

Solar Angles and Light
Name: Stephen
Status: student
Age: 15
Location: N/A
Country: N/A
Date: 20002001
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
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Update: June 2012

