Mark across 1 cell ?

[Ajpepe72]

Bought 3 used 250w panels (1 each for me and two mates)
Sods law that the one I left for myself has a mark across one cell.
will test current tomorrow but its putting out its full open circuit voltage.
any ideas what the mark is or what would have caused it, I cant tell if its on the cell of on the glass.

[bcroe]

A panel will deliver full voltage under no load (open circuit), but the real test is maintaining around
80% of open circuit voltage while delivering serious current, which equals power. A sanity check
is short circuit current, but the real test is maintaining near that current under load.

Putting an MPPT load on the panel should reveal ability to deliver power. If it losses 1/3 or 2/3
voltage at full current, a section is bypassing. I weeded out some no name panels failing this
way with the voltage test. One test you might easily do, is run it in short circuit for a while,
meanwhile scan for hot or cold cells with an infrared temp gauge. Bruce Roe

[Ajpepe72]

Thanks, I short circuited the panel at around 2pm today and angled it towards the sun which was pretty low and got 7amps, short circuit current rating is 8.65amps. I then put it up on the roof of my camper and it was producing 65w (around 5amps coming out of mppt controller) obviously this was at a less than perfect angle as this was around 2:30 uk time so sun is low (at a guess if you consider the panel to be 90 degrees then sun was at about 40 degree angle. now its connected to the van system the controller app will give me the max wattage reached each day now so will check it tomorrow after work. solar1.jpg

[bcroe]

I am estimating the panel is rated 7A at 35V, about 250W. With an MPPT controller the panel voltage
should remain around 35V for varying sun, but varying current. Then a panel output of 7A should give
250W output, MPPT output of some 17A at 15VDC. If your controller is not MPPT, expect its output
current to equal the input current. Bruce Roe

[Ajpepe72]

Here is details of panel. Controller is mppt.

rated power ; 250w
rated power voltage: 30.4v
rated power current: 8.24A
open circuit voltage: 37.9V
Short circuit current: 8.65A