Votey Solar Roof Array Test Facility Team 3: Gabrielle DaGama (ME), Shane Bluto (ME), Anthony Lauzon (EE), Lawrence Thurber (EE), Jack Christoforo (CS)
Funded by the UVM Clean Energy Fund Client: Mieko Ozeki and the Office of Sustainability Mentor: Paul Hines
Problem Statement The project involves designing 1-D and 2-D solar panel trackers in order to compare the power production of these systems with a fixed panel mount and with each other. The devices will be designed to maximize net energy production under a variety of weather conditions, while minimizing materials cost. We will also design a web-based interface that relays information on Votey energy consumption and the energy production of both the dynamic and static panels. The interface will be educational, accessible, and understandable for the layperson. An interactive kiosk will also be installed on the first floor of Votey Hall.
Mechanical Design Overview
• Mechanical design of the project underwent •
numerous changes throughout the course of the year Setbacks o limited amount of source voltage o large non-uniform wind loading selection of the drive mechanism was difficult -originally, a slewing drive was chosen to rotate the panel along the azimuth, however the size which fit our design best was powered with 24 V, which was too large for this application
Mechanical Components
• Racking & panel clamps • Threaded rod • 4 bearings per system • Linear actuators take the place of slewing drive • Aluminum plates • U-Channel • •
o connects panel racks to rotational mechanism Hinge system for the 2D tracker o for elevation change Panels are supported by three, five foot tall posts on the roof of Votey Hall
Mechanical Analysis
• Max stress, strain and deflection from a snow load. Max Stress
149 MPa
Max Strain
56
Max Deflection
13.44 mm
• Wind load calculations were done using a
90 mph wind speed, from this the force of the wind was calculated to be 711 lbf o
This force was applied to solidworks model and revealed similar results to snow load
Mechanical Testing
• Measuring angle of rotation along the azimuth with actuators attached o o
too much force for the actuators to overcome to obtain the full 230 degrees can achieve about 170 degrees across the azimuth
• A lot of methods learned along the way o
machining was difficult at times based on the way we had designed different components
1 D
2 D
Mechanical Obstacles
• The panels were not rotating as far as we desired o
mounted the linear actuators off-axis to achieve larger degree of rotation
• There was too much slop in the stock mounting
brackets for the linear actuators o drilled out the holes on the brackets and inserted a larger bolt into the hole o added nylon spacers and washers to solidify the mounting of the actuators
Electrical Design Overview The electrical portion of the design consisted of three key tasks: Get the local time and sunrise and sunset times for the current date by using an RTC and crystal oscillator 1. Continuously calculate the current sun azimuth and elevation angles 2. Move the panel to the correct position using a feedback-based control algorithm and actuators with feedback capability.
Electrical Design Overview Continued
• actuator control algorithm function
• get feedback from actuators • determines panel's position • compare it to the sun's position • instruct motors to move if panel is not within the required angle
• linear equations were developed to relate feedback voltage to degrees rotated
Electrical Issues/Obstacles • Inaccurate feedback voltage due to transients coming from the Arduino Motor-Shield (motor drive circuit),
o
Solution: Since the high voltage (5 VDC) on the positive terminal of the potentiometer had the same transient waveform as the potentiometer's wiper, we used the ratio of the two in our equation to cancel the transients out.
• The RTC not working and not working consistently o
Solution: At first the RTC didn't work at all. We realized we needed to use a crystal oscillator to trigger the RTC with a 32kHz signal. Long wires, crossed wires, and an old breadboard (we suspect) were allowing external noise to couple into/disrupt our RTC signal. Soldering components onto a permanent PCB resolved this problem.
Electrical Components The electrical subsystem for each tracker consisted of:
• One RTC (Real-Time Clock) chip • One 32kHz oscillator chip • One Arduino Mega 2560 MCU • One Arduino L298 Motor-Shield • One 12VDC power supply • One 3.3VDC power supply • Five 1/4W, 5% resistors (two 2.4k, one 1MEG, •
one 62k and one 69k) Two ceramic/poly-film capacitors (one 1nF and one 1.5nF)
RTC & Oscillator Schematic
Electrical Testing
• Connected linear actuator to a 12VDC power supply under panel load o o o
Maximum torque (and hence max current, ~2A) was required to move panel from sunrise position. Motor-Shield can not exceed 2 amps without failure; Was solved by lowering drive voltage: as little as 1.75V can drive the actuator, which in turn reduces the drive current.
• Connected linear actuator to a 12VDC power supply with no load o
Pulled an average of 0.5 DC amps under no external load, initial DC spike was 0.9 DC amps
Electrical Testing - Section 2
• The graph shown in the next slide depicts the
relationship between the azimuth angle of the panel and the current drawn by the linear actuator. The biggest and smallest angle (0 and 130 degrees) will require more torque to drive the actuator, which in turn increases current. When the panel reaches the middle (~65 degrees), the torque is minimal, so the drawn current won't be as high. As we decrease voltage, we decrease the current drawn by the actuator, but the actuator will still drive as needed.
• • •
Electrical Testing - Section 2 Continued
Computer Science Overview Main Task: Provide a user friendly, accessible interface to view and analyze the energy production data of the solar arrays. Implementation: We have designed and built a web based GUI(Graphical User Interface) to display data production data in formattable charts. Also, a touchscreen computer kiosk will be installed in Votey to interact with the GUI.
CS: Issues/Obstacles
• EnLighten API o
Beta
The enlighten API was at first in its pre-stable release Beta testing phase. The potential for interruptions in service were a concern. Fortunately the API left Beta recently.
o
API Activation In order to activate the API and receive data, we needed at least one reporting micro-inverter/solar array. This was delayed due to mismatched cables as well as zoning issues.
o
API Report Resolution
The API limits requests to one day reports at high resolution. This is a standing issue. The potential solution being implementing a local database.
The Kiosk
The GUI
System Flow
Results Relative to Objectives & Requirements
• Achieved an array of a static, 1D, and 2D solar panel tracking system
• Achieved programming an algorithm which guides panels to track the sun
• Achieved producing a user interface to interact with the production data
• System is energy efficient
Conclusion and Future of Project
• Future options to improve the tracking system
would be implementing a mechanism to create more rotation across the azimuth o
Slewing drive or gear system
• Incorporate a power down (sleep) function •
between sunset and next day sunrise Compensate for actuator overshoot o o
Use the brake function, Drive to precisely 5 degrees beyond sun's azimuth
• Use closed-loop tracking with LDR's to increase radiation capture on cloudy days
Conclusions and Future of Project cont.
• GUI o o o
Further functionality needs to be added. Implementation of local database to allow for multiple day charting. Integration with the remaining two panels solar arrays after installation.
• Kiosk o
The Kiosk needs to be installed in Votey.
Thank You! Thanks so much to all those who made this project possible: Mieko Ozeki (Client) Paul Hines (Faculty Mentor) John Novotny Jeff Frolik Mike Fortney Kurt Anthony Floyd Vilmont Michelle Smith