Should I buy these?

[Tariq0101]

A local merchant is selling solar panels that were used in solar farms,
200watts for 17$ a piece, pretty cheap isn't it?
I asked him for a picture and I've attached it to this post.
I'm really on the budget and if those can last five years it would be great.
What should I look for when I check them? Is there a manufacturing date on the back?

 

[Deleted member 23531]

Yes, that's very cheap. Even if they are only 50% of their stated capacity, that's only $0.17/W which is still extremely cheap for a consumer scale project. The only downside is you need a lot more area, mounting structure, cabling, etc. if they are old/inefficient panels to get to the same power output you could get with newer, more efficient panels. If you have a lot of space and willingness to have a large, lower-efficiency PV setup, then yeah that seems like a good price to do it.

 

[the_uglydog]

If they'll do a volt and amp output reading on them for you and you can compare that to the original specs, that way you'll know if they're any good. Many solar farms mount panels on frames on the ground so they don't get as much damage from heat as ones that are mounted on a roof, so they might be in great condition. Also, some suppliers in China sell replacement parts so you could replace the stuff in the box on the back if you need to. That's about it. the dog

 

[Tariq0101]

If they'll do a volt and amp output reading on them for you and you can compare that to the original specs, that way you'll know if they're any good. Many solar farms mount panels on frames on the ground so they don't get as much damage from heat as ones that are mounted on a roof, so they might be in great condition. Also, some suppliers in China sell replacement parts so you could replace the stuff in the box on the back if you need to. That's about it. the dog

Will it be enough if I measure the volts?
I don't have an amp reader

 

[Deleted member 23531]

A multimeter can *maybe* measure both open circuit voltage and short circuit current if it's sunny. Read the sticker on the panels or just check them for Voc consistency panel to panel if there is no sticker.

First point them at the sun.

All multimeters that I know of can measure the open-circuit voltage (Voc) which should be tens of volts (ex: 40V). Just put it in the sun and set your multimeter to DC volts and probe the leads.

Most cheap multimeters have 10A fuses so may not be able to test the short-circuit current (Isc) if it exceeds 10A. Check if your multimeter can do 20A or if the panels are somewhere less than 9.5A short-circuit current. If your multimeter can do 10A and it only costs $10 to replace I would try it anyway. Usually you have to switch the leads to the "10A" port of the multimeter, which is a different red terminal than the "voltmeter" terminal.

If this makes no sense to you then you'll probably have to read up on solar panels and multimeters before you attempt to measure them yourself.

 

[Tariq0101]

A multimeter can *maybe* measure both open circuit voltage and short circuit current if it's sunny. Read the sticker on the panels or just check them for Voc consistency panel to panel if there is no sticker.

First point them at the sun.

All multimeters that I know of can measure the open-circuit voltage (Voc) which should be tens of volts (ex: 40V). Just put it in the sun and set your multimeter to DC volts and probe the leads.

Most cheap multimeters have 10A fuses so may not be able to test the short-circuit current (Isc) if it exceeds 10A. Check if your multimeter can do 20A or if the panels are somewhere less than 9.5A short-circuit current. If your multimeter can do 10A and it only costs $10 to replace I would try it anyway. Usually you have to switch the leads to the "10A" port of the multimeter, which is a different red terminal than the "voltmeter" terminal.

If this makes no sense to you then you'll probably have to read up on solar panels and multimeters before you attempt to measure them yourself.

I understand all of that but the problem is that I only (currently) have a voltmeter, so it's not enough to measure the volt? Can you have high volts with low amps?

 

[Deleted member 23531]

I understand all of that but the problem is that I only (currently) have a voltmeter, so it's not enough to measure the volt? Can you have high volts with low amps?

Yes. if a wire is cracked and barely hanging on, it would still read normal voltage but amps would be restricted when current is actually flowing. There is certainly a degradation of the cells themselves from time too; I'm not sure if it is volts or amps or both but I bet it's mainly amps (totally a guess based on my knowledge of P/N diodes).

How common is that in used panels? I have no idea. I'm just speaking theoretically about stuff that could go wrong in the circuits when they're used. Multimeters aren't expensive, just get a cheap one that can do 20A and you're good. Even a 10A one may do fine (which is pretty much all of them).

Can you:
1) ask the seller for a picture of the sticker on the back of the panel (if there is one)?
2) post a picture of your voltmeter?

 

[Deleted member 23531]

As a follow-up, see Figure 8 of this paper (https://www.nrel.gov/docs/fy12osti/53713.pdf), which confirms that it is mainly the current which degrades as I said above, and not the voltage. I'm not vouching for this paper in particular (I didn't read it, and spent only 15 seconds finding it), but NREL is a legit energy agency of the federal government and knows what they're doing, generally.

 

[Tariq0101]

Yes. if a wire is cracked and barely hanging on, it would still read normal voltage but amps would be restricted when current is actually flowing. There is certainly a degradation of the cells themselves from time too; I'm not sure if it is volts or amps or both but I bet it's mainly amps (totally a guess based on my knowledge of P/N diodes).

How common is that in used panels? I have no idea. I'm just speaking theoretically about stuff that could go wrong in the circuits when they're used. Multimeters aren't expensive, just get a cheap one that can do 20A and you're good. Even a 10A one may do fine (which is pretty much all of them).

Can you:
1) ask the seller for a picture of the sticker on the back of the panel (if there is one)?
2) post a picture of your voltmeter?

1) I asked him he didn't reply yet
2) it's a simple 0-50volts meter for batteries, I don't currently have a picture of it because I'm at work

 

[Tariq0101]

As a follow-up, see Figure 8 of this paper (https://www.nrel.gov/docs/fy12osti/53713.pdf), which confirms that it is mainly the current which degrades as I said above, and not the voltage. I'm not vouching for this paper in particular (I didn't read it, and spent only 15 seconds finding it), but NREL is a legit energy agency of the federal government and knows what they're doing, generally.

Very informative thanks, amps reading is much more important I see

 

[Tariq0101]

Does anyone knows why the panels look like that? Is that an old technology that looked like this or all old panels look like this?

 

[squowse]

I understand all of that but the problem is that I only (currently) have a voltmeter, so it's not enough to measure the volt? Can you have high volts with low amps?

Multimeter measuring up to 10 amps is very cheap. Make sure you know how to use it though.

 

[Tariq0101]

Multimeter measuring up to 10 amps is very cheap. Make sure you know how to use it though

I'll look for one, thanks

 

[Deleted member 23531]

Very informative thanks, amps reading is much more important I see

Hey, I had a few minutes to look at the paper I linked more carefully. There are actually a multitude of causes and it depends on the panels; for example this form of degradation shows that Voc and Isc stay roughly constant and the degradation is at the "knee" of the curve, exactly where you would like to operate for maximum power output:



Some of the causes are: cracked cells, soiled / dirty glass or cells, increased series resistance, increased shunt conductance, and I'm sure some silicon device level stuff like dopants and other charged particles moving around as the panels age.

This suggests it's pointless to test Isc or Voc. You could find serious flaws (like an open circuit) by testing either one, but the normal degradation is not going to be easy to figure out based on some quick measurements you do when you meet the seller. Also since they're so cheap it probably doesn't make sense to worry about it too much. I'd vote that you just check for similar Voc between all of them! Good luck and let us know how it turns out!

 

[Deleted member 23531]

Does anyone knows why the panels look like that? Is that an old technology that looked like this or all old panels look like this?

I think that's what amorphous silicon looks like. Ie, these are not monocrystalline silicon cells. Yes, it's older but you knew that already.

I think the silicon grain size going from largest/least crystalline to smallest/most crystalline is: amorphous, polysilicon, monocrystalline. You'd have to do some silicon technology reading to find out exactly what generation these were from based on their appearance.

 

[Tariq0101]

T

Hey, I had a few minutes to look at the paper I linked more carefully. There are actually a multitude of causes and it depends on the panels; for example this form of degradation shows that Voc and Isc stay roughly constant and the degradation is at the "knee" of the curve, exactly where you would like to operate for maximum power output:

View attachment 41710

Some of the causes are: cracked cells, soiled / dirty glass or cells, increased series resistance, increased shunt conductance, and I'm sure some silicon device level stuff like dopants and other charged particles moving around as the panels age.

This suggests it's pointless to test Isc or Voc. You could find serious flaws (like an open circuit) by testing either one, but the normal degradation is not going to be easy to figure out based on some quick measurements you do when you meet the seller. Also since they're so cheap it probably doesn't make sense to worry about it too much. I'd vote that you just check for similar Voc between all of them! Good luck and let us know how it turns out!

Thanks for all of your great info, I eventually passed on them since the amperage was too low.

 

[Deleted member 23531]

That's understandable. I didn't want to discourage you if you really are that price sensitive, but it's good to know you gave it a thorough examination. Check out SanTanSolar or similar retailers which can provide both new and used options for panels. I haven't purchased from them as my panels are new from the manufacturer, but if you're trying to minimize the panel cost they might be worth a look as their inventory changes pretty frequently and they offer both new and used panels.

 

[Tariq0101]

That's understandable. I didn't want to discourage you if you really are that price sensitive, but it's good to know you gave it a thorough examination. Check out SanTanSolar or similar retailers which can provide both new and used options for panels. I haven't purchased from them as my panels are new from the manufacturer, but if you're trying to minimize the panel cost they might be worth a look as their inventory changes pretty frequently and they offer both new and used panels.

I'm from Syria so that's not an option, I bought two chinese cheap mono 200 watts panels for 60$ a piece and they've been doing very good.