Solar PV Array Switching

[Warpspeed]

Its all relative...

At night there is zero measurable voltage.
In dawn twilight, the voltage starts to rise above zero, and can be quite low before the sun appears above the horizon.
So saying Voc always get the same voltage shaded, is almost true but not strictly true in really gloomy twilight.

As stated above ^^ under really marginal conditions, it takes very little loading or leakage to pull down Voc by a lot.

 

[McKravitts]

As mentioned in previous post, blocking diodes are the solution.
However, if you want/need a relay, I am using 3 Functional Devices Inc. RIB24P30 Prewired Relay,24VAC/DC,30A,DPDT relays. You can parallel the poles for even better preformance.
I've been using them to switch solar outout from an off grid inverter to a grid tie inverter and back for over two years with no issues.
They are relatively inexpensive.

 

[Hedges]

Blemished Canadian 250W Solar Panel | SanTan Solar

These Canadian 250W Solar Panels have water intrusion, which has caused discoloration on the vinyl and busbars. Please see pictures for more details.

www.santansolar.com

I think these ones, they were $45 when I got them

"I do sometimes see almost double the voltage on one of them than the other."

Could be a shorted diode or other such issue.
Worth testing individually for Voc, Isc, Vmp & Imp (or Vload and Iload into a resistive load).
Then you might repair or replace. I found a few bad panels limiting string performance.

 

[gotbeans]

OK, that explains it. Worn out blemished panels can develop cell to frame leakage due to moisture ingress and i suspect old cells can wear out and develop internal leakage current which would pull your low light open circuit voltage down. You probably still have very insignificant amount of leakage current noticeable only in low light and in open circuit measured with your voltmeter. Chances are your diodes produce more loss at full light vs. just letting shaded panels "steal" couple of milliamps from working array.

You really think the diodes take more than they save? <__<

"I do sometimes see almost double the voltage on one of them than the other."

Could be a shorted diode or other such issue.
Worth testing individually for Voc, Isc, Vmp & Imp (or Vload and Iload into a resistive load).
Then you might repair or replace. I found a few bad panels limiting string performance.

when I got them I tested each voc in the sun within 30 mins of each other, in the same position
some were crap hence not being connected
what's the other ways to test those things? short the two wires together on one panel for amps?

 

[Hedges]

Yes, that gives Isc.

But I've had panels where Voc and Isc both looked good, but they put out reduced power.
I repeated the voltage and current tests with a couple electric heaters connected as a load.

Measuring PV panel performance

I suppose I could buy a solar panel tester like Will reviewed, but that doesn't feel DIY enough to me. Besides, I'm a cheapskate, and I try to do things in the most difficult (and expensive if the equipment wasn't on hand) way. I'm presently working on an underperforming string of Sharp 165W...

diysolarforum.com

 

[gotbeans]

I got too much other stuff to do than rig that up

https://www.amazon.com/FrogBro-Photovoltaic-Multimeter-EY1600W-Troubleshooting/dp/B0C3M1TFP3/

This thing is good? It's $61 on aliexpress

 

[Hedges]

That's the right way to do it.
Will reviewed a couple, but I can't locate links.

Measurements won't match specs because illumination isn't same, but you can compare all panels and note outliers.

 

[gotbeans]

That's the right way to do it.
Will reviewed a couple, but I can't locate links.

Measurements won't match specs because illumination isn't same, but you can compare all panels and note outliers.

Yea I see that, almost all my panels are 38-39volt (rated at 37.2) except 3 of them .. one didn't work, and other 2 were 18 and 24 volt lol...
I'll just get this tester might as well since I'm getting more panels anyway

I think one of the internal arrays is busted on the 24 volt since you can see they have 3 sets of cells in series with the wiring there, so I assume each set is 12v and 12*2 = 24 but normally it's 37 which is close enough to 36.. is my thinking right? I'll return it to santan regardless

 

[Hedges]

Freshly bought from Santan, and DOA or at least sick?
Or did they decay later, within the seller's warranty.

Being 1/3 or 2/3 of expected voltage would not be surprising for panels with 3 bypass diodes.
I think some of mine had the issue of very low current from some cells, so able to deliver Voc, also Isc from the good cells, but not full current while loaded.

I thought Santan was in the habit of testing panels, but that might be too much added cost for $30 to $50 ones. Maybe they just sample test lots.

I should really get a tester. And a light meter, so I can attempt to document some degraded panels for Sharp's warranty.

 

[gotbeans]

Fresh from santan they were like this, they never responded (sent an email 2 days after I got them) so I'm just going to bring them there. Still have like 8 months of warranty (1 year)
I have to go through arizona for a business thing anyway so I'll just bring a trailer with them
What are you talking diodes? internal in them? the other 30+ ones are all 38-39 volt as I said, so no it doesn't make sense they're lower

oh you're talking about what I said? I'm talking about how the panels themselves are made, internally they have 3 arrays in series and bypass diodes or whatever? that is what they are rated at with those diodes already. the one at 24 volts has like 1 of the arrays dead or something

 

[Hedges]

Bypass diodes. Used to be 2 per 12V panel, now 3 per 24V or 36V panel.
If one shorted, it would knock off 1/2 or 1/3 of Voc.

If there was an open circuit in one of the three PV cell strings, I think it would look same as shorted diode; the diode would be forced into bypassing any current. This might be the more likely failure, if water intrusion could cause traces to corrode through.

"These Canadian 250W Solar Panels have water intrusion, which has caused discoloration on the vinyl and busbars."

Was $0.20/W, now $0.12/W. Plus shipping.
My most recent purchase was pallets from Inxeption, $2000 for 31 pieces 370 watt brand new, came to $0.19/W including shipping.
Prices have been falling, and then bargains appear like that one, around 1/2 what some other vendors charged for same.

Just came to my inbox:

Do Business Better with Inxeption

Inxeption is the leading technology platform digitizing the global Industrial Commerce value chain. We are advocates for our ecosystem of suppliers and buyers, enabling them to do business better.

inxeption.com

 

[gotbeans]

Yea it says was $50 but they were $45 lol for like a year, because I was watching them since 2022 and just got them few months ago.

I was looking at pallets but for those panels the pallet was more per panel for whatever reason.. so I just got 40 individual ones lol (still came on 2 pallets of course)

hopefully the deal lasts. I'll be there in a month it'll probably be over though.

 

[400bird]

Bypass diodes. Used to be 2 per 12V panel, now 3 per 24V or 36V panel.
If one shorted, it would knock off 1/2 or 1/3 of Voc.

3 is normal?

 

[Hedges]

I think so.
But not everybody's normal.

 

[gotbeans]

is that in the back of the panel?
How do you count that, 5 "internal arrays" within the panel itself?

 

[400bird]

is that in the back of the panel?

Yes, I had a failure recently that was replaced under warranty. This is inside the junction box.

Solar Panel Warranty

Well, I never thought I'd need the warranty on my solar panels, but here I am. 5 years into the 25 year warranty. Anyways, on to my story. Yesterday evening, I logged into the Solar Edge monitoring platform and had this alert: I like how at the end they basically says, our stuff isn't the...

diysolarforum.com

How do you count that, 5 "internal arrays" within the panel itself?

I believe it is most negative, then the positive each of 4 quadrants.