Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Solar Angles and Light
Name: Stephen
Status: student
Age: 15
Location: N/A
Country: N/A
Date: 2000-2001


Question:
I'm doing an experiment which involves how the change of angle of a solar panel will affect the output it'll produce. The light source is an open 6 Watts light bulb, and a voltmeter will be connected to the solar panel to measure the output. Can you tell me what I can expect if the degree changes? And is there any formulas which I can use to measure the output whilst the change in degree?

Thank You,
Stephen


Replies:
Stephen,

The solar panel is converting light energy to electrical energy. The efficiency of the conversion can be considered a constant for your setup (you're not changing the wavelength of light falling on the panel) so you're main challenge is identify how much light falls on the panel. In your case, you are interested in the relative amount of light under different conditions, so that makes things a little simpler.

If you draw a picture of the setup you have described you will see that there are two geometrical effects. In addition there is one optical effect that will impact the amount of energy hitting the solar cells.

The first geometrical effect is the spreading of the light from the source. For a fixed area panel, the energy it can generate will be inversely related to the square of the distance between the light source and the panel. If the energy produced by the panel is 'x' when it is 3 feet from the source it will be 'x'/4 when it is 6 feet from the source.

The second geometrical effect is due to the angle with respect to a line drawn from the light source to the middle of the panel. If the angle is 90 degrees the panel 'catches' the maximum amount of energy from the source. If it is at 0 degrees the panel 'catches' none of the energy. In essence, the amount of energy the panel will 'catch' is related to the sine of the angle times the amount when the angle is 90 degrees.

The optical effect has to do with how much light is reflected. For a simple model I would assume that this is unimportant. In reality, more of the light will be reflected as the angle approaches 0 degrees.

Note that the first two factors, the geometric ones, are only independent of each other if the light source is very far away relative to the size of the panel so that all the light rays hitting the panel are essentially parallel.

Good luck with your project!

Greg

Bradburn



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory