How to test a Solar Panel before Installation

[dr_nelson]

Hey y'all,

I wanted to test my solar panels that have arrived.
It was already 7 pm and a little cloudy. I am in SC. I know I should do it around noon, but I work and didn't want to wait till Saturday (but will test again on Saturday noon).

From what I read, I want to test the Open Circuit Voltage (Voc) and the Short Circuit Current (Isc).

What I have:

• 1 x sun in the sky
• 2 x solar panels
• 1 x Voltmeter
• 1 x flat screwdriver
• A sticker on the solar panel saying Voc is 24.06 V and Isc is 9.77 A

What I did:
First, test the Voc

1. Open the junction box with the help of the screwdriver (because it was tricky to ensure the leads are actually touching the metal inside the MC4 connectors)
2. Take the solar panel outside
3. Position the solar panel, so that the sun is hitting the cells
4. Set the Voltmeter to 200 Volts
5. Put the negative lead to the negative metal thing inside the junction box.
6. Put the positive lead to the positive metal thing inside the junction box.
7. Read the Voltmeter

Then, test the Isc

1. Open the junction box
2. Take the solar panel outside
3. Position the solar panel, so that NO sun is hitting the cells
4. Set the Voltmeter to 10 Amps
5. Put the negative lead to the negative metal thing inside the junction box.
6. Put the positive lead to the positive metal thing inside the junction box.
7. Turn the solar panel so that the sun hits the cells.
8. Read the Voltmeter

Then, repeat the above on the other panel (which I will do this Saturday. Hopefully, the weather will be good.)

Am I doing this right? Or did I miss something?
Any help appreciated!

In case you're wondering, the Voc said 21.0 V, and the Isc said 0.40 A. It is the 180 W Grape Solar Monocrystaline panel (GS-Star-180W-US).

 

[AbuelaLoca]

Excellent how-to (if it's correct LOL)!! Thanks!!

 

[BradKW]

You've gone much further than I did...I simply stuck the meter prongs into the MC4 connectors while it was sitting in the sun. Figured that was close enough.

A couple things I don't understand from your post though that I'd be curious for more explanation:

1) what is the point of hiding the panel then turning it into the sun?

2) I looked up ISC and found this: 
"Short Circuit Current (Isc)

The maximum possible current flowing through the solar panel (when resistance is zero, which is also when voltage is zero)."

I don't get how you have amps but no volts, or how it's a short circuit.

I kinda figure these questions are related to each other...

 

[dr_nelson]

(..)
1) what is the point of hiding the panel then turning it into the sun?

2) I looked up ISC and found this: 
"Short Circuit Current (Isc)

The maximum possible current flowing through the solar panel (when resistance is zero, which is also when voltage is zero)."
I don't get how you have amps but no volts, or how it's a short circuit.
(..)

1) What I read is that testing current/amps is more dangerous than testing volts. So, to avoid sparks and injuries, I was told to hide first, connect, and then turn into the sun.

2) You totally lost me here. Remember, I have no idea what I am doing here with this electrical stuff... I was hoping you guys can clarify for me. Is 21.0 Volts considered "no volts"?

 

[Trebor English]

The .4 amps is a problem.  Shading part of the panel could do that.  Your hand holding it could do that.

 

[highdesertranger]

ISC is short circuit amps. the outputs must be connected together(ie short circuit) for this reading, not for the week of heart. highdesertranger

 

[dr_nelson]

ISC is short circuit amps.  the outputs must be connected together(ie short circuit)  for this reading,  not for the week of heart.  highdesertranger

So, are you saying that I have to connect the panel's positive and negative MC4 connectors together and then measure the Isc?

 

[jimindenver]

Doc

Monocyrstaline don't like cloudy and low light. Their voltage slips as does the amp output. Test them again in bright light and you will likely see the numbers you expect.

When you check them, stick the ends of the multimeter leads into the MC4 connectors. I wouldn't be surprised if they exceed either rating if they are new. I blew a few cheap multimeters limited to 10a testing panels rated for less than 10a Isc.

 

[blars]

Cheap meters come with cheap leads that can't handle much current. The lead resistance limits the current, and the heating will cause the lead insulation to melt after a few seconds.

 

[GotSmart]

Doc

Monocyrstaline don't like cloudy and low light. Their voltage slips as does the amp output. Test them again in bright light and you will likely see the numbers you expect.

Well gee Wally, then how come my monochrystaline panels work until full dark?  

Polychrystaline panels not only have a lower output, but most will not even produce if partialy shaded.

 

[shadowmoss]

Don't shot the terminals together. Put the amp meter in the circuit. Short-circuits should usually be avoided, they tend to let smoke out.

 

[shadowmoss]

In the above shot should be short, don't short the terminals together. Bad juju.

 

[Weight]

Tool needs; (A) 1 volt meter set for above the Voc of the panel, 50 volts range would be enough, but some volt meters range 20 then next step is 100, so then use 100. (B) 1 amp meter that can read above the Ioc of the panel. I would hope for a 20 amp meter if trying to measure near 10 amps. (-C) A cardboard or other material to cover the panel. (Procedure) Set the panel in full sun. Cover the panel. Connect the Amp meter & shunt across the two leads from the panel. Connect the volt meter across the same leads. Uncover the panel. Check the readings on both meters. Re-cover the panel. disconnect the meters. My guess from your reading is your amp meter is not up to standards. Reading no volts when wires are connected with no load? The volt meter is measuring voltage drop, no resistance, no voltage drop.

 

[Trebor English]

Open circuit voltage (Voc) and short circuit current (Isc) have to be measured individually, not both at the same time.

 

[dr_nelson]

Don't shot the terminals together.  Put the amp meter in the circuit.  Short-circuits should usually be avoided, they tend to let smoke out.
In the above shot should be short, don't short the terminals together.  Bad juju.

OK, I guess this means do not connect the positive MC4 connector to the negative MC4 connector.

(...)  Reading no volts when wires are connected with no load?  The volt meter is measuring voltage drop, no resistance, no voltage drop.

I don't understand what you mean. You are the second person that says "no volts". My voltmeter was reading twenty point zero (20.0) volts at 7PM in the evening. 
Good idea, just covering the solar panel instead of tilting it towards the sun.

Open circuit voltage (Voc) and short circuit current (Isc) have to be measured individually, not both at the same time.

Yes, as outlined in my first post, I did not measure it at the same time. I only have one voltmeter and have to unplug and switch the control on the voltmeter do read volts or current/amps.

 

[dr_nelson]

(...)
When you check them, stick the ends of the multimeter leads into the MC4 connectors. I wouldn't be surprised if they exceed either rating if they are new. I blew a few cheap multimeters limited to 10a testing panels rated for less than 10a Isc.

OK thanks, no need then to extra open the junction box.
Yes, the panels are new, but they came with some damage in the aluminum frame (see here).
I will test this Saturday noon. The solar panel specs say Isc is 9.77 A. My voltmeter is a Etekcity MSR-R500 and it's max is 10 A... I hope I don't die.

 

[Spaceman Spiff]

https://www.windynation.com/cm/Testing a Solar System_R1.pdf

  -- Spiff

 

[user 37446]

OK thanks, no need then to extra open the junction box.
Yes, the panels are new, but they came with some damage in the aluminum frame (see here).
I will test this Saturday noon. The solar panel specs say Isc is 9.77 A. My voltmeter is a Etekcity MSR-R500 and it's max is 10 A... I hope I don't die.

Doc, can I send you my address in case you die, please leave me the panels in your will, pre-paid shipping of course... 

 

[jimindenver]

Well gee Wally, then how come my monochrystaline panels work until full dark?  

Polychrystaline panels not only have a lower output, but most will not even produce if partialy shaded.

Not in my side by side testing

 

[GotSmart]

Dont know what to tell you Jim.  The industry does not agree with your test results.  But I am sure the test peramiters are not the same.  

This is why I only recommend Renogy.  The quality and preformance is uniform unlike cheaply made unknown brands.  

The cost difference is not worth it in the long run buying cheap panels. 

You get what you pay for.