buying second hand pv, what to look out for?


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100kwh-hunter

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As the title is saying:
I would like to buy some second hand solar panels.
I only have a multi meter that i can bring, my oscilloscope is a bit to heavy.

The panels are in a storage, all is unknown v, a, open circuit ect
Age? could be a thing? what is the max age?

250 euro per 10 panels, they all look the same.
Wednesday i want to check them out.

Btw no cracks or any known (outside/visible) damage.

Thanks in advance, Igor
 

OffGridInTheCity

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As the title is saying:
I would like to buy some second hand solar panels.
I only have a multi meter that i can bring, my oscilloscope is a bit to heavy.

The panels are in a storage, all is unknown v, a, open circuit ect
Age? could be a thing? what is the max age?

250 euro per 10 panels, they all look the same.
Wednesday i want to check them out.

Btw no cracks or any known (outside/visible) damage.

Thanks in advance, Igor
I bought 40 used panels and just verified them against a known good panel by pointing both in same direction/angle (roughtly) and measuring voltage and then short-circuit amps. I found the 9yr old Suntechs measured 95% (or same) as the reference panel - so that was good enough for me.

Suggestion: I negotiated with the seller for 90%+ as minimum acceptance based on my plan to test against reference panel and they agreed - so you might want to put your expectations in writing. After all, panels have straight-forward warranty/degradation curves and the age/power-output should not be a mystery! Used panels does not mean they have to be physically 'broken' panels. In my case the seller said they upgraded the array to newer panels and these were taken down - perfectly sound panels, just 9yrs old.

I found 1 panel with 24v instead of typical 36v - and it was just a bad diode. Replaced the diode pack and it worked. 1 panel was smashed in shipment or when prepared for shipment and shipping is just too high to do 'replacement' as a practical matter.

Suggestion: Order a couple more than you need. Can always use them as spares.

1646681122625.png

1646681422593.png

Sugg
 
Last edited:

Korishan

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If you have pictures of what the panels look like, you could probably search for similar looking panels to get a rough guess of what they should deliver new. Then you have a pretty good ballpark of what to look for when you go to inspect them onsite.

Spidering, or Snail Trails, is something else to look out for. Some times they don't effect the panels, but other times they can do some major damage if they gain access to the air. O2 is very bad for the raw panels in the heat. Not to mention it'll wick moisture into the panel.

A DMM should be able to measure short circuit current. I would take some alligator wire clips to make testing easier. Or if you have clips that go on the ends of your probes even better.
 

Redpacket

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Might also test for any voltage leakage between cells & the frame.
+1 Test open cct voltage, short cct current in full sun as a minimum. If you can rig up a load, test under some load too.
 

Korishan

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If you can rig up a load, test under some load too.
Oh yeah, this is a good idea, too. Loads are easy. If you have a few ceramic resistors, put them in parallel to give a wattage rating.
Added benefit of being small enough to carry in your pocket. Just don't put them there right after a test. Might get a little, toasty, downstairs :ROFLMAO:
 

100kwh-hunter

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Shoot, i read some comments to late.
The first initial buy was/where 14 solar panels 100w each
???module type: pw 1000 24v????

vmp 34.4v
imp 2.9 a
isc 3.0 a
voc 43.2
pmin 95.1 w
maximum system opp v 600v
bypass diode 6 a
series fuse rate 5 a


Those where the specs i could barley read of several pv panels.
Yes i bought them because i thought there where good...
But in the car back home, i had a funny but not tasting good tast in my mouth.(dutch saying)
I thought 2 times 14.3v is 28.6v?
I put the panels in to the full sun, scale one to ten the sun was a 8.
V on my meter was 14.1 to 14.3 when the angle was adjusted.
Almost 90 degrees towards the sun at 15c temperature at the almost beginning of the evening.

What did i measured?(14.2v)
20220309_195513.jpg

Between 0 and 1 AND between 5 and 6 in both i got 14.2v.
So if my thinking(connecting them) is right i must have 28v???? per panel
But when driving to home i got this nagging feeling
I bought really old panels? more then 20 years of age? and instead 34v there are back to 14v? sheeeeet
The product tag does not nor reveal much about production year....
So i think i bought "a cat in a bag"(dutch saying) 15 euro per panel.

I bought also some other panels, but first this batch/lot(he has 30 more of those (133cmx67cm-100w)

Thanks in advance for all your answers, with best regards Igor K
 

100kwh-hunter

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Spidering, or Snail Trails,
Ï think the second batch i bought has them? will make pictures when i have more light in the garden.
A DMM should be able to measure short circuit current
Could you please explane what this is, a dmm
English is not my native language sorry, technical i am learning every time when i am here :eek:
From you i learned the most btw, thanks again for your patience.

Might also test for any voltage leakage between cells & the frame.
And how do i do that? test grounding wire with the positive wire on v?

With best regards Igor K
 

Korishan

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Could you please explane what this is, a dmm
Digital Multi-Meter ;)

And how do i do that? test grounding wire with the positive wire on v?
With the DMM in Continuity test mode (also called Beep mode) take a lead from the panel, connect one of the wires to the Probe, and connect the other Probe to the frame. You shouldn't get any continuity between them.
You could also have it in Resistance mode, which will at least give you the resistance between the frame and the wire.

The panels frame is not supposed to be tied to the Pos or Neg of the power leads. Otherwise, a lightning blast could still destroy your equipment even if the panels are grounded.

Measuring AMPs with the DMM, you make sure the Pos Probe is connected to the A (amps) port, and not the mA (milliAmp) port. Then with the panel in direct sunlight, you connect the probes to the wires of the panel. This creates a dead short circuit condition, and allows you to find out what the max amps the panels are capable of.

And I'm sure you know the method for measuring the Voltage :p Just make sure that you switch the Pos probe "back" to the other port when measuring voltage.
And more importantly, do not test short circuit with the Pos Probe in the mA slot. You'll kill your DMM for sure. Or at least blow the fuse. Either way, you'd be out of a DMM until one or the other is replaced.
 

Redpacket

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Between 0 and 1 AND between 5 and 6 in both i got 14.2v.
So if my thinking(connecting them) is right i must have 28v???? per panel
Full voltage will be between terminals 0 (+) & 6 (-). These are the output terminals for the panel.
Assuming no load:
You should get approx 1/3 of VoC 43.2V (ie approx 14.4V) between each of 0 & 1, then 1 & 5, then 5 & 6 (ie across each diode).
The exact voltages you get will depend on temperature of the panel (higher when colder) & will change (drop) as the panel warms up in the sun.
If one section is 0V, you might have a shorted diode.

Re testing for any leakage to the frame:
- test with the panel face down, not in sun
- you can test like suggested above but from terminals 0, 1, 5 & 6 to the frame as these are different sections of the panel string.
- note a DMM on continuity is not likely to have enough test volts to find some leakages (eg mid string) due to the cell voltages being more than the approx 3V a DMM uses to test with.
- you may want to test with a "megger" (high voltage tester) if you plan using the panels in series.
 

OffGridInTheCity

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If you have significantly lower voltage as @Redpacket described and the panel is physically OK otherwise, it could be the diode pack. You may be able to just replace the whole diode pack. In my case I found some packs on ebay like this - https://www.ebay.com/sch/i.html?_fr...for+Solar+Panel+Connect+PV+Junct...+&_sacat=0

Depending on the panel size in watts, they may have 2 or 3 or 4 diodes... (I'm no an expert) but if you remove (scrape off / unsolder) the existing diode pack it will have little tabs (like nickel strips) that you unsolder from the old diode pack. You may have to scrape out any sealant to uncover the tabs. In my case I had 4 nickel tabs coming from the panel. Then order a new diode pack, re-solder the tabs and use RV glue or something to reattach the new diode pack to the back of the panel against water.

You might be able to just replace the diodes directly instead of the whole diode pack - but for me it was cheap / easy to just replace the whole diode pack since I didn't know how to test diodes etc.

My point - just to be encouraging :) - its not as mysterious or difficult as it might seem to spend $10 and a little DIY effort and recover a panel 'like new'.
 

100kwh-hunter

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My point - just to be encouraging :) - its not as mysterious or difficult as it might seem to spend $10 and a little DIY effort and recover a panel 'like new'.
Exactly my point of view, but this trick i need to do with those other panels, 10A and 54V.
O blame me, i will post a pic, there is one that is troubling me, 1 out of 5 of the second batch, but first the first batch, sorry, sun was going watery and down also----->6 on a scale from 1 to ten, he give me 43V and 0.05A...
Second not really important batch right now:
20220311_170937.jpg

The front: perfectly sound with some scratches.
The back....please sit down first before scrolling down.....

20220311_171015.jpg

But with those panels i would like to have some advise, but I DID NOT tested them yet fully, yes this one i tested with a watery sun going down....
0.05A and 43V,
But sorry lets go back to those other panels(NO offence from my side, any info is Very welcome about those panels!)
With best regards Igor K
 

100kwh-hunter

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I could test some( just three of them) of the first batch of panels on how @Korishan described.
Before the sun was really low on his power(tested at a 7 from 1 to 10)
I got NO beeping, a solid 1.70-1.80A and a solid 13.8-14.0V out of three tested panels.
But this is the connection:
20220309_195513.jpg

I only measured each string, so not the whole panel!
Only 0 and 1 AND 5 and 6 in between, i need to connect 1 and 5 to get full V and Full A
Or i am very wrong in this?
Any way the 3(panels) i could test(6 strings) where pretty much the same in low sun:
I got NO beeping, a solid 1.70-1.80A and a solid 13.8-14.0V out of three tested panels, according to @Korishan methode.
I think those three are pretty good?.
No sign of snailing?:
20220311_170014.jpg

20220311_170039.jpg

With best regards and again thanks for sharing all af your knowledge.
Igor K
 

100kwh-hunter

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Messages
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O yes sorry the fabric data
vmp 34.4v
imp 2.9 a
isc 3.0 a
voc 43.2
pmin 95.1 w
maximum system opp v 600v
bypass diode 6 a
series fuse rate 5 a
 

100kwh-hunter

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Messages
793
That's broken glass everywhere - personally, I wouldn't fool with it.
That is the back.
I thought put some epoxy over it? and its oke?
So then i will take it apart and salvage the cells for a experimental project?
Or just don't waste time and put it in the bin?
This is one of the second batch panels btw...54V x 10A....pretty big aswel.
Your call @OffGridInTheCity , if you say trow away i will not hesitate, but it will be used in other fun projects!
With best regards Igor K
 

100kwh-hunter

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Measuring AMPs with the DMM, you make sure the Pos Probe is connected to the A (amps) port, and not the mA (milliAmp) port. Then with the panel in direct sunlight, you connect the probes to the wires of the panel. This creates a dead short circuit condition, and allows you to find out what the max amps the panels are capable of.
I am doing something wrong, or they are beyond 20 amps at 41 volt in direct sunlight.
Sun was going down with the v numbers also...sun is setting to night
20220621_193009.jpg
20220621_193115.jpg
20220621_192948.jpg
20220621_192931.jpg
20220621_193130.jpg

where to put my leads to get the A, clearly i did it right??but i forgot how to?
End of this week they will be on my roof fially, but what are they cable off?
And how to measure properly, again: now i am doing something clearly wrong.

With best regards Igor K
 

Korishan

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or they are beyond 20 amps at 41 volt in direct sunlight.
When you dead short, there won't be really any voltage. They won't be at 41V, almost read 0V.

looks like your meter can't do anything higher than 20A, unfused. Not a good idea to try to use that to measure full sunlight/current capacity of those panels.
You might be able to measure smaller batch of cells instead. looks like there are 2 strings, so you could test each one individually. Tho, I may be incorrect on this assumption.
I'm guessing the 2 tabs on the edges are each a series set of cells. Then there's a diode that goes from Series A to Series B. To get full voltage/amps, you connect to the outer most connections. But you should be able to measure the first bank by testing via the tabs that are close together. But again, this is just a guess. I haven't messed with solar panels enough to work out what their rates are without the label there. Sorry :rolleyes:
 
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