, thermal runaway, explosive, needs protection circuitry Nickel-Metal Hydride Good energy capacity, reasonable High self-discharge, sensitive to W/kg, constant voltage output overcharge damage, needs protection circuitry Lead-Acid Very durable, least susceptible to degradation due to multiple cycles Low energy density, heavy mass, lead is toxic

Selected Battery • • Ni-MH is the battery used for this project. 7. 2 V 3300 m. Ah from Radio. Shack (See Figure) Purchased for about 1/3 the price of similar Li-ion packages It is powerful, but the main concern will be lifespan.

Battery Charging Method • • The battery will be charged using a –∆V sensor fast charge method In this method: Charge voltage increases to peak, then falls to a voltage where charge is terminated. • This retains 100% charge capacity • Operates in 0 -40°C temperatures • This method can be moderated by a microcontroller algorithm controlling a switch Provide by SBS organization.

Battery Protection Circuit to the right provides basic reverse current protection with a MOSFET and Schottkey diode. Provided by Texas Instruments The figure on the left is the diagram of the battery protection circuit implemented on the PCB to protect against overcharging the battery.

Microcontroller For this project, the MCU of choice is the Atmel atmega 168 Microcontroller. • 20 I/O pins • Of the 20, 6 are analog pins • 14 digital pins • Of the 14, 6 are PWM pins • Can supply components up to 5 V • Operating voltage of 2. 7 -5. 5 V • Has lower power consumption mode

Microcontroller Cont’d

Microcontroller Cont’d To connect the pin outs for the various components are : • LCD requires 6 digital pins • Servo require 1 digital (PWM) pin each • Photoresister requires 1 analog pin each (4 Photoresister) • Compass requires 2 analog pins • Battery monitoring requires 1 digital pin • REED relay requires 1 digital pin • Pololu switch requires 2 digital pins

Motors Before the selection of a motor could be done, initial research into servo motors and DC motors was conducted. Servo Motor DC Motor Low Power Consumption Greater Torque/Speed Low Price Requires Motor Controller Simple 3 Wire Interface Higher Power Consumption Low Torque/Speed Greater Complexity

Motors A servo motor was chosen for the reasons listed below: • Low Cost ($9. 99) • Low Power Consumption (0. 036 W) • Ease of use/Familiarity Because the Solar Tracker follows the sun across the sky gradually over the course of a day, speed was not taken into consideration. Torque on the other hand was, but because of the portability of the Solar Tracker weight of the optical configuration was determined low enough for a servo motor to handle.

Servo Motors Once a Servo motor was chosen, a fixed rotation servo was compared against a continuous rotation servo. Continuous rotation was not required because the sun is never visible for over 180º at ground level. Name HS-322 HD S 9405 S 3001 Torque @4. 8 V 3. 0 kg. cm @6. 0 V 3. 7 kg. cm @4. 8 V 5. 8 kg. cm @6. 0 V 7. 2 kg. cm Speed @4. 8 V 0. 19 sec/60º @6. 0 V 0. 15 sec/60º @4. 8 V 0. 13 sec/60º @6. 0 V 0. 11 sec/60º Additional Idle Current Draw @4. 8 V - 7. 4 m. A @6. 0 V - 7. 7 m. A 180º Range Temp Range -4º - 140º F Coreless Motor Weight - 55 g Available Yes Price $9. 99 Yes $64. 99 @4. 8 V 2. 4 kg. cm @6. 0 V 3. 0 kg. cm @4. 8 V 0. 28 sec/60º @6. 0 V 0. 22 sec/60º Temp Range -4º - 140º F Single Ball Bearing Weight - 44 g Yes $16. 49

Compass A feature of the Portable Solar Tracker is an electronic compass which will allow the user to determine the current direction the base is facing via the LCD Display. The factors that were important when selecting a compass were: • Low power consumption • Modes of operation (Standby) • Reliability • Price

HMC 6352 The HMC 6352 is the compass chosen for use with this project. Name Axis Additional Available Price HMC 6352 Operating Voltage 2. 7 V - 5. 2 V Dual Axis Yes $34. 95 HM 55 B 3. 0 V - 6. 7 V Dual Axis Yes $29. 99 HMC 5843 2. 5 V - 3. 3 V 3 - Axis Heading Repeatability - 1º Heading Resolution - 0. 5º 3 Modes of Operation Standby Mode 1 µA Current Draw in Standby Voltage Regulator 5 Different Operating Modes I 2 C 551 Spark. Fun $49. 95

Displaying To represent the information to the user, an LCD with HD 44780 controller is used. Features • 16 x 2 characters • 5 x 8 dot matrix • Operates at 2. 7 to 5. 5 V • 8 or 4 -bit interface is used to save I/O pins.

Displaying The Pololu switch is used to help display information on the LCD screen. Once the button is press the following information will be Displayed • Battery life • Battery Voltage • Load current • Temperature • Directional Heading

Output USB female adapter To power handheld devices such as cell phone, Mp 3 player, and camera.

Output To replicate a USB charger, the Data + and Data – pins must produce 2. 5 V and 2 V, respectively.

Battery Monitoring Specifications of the monitoring system • Battery life • Charging and discharging state • Sleep mode • Overcharge protection Maxim DS 2438 battery monitoring IC • 1 -wire interface • Temperature sensor • End-of –charge and discharge detection • Measure Voltage • Measure current through sense resistor Provided by Maxim-IC Co.

1 -Wire Bus System Allows the microcontroller and the device to communicate with a single connection. When idle the wire is resistively pulled up to a high state. Communicating by using a controlled lowduration time pulse. Logic 1 transmits as a short pulse and logic 0 transmits as a long pulse. Provided by Maxim-IC Co.

Battery Monitoring Circuit

Method of Tracking Photoresistor is a device that changes its resistance depending on the amount of light exerted on it. Provided by Perkin Elmer inc. As the level of brightness increases, the resistance decreases.

Method of Tracking The position of the sun can be determined by differentiating the voltage drop across the two photoresistors. The voltage vaules are quantized by the Arduino’s A/D converter.

Method of Tracking To find the photoresistor that has high sensitivity, each one is measured for its responsiveness to the change in position of the sun.

Interfacing with the Microcontroller Interfacing of components used in this project is displayed to the right. The microcontroller is the heart of the device. • LCD • Compass • IC’s • Servo motors • Battery • Solar panel

Interfacing Circuitry

Interfacing Circuitry

Interfacing Circuitry

Interfacing Circuitry

Interfacing Circuitry

Programming The Arduino microcontroller is programmed in it’s own Arduino programming environment. The language is based on C and C++. There are three main parts Arduino programs are divided up into: Structure (if, for, do while, etc…), Values (constants and variables), and Functions. There also many libraries to control components such as Servos, LCD displays, and EEPROM.

Programming Flow Chart

Programming Samples Void Photocheck 1 ( ) voltagearray[x] = Meas. ADC(_1 W_Pin, V_AD); { for(i = x; i > 0; i--) if (photo 1 < photo 2) { if(voltagearray[i] < voltagearray[i-1]) { if (timeelapsed < 10000) dropping++; { temparray[y] = Meas. Temperature_2438(_1 W_Pin); rotate. Xservo (10) for(j = y; j > 0; j--) } { else if (timeelapsed < 150000) if(temparray[j] > pow(voltagearray[j-1], 1. 25)) { rising++; rotate. Xservo (15) if(dropping >= 3 || rising >= 3) } digital. Write(relaypin, LOW); else } { } } } Battery Protection Photoresistor Comparison

Mechanical Structure The picture shown is a representation of the mechanical structure that is used in this project. The trough system will be setup as depicted in the picture shown. Motors will be attached on the side of the trough so that it can rotate 180 degree across the sky, as well as a servo on the base to move it left and right. All of the components will be placed within the enclosure. The enclosure will be a box with dimension 14. 5 in long X 8 in wide X 20 in high and is made from acrylic.

Milestones

Milestones

Budget Initial Estimated Budget Solar Panels: $50 Battery: $50 Microcontroller: $50 Motors: $30 LCD Display: $30 Optics (Mirrors and Lenses): $40 Frame Components: $50 Cooling System: $30 Miscellaneous Components: Total: _______$70_______ $400

Budget Current Expenditures (as of 7/31/10) Solar Panels: $150 Battery: $22 Microcontroller: $37 Motors: $50 LCD Display: $8 Optics (Mirrors and Lenses): $16 Frame Components: $129 Miscellaneous Components: Total: _______$133_______ $545

Manufacturability This project can be reproduce with the following amount Solar Panels: $120 Battery: $22 Microcontroller: $4 Motors: $20 LCD Display: $8 Optics (Mirrors and Lenses): $16 Frame Components: $60 Miscellaneous Components: Total: _______$30_______ $280

Progress Research Design Part Acquisition Progress Prototyping Testing Overall 0 20 40 60 80 100

Work Distribution Chris Tuyen Stephen Tri Circuit Design - X X - Programming Architecture - X X X Mechanical Design X X Optical Design X - - - X X PCB Fab.

Work hours Distribution Chris Tuyen Stephen Tri Total Circuit Design 30 40 40 20 130 Programming Architecture 10 50 50 10 120 Mechanical Design 35 35 140 Optical Design 15 5 15 10 45 PCB Fab. 30 5 35 20 90 Misc. 20 20 80 Approximated

Challenges 1. Power 2. Panel Configuration 1. 12 parallel -> MCU 2. 4 – 2 set in series then in parallel -> Battery/Output 3. Compass readings distorted by wire mesh/metal screw and washers 1. Compass calibration 4. Replacement servo 1. Original motor burnout

Future Improvements 1. 2. 3. 4. 5. 6. 7. More precise values for photoresistors More efficient solar panel Bigger tracker More efficient concentrator Plastic screws Weight reduction Heat dissipation system

Questions ?