Solar panel testing

[RV Jim]

Hello everyone and a thank you for the awesome advice I am going to receive. Here's my question(s)
1. I have 4 panels on the roof of a cargo trailer I purchased and decided to check the voltage output. Much to my surprise I got 36.4 ...I'm confused about that number. Do I have a dead panel ?
2. What should 1 panel have for voltage...12v ?
3. I plan to purchase a Lifepo4 battery(12v) to supply charging power for phone or other small devices so do I need to rewire the panels for 12v output ?
5. Sorry for the ignorance of the correct terms as I confuse series and parallel...one should give 12vdc output and the other 48vdc out I think.

 

[Scixxor]

Okay, there's a lot to unwrap here.
1. Okay how many panels do you have and how do you currently have them wired?
2. The voltage per panel varies on how much power it produces and who makes them. Under your panels it should have a spec sheet, can you tell me what it says, or even better give me a pic of it?
3. No, your voltage needs to be higher than your batteries and needs to be hooked up to a charge controller to connect them to your batteries.
5. Okay so there are 2 ways to connect solar panels, series and parallel. Connecting them in series adds voltage, connecting them in parallel adds amps. For example, if I have 4, 24 volt, 5 amp solar panels and connected them all in series it would be 96 volts 5 amps. If I connected them all in parallel it would be 24 volts 20 amps. In general, you want to get the highest voltage your charge controller will allow to minimize the amount of power you lose as that electricity goes through your wires. With all this being said say your charge controller has a 50-volt input limit, you could wire them in 2s2p. 2 sets of 2 in series, connected together in parallel. This would give you 48volts and 10 amps. It looks complicated but it's pretty simple.

 

[Bobert]

Hello everyone and a thank you for the awesome advice I am going to receive. Here's my question(s)
1. I have 4 panels on the roof of a cargo trailer I purchased and decided to check the voltage output. Much to my surprise I got 36.4 ...I'm confused about that number. Do I have a dead panel ?
2. What should 1 panel have for voltage...12v ?
3. I plan to purchase a Lifepo4 battery(12v) to supply charging power for phone or other small devices so do I need to rewire the panels for 12v output ?
5. Sorry for the ignorance of the correct terms as I confuse series and parallel...one should give 12vdc output and the other 48vdc out I think.

Each panel has a voc (voltage open circuit) rating it should be printed on a sticker on the panel or in documentation that came with them. If you can find the specs for your panels and share them someone will be glad to help you get the right combination of controller and wiring for the best results. It’s really easy and fun stuff once you get the hang of it.

 

[RV Jim]

Ok I do not have any paperwork on the panels and the are already glued on the roof so looking for a label on the back in not an option unless I absolutely have to. I will climb on the roof and see what I can see but they have been on the roof for 18 months already so things will mostly be faded also it is 95 plus degrees out and would think there would be a slight voltage drop due to the temperature.

 

[Scixxor]

Ok I do not have any paperwork on the panels and the are already glued on the roof so looking for a label on the back in not an option unless I absolutely have to. I will climb on the roof and see what I can see but they have been on the roof for 18 months already so things will mostly be faded also it is 95 plus degrees out and would think there would be a slight voltage drop due to the temperature.

Okay, do you know who makes them and how many watts they are?

 

[RV Jim]

As best I can tell they are TP/SOLAR this is
What Amazon has listed that best matches the panels I was told they were.

 

[RV Jim]

There is a barcode that I can try and get a clear picture of if that will help.

 

[RCinFLA]

Looks like 3 x12 cell panel = 36 cells. Expect about 23v Voc and 18v Vmp per panel. A bit lower after they warm up in sunlight.

Find out from spec sheet or count how many series cells there are per panel. The number of series cells in a panel determines its Voc and Vmp voltages. The size of cells determines the current output in sunlight.

If panel Voc does not match the number of cells there may be a shorted bypass diode in the junction box. Not sure what the flexible panels do for bypass diodes. Either no bypass diodes or molded into laminate.

 

[RV Jim]

I'm not sure exactly how count the number of cells BUT it appears to me that there are 3 columns of 60 cells so 180 cells per panel x 4 panels = 720 cells i am attaching pictures of the panels and volt and amp readings at 4pm central time near corpus christi tx.

 

[RV Jim]

Sorry for the poor panel picture but the sun had a huge glare on the screen I was able to see what I was looking at. It shows 2 columns and the 3rd one is on the right. The rows have a half cell on each side and 4 full cells in between.

 

[Bud Martin]

To clear out the confusion, do you have wiring diagram showing us how the panels are wired up?
You should also provide the info on the Solar Charge Controller.

 

[Scixxor]

To clear out the confusion, do you have wiring diagram showing us how the panels are wired up?
You should also provide the info on the Solar Charge Controller.

Yeah, and when there's no load on my system and my battery is fully charged my charge controller only shows my panels as bringing one 1/5th of what they actually are. I imagine something similar is happening here if there's no load on those panels.

 

[RV Jim]

I haven't gotten to the point purchasing parts yet. Again I am sorry for ignorance of terminology. I have 4 panels in total. There are "Y" connectors connecting 2 panels together and those are connected to the other 2 panels then the 2 sets of panels are connected to a "RED and BLACK pair of what like at least 8 or 10 gage wire through the roof that is sealed and water resistant. Which is terminated with a connection that looks like it will plug directly into a charge controller or a solar power station.

 

[Bud Martin]

I haven't gotten to the point purchasing parts yet. Again I am sorry for ignorance of terminology. I have 4 panels in total. There are "Y" connectors connecting 2 panels together and those are connected to the other 2 panels then the 2 sets of panels are connected to a "RED and BLACK pair of what like at least 8 or 10 gage wire through the roof that is sealed and water resistant. Which is terminated with a connection that looks like it will plug directly into a charge controller or a solar power station.

Looking at the second pictures, it looks like the panels are setup as 2s2p configuration.

So are you saying you did not buy or have the charge controller yet?
So if you do not have the charge controller yet then how the Voltage and the current readings of the panels are performed?

 

[Scixxor]

So if you do not have the charge controller yet then how the Voltage and the current readings of the panels are performed?

They used a multimeter as can be seen in #9

View attachment 98205View attachment 98205View attachment 98209View attachment 98209

 

[Bud Martin]

They used a multimeter as can be seen in #9

I know he uses the meter, but with anything connected? and is he doing shorted circuit test by shorting the MC4 together, not sure if OP knows how to test the panel if he does not understand how the panels are wired up.
Based on the spec (Isc =4.90A) of the panel provided by OP, he is only getting about 2.5A from the setup instead of close to 10A.

 

[RV Jim]

Correct a multi meter..so the question is the voltage and amperage within acceptable for me to continue on with the project of battery, charge controller and inverter ?

 

[Bud Martin]

Correct a multi meter..so the question is the voltage and amperage within acceptable for me to continue on with the project of battery, charge controller and inverter ?

Based on the spec (Isc =4.90A) of the panel provided by OP, he is only getting about 2.5A from the setup instead of close to 10A.
How did you perform the current test? By shorting the red and the black wires together? You did not use the red and the black wires of the meter, correct?
BTW, the Voc of the panel is around 25Vdc (per your spec) so two panels in series, the Voltage should be close to 50Vdc, you only have about 35Vdc.
I also see so many smears on the panels.

 

[RCinFLA]

Looks like 36 half wafer cut cells arranged 3 columns of 12 cells, so 36 cell panel with about 0.63v x 36 = 22.7v Voc and 0.501v x 36 =18.1v Vmp. Will be a little lower voltage if panel is hot by sun heating. Likely either no bypass diodes or one diode across whole panel in the little black plastic terminal block.

Double the voltage numbers for two panels in series, but check panels individually first.

Panels put in series should have matching Isc. Panels, and series groups in parallel should have same Voc. Try to select the panels connected in a way to best satisfy both the two in series Isc and two groups in parallel Voc voltages. Isc of series is a little more important as the current result of the two in series will only be that of lowest current panel.

I don't like the plastic cover lay delamination though. Moisture may get into them. The wrinkles may have some impact on illumination to cells.

Check open circuit Voc voltage and short circuited Isc current in good sunlight for each panel. For Isc you can use a DVM with 10amp current inputs, realize it uses different positive banana plug input on DVM. Isc is linearly proportional to sun illumination level so if sunlight not at maximum the Isc will be lower than spec. You likely know what maximum sunlight feels like on your face so use that to judge.

 

[RV Jim]

I set the multi meter to dc amps red probe to the red wire in the connector and black probe to the black wire of the connector