What I found out today. . . panel arrangement matters

[Shotgun]

Experienced guys probably know this without even knowing that you know it, and I guess I should have known it, but it was still surprising to me.

I've got six panels, arranged 2S3P. I've been working on getting them up off the ground, but haven't quite completed that job yet. Three are racked at the optimum angle, while three are "the best I could do". Doesn't mean I can't draw some kWh off of them while the process is ongoing, though. Right?

Well, I just checked the PowMr All-in-one MPPT charge controller/inverter thingy. It show I was drawing ~10A at ~30V. Given that I have six 32V/8A panels, I wasn't happy with that. I went out and looked, and the panel mated to the third racked one was totally shaded. That is, I had two racked and in series that are producing at optimal rate. Two on the ground that are half shaded and completely at the wrong angle and in series that ain't doing squat. And then two in series where one is optimally racked and the other is on the ground not doing squat.

Panels will not create current until the voltage of the sink (the controller) drops below their output voltage. If you have two voltage sources, one 6V and the other 12V, in parallel, the 6V won't start pushing electrons. The completely racked series would be pushing electrons at ~60V. The series on the ground would push at 30V (maybe). But, the split series might be pushing at 45V. If the. controller can draw enough current, the internal resistance of the racked panels would cause its output voltage to drop, and then the split series could start contributing.

So, I went out and moved the unracked panel of the split series out of the shade. I'm now getting ~45V at ~20A!!

It would be great if we all lived on farms with large, open fields for solar panel sighting, but many of these panels are going up in residential areas. I'd ask my neighbor to lower his roof so that my panels would have line of sight to the sun all day, but I don't foresee him being amenable to that request. Therefore, it is on me (us?) to be cognizant of how our panels are arranged. A half-shaded series in parallel with a non-shaded series is NOT going to produce power.

 

[MisterSandals]

Given that I have six 32V/8A panels,

What is the Voc and Isc?

and the panel mated to the third racked one was totally shaded.

Specs on this panel?

If you provide info about your panels, we can help you arrange them for your charge controller. If your charge controller isn't a secret also, its max input voltage and your battery voltage would help.

 

[LB3]

As you’ve noticed, panel placement is critical. Even shading a single cell can significantly degrade performance so you want to group panels such that shaded panels aren’t in series with unshaded panels.

 

[Bob B]

If bypass diodes are installed and 2 panel are in series with one partially shaded .... you should still get some juice.

I'm not an expert on this, but maybe do some research on the use of bypass and blocking diodes. Not having them installed can result in overheating in the panel.

 

[squowse]

My understanding is that in a series string of panels the current has to be the same through every panel by definition. The shaded panels will offer high resistance compared to the non shaded and reduce the current of all down to their current.

 

[Bob B]

My understanding is that in a series string of panels the current has to be the same through every panel by definition. The shaded panels will offer high resistance compared to the non shaded and reduce the current of all down to their current.

That's what the bypass diodes do .... they bypass current around a panel or section of panel so that it doesn't have to flow thru the shaded portion.

 

[Shotgun]

What is the Voc and Isc?

About 37.6V and 8.85A. At Pmax, the panel says 30.3V and 8.27A

Specs on this panel?

Yeah. They have few specs. I bought them used, and half of them are still sitting on the ground, but I'm trying to keep them clean. It'll be easier once I get them mounted.

If you provide info about your panels, we can help you arrange them for your charge controller. If your charge controller isn't a secret also, its max input voltage and your battery voltage would help.

The charge controller is a PowMr HF2430U60-100. It'll take between 30V and 85V with a max of 40A, and drive up to 60A into a 24V battery pack. The Voc is too high to put more than two in series, and the current would be exceeding comfortable to put more in parallel. The wiring is also favorable to 2S3P, requiring just one 3-way splitter set and a couple extension. It won't be a problem once they are all off the ground and racked properly.

 

[Shotgun]

My understanding is that in a series string of panels the current has to be the same through every panel by definition. The shaded panels will offer high resistance compared to the non shaded and reduce the current of all down to their current.

In DC electronics:
With series anything, the current is the same through all and the voltage varies across each element.
With parallel anything, the voltage is the same across all and the current varies through each element.

Solar cells are diodes that act as a current source when exposed to light. They don't "reduce the current of all down" as much as they don't help push the train, and act as another load instead.

In fact, that is a good analogy. The circuit is a railroad track. The the solar cells are train engines. The train cars are the loads we're trying to drive (the battery charge controller or inverter in this case). With two engines in a string, when one engine runs out of fuel, the other engine has to pull it along. If there are trains on parallel tracks (and this is straining the analogy), and those trains have both engines working, then our train won't be able to get into the train yard, because he gets shouldered out by the more powerful train. The only way for our train to be able to deliver our load is to put so many cars on the more powerful one that he has to slow down.

 

[Shotgun]

That's what the bypass diodes do .... they bypass current around a panel or section of panel so that it doesn't have to flow thru the shaded portion.

So then you'd have a 2S/1S2P hybrid. I don't see how that helps.
I had:

-> 30V -> 30V -> 8A
-> 30V -> 30V -> 8A
-> 30V -> 30V -> 8A

Put a diode to bypass what is essentially a very large diode because it isn't acting as a current source, and I get:

-> 30V -> ~~~ ->
-> 30V -> 30V -> 8A
-> 30V -> 30V -> 8A

The first series isn't going to push ANY electrons, because it has to meet or exceed the voltage of the other strings. What I had was:

-> 30V -> ~~~ ->
-> 30V -> ~~~ ->
-> 30V -> 30V -> 8A

And, I rearranged it to:

-> ~~~ -> ~~~ ->
-> 30V -> 30V -> 8A
-> 30V -> 30V -> 8A

It's like @LB3 said. Strive to keep all your shaded and unshaded panels segregated. It wasn't obvious to me until it smacked me in the face.

 

[Bud Martin]

Reverse-bias-due-to-shading-and-bypass-diodes

Reverse Bias due to shading and Bypass Diodes

Interesting reading from Sunpower. I was looking to learn about shading effect and bypass diode, I did not know about heating issue due to shading, I member one of the member shows the pictures of burnt up cell that melt the panel. Reverse Bias and Bypass Diodes When cells are put into reverse...

diysolarforum.com

 

[LB3]

So then you'd have a 2S/1S2P hybrid. I don't see how that helps.
I had:

-> 30V -> 30V -> 8A
-> 30V -> 30V -> 8A
-> 30V -> 30V -> 8A

Put a diode to bypass what is essentially a very large diode because it isn't acting as a current source, and I get:

-> 30V -> ~~~ ->
-> 30V -> 30V -> 8A
-> 30V -> 30V -> 8A

The first series isn't going to push ANY electrons, because it has to meet or exceed the voltage of the other strings. What I had was:

-> 30V -> ~~~ ->
-> 30V -> ~~~ ->
-> 30V -> 30V -> 8A

And, I rearranged it to:

-> ~~~ -> ~~~ ->
-> 30V -> 30V -> 8A
-> 30V -> 30V -> 8A

It's like @LB3 said. Strive to keep all your shaded and unshaded panels segregated. It wasn't obvious to me until it smacked me in the face.

This is a great example, you don’t want to pair panels from the top row with panels from the bottom row.

 

[svetz]

... shade....

String systems are always tricky with shade. Microinverters or DC optimizers are the way to go if you have varying shade throughout the day and can't optimize the string. But, it can be expensive to get them to work with a battery.

How shade falls on a panel can be important too, you might enjoy this thread: https://diysolarforum.com/threads/what-ever-happened-to-the-maxim-chip.240/post-56499

 

[WYtreasure]

Experienced guys probably know this without even knowing that you know it, and I guess I should have known it, but it was still surprising to me.

I've got six panels, arranged 2S3P. I've been working on getting them up off the ground, but haven't quite completed that job yet. Three are racked at the optimum angle, while three are "the best I could do". Doesn't mean I can't draw some kWh off of them while the process is ongoing, though. Right?

Well, I just checked the PowMr All-in-one MPPT charge controller/inverter thingy. It show I was drawing ~10A at ~30V. Given that I have six 32V/8A panels, I wasn't happy with that. I went out and looked, and the panel mated to the third racked one was totally shaded. That is, I had two racked and in series that are producing at optimal rate. Two on the ground that are half shaded and completely at the wrong angle and in series that ain't doing squat. And then two in series where one is optimally racked and the other is on the ground not doing squat.

Panels will not create current until the voltage of the sink (the controller) drops below their output voltage. If you have two voltage sources, one 6V and the other 12V, in parallel, the 6V won't start pushing electrons. The completely racked series would be pushing electrons at ~60V. The series on the ground would push at 30V (maybe). But, the split series might be pushing at 45V. If the. controller can draw enough current, the internal resistance of the racked panels would cause its output voltage to drop, and then the split series could start contributing.

So, I went out and moved the unracked panel of the split series out of the shade. I'm now getting ~45V at ~20A!!

It would be great if we all lived on farms with large, open fields for solar panel sighting, but many of these panels are going up in residential areas. I'd ask my neighbor to lower his roof so that my panels would have line of sight to the sun all day, but I don't foresee him being amenable to that request. Therefore, it is on me (us?) to be cognizant of how our panels are arranged. A half-shaded series in parallel with a non-shaded series is NOT going to produce power.

Howdy Shotgun,

Just curious how that "PowMr All-in-one MPPT charge controller/inverter thingy" is working out for you.

 

[Kornbread]

And this makes me wonder why things are not always as the seem.

 

[12VoltInstalls]

NRG. The Vermont company?
.
No things aren’t always as they seem. There was a self-proclaimed solar youTube guru that did a video on the drastic effects of “a leaf” on solar output. I heard his words but LOL his meters in the shot would have changed more with a passing cloud.
When I was 200W/PWM I had shading until 12:30pm so I faced them SW. As the sun came up each day there was 30-45mins where the sun hit the panels backsides but yet I’d get ~13V at ~2A-ish (probably some reflected light on fronts)

No, things are not always as they seem.

 

[wattmatters]

NRG. The Vermont company?

No.

It's an Australian solar PV system installer which uses both string and micro inverters for grid tied systems.

They did 2 or 3 videos with some neat testing doing a like for like comparison of a Fronius string inverter and Enphase micro inverter systems, with controlled equivalent shading scenarios on each system's array.

The results put paid to the marketing message often seen about how micros are vastly superior when it comes to shade performance. As with all such things, it will depend on the nature of the set up and shade experienced, and of course this is for modern panel design as well, using bypass diodes and half cut panels, coupled with a high quality inverter with an excellent global MPPT system.

 

[Kornbread]

↑↑↑ What he said. I though micro inverters were the cat's meow when dealing with shadeing, but after watching some of those videos, I'm not as convinced as I once was.

 

[12VoltInstalls]

I'm not as convinced as I once was.

The several years I rented my beautiful little private spot for my camper I had heavy tree-shaded panels until 12:30pm. One of my first lessons was learning not to scratch my head ‘til it bled over the watt hours I’d record between leaving for work and getting home for lunch.
Cuz there weren’t no sun on Saturday and Sunday mornings for sure…

Where I am now (other than the mountain ridge that makes sunset slightly early) I get unobstructed sunlight all day long.

 

[Shotgun]

Howdy Shotgun,

Just curious how that "PowMr All-in-one MPPT charge controller/inverter thingy" is working out for you.

It does the job, but the company sucks and I've not been able to get any technical details about it so that I can track its performance. The data it reports is not believable, as some seem to be off by a factor of two. If I had it to do again, I would go with the company that they stole the technology from (Victron? No sure).

 

[WYtreasure]

It does the job, but the company sucks and I've not been able to get any technical details about it so that I can track its performance. The data it reports is not believable, as some seem to be off by a factor of two. If I had it to do again, I would go with the company that they stole the technology from (Victron? No sure).

I purchased numerous volt/current/amp devices to see what's going in and what's coming out. I plan to track DC in, AC in, DC to and from batteries and AC produced. We shall see someday, my system is not operating yet.

I heard a buncha crap about the technology being stolen right after I purchased mine. Not sure how I could have known beforehand. I thought everything built over there was taken from someone else.