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What to expect
In this activity you will get hands-on experience using solar a.k.a. “photovoltaic” cells. First, you will connect solar cells in different kinds of circuits, and you will measure their output. Then you will use the electricity produced by the solar cells to create “spin art” by powering an electric motor.
Community Connections
In the previous several activities, you have explored different forms of energy, and you have measured the amount of energy that some devices consume. This activity focuses on one particular kind of energy: solar energy. We will cover the basics of solar energy today. Next week's activity will use the same solar cells along with the micro:bit to show some interesting applications.
The Solar Pyramid is a 16 feet tall art installation in the Bronzeville neighborhood by artist Shala Akintunde that also powers a building.
Solar Art and Technological Design in Bronzeville
(Solar Pyramid starts at 56 second mark)
Part 1: Making Circuits with Solar Cells
Materials
2 mini solar cells from solar classroom kit
Multimeter with red and black probe
Halogen light lamp, or, outdoor sunshine if it’s a sunny day
Scratch paper with pen/pencil
Cardboard pieces (not included in materials kit)
How does a solar panel work?
Most solar cells are made primarily of Silicon combined with small amounts of other “doping” materials like Boron and Phosphorus. The materials combine to form a “p-n junction”, which is a one-way valve for electrons. When a particle of light (a photon) hits an electron in the solar cell, the photon gives energy to the electron, and the electron can move only one direction through the solar cell: up towards the surface. If a wire is connected from the top of the solar cell, through a load, and back to the rear side of the solar cell, a complete circuit is formed. When many individual solar cells are connected together to increase the power output, we call it a solar panel.
From the American Chemical Society: Schematic representation of a solar cell, showing the n-type and p-type layers, with a close-up view of the depletion zone around the junction between the n-type and p-type layers. Anthony Fernandez
In this activity we will use a multimeter to measure the output of solar cells. A multimeter (shown in Figure 1) is a device that can measure voltage and current of an electrical circuit. First, you will measure the voltage and current of an individual solar cell. Then you will connect several cells together to make series and parallel circuits.
Figure 1. Components of a Multimeter
Multimeter Setup:
The black plug should always be connected to the bottom right port on the multimeter, labeled COM.
The red plug is usually be connected to the middle port on the multimeter, labeled V𝛀mA.
Hint: if your multimeter is not working as expected, check your red and black plug connections!
Figure 2. Multimeter plug connections for measuring voltage, resistance, and small amounts of current (left), and larger amounts of current up to 10 Amps (right)
You can use these plug connections (shown on the far left) to measure voltage, resistance, or small amounts of current. However, if you want to measure larger amounts of current up to 10 Amps (as we will do in this activity), you can connect the red plug to the top port on the multimeter labeled 10A and turn the rotating dial to “10” in the DC Current section.
Figure 3. A solar cell connected to the multimeter
Measuring a single solar cell
In groups of about 2-3 people, collect the materials: a multimeter, halogen lamp, and a few mini solar cells. If it’s a sunny day and you can go outside, you can use sunshine instead of a lamp.
Connect a single solar cell to the multimeter, as shown in Figure 3.
3. First we will measure the solar cell’s voltage. Voltage is an electrical force that pushes charge (e.g. electrons) through a circuit. Make sure your black multimeter plug is connected to the bottom (COM) port, and the red plug is connected to the middle (V𝛀mA) port. Rotate the multimeter dial counter-clockwise to the “20” in the DC Voltage section of the multimeter. Shine your halogen lamp at the solar cell. You should see a voltage of around 0.5 - 0.6 Volts. Write your measurement down on your scratch paper.
4. Hold your hand over the solar cell so that it is shading the solar cell. Has the voltage changed? Write down your new voltage measurement on your scratch paper.
5. Next we will measure the cell’s current. Current is the rate that charge is flowing through the circuit. These mini solar cells can produce a surprising amount of current, so, remove your red multimeter plug from the middle (V𝛀mA) port, and connect it to the top (10A) port. Rotate the dial of the multimeter to the “10” in the DC Current section. Now shine your halogen lamp at the solar cell. Depending on how far away your lamp is from the cell, you should see around 0.05 - 0.2 Amps. Write your measurement down on your scratch paper.
6. Hold your hand over the solar cell so that it is shading the solar cell. Has the current changed? Write down your new current measurement on your scratch paper.
7. You have finished measuring the electrical output (voltage and current) from a single solar cell. On your scratch paper, make a table like Table 1 below, and fill in the first column of data. In the next section, we will fill in the second column.
Table 1. Voltage (V) and Current (A) in Series and Parallel Circuits
Measuring two solar cells connected in series:
In the real world, one single solar cell is not powerful enough by itself, so we connect them together to increase the power output. First we will connect them in a series circuit, and then in parallel.
Figure 4. Two solar cells connected in series
Connect two solar cells in series as shown in Figure 4. The red wire of one solar cell should be connected to the black wire of the other solar cell. Then connect the remaining black wire from the solar cell to the black multimeter probe, and the remaining red wire from the other solar cell to the red multimeter probe. When the cells are in series, the current has to go through one solar cell and then the other.
2. Now measure the total voltage output from the two cells combined in series, just like you did for the single solar cell. Hint: make sure your black multimeter probe is connected to the bottom (COM) port, and the red probe is connected to the middle (V𝛀mA) port. Rotate the multimeter dial to the “20” in the DC Voltage section of the multimeter, shine the light on the solar cells, and record your measurement in the second column of your data table.
3. Hold your hand over the solar cells so that it is shading at least one of the solar cells. Write down your new voltage measurement in your data table.
4. Next measure the total current from the two cells combined in series. Hint: remove your red multimeter probe from the middle (V𝛀mA) port, and connect it to the top (10A) port. Rotate the dial of the multimeter to the “10” in the DC Current section, shine your light at the solar cells, and record your measurement in your data table.
5. Hold your hand over the solar cell so that it is shading the solar cell. Write down your new current measurement in your data table.
Measuring two solar cells connected in parallel:
The other way that we can connect solar cells is in parallel. We will connect the two cells in parallel, and then complete the measurements for your data table.
Figure 5. Two solar cells connected in parallel
Connect two solar cells in parallel as shown in Figure 5. The red wires from both solar cells are connected together and attached to the red multimeter probe, and the black wires from both solar cells are connected together and attached to the black multimeter probe. When the cells are in parallel, the current goes through one solar cell or the other, but not both.
Complete your data table by measuring the voltage and the current when the cell are in shade and when they are not.
3. Be sure to turn the multimeter to OFF when you are done. Otherwise, it will drain the battery.
4. Take a look at your completed data table. What are the differences in the output between each circuit type? In general, what you will likely see is that for series circuits, the voltages add together but the current remains roughly constant. Whereas for parallel circuits, the currents add together but the voltages remain roughly constant.
Part 2. Solar Spinner Art
Now that you know how solar cells work, it’s time to have some fun with them! In this short activity, you will make “spinner art” by connecting a solar cell to a motor. The motor will spin a piece of cardboard, and you will use markers to draw on the cardboard as it is spinning.
Materials for Part 2
1 piece of cardboard approx. 5 inches x 5 inches (doesn’t have to be exact)
Markers
From the classroom solar kit:
4 Brass push-pin fasteners
1 motor
1 mini solar cell
1 yellow plastic wheel (used to attach the motor)
Instructions
Figure 6. Spinner Art Assembly Mechanism Top View
To begin, use the brass push-pin fasteners to connect the piece of cardboard to the yellow plastic wheel, as shown in Figure 6.
Figure 7. Spinner Art Assembly Mechanism Side View
2. Connect the motor wires to a solar cell and shine light on the cell. The motor should start to spin. What happens if you swap the red and black wires from the solar cell?
3. Use markers to draw on the cardboard as it is spinning. Try making a spiral shape, or concentric circles, or some other design from your imagination.
4. How could you make the motor spin faster or slower? Think about the first activity today, where the output changed when the solar cells were connected in series and parallel.
Think about it
In this activity, we did experiments that showed how the output from solar cell circuits changes in series and parallel. Then we used solar cells to make creative spinner art designs.
Do you have any questions about how solar panels work? Feel free to reach out to us!
Do you have more ideas for fun things that you could do with the solar cells? What else could you power?
Was there anything about this activity that surprised you?
Feedback link: Click on this link to provide feedback on this activity.
Next Activity
In the next activity, you will continue to work with solar cells. Next time, you will use solar cells combined with the micro:bit to make musical circuits!
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