Weird IV Curve under low insolation

[richieza]

Hi all,

I have been playing around with some DIY PV Cells and have come across the following issue while testing the module at low insolation and thought it time to ask for help.
(i currently dont have too much info on the module will try get it...)

At +-400W/m2 the following occurs:

IV info.png

Im not sure if this has something to do with the tester im using something like:

http://www.mecoinst.com/meco-product-details/Solar-Module-Analyzer.aspx

At AM1.5G i get the following using the exact same set, only difference is the irradiance levels.

info 2 - Copy.png

Not sure if this is an obvious error.

Thanks for help!

Looks like an awesome forum

[inetdog]

Without looking too hard at the details of the panel or the test methods, one thing comes to mind:

If the performance of one or more of the cells at low light levels is poor, there will be a point where the poor cells will drop in voltage or even end up dropping voltage as the current increases. That will lead to a step, especially if there is a bypass diode the is capable of bridging around those cells.

But the direction of the step in your case seems to be opposite of the above effect.

I am also puzzled and would look more carefully about the testing device. Supplementing the automatic sweep with individual point measurements using fixed load resistors may clear things up.

[richieza]

Without looking too hard at the details of the panel or the test methods, one thing comes to mind:

If the performance of one or more of the cells at low light levels is poor, there will be a point where the poor cells will drop in voltage or even end up dropping voltage as the current increases. That will lead to a step, especially if there is a bypass diode the is capable of bridging around those cells.

But the direction of the step in your case seems to be opposite of the above effect.

I am also puzzled and would look more carefully about the testing device. Supplementing the automatic sweep with individual point measurements using fixed load resistors may clear things up.

Thanks, Will try get info/specs and get back.