Hello Vladimir,

- I would expect net power balance of the solar panels is equal in both modes.

  (SC and OC).

- However, power distribution is not. In OC mode, more power is dissipated in the solar cells (the solar energy is converted to heat in the solar cells.), while in SC mode, more power is dissipated in the conductors (of the solar cells, and the conductors connecting the panels.)

- Question is where you measured the temperature. I dont think the temperature distribution is uniform, and temperature distribution will be different between SC and OC mode.

The results would be more useful with different electrical loading of the cells not only the open and shortcircuit conditions. It is clear from the figure that the temperatures of the two panels under open circuit conditions are more or less equal while the temperature of one panel decreases with the shortcircuit, the other panel shows an opposite behavior where its temperature according to your experimental results increases. So, there is no systematic behavior to try to explain it. I would like to add that the cell1 behavior with T1 is an agreement with the electrical energy balance deduced by me in a similar question referenced by you in your question given in the Link:  ttp://www.researchgate.net/post/In...ort-circuit_Isc_or_open-circuit_Voc.

I agree with Henri that the dissipated power is not homogeneous through out the panel and therefore single point measurement may not be sufficient to explain the this contradicting behavior of the two panels in the short circuit case.

I think that more investigation are required to reach a decisive conclusion..

- temperature is to be measured at multiple points.

-measuring the temperature at different loads.

- Repeating the experiment for  many cells to get out the systematic behavior.

- The panels are not identical. If they are identical they would show the same behavior for the same operating conditions

Hello Henry.

The curent modes are identical  for two identical PV-panel. Both panels are on OC-mode at the begin of experiment, and both panels are on SC-mode at the end.

Temperature sensors are in the middle of backside of panels.

The photo of PV-backside and sensor location drawing are in attachment.

Hello Vladimir,

Sorry, I misunderstood.

I think this temperature effect is due to unequal voltage sharing over the solar cells because of tolerances, and/or difference in illumination of the panels (due to shading).

I mean, in approximation, each solar cell is a (blocking) diode, with a current source in parallel, whose current is proportional to the amount of sunlight falling on the panel.

Now, there are many cells like this, lets say 48.

Now, you short-circuit the total.

You will then get a pseudo-random voltage distribution over the cells. On average, the voltage is 0 volt, but because of small cell tolerances, anything from e.g. + 0.5 volt to say -12 volt is possible.  Due to tolerances and shading, some cells will have a smaller current than others, and the voltage over these cells will be more negative.  The string is spit in eg 3 sub-strings by the junction box diodes. So, each sub-string has 16 cells. Now, assume that in each of these sub-strings there is a 'bad' cell, whose current is 1 % less than the average. Then, the voltage over this cell will go negative, say -12 volt, while all the others are positive. It will then also get hot.

This voltage distribution causes a net flow of energy from the cells with positive voltages, to the cells with negative voltages. And that is what you see. I dont know to what extend, however. If you want proof, you need to measure the voltage distribution in the panel during the short circuit condition.

Cheers, Henri

does anyone has information of a panel let in open circuit condition will degrade faster than a panel under load?

Thank's All.

Today I have solve the problem. The source of temperature difference is Temperature Heterogeneousness or Hot-Spots on PV surface. This Hot-Spots are appeared mainly on SC-mode.

The average PV surface temperatures for OC- both SC-modes are equal.

Hi, Elías Urrejola. You have chance to get ansvere to Your question. I use two identical PV-panels in SC and OC modes near 2 years. The initial difference were near 5%. I will measure today difference and will report You.

How are  Vladimir, hope you are well. 

How may hot spots do you have? 

As for Elias question, i would expect that the loaded module is subjected to higher degradation rate than the open circuit module. The loaded module can lead under shadowing conditions to hot spot formation in the shadowed solar cell and thermal failure if not protected by a bypass diode. In case open circuit all cells will be open and there is no redistribution of the voltage in case of partial shadowing.

Best wishes

There is image of Hot-Spots in presentation

Presentation Thermoelectric Feedback Model of Photovoltaic Panels Hot Spots

Hi, Elías Urrejola. There are comparative data for PV-panels with essential different load. I donot observe any essential difference in degradation.

Data Comparative data for PV-panels photocurrent separated by sev...

Hello every one,

Thank you for this interesting conversation,

Let s me give you an experimental resulat comparing the loaded and no loaded systems

So, After 2 years of outdoor exposure in a semi-arid climate of Morocco, We noticed that, the degradation rate of a thin film loaded PV modules is very low compared with the same modules operating in OC

Hi

does any body have information about the effect of the temperature on current distortion of the PV systems ?