Are Photovoltaic Cells Considered Ohmic Devices?

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Discussion Overview

The discussion revolves around whether photovoltaic (PV) cells can be classified as ohmic devices. Participants explore the implications of this classification on the use of electrical equations, particularly in relation to power generation and heat dissipation in PV cells and modules.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant questions if photovoltaic cells or entire PV modules can be considered ohmic devices and whether the equation P = I²*R = V*I is applicable.
  • Another participant asserts that photovoltaic cells are not ohmic devices due to the presence of saturation current and constant voltage characteristics influenced by the semiconductor material.
  • A participant suggests that while Pout = V*I is valid for DC, the original equation may not apply to PV cells.
  • One participant expresses interest in understanding the heat generated in PV cells due to current and voltage, and its relationship with incident solar radiation.
  • Another participant speculates on whether a PV cell would be cooler when electrical power is drawn from it, suggesting that this could indicate some incident radiation being dissipated externally.
  • A participant proposes plotting Vload vs. Iload to analyze power output and internal dissipation, referencing the maximum power transfer theorem.
  • One participant is attempting to create a thermal model that considers electric current generation in relation to heat generation and solar radiation loss.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether photovoltaic cells are ohmic devices, with multiple competing views presented regarding their electrical characteristics and behavior.

Contextual Notes

Participants express varying levels of familiarity with photovoltaic cells, and there are indications of assumptions regarding the relationship between electrical performance and thermal behavior that may not be fully explored.

sj21
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Hey,

I needed a clarification regarding this.
Are photovoltaic cells ohmic devices? Or if I consider an entire PV Module, will that be an ohmic device or not?

I basically need to know whether I can utilize the equation P = I2*R = V*I for a cell or not.
 
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No, they are not. There is a saturation current that depends on amount of light the cell receives, and the voltage across the cell is a constant step that depends on semiconductor used. As you are nearing the saturation, of course, the apparent voltage will drop, which will have properties similar to internal resistance of the battery, but you are still not looking at anything remotely ohmic.
 
sj21 said:
I basically need to know whether I can utilize the equation P = I2*R = V*I for a cell or not.
You can use Pout = V*I
this always works for DC
 
Ohk. Thanks a lot.

I was basically trying to obtain how much heat is generated in the PV Cell because of current/voltage being generated? And how it (the heat generated) is related to the incident solar radiation on the cell. Can you help me with that if you have any idea?
 
sj21 said:
I was basically trying to obtain how much heat is generated in the PV Cell because of current/voltage being generated? And how it (the heat generated) is related to the incident solar radiation on the cell.
That is an interesting question. I'm sure textbooks on PV cells would deal with it. Not having studied PV cells, I'm wondering whether it would be naive of me to ask would a cell be cooler when you are drawing electrical power from it because that represents some of the incident radiation being dissipated outside the cell.

Anyway, one thought I have is could you plot Vload vs. Iload for your array, and then convert this to a power graph, Pload vs. Iload? If so, then it should show a peak, and knowing the maximum power transfer theorem, you can say where the power output peaks, an equal power is being dissipated internally.

That might be a start. :smile:
 
I am trying to prepare a thermal model. Using Maximum Power Point methods makes it more of an electrical model. I am trying to consider electric current generation by limiting it to the amount of heat generated because of that and loss in incident solar radiation transmitted through the PV Module.
Still, thanks for your suggestion! :)
 

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