Preliminary Design Specification for a Solar Tracking System, Study Guides, Projects, Research of Electrical and Electronics Engineering

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Project 20 - Daylight tracking system

Group Members: Group Mentor:

Darin Andrews Dr. Tom Plant Alex Johnson Brian Miller Matt Reich

Table of Contents

• 1. Revision History…………………………………………………..
• 2. Introduction……………………………………………………….
  • 2.1. Customer Requirements and Product Background…………
  • 2.2. Competitive Analysis…………………………………….....
    • 2.2.1. Product Space Analysis………………………………..
    • 2.2.2. Target Feature Set……………………………………...
  • 2.3. References…………………………………………………..
  • 2.4. Naming Conventions……………………………………......
• 3. Architectural Overview…………………………………………...
  • 3.1. Implementation Approaches………………………………...
• 4. Top Level Description…………………………………………….
  • 4.0. Executive Level Block Diagram……………………………
  • 4.1. Top Level Block Diagram………………………………......
    • 4.1.0. Interface List…………………………………………..
    • 4.1.1. Top Level Interface Definition………………………...
    • 4.1.2. Environment……………………………………………

and reduced cost. We have not decided whether to use a single axis system or a dual axis actively controlled system. The single axis allows us to reduce cost, decrease motor power consumption, and increase reliability/durability without significant loss of power generation due to longitudinal discrepancies. Using a dual axis system can increase costs, but could reduce maintenance by eliminating quarterly adjustments of the azimuth angle. We will be weighing the two options for increased efficiency before making our final decision. The target customer for our product is anyone who wishes to decrease reliance on non-renewable sources at a minimum cost. This could be home systems of 1 kW or commercial systems up to 100 kW. A large system would use many separate tracking controls for separate photovoltaic arrays.

2.2 Competitive Analysis –

We have developed a detailed spreadsheet (Table 1) of products/designs that are similar in function or performance in order to gain a better understanding of which features distinguish the best products from the rest. Model Manufacturer Power Req. Tracking Method Cost Number of Axis Dynamic Control

PV

Size Comments ETATRACK active 1500 Lorentz 24VDC Time- based operation $15,000.00 1 Linear Actuators Up to 2.5kW price includes PV panels Davy Solatraka LD Davy Industries

24VDC

Unknown $1,400.00 1 Linear Actuators 0.5kW SP675/4150 Sunwise Pacific Sun Tracker 24VDC Time- based operation $1,900.00 2 Linear Actuators 0.5kW ST-8 Solenergy 12- 48VDC Active Sun- sensing operation Unknown 2 Linear Actuators 1kW Power Tracker Power Light 120VAC GPS- controller tracking $8,000.00 1 Linear Actuators 1kW TR-15 Watt Sun 24VDC Active Sun- sensing operation Unknown 1 Linear Actuators 0.25kW TOP Tracker

DEGER

Energie 24VDC Active Sun- sensing operation $6,450.00 1 Linear Actuators 1kW Table 1-Competitive Analysis

2.2.1 Product Space Analysis –

In order to compare existing solar tracking systems we evaluated the following categories: power requirements, tracking methods, cost, number of axis, dynamic control method, and photovoltaic (PV) array size. From these different specifications we were able to see which methods had become industry standards, and which ones varied from company to company. The power requirements varied from 12-48VDC and 120VAC.

These voltages are mostly chosen based on the size of the array. If you are combining two 12V arrays, it may be best to put them in series for a 24V output, whereas if you are using four 12V arrays, you could create a 48V output. The tracking methods vary widely and our selection of which method to implement must result from careful analysis of all options and how we can improve upon them. Many companies use a time-based tracking method where the unit is inactive for the majority of the time, and turns on for a short period to check the sun’s location and rotate the panels to be normal to the sun. The frequency of these alignment checking operations for the primary axis varies from as often as every couple of minutes to only once or twice an hour. In the case of the secondary axis, this frequency may be even less, sometimes only once per season. Another tracking method used is the 'active sun-sensing' operation. This method uses an optical sensing network mounted on the controller chassis to feed information about the direct component of sunlight available, diffuse amount of sunlight, and differential amount of sunlight into the control electronics. The controller then adjusts the tracker sensitivity and solar array angle accordingly. The final tracking method we encountered uses GPS control to adjust the panels to a direction derived from known data about the sun's position relative to the position of the array. The cost section was the most difficult to compare due to differences in the products evaluated. Some products came as a complete package with solar panels and installation included, while others were bare bones systems where the solar panels had to be purchased and mounted separately. The number of axis selected has various effects on price as well as performance. A single axis system would be cheaper and simpler, but may sacrifice power from not being able to completely orient itself toward the sun. The decision of how many axes to use depends on the individual application, including the geographic location, and cost/maintenance considerations. The dynamic control method for all of the products we researched was a linear actuator. This commonality stems from the fact that linear actuators are easier to control, more reliable due to less chasing, and are more durable. Although linear actuators are more expensive than other types of dynamic control, their presence in almost all of the observed systems suggests that their benefits far outweigh the added cost. Furthermore, field tests have shown that linear actuators track the sun to a higher degree of resolution than other comparable control devices. The last category we compared was the size of the PV arrays. This information is helpful in telling whether the design constraints of these existing systems are the same as the design constraints in our project. The researched systems ranged from .5 kW to 2. kW, and our prototype system will be designed to control a variety of arrays, but for exhibition purposes will most likely not exceed 500W. We would now like to take a closer look at a few of these products in order to compare them and also to highlight some of the advantages and disadvantages of each.  Power Tracker: This solar tracking system from Power Light utilizes GPS control to adjust the panels to a direction derived from known data about the sun’s position. The Power Tracker is capable of increasing the energy output by up to 30% more than fixed-tilt systems. This tracker requires few moving parts which significantly reduces operating and maintenance costs as well as power consumption. This model is fully scalable from small to large scale installations, which is something that we should consider because our design is intended for similar purposes. Moreover, this tracker uses active tracking with microprocessor support, another feature we consider valuable. While the Power Tracker can reduce operating costs, the cost of the GPS tracker outweighs this advantage. Another characteristic we do not intend on modeling is the fact that it uses a “linked” design, while our product would be intended for independent single unit applications.

[1]Davy Solatracka LD, http://www.solazone.com.au/tracker.htm [2]Power Tracker, http://www.powerlight.com/products/powertracker.php [3]ST-8, http://www.solenergy.com.au/SolarTrackers.htm [4]TOP Tracker, http://www.degerenergie.de/ [5]TR-15, http://www.wattsun.com/ [6]ETATRACK active 1500, http://www.lorentzpumps.com/ [7]SP675/4150, http://www.solazone.com.au/tracker.htm

2.4 Naming Conventions Used –

Definitions: Photovoltaic - Capable of producing a voltage when exposed to radiant energy, especially light. Azimuth - Astronomy, Navigation. The arc of the horizon measured clockwise from the south point, in astronomy, or from the north point, in navigation, to the point where a vertical circle through a given heavenly body intersects the horizon. Linear Actuator – A motor that produces a translational stroke/motion. Chasing – A situation occurring where more energy is wasted moving the panels than is gained from achieving the best incident angle.

Wiring Nomenclature:

LA - Linear Actuator INV - Inverter PV - Solar Panel (Photovoltaic) BATT - Battery SS - Solar Sensor CC - Charge Controller MC - Motor Controller AZI - Azimuth EW - East/West _P - Positive GND - Ground UC - Microcontroller WS - Wind Sensor POS - Position DIR - Direction ENAB - Enable VOLT - Voltage

3. Architectural Overview –

This is a technical document and is not intended for the use of a general audience. This section of the document is an architectural overview of our new design, and gives an overall view of the functionality of the system, including how various operations and features interact with each other and the system. In this project we will build a solar tracking system at minimal cost, intended for use in single dwelling homes or large scale applications. We will implement the design, fabrication, and testing of a tracking system that meets the requirements and specifications for similar tracking systems already on the market, such as providing maximum output power, protection from inclement weather conditions, and being completely self-sustaining. In other words, we seek to create a tracking system that retains the standard capabilities expected from consumers, at a lower cost and with greater efficiency.

The main reason we chose to do this project is because we realize that our heavy dependence on renewable resources, such as oil, cannot last forever. The prices of these commodities are growing daily, and, aforementioned, these resources are becoming scarce. Therefore, we know that if we are able to improve upon existing solar tracking systems considerably, we will allow for much energy to be conserved. We expect to create a design that is more efficient and cheaper than existing systems, without a reduction in efficiency. In the next few sections, we describe the architectural roadmap for implementing this solar tracking system. We have explicitly developed a framework for our design, and explained why we made some of the preliminary design decisions we did. Our basic design will utilize two axes control of the array, one for east and west and one for azimuth angle. We intend this system to be a complete self-sustaining one, which can run on any common 12 VDC car battery or other commercial battery. The tracker will implement linear actuators and pulse width modulation to refine the movement of the PV array, for a ten-minute full swing from east to west. In a similar fashion, we will attempt to improve on more expensive units already on the market by eliminating unnecessary costs, without a reduction in efficiency. More importantly, this system will be nearly wind and weatherproof, as a wind sensor will be used to detect dangerous winds. No matter what the consumers intended use, the system we are designing will be scalable for single home use to large commercial arrays. Another crucial feature we plan on implementing is time-based tracking operation during inclement weather conditions, which overrides the active sensing method in order to prevent the system from chasing. In summary, when we are finished with this project we will have a reliable time-based tracking system that is cheaper than existing products, with better results during adverse weather conditions.

3.1 Implementation Approaches –

After gathering information from other similar designs on the market, we have a superficial idea of some of the features we might adopt into our system. We know some of the ways in which these systems work, but many of the inner workings are not advertised publicly. We are designing our controller to be a cheap, yet reliable and scalable alternative to these high priced products. One of the first things we encountered was how to track the sun. Many of the products on the market use active sun-sensing techniques. Some of the products we examined used timer-based trackers, whereas, even fewer utilized a GPS tracker. Our design will incorporate both of these approaches. This product is intended to actively sense the sun when running in default mode, allowing the array to always receive the most efficient (normal) incident angle of light. The sensors will also detect when direct sunlight cannot be found through an absolute light intensity detector. In these instances the controller will change the array into a time-based set of motion to prevent chasing. Furthermore, we had to decide the number of axis that we would track. While the majority of systems we researched only tracked one axis, we will implement tracking and motion of two axes. We discovered that most of these systems used various ways to manually adjust the array, requiring changing seasonally. We will concentrate the motion on the east-west axis, but will actively sense and control the azimuth angle as well. Moreover, we needed a system to provide the motion to the array. In earlier stages of this project we had considered using motors to control the direction of the arrays. Upon second thoughts, not a single system we studied used motors, as the commonality in all products was the use of linear actuators due to their ease of control and lower maintenance costs. Therefore, we will use linear actuators to control the motion of the array. To control the entire system we will be using the atmega128 microcontroller in large part due to its availability, but more so the working knowledge we have already

of these components is contained in the following pages, as well as block diagrams for each indicating all of the major interfaces between components, excluding the detailed inner workings of each.

4.0 Executive Level Block Diagram –

Figure 1: Top-Level Diagram

4.1 Top Level Block Diagram –

4.1.1 Top Level Interface Definition –

Figure 3: Motor Controller This motor controller is designed to improve the accuracy of the movement required by our linear actuators, and it is controlled by the microcontroller. There will be a total of six inputs into this device, all indicated in figure two. They will consist of an azimuth direction control, labeled AZI_MC_DIR, and an east-west direction control, labeled EW_MC_DIR. These will be one-bit signals, either having a 0 or 1 on them. This will control which direction the linear actuators move, (i.e. forward or reverse). There will be two inputs for enables, one for azimuth labeled AZI_MC_ENAB and one for east-west labeled EW_MC_ENAB. Normally, these actuators would function at one speed. In order to get the control we desire and to have an adjustable speed, these linear actuators require pulse width modulated (PWM) signals on the motor controllers’ enables to slow down the linear actuators. By reducing the speed of the linear actuators, it can make more accurate movements and allows for finer adjustments. It is undecided at this point which linear actuator we will be using. We do know that we want to find one with a stroke length from 9 to 14 inches, capable of pushing up to 35 pounds. It will be difficult to find actuators within our price range capable of meeting these specifications.

Figure 4: Charge Controller The charge controller’s main purpose is to distribute and regulate power coming from the solar panel. The controller takes the hot lead from the panel, PV_VOLTAGE, which may go as high as 17 volts depending on the panel selected, and converts it to a voltage appropriate for charging the battery and supplying the inverter. Inside the charge controller there is a switching network that allows the current from the panel to flow into the battery or directly to the inverter. Similarly, a voltage monitor is used to check the battery terminal voltage and instruct the switching network to stop charging when the battery reaches capacity, around 14.4 volts. This voltage monitor will most likely use a timing system to disconnect the solar panel when it checks the battery terminal voltage to obtain more accurate results. When the controller is charging the battery, the path from the solar array to the battery is interrupted by a current limiter (capable of adjusting the current level as the battery approaches its maximum capacity) to ensure the battery is charged at the proper rate. This rate will be calculated based on the battery manufacturers specifications, which is usually around c/20, where c is the total capacity in Amp-hours of the battery. The final element in the charge controller is the five volt voltage regulating circuit, which supplies the microcontroller with a constant regulated five volt supply. The charge controller requires five connections to adjacent devices; the solar panel power input, PV_VOLTAGE, which is distributed as described above; the positive and negative battery terminals, BATT_P and GND, which provide power to the internal circuitry and the power inverter; the inverter input, INV_P, which provides power to be converted to 120V at 60Hz for standard appliances; and the supply line for the microcontroller, +5V, which supplies a regulated five volt output.

Figure 6: Microcontroller The microcontroller will be the functioning brains of our project. It will begin in power down mode and use a light intensity sensor as an external interrupt to wake. The array will begin the day pointed in the direction of the sunrise, and the microcontroller records this initial position. The controller will receive inputs from four different sensors to determine where to point the array and where the array is pointing. Then, a signal is sent to the linear actuators instructing them to move the array. Also, the controller will detect/display the voltage coming from the array. We have not determined pin numbers for the signals as the design is not yet finalized. The first sensor will be a four-piece sun direction sensing unit which will send four signals into the microcontroller AZI_SS_COMP, AZI_SS_DIR, EW_SS_COMP, and EW_SS_DIR. One of the signal types will be a compare signal that will have one compare for the east-west and one for the azimuth sensors. This signal will tell the controller when the sun is at equal intensity between two sensors. When the signal has equal intensity between the sensors the array will not move. As soon as there is a difference detected between the sensors, the array will move to return the sensors to equal intensity. The other signal will be a direction signal from both the east-west and azimuth sensors, capable of telling the controller which direction the array needs to move to reach equal intensity.

The next sensor is the light intensity sensor, which sends the signal named INTENSITY_SENS to the microcontroller. This sensor will be the external interrupt that wakes the controller from power down mode. Moreover, it will be used to sense the overall intensity of the light coming into the array. The sensor will give the controller an idea of what weather conditions exist. If it’s overcast the controller will prevent itself from chasing to find the best incident angle. The final aspect of this sensor will be to tell the controller when it’s time to return the array to facing west and power down. The next sensor group will be two position sensors. The signals coming from these position sensors will be EW_POS_SENS and AZI_POS_SENS which communicate the current position of the array to the controller. There will be one to sense the east-west position and another to indicate the azimuth position. For now, we have included one wire from each of these sensors, which could change in the final design as we have not figured out how we will be doing the position sensing at this time. It will either be an active sensing of the actuator position or it will be a limit switch designed to reset the controller angle once a day. The final sensor input will be the wind sensor alarm. The signal coming from this sensor will be named WS_ALARM, and will indicate to the controller when the wind speed is high enough to damage the array. In response to this alarm, the controller sets the array to become flat to prevent wind damage. The alarm signal will be connected to an external interrupt so the controller can wake and set the array flat at night. The linear actuators will be controlled by four signals from the controller, including AZI_MC_DIR, AZI_MC_ENAB, EW_MC_DIR, and EW_MC_ENAB. The actuators we intend on using only have the ability to be fully on or off. To control the speed of the actuators we are going to use a pulse width modulated signal. There will be one PWM signal for each actuator, the east-west and the azimuth actuator. The azimuth actuator will use a slower speed so the signals will be different. We have not determined the PWM signal as we do not yet know which type of actuator that is going to be used. The other signal will be a direction signal from the microcontroller, which will tell the motor controllers which direction the actuators need to move. The controller will take a voltage signal from the array. This signal will be scaled to less than 5V for the microcontroller inputs using a voltage divider and will be named PV_VOLT_MEAS. This signal will run into the microcontrollers Analog to Digital Converter and will output a voltage to the LCD display. The charge controller will supply power to the controller board in the form of a regulated +5V input, and will also provide the GND input for the controller board.

4.1.2 Environment -

This model will need to be designed with Mother Nature in mind. It is more than likely that wherever this design is implemented, it will be exposed to the elements. This will depend largely on where, geographically it is installed, but could potentially be exposed to rain, heat, dust, etc. In order to combat this, we will be housing our electronics inside either a NEMA 3R, or NEMA 4X enclosure. NEMA (National Electrical Manufacturers Association) is the standard by which enclosures are rated. The 3R rating means that it is able to handle indoor and outdoor conditions, and provide a degree of protection against falling rain, and the formation of ice. These are the majority of our environmental concerns. For installations near coastal waters an enclosure with a 4X rating would be preferred. This enclosure provides equal protection in 3R categories, while exceeding it in others. The 4X means that it can withstand the ingress of water (hose down) and resists corrosion. There are other considerations that may impact our design and they must be addressed. The identified weak points in our system are as follows: our PV panel, mechanical connection between the linear actuators and panel, and our supporting structure. The intent is that our design will move the panels to a predetermined position