# Are PV cells ohmic devices

1. Apr 1, 2012

### sj21

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.

2. Apr 1, 2012

### K^2

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.

3. Apr 2, 2012

### Staff: Mentor

You can use Pout = V*I
this always works for DC

4. Apr 4, 2012

### sj21

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?

5. Apr 6, 2012

### Staff: Mentor

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.

6. Apr 8, 2012

### sj21

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! :)