Investigating Solar Energy through Solar Cars and Sun Path Diagrams

Transcription

1 Investigating Solar Energy through Solar Cars and Sun Path Diagrams Subject/s and Grade Level/s: Technology, Physics Middle School High School Overview: This lesson will introduce students to solar energy and how solar panels convert solar energy from the sun to electrical energy. The students will work in groups to build a solar car and approximate what times throughout the year an obstacle such as a building or tree will shade a solar panel. Objectives: Students will be able to work together as a team to build a solar car. Students will be able to use a protractor and plumb-bob to measure the altitude angle of an obstacle. Students will be able to use a compass or protractor to measure the azimuth angle of an obstacle. Students will be able to see a solar panel provide energy to a motor (solar car) Students will be able to estimate what time of the year an obstacle will shade a solar panel. Materials required: Sunny-Side Up Solar Car Kit Classroom 10-Pack (1) - $200 Protractors (at least one for every group but ideally one for every student) ~ 6 inch Piece of String (same quantity as protractors) ~1 inch Piece of Tape (same quantity as protractors) Weight (e.g. a paperclip or metal nut) (same quantity as protractors) Scissors (1 for every group) Compass Smooth board to race the solar cars on (optional) Prep Work: Solar Cars The required parts to build a Sunny-Side Up Solar Car are the following: Coroplast frame (1) Push pin (1) Screw eyes (4) Wood Blocks (2)

2 Shorter Axel Shaft (1) Longer Axel Shaft (1) Wooden Wheels (4) Piece of Sandpaper (1) Piece of Tubing (1) Pulley (axel) (1) Pulley (motor) (1) Motor (1) Motor Mounting Clip (1) Elastic Band (1) Solar Panel w/ Alligator clips (1) Set of Instructions * You can find this list with the provided instructions in the Sunny-Side Up Solar Car Kit Classroom 10-Pack. Divide the necessary parts of Sunny-Side Up Solar Car Kit Classroom 10-Pack to make 10 complete kits (note there will be some extra parts and some parts that will not be used to make the solar cars). Plumb-bob and Protractor The following instructions are used to make a device (plumb-bob and protractor) to measure the altitude angle of an object (for the Sun Path Diagrams worksheet). 1. Tie/Attach the weight to one end of the string 2. Tape the other end of the string to the center mark on the protractor (found along the straight-edge of the protractor) Procedure: After providing information on solar energy and how solar panels works (see powerpoint slide) divide the class up into at most 10 groups. If the groups have a small number of students (3 or less) then they all can collaborate on building the solar car and then work together on the Sun Path Diagram worksheet. However, if the groups are large (greater than 3), I would suggest having 2-3 students start to build the solar car while the rest work on the Sun Path Diagram worksheet and when the group working on the worksheet is finished have the two groups switch roles. This avoids too many students standing around with nothing to do when the groups are large.

3 SOLAR CARS Have the groups construct the solar car. This should take approximately minutes. Detailed instructions with graphics are provided with the Sunny-Side Up Solar Car Kit Classroom 10-Pack. An alternative to building the specific car from the kit, the students could be provided with additional material (e.g. smaller or larger wheels, different size pulleys, etc.) to design their own unique car. When all the groups have finished building their cars, have them test them to make sure the leads from the solar panel are correctly wired to the terminals of the motor. If the car travels in the reverse direction than intended then simply swap the leads on the motor. The groups will compete in a drag race style competition, head-to-head against another group. Mark a starting line and a finishing line with a distance of approximately 3 4 ft between the two. First have a time-trial competition in order to seed the groups. If there are more than eight groups then the slowest teams (the 3 slowest if there are 10 groups, the 2 slowest if there are 9 groups) race against each other in a round robin (each team plays each other once) for the final 8 th seed.

4 SUN PATH DIAGRAMS FOR SHADING ANALYSIS WORKSHEET The amount of solar energy that gets converted into electrical energy decreases if the solar panel is partially shaded (or covered in dirt). So when installing panels, one wants to position them where they will least likely be obstructed by surrounding objects such as trees, buildings, etc. Depending on your latitude location, the sun will be at different altitudes throughout the year depending on what day it is and what time of day. One can sketch nearby objects surrounding the solar panels on a sun path diagram to see if they will obstruct the panels, and if they do, what time of the year do they obstruct the panels. To get the most accurate shading analysis, use the sun path diagram closest to your location s latitude. Have the groups go outside with their worksheet and plumb-bob-protractor measuring device. Walk to a location and stand where the solar panel would be located. Now face south and locate an obstacle such as a tree or a building. Measure the height (altitude angle) using the plumb-bob protractor. Sight the top of the obstruction with the top edge of the protractor and measure the angle. (Remember the angle is the offset from 90.) Using a compass when facing south or a protractor with the 90 mark facing toward the south, measure the width (azimuth angle, Φ) to one side of the obstruction correcting for the magnetic deviation (i.e. the fact that a compass points to magnetic south not the true south). This correction factor can be determined from the figure below. From Troy, NY the correction factor is approximately 13. Φ 13 Φ 13 Φ = compass + 13 Φ = compass - 13 Φ = 13 - compass

5 Now sketch the outline with the corresponding altitude and azimuth angles on the sun path diagram (see Figure below) Where your sketch overlaps any of the paths is when that obstacle will be shading the solar panel reducing the amount of energy output from it. One needs to minimize shading as much as possible. REFERENCES: Masters, Gilbert M. Renewable and Efficient Electric Power Systems. Hoboken, NJ: John Wiley & Sons, Print.