Learning Library

# Efficient Solar Energy

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• Define angle of incidence. How does it relate to the efficiency of a solar cell? Is this a linear or non-linear relationship?
• How can solar cells be optimized with respect to the angle of incidence?
• What are the independent variables in this experiment? The dependant variables?What are the constants?
• How does a solar cell work?

Solar cells convert sunlight into electrical energy. Different types of solar cells have varying degrees of efficiency and cost. The term “angle of incidence” refers to the angle of a ray to a surface is measured by the angle between the ray and the normal vector of the surface (generally, a line vertical to the earth). Since solar cells are expensive, their efficiency can be bolstered by mounting them to devices that move them so that they are always at the optimal angle of incidence with respect to energy output. In this experiment, students will determine the optimal angle for energy output.

If you don’t already have a voltmeter and ammeter at home, they’re available at Radioshack or other electronics supply stores (as are the solar cells and resistors).

Resistors are often sold in packs of five. If you are using a child’s wooden blocks, you want to use a saw in a woodshop so that the angle of the cut can be precisely measured.

• Saw (needed if you use wooden blocks)
• Protractor
• Double-sided tape
• Seven cubes made from wood (such as a child’s blocks) or cardboard (cubic jewelry gift boxes or similar boxes)
• Voltmeter
• Ammeter
• One 0.25 ohm, 4 watt resistor
• Seven polycrystalline 0.5V, 2.0 A, 1 watt solar cells
1. Using the protractor, pencil and straightedge, draw a line on each of the five of the blocks so that the angle of line forms either a 75, 60, 45, 30 or 15 degree angle with the side of the block. This line will be the new top face of the cube. Saw along the line using a power saw in a wood shop.Alternatively, if you have a set of small cardboard boxes, cut one side of the box so that it is free on three sides and hinged on the bottom.Bend the side so that stands at the correct angle and tape into place. Cut the two adjacent sides so that they are flush with the side you taped into place. After you prepared the cubes, you will have two cubes left over that do not require cutting.
2. Mount the solar cell to the top face of each of five blocks with double-sided tape.With respect to the sixth and seventh blocks, mount the solar cell on the top and side of the block respectively. If the solar cell is on the top of the block, it will form a 90-degree angle with the sides. If the solar cell is on the bottom of the block it will form a 0 degree angle.
3. Couple a 25-ohm resister to both ends of each solar cell on every block.
4. Move your cubes so they are outdoors. Conduct this experiment when the sun is directly overhead.
5. In the first cube, couple one of the alligator clips on the ammeter to one of the clips on voltmeter. Couple the free clip of the ammeter to the resistor. Couple the free clip of the voltmeter to the other side of the resistor. The ammeter and voltmeter should be reading the voltage and current in the circuit across the resistor. Record the volts and amps in the circuit. Repeat step 5 for each of the blocks.
6. Calculate the power (measured in watts) for every circuit. The formula for the calculation is VA=W, in which V represents volts, A represents amps and W represents watts. Repeat step 5 for each of the blocks.
7. Create a data table showing the volts, watts and amps of every cube. Graph your data. The x-axis should represent power in watts and the y-axis should represent the angle of incidence. Is there a relationship between the two? Is it linear or non-linear?

Terms/Concepts: Angle of incidence; Solar cell; Photovoltaic effect; Dependent vs. independent variable; Types of solar cells; Constant; Parallel circuit, series circuit

References:

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