Does a Fresnel Lens Affect the Output of a Solar Cell?

Talk It Over

In a solar cell, the energy in sunlight is converted directly into electricity. How might a solar cell be designed to make the most electricity possible? A Fresnel lens (pronounced freh-NEL—the "s" is silent) is a thin, flat lens made by cutting concentric circular grooves into a glass or plastic surface.

The grooves act like prisms; they bend and focus light. What effect might a Fresnel lens have on the output of a solar cell? How can you find out?

Get

• Picture frame, with glass plate and removable cardboard back with hinged support
• Solar cell*
• Tape or glue
• Electrical tester (with a 0–250mA DC range) *
• Electrical tape
• Sunny spot to work in
• Modeling clay
• Ruler (metric)
• Fresnel lens (also called a magnifying sheet)*

Go

1. Remove the glass from the picture frame. Also remove the cardboard backing with its hinged support. Glue or tape the solar cell to the cardboard, like this:



2. With electrical tape, connect the red and black output wires from the solar cell to the red and black probes of the electrical tester. Do not turn the tester on.
3. Set the solar cell in the sun. Bend the cardboard and support so you get a good angle of sunlight on the solar cell. (See the preceding project: "Does the sun's angle affect the output of a solar cell?") Hold in place with a lump of clay.
4. Turn on the tester. Set it to the 0–250mA DC range. Read the output of the cell. Hold the plain glass plate (from the picture frame) 1 cm (½ inch) in front of the solar cell. Read the output on the tester.



5. Move to 2 cm and read again. Continue moving 1 cm (½ inch) at a time and taking readings until the glass plate is 15 cm (6 inches) from the cell.
6. Without changing the position of the solar cell, repeat steps 4 and 5 using the Fresnel lens (magnifying sheet) instead of the glass. Turn its smooth side to face the sun.

Stay Safe

Wear sunscreen, hat, and protective clothing when you are in the sun. The sun's radiation causes wrinkling, spotting, and skin cancer. Never look at the sun. It can blind you. Be careful of the edges on the glass, because they can be sharp.

Go Easy

The "Go" procedure will work for you. Take output readings at 1, 5, 10, and 15 cm (½, 2, 4, and 6 inches) only. Get an adult's help with the setup, measuring, and recording.

Go Far

Efficiency is a mathematical measure of how well the solar panel changes the sun's light to electricity. A panel with 10 percent efficiency, for example, changes 10 percent of the light energy that hits it into useable electrical energy. Do some research on the Internet or in your library to find out how to estimate the amount of light energy that hits your solar panel. Then calculate percent efficiency using the "Go" procedure. Modify your setup to obtain the maximum efficiency.

Show Your Results

Put data in a table like this for "Go Easy":

For "Go," add rows for the intermediate distances at 1-cm intervals. For "Go" and "Go Easy," make bar graphs that compare the output of the solar cell using plain glass and the Fresnel lens. For "Go," make a line graph of outputs (on the vertical axis) by distance (on the horizontal axis). Use different colors of lines to compare plain glass and the Fresnel lens.

For "Go Far," calculate efficiencies using different angles and arrangements of the cell and the Fresnel lens. Make bar and line graphs to show under which conditions maximal efficiency was achieved.

Tips and Tricks

• Be careful with your Fresnel lens. It can focus a spot of light energy hot enough to start a fire!
• Extend your project by turning your Fresnel lens over. Does it matter which side faces the sun?

This article is brought to you by:

From this Book:

CliffsNotes Parent's Crash Course Elementary School Science Fair Projects
Buy this book »