Embedded Files
What to expect
In this activity, we will create and learn how to read a sun path diagram. This will help us understand where the sun will be in the sky at any date and time of the year. Using this information, we will create a simple heliodon that will allow us to visualize the sun's path with the help of the diagram.
Connections
In our previous activities, we explored the technical features of hardware such as servos, DC motors, and sensors. To create a solar panel that tracks the sun, we must know the technical constraints and how to accurately predict where the sun will be at any time and date. This activity will help familiarize you with the sun’s path throughout the year.
Materials
Cardboard
String
Clip Pin
Hot Glue Sticks
Tape
Protractor
Ruler
Instructions
We will learn terms like elevation, azimuth, and zenith angles to help us pinpoint the sun’s location at any time of the day. This information will allow us to point the solar panel directly at the sun.
You will build a simple heliodon. This device will help us understand why a solar array would be better off with solar tracking capability in the first place.
Part 1
Figure 1. Sun Angle Explanation
First, we must learn the important angles to locate the sun, as shown in Figure 1.
Image Credit: https://www.researchgate.net/figure/Local-coordinates-of-the-sun-elevation-zenith-and-azimuth-angles_fig1_337214527
Elevation Angle: This is the angle from the horizon or ground to the sun.
Azimuth Angle: This is the horizontal angle from a reference angle to the horizontal position of the sun. Directly north is 0 and increases when moving clockwise from straight north: East is 90 degrees, South is 180 degrees, and West is 270 degrees.
Zenith Angle: This is the angle from straight up in the sky to the sun.
Now that we understand the angles that tell us the sun’s position in the sky, we will learn how to read the sun path diagram before we start building a heliodon. Watch 4:00 - 6:03 from this video.
Part 2
We learned the important angles for tracking the sun and how to read a sun path diagram. Now, we can create a simple heliodon for a location of our choice.
Open up Google Maps on your computer.
Type in the address of your school, home, or somewhere else in your local community where you would like to explore the sun path.
Right-click on the red marker above the location you looked up, as shown in Figure 2.
Figure 2. Google Maps Drop Down Menu
4. A menu like this one should pop up. The numbers at the top are the longitude and latitude of the place you picked. Click on those numbers, which should automatically be copied to your clipboard.
Figure 3. Tab Feature
5. Now open up this website on your computer to create our sun path diagram. Ensure you are on the “Sun Position” tab on the screen's left side, as shown in Figure 3.
Figure 4. Coordinates Box
6. Make sure that “select your points” is selected in the top left box. Next, paste the coordinates from Google Maps into the “search” box, as shown in Figure 4.
Figure 5. Box to Set Date
7. Select the “GMT-6” in the “Time Zone” box on the right side of the tab. You can enter a date, as shown in Figure 5. This could be the current day, your birthday, or anything you want.
Figure 6. Execute Button
8. Once you complete all these steps, click the blue “execute” button at the top of the page, as shown in Figure 6.
Figure 7. Completed Sun Diagram
9. Take a screenshot of the sun path diagram in the middle of the webpage or hit the “download PDF” button under the sun path diagram, as shown in Figure 7. You only need to print out your sun path diagram.
10. Cut out the sun path diagram. MAKE SURE YOU DON’T CUT OFF THE DATES ON THE RIGHT SIDE OF THE DIAGRAM.
Figure 8. Heliodon Base with Center Lines
11. Cut out a 1 ft by 1 ft square of cardboard and draw two straight lines to split the cardboard into four equal sections, as shown in Figure 8.
Figure 9. Base with Sun Path Diagram Added
12. Put a hole through the center point of your Sun Path Diagram and a hole through the center of the cross created by your center lines. Glue the Sun Path Diagram down so that the center holes match up. Line up the N-S line on the chart with one of the lines on the cardboard. Line up the W-E line on the chart with the other line on the cardboard, as shown in Figure 9.
Figure 10. Base with Solstice Lines Added
13. Line a ruler up with the center hole of your Sun Path Diagram and where the June solstice line intersects with the outside of the chart. Measure 6 inches from the center hole and draw a dot on the cardboard. Connect the dot to your diagram with a straight line. Repeat this process for the other end of the June and December solstice, as shown in Figure 10.
Figure 11. Actively Measuring Solstice Lines
14. Measure the distance between the dots you drew for the June solstice or between the dots you drew for the December solstice. They should be roughly the same, as shown in Figure 11.
Figure 12. Pencil with Measured String
15. Tape a piece of string to the bottom of a pencil. Cut the piece of string so that the excess string attached to the pencil is half the distance between the dots of either solstice, as shown in Figure 12.
Figure 13. Cut out Solstice Arches
16. Mark a dot on the bottom of another piece of cardboard. Hold the loose end of the string on that dot. Use the pencil to trace a semicircle around the dot, making sure that the pencil is pulled as far away from the dot as the string allows. Take the pencil and trace another semicircle inside the first one. Cut out the arch you made, as shown in Figure 13. Repeat this process to make two arches.
Figure 14. Backside with String Taped Down
17. Cut out a piece of string that is at least a foot long. Thread a small amount of string through the center hole in your chart. Tape the string down on the back of the chart, making sure that the excess string is coming through the top of your diagram. On the back side, the string should be taped down as shown in Figure 14.
Figure 15. Arches Aligned to Dots
18. Take one of your arches and line up the outside edges of the ends of the arch with both the dots for the June solstice as Shown in Figure 15.
Figure 16. Arch with Triangle Wedges Glued On
19. On the sun path chart for your location, find the altitude angle at solar noon on June 21 (Summer Solstice). “Solar noon” occurs when the sun is positioned due south of your location. In the given example, the altitude angle is about 75 degrees. Make two wedges to support the arches using the protractor provided, as shown in Figure 16. The wedge angle should match the elevation angle. Cut it out and glue it to the bottoms of your arch.
Figure 17. Model with June Solstice Added
20. Glue the bottom of your arch onto the base piece of cardboard so that the outside edges of the ends of the arch line up with both dots for the June solstice, as shown in Figure 17.
Figure 18. Model with June and December Solstices Added
21. Repeat this for the December solstice. The December solstice's elevation angle at solar noon is about 25 degrees. Your Sun Path Model is now complete, as shown in Figure 18.
Part 3
Use the end of the string to represent the sun in the sky.
Set the end of your string (representing “sun”) to 3:00 pm on the winter solstice (December solstice). Does the elevation action match your reading from the sun path chart? What should the tilt angle of the solar panel be? (Hint: Optimal solar array tilt angle=90 - Elevation Angle)
Now, set the “sun” or end of your string to 11:00 am on the winter solstice. Would the position you set your solar panel change for this time even though it is the same day?
Set the “sun” or end of your string to noon on the summer solstice. Would you change the tilt angle of the solar array from the previous example? If so, at what angle?
Now, set the “sun” or end of your string to 3:00 pm on the summer solstice. Would the position you set for your solar panel change for this day even though it is the same time you set in the previous step?
Use your heliodon to explore the sun’s position at different times of the year. Think about how you would determine your solar panel's best azimuth and tilt angle.
Think about it
In this activity, we took a sun path diagram and created a heliodon. We can use this device to predict the sun's position for the location we picked at any point in the year.
Can the sun ever be positioned outside of the arches you created?
How would the position you would set your solar panel change depending on the time of year? How about the time of day?
Was there anything about this activity that surprised you?
Feedback survey
Next Time
In this activity, you learned how the sun moves using the sun path chart and created a simple heliodon. Next, we will create several solar tracking systems to understand the structure and programming of automated solar trackers.
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