# Solar Energy Exploration Kit

The Solar Energy Exploration Kit includes a class set of materials to build on the the activities from the SunDawg bags.

Activities

1. Mini Solar Cars Lessons
Conduct the initial SunDawg activities (see included lesson cards), a solar car race, experimenting with solar angle, color filters, and car customization. Note: the inexpensive cars work well but they do easily lose their rubber tires which stop them from rolling. Check each tire to make sure it is on its wheel straight and not rubbing the car. The lesson works best if done in student pairs. You can download additional copies of the lesson plan cards and this solar energy exploration lesson with the link below.

http://www.cei.washington.edu/education/lessons/sun-dawg-solar-car-bags/

1. Meter Measurement
Assemble the multimeter. Place the red clip lead in the socket labeled Vma, and the black lead into the one label COM. Rotate the dial to DCV 20 (volts) or 2000m (millivolts) and measure the voltage across the leads of a solar cell under full illumination. Rotate the dial to dc amps 20m to measure the current in milliamps (1000th of an amp). Guide the students to make these observations or discoveries.
1. Solar cells produce positive voltage from one lead and negative from the other. If you look carefully you can see that the negative lead is coming from the top (light facing) side of the cell.
2. As you increase the amount of light the voltage increases up to a point (about .5 volts for a single cell or more if several cells are wire in series) and then no more.
3. The current continues to increase with additional illumination once you have reached the operating voltage for the cell.
4. The total power from the cell is calculated by multiplying volts x amps. P=V x A. Note: to calculate the power in watts the measured current in milliamps should be expressed in terms of amps. Eg 200m x .001 = .2 amps. See if you can confirm the manufacturer’s rating of .65 watts.
5. Connect the panels in series and measure the voltage and current. Repeat with the cells wired in parallel. Voltage is added in series, current is added in parallel.
6. Measure the power from a panel as you tilt it with respect to the sun at 10 degree intervals. Plot angle vs power. Discuss the implications of this data for placing solar panels on a roof.
2. Motor Spinner
Connect the DC motor to one or both solar cells. Place a gear or some kind of object on the shaft so that you can see it spinning.
1. What happens when you reverse the polarity of leads leading to the cell?
2. How does the speed of rotation relate to the power available from the panel(s)?
3. Can you design some kinetic art that spins when the sun shines?
4. If you were going to place this sculpture outside year round what engineering challenges would you have to solve?
5. Can you design a car or boat that is powered by the solar cell and motor?
3. LED Light– Connect the flashing Light Emitting Diode (LED) light to the solar cell. LED generally require about 3 volts so it will be necessary to connect both solar panels in series to get 3 volts. Also the LED needs to have its positive lead (the longer lead) connected to the positive (+) power source. The flashing LED has 3 colors of LEDs built into a single bulb and has a simple electronics inside that turns the three LEDS on and off in a cycle. Notice what how the speed and intensity of LED blinking changes when the power from the solar panel changes.
4. Mini Solar concentrator Design a reflector that increases the amount of light reaching the solar cell. There are plans for a mini reflector that fits the solar car in the Sun Dawg lesson cards. Trace the pattern on the reflective poster board, cut it out with scissors and the tape the reflector together. An enlarged pattern that fits the 1.5 volt panels is provided below. Measure the power with and without the reflector in place. Measure the area of the opening and the area of the cell. How much increased power would you have predicted based on the ratio of opening to solar panel? Is there a limit to the amount of light you can collect with a front opening reflector?
5. Parabolic reflector– Use the online geometery program Geogebra to design a reflector that focuses light to the panel. What is the ratio of magnification? (Area of reflector / area of solar panel at focal point)

https://www.geogebra.org/m/HS4nMUqf solar oven reflectionshttps://www.geogebra.org/m/xXJEkEvV spherical vs parabolic mirrors

http://tube.geogebra.org/material/show/id/1204549 segment mirror model

1. Solar Tracker- Concentrating solar systems only work when the device is facing the sun directly. Can you devise a support system that turns your concentrator gradually so that it faces the sun directly as the sun moves overhead?
1. Temperature Effects. If you succeed in making a solar concentrator, the solar cell may get quite warm in full sun. Use a thermometer to measure its temperature. Solar cells work better when they are cool because the thermal energy scatters the electrons as they diffuse towards output wires. Can you design an experiment that proves that solar cell performance decreases as the temperature increases? Hint: Heat the solar cell up, then let it cool down as you measure both the temperature and voltage under constant lighting. Plot voltage versus temperature.
1. Shading Effects. Solar cells in a panel may at times be partially shaded. What effects do you predict? Design a set of experiments to find what direction and amount of shading causes the biggest impact on performance. When individual cells in a series arrangement are shaded they effectively become resistors pulling down the power of the whole string. This is not necessary proportional to the amount of cell that is shaded. A single cell will lose power proportional to the percentage of shading.

#### Build your own Solar Energy Exploration Kit

1. Print out the Solar Energy Exploration Kit instructions

2. Print out 18 sets of Mini Solar Cars and Lessons

3. Print the box label on a full sheet adhesive label

3. Order:

• 18  mini solar cars (\$4-5 a piece from ebay or Amazon)
• multimeter (\$4 at Amazon)
• mirror board (\$10 at Amazon)
• acrylic mirror-polystyrene 2) 6”x 9” (\$4 from Amazon)
• Color Filters (\$14.99 from Amazon)
• DC Motor (\$1.49 from Electronics Goldmine)
• High Efficiency 300 Quiet Solar Panels Motor (10 for \$16 on ebay)