Voc much higher than specified on the back

[evilkos]

Hey all! Simple newb question. Bought some used panels that specify Voc 33.8V (Vmp 27.2V), but when I measured one panel's voltage in shade with a multimeter its voltage showed up as 55V. I thought it shouldn't ever get over Voc specified. Does that mean it's trash and I shouldn't attempt to connect it? What sort of fault is this and what are the physics behind this unexpectedly high voltage? Can this panel still be salvaged?

I thought about connecting 3 of those to Ecoflow Delta Max in series and it has 100V max solar input, so concerned it'll burn the unit. I'll measure the rest of them when I get back to the acreage in a couple of days.

 

[WYtreasure]

What was the temperature when you checked VOC? Low temps increase the VOC

Welcome to the party

 

[WYtreasure]

VOC is measured under specific conditions. Real world numbers rarely if ever match those numbers.

Anytime "all the panels I know of" get cold they exceed the manufacturers VOC.
I have read folks here stating that if you exceed VOC on your controller, you will ruin it. There are a few exceptions with some nice controllers.

In my signature is a link to midnitesolar, use it to see how temp affects voc.

55 volts is like way out there though. Maybe you have some good and some bad panels.

 

[Lt.Dan]

Also ensure your DMM is accurate.

 

[45North]

Also ensure your DMM is accurate.

That's what I was thinking. When mine reads funny if I look close it's actually mv.

 

[rmaddy]

I thought about connecting 3 of those to Ecoflow Delta Max in series and it has 100V max solar input

You can't connect 3 in series. 3 x 33.8V = 101.4V. And that's at 25ºC (77ºF). So ignoring your 55V reading for the moment, even as rated they will be too much for a 100V SCC.

 

[rmaddy]

What was the temperature when you checked VOC? Low temps increase the VOC

It would take far worse cold than you are about to have to raise the Voc from 33.8V to 55V. And I mean something like -185ºC (-300ºF).

 

[WYtreasure]

It would take far worse cold than you are about to have to raise the Voc from 33.8V to 55V. And I mean something like -185ºC (-300ºF).

Yup and nothing else would matter much. We would all be ?

 

[evilkos]

Thanks everyone for the quick and helpful responses! ?

I do think that it's a bit too high to just be due to temperature, but a valid point that Voc can be higher in lower [EDIT: initially typed "higher"] temps. Temp was around 30C as it was midday Brisbane and they've been sitting in the sun before picking up so they probably were even hotter. So yeah that's why I thought 55V is a bit too high but that was a panel that was cracked throughout. Others are much better but I haven't gotten around to measuring them.

I will probably start with just one, then a 2 panel string, to make sure I won't go over 100V max. I'm then planning to try 2s2p which I think Ecoflow Delta Max should be fine with. I have the blocking diodes and splitters for that as well.

Anyway I will measure the other panels tomorrow and see what the voltage reads! And will try my DMM on a known voltage like my car battery.

I'm curious what happens inside the panel that could lead to a higher than specified voltage, and how bad is it - does this indicate aging or a catastrophic failure?

 

[evilkos]

You can't connect 3 in series. 3 x 33.8V = 101.4V. And that's at 25ºC (77ºF). So ignoring your 55V reading for the moment, even as rated they will be too much for a 100V SCC.

Oh ok, I thought I'm supposed to sum the Vmp, but that's because I really wanted to squeeze in 3 panels good thing I haven't tried then

 

[rmaddy]

Voc can be higher in higher temps

That's backwards. Voc goes up in lower temps, not higher temps. So at 30ºC your 33.8Voc would be about 33.3V.

 

[evilkos]

That's backwards. Voc goes up in lower temps, not higher temps. So at 30ºC your 33.8Voc would be about 33.3V.

That's what I took away, and then wrote it down backwards ? thanks for the correction!

 

[Bud Martin]

If your battery meter is low it will cause your meter to show higher Voltage reading than it should be, so check your meter as suggested.

 

[WYtreasure]

Can this panel still be salvaged?

You could run copper pipe through it and heat water.

 

[SpongeboB Sinewave]

I would worry more about it being too LOW of Voc. But yeah, that is REAL high for normal humanoid temperatures !

 

[robby]

Excluding the temperature which as pointed out cannot be the issue I cannot see any mode of failure or aging effect with a PV panel that could cause the voltage to go up, any failures would cause the voltage to go down.
It must be the meter that is giving problems.

 

[evilkos]

Excluding the temperature which as pointed out cannot be the issue I cannot see any mode of failure or aging effect with a PV panel that could cause the voltage to go up, any failures would cause the voltage to go down.
It must be the meter that is giving problems.

Is there a simple way to make sure the meter is more or less accurate with only household items? :D I was thinking to just measure the car battery voltage at the outlet, as I have a car cigarette plug splitter that also shows voltage and it's something like 13.3V, so if my multimeter shows approx the same value it must be more or less fine :D An AC outlet comes to mind also, or an output of a DC power adapter like a PC / laptop power source... When googling about this, it mostly shows weird dudes tinkering with specialized electronic circuits to calibrate their DMM.

 

[evilkos]

I would worry more about it being too LOW of Voc. But yeah, that is REAL high for normal humanoid temperatures !

What do you mean by too low? But yeah, everything I came up with by Googling is when Voc lower than specified, which is why I thought I'd post here for an explanation. It's possible my multimeter is crap, yes. I will try to verify that.

 

[robby]

Is there a simple way to make sure the meter is more or less accurate with only household items? :D I was thinking to just measure the car battery voltage at the outlet, as I have a car cigarette plug splitter that also shows voltage and it's something like 13.3V, so if my multimeter shows approx the same value it must be more or less fine :D An AC outlet comes to mind also, or an output of a DC power adapter like a PC / laptop power source... When googling about this, it mostly shows weird dudes tinkering with specialized electronic circuits to calibrate their DMM.

That’s a Mcguyver type question. Limited to house hold items the most accurate might be a usb charger like an Apple charger but you would have to sacrifice a cable and cuttof the end then separate out the wires to find the two that put out 5Vdc. You are not going to get accurate least significant digits. I cannot think of anything better that is non technical and lying around your house.

 

[timselectric]

Simple solution
Change battery in meter
See if readings improve
Compare multiple panel readings