Is there a linear relationship between the two?

I ask because I'm investigating the effect of a different variable on the power output of a solar panel, and intensity is meant to be one of my control variables.

However due to insufficient apparatus I could not control the intensity of light.

For example, say I wanted to control the intensity at 40 lx. However in one of my tests the intensity of light was 120 lx. If I were to divide its power output by 3, would I get the (approximately) same value as I would if the intensity were truly 40 lx?

If any clarification is needed let me know. Thanks in advance.

  • \$\begingroup\$ What's the light source? Most lamps are non-linear. Can you change the distance? Put an attenuator on the lamp? Cover 2/3rd's of the lamp. (A screen that's 1/3 holes by area.) \$\endgroup\$ – George Herold Jun 8 '15 at 15:37

In theory, a photovoltaic cell (a single cell) produces a current proportional to the intensity of the incident light. This is due to the photovoltaic effect. The voltage shouldn't change, much, and so power is linearly proportional to intensity.

However, in an array, there will be other effects from the interconnected cells. Furthermore, voltage does show some dependence on intensity, and you need to ensure that none of the panel is shaded, since that severely reduces panel voltage.

Therefore, in your case, I would say that you cannot simply assume that if the intensity is three times greater, that power will be three times greater.

It might be helpful if you describe your application, since you might get answers that detail alternate ways to accomplish your goal.

For example, if I understand you correctly, perhaps you could build a controlled light source using LEDs, and enclose the entire apparatus in an internally mirrored box. You would know the power going to the LEDs, their spectral emissions, and their intensities based on viewing angle and distance. Furthermore, you should be able to get a datasheet for the panel and determine optimal wavelengths and predicatively model the panel's response.

  • 2
    \$\begingroup\$ Perhaps worth mentioning that this is most true if the temperature of the solar cells is kept constant. The cells will tend to be cooler (and thus more efficient) with less light. \$\endgroup\$ – Spehro Pefhany Jun 8 '15 at 12:47

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