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Simple Solar Cell Demonstration

Objective: To introduce students to solar (electric) cells.

Note: There are many possible variations on this project. Our intent here is to provide you with specifications to make a minimal demonstration at minimal cost, and also to suggest kits from various companies offer more sophisticated solar cell projects. We especially recommend building solar car kits. These are really fun! NMSEA has a special Toy Solar Car Program for interested teachers.

Commercially available solar cell kits

See our listing of companies and stores that sell solar energy kits for kids

New Mexico Standards and Benchmarks: 

Time: 1 hour

Vocabulary

Materials for a very simple solar fan project

  1. A sunny day, or a bright light bulb (greater than 40 watts). 

  2. A small array of solar cells: The array should be wired to provide between 1.75 to 3 volts and more than 300 mA (milli-amps). Pitsco (www.shop-pitsco.com/  -do a search on "solar"), for example, offers such an array (they call it a "solar battery" - very bad terminology, product # W50943). Many hobby and science toy stores sell small solar cells too.

  3. A small dc motor, with an operating range of roughly 1.5-4 volts (Pitsco also offers such a motor, product #W54428).

  4. Two pieces of electrical wire: the motor may come with this already. Don't use very thin wire, as this might offer too much resistance. You may want to add alligator clips to the wires.

  5. A small propeller, or something to mount on the motor

Preparation

  1. Mount the motor in some way, for example, make a small stand for it out of cardboard, or tape it to a small piece of wood (as in the photo above).

  2. Connect the solar to the motor to solar array: connect one wire from one contact of the motor to one contact of the solar array, and the other wire from the other contact of the motor to the solar array:

  1. Place the unit under direct light, and watch it go!

  2. Explain that sunlight hitting the array causes electrons to get pushed through the wires and the motors, and that this transfers energy from the sunlight to the motor.

Some Measurements

  If you have a voltmeter, you can:

  1. Measure the voltage across the solar panel (which should somewhere between 1.5 -10 volts depending on the panel you buy). Do this by setting the voltmeter to measure volts and place the meter probes at the output terminals of the solar panel with light shining on the panel. Try this with the panel connected and disconnected to the motor and see if there is a difference. Record your results.

  2. Then set the voltmeter to measure amps (milliamps), and place the voltmeter in series with the motor. To do this, connect one probe to one terminal of the panel. Connect the other probe to one terminal on the motor. Then connect the remaining terminals of the motor and the panel with a wire. Record your results.

  3. Now calculate the power the panel was producing and motor was drawing: Use the formula P = I V. See the Introduction to dc Electricity if you don't understand this formula. If the current is in milliamps, and the voltage in volts, then the power calculated will be in milliwatts (thousands of a watt).

  4. Now calculate the resistance of the motor from Ohm's Law: R = V / I (this is simply rearrange of I = V / R, the form which you might be more familiar with). Again, see the Introduction to dc Electricity if you don't understand this formula. If V is in volts, and I is in milliamps, then the calculated value of R will be in kilo-ohms (thousands of ohms). 

Discussion

Electric solar cells are called "photovoltaics", or PV for short. The word photovoltaic derives from the words "photo" which means light (Greek for light is "phos"), and "volt", the fundamental unit of electrical energy potential. Therefore, "photovoltaic" literally means "light-electricity". 

PV cells are special "semiconductor" devices which convert sunlight directly into electricity, and that they are primary made of purified silicon (the most prominent component of sand).

The French scientist Alexandre Edmond Becquerel, who also discovered radioactivity, discovered around 1840 that some materials produce a current (electricity) when light shines on them. 

PV cells, as we know them today, were first developed in 1954 by Bell Telephone researchers and first applied to power satellites in space. 

Explain that PV panels can be used to power entire houses, or provide electrical energy to the utility grid.

Additional Information

More info that you may want to discuss appears in our Teacher Primer "From Oil Wells to Solar Cells", including:

You may also want to calculate the costs of a PV system.

You may also want to get involved with building a toy solar car.

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