Testing Panel Output (Used Panels)

[inetdog]

I don't know much about solar panel failure modes, but here is one at least that a loaded tests would have detected whereas the Voc/Isc would have failed to detect. The load tests would need to be done with panel comparison to identify the culprit. Voc/Isc tests would not detect any series resistance correct?

http://www.pv-tech.org/news/fire_ris...ten_solar_modu

Voc testing will not detect resistance in the range involved.
And with Isc testing the difference in current of a string might not be noticeable without a calibrated light source or simultaneous measurements on individual panels.

PS: loved the reference to "route-cause analysis."

[posplayr]

PS: loved the reference to "route-cause analysis."

One of my last carreers involved working on theoretical aspects of failure detection (a part of CBM+); I guess it shows. It was entirely inadvertent: geek: .

[posplayr]

That is incorrect. The Voc test confirms the bypass diodes are working, and the Isc confirms th ecells are producing maximum rated current.

I asked this before. Why does the Voc/Isc test not work for TFP? I assume you can't short circuit the output.

THIS DOES NOT APPLY TO THIN FILM PANELS.

I assume a rated load would work?

[Sunking]

I really have to disagree with you on this one, Dereck.

How dare you

OK I agree and get your point. Point I am trying to make is what can be done in the field? All you got is Voc and Isc. You could build a device but it would have to be capable of sinking 9 amps of current, dissipate up to 400 watts, and vary its resistance from 2 ohm's to Infinity to mimic a MPPT Tracker. Even if you did that and found Vmp, the readings would be meaningless because you have no idea what irradiance is striking the panel.

Well wait a minute, I just figured out how to do it. Well sort of. Buy a 30 amp MPPT controller and a 12 volt 100 AH battery that is discharged.

[inetdog]

Well wait a minute, I just figured out how to do it. Well sort of. Buy a 30 amp MPPT controller and a 12 volt 100 AH battery that is discharged.

That is probably the cheapest way to do it too, unless you are willing to play around with various light bulb arrays.
You would still need the light bulbs to discharge the battery.

[Sunking]

That is probably the cheapest way to do it too, unless you are willing to play around with various light bulb arrays.
You would still need the light bulbs to discharge the battery.

Car head lights. Cheap and high wattage. I use to make load boxes out of them when I made DC power supplies in the 70/80's for ham radio operators. Still works today.

[bcroe]

As discussed, you are going to need to operate the panel at around its peak power for the sun its getting then. Too
low a voltage won't show up bypassed sections, and too little current misses the point.

I managed to debug some marginal panels in a string arrangement as described in another thread. The system
was applying an MPPT load, and I made a few assumptions
1. the Vmpp doesn't vary much;
2. several identical series panels all receiving the same sun should all perform about the same.

I added 3 way MC4 taps to get a voltmeter where needed. When one string didn't keep up with another
(clamp on DC meter), I started checking voltages across individual panels. Sure enough, I found a panel
running at 1/3 voltage, because 2/3s of its cells were being bypassed. Although it did OK at lower sun, it
dropped out at peak sun.

Replacing this panel wasn't the end; now ANOTHER panel became the weak link, running 2/3s voltage.

So the the weak panel gave itself away under full sun, compared to other identical panels, by bypassed level
voltages in a string ap. I may still find a place for it, maintaining some starter batteries? Bruce Roe