Solar panel shading and parallel versus series connections

[derekisastro]

Hi all,

I had an interesting experiment over the last weekend with 2 of my 240W panels.

They are side by side and I was measuring their individual outputs as well as their combined parallel and series outputs. I got a result I could not explain (I am sure I am missing something?).

Individually, due to partial shading of 1 panel, I got 33.3V @ 7.05 amp (230W) for the non-shaded panel and 33.4V @ 0.32 (10W) amp for the partially shaded panel.

In parallel, I got 33.3V @ 7.3 amps. About 240W, makes sense.

In series, I got 66.6V @ about 7amps ... about 460W ... this doe NOT make sense to me. This was all measured with my DC clamp multimeter, either short-circuiting or measuring the output at the cabling attached directly to the panels. What am I missing? When connected to a charge controller, in series, is this when I will see the amperage/shading from the other panel affect the output?

I was assuming that with a saded panel or different shading on each of the panels that putting them in parallel would be best for output but my testing suggests the opposite ... right?

 

[wattmatters]

This was all measured with my DC clamp multimeter, either short-circuiting or measuring the output at the cabling attached directly to the panels.

Can you clarify?

You are testing short circuit current.
But which voltage are you testing? Open circuit? (i.e. the cables unplugged so you can probe the cable ends to test voltage).

If so then all bets are off. You can't combine short circuit current measurement and an open circuit voltage measurement and assume that will translate to actual deliverable power.

Apply an actual load and report back.

 

[derekisastro]

Can you clarify?

You are testing short circuit current.
But which voltage are you testing? Open circuit?

If so then all bets are off. You can't combine short circuit current measurement and an open circuit voltage measurement and assume that will translate to actual deliverable power.

Apply an actual load and report back.

Yes, VoC.

It is good to know that the VoC and Isc cannot be combined, that the underload would show something significantly different.

I had assumed, incorrectly it seems, that the Isc of series-connected panels would show the effects of the partial shading of 1 panel. I now assume that my results are as expected for the conditions in which I tested?

 

[wattmatters]

I had assumed, incorrectly it seems, that the Isc of series-connected panels would show the effects of the partial shading of 1 panel.

One unshaded panel is all that is required to generate that current. The other shaded panel will pass that current through via the bypass diodes. That's what the bypass diodes do, help to prevent the string's current from being dragged down because one panel (or part of a panel) is shaded.

Meanwhile because there is still some light hitting both panels (even the shaded one is getting some light) they will both have an open circuit voltage and because they are connected in series, the open circuit voltage of each panel will add together.

One you place the panels in a circuit with a load/resistance, then the lack of contribution of the shaded panel will manifest.

Here's a test to perform:

Connect the panels in series to the MPPT.

Make sure the MPPT has a load demand which will ensure the MPPT is drawing the max power it can (e.g. your battery needs charging, or add a load to the system at least the same or higher than the panel's peak output rating).

Place both panels in full sun. Note the power output it settles on after a little while.

Now with a piece of cardboard or something similar, perform tests with one panel being partially shaded and report the resulting power output.

Shade the following and report the MPPT power output each shade condition settles on:

- One cell on one panel
- The bottom (or top) row of cells of one panel
- The left (or right) column of cells on one panel
- Half of one panel lengthwise
- Half of one panel widthwise
- All of one panel
- Unshaded for a check it reverts to similar output as you started with

Now repeat that test with the panels in parallel and compare the results.

 

[Bob B]

How much time elapsed between the series and parallel testing? What was causing the shading?

I agree that is would be good to do more controlled shading.

 

[Berseker]

One unshaded panel is all that is required to generate that current. The other shaded panel will pass that current through via the bypass diodes. That's what the bypass diodes do, help to prevent the string's current from being dragged down because one panel (or part of a panel) is shaded.

Meanwhile because there is still some light hitting both panels (even the shaded one is getting some light) they will both have an open circuit voltage and because they are connected in series, the open circuit voltage of each panel will add together.

One you place the panels in a circuit with a load/resistance, then the lack of contribution of the shaded panel will manifest.

Here's a test to perform:

Connect the panels in series to the MPPT.

Make sure the MPPT has a load demand which will ensure the MPPT is drawing the max power it can (e.g. your battery needs charging, or add a load to the system at least the same or higher than the panel's peak output rating).

Place both panels in full sun. Note the power output it settles on after a little while.

Now with a piece of cardboard or something similar, perform tests with one panel being partially shaded and report the resulting power output.

Shade the following and report the MPPT power output each shade condition settles on:

- One cell on one panel
- The bottom (or top) row of cells of one panel
- The left (or right) column of cells on one panel
- Half of one panel lengthwise
- Half of one panel widthwise
- All of one panel
- Unshaded for a check it reverts to similar output as you started with

Now repeat that test with the panels in parallel and compare the results.

Seems OP lost the zeal to do this test.

 

[derekisastro]

Seems OP lost the zeal to do this test.

Less about zeal and simply more about life to care-factor ratio ... my panels are performing more than adequately at the moment, such that with my limited time the impetus to do such testing is quite low ...

I will still do it and hopefully might find time soon so stay tuned!

 

[newbostonconst]

 

[efficientPV]

A little misleading. I'd comment, but isn't she dead.

 

[JoeHam]

A little misleading. I'd comment, but isn't she dead.

She is but her work was rock solid and she was an asset to the forum.

If you see an issue speak up already.

She was a fan of the truth.

 

[JRH]

She is but her work was rock solid and she was an asset to the forum.

If you see an issue speak up already.

She was a fan of the truth.

I liked her . Watched her for years… I had no idea about her passing.. bummer..
Jim.

 

[120vjohn]

At what age she died, was natural death, illness or accident?

About health issues, i am a health care specialist that live offgrid.
Now days are new health challanges some of them can be managed whit some know how.
E.G. some digestive cancers are related with H.pylori chronic infection, I encounter this problem quite frequent, but are many strains of helicobacter/ campylobacter, one of them are wild, most harmful are those imported from Asia/Japan.
I found a way to get it out using Rife method, i tested it years against lab tests, antigen/ antibody, PCR it proved it effective.
Polluted food especially meat, that is usually polluted with hormon like chemicals can produce some cancers.
Other chronic parasitic, bacterial, fungal infections may pave a way for cancer in different locations.

It is possible that electromagnetic fields to be harmful too, when I used unipolar modulation a filled bad. after that i built by electronics symmetrical in respect to ground to minimize common mode radiation.

About shading, in parallel you lose power of shaded string, but hot spot issues are unlike, in series you lose voltage, but hot spot is a problem.
Hot spot can occur in a cluster of cells clamped by a bypass diode, worst case scenario is only one cell shaded, it drows power from rest of illuminated cells.
Typically 20 or 24 cells are covered by a bypass diode, if one of 24 is shaded and efficiency is 20%, 4.6 times more power is aborbed in that cell, This is enough to destroy it and set fire.
Also bypass diodes may fail under heavy load, short, or set fire in connection box.
For that reason now are available half cut cell panels, two panels in parallel in one, or bypass diode at cell level(uncommon).

 

[efficientPV]

I think many are confused by this demonstration and her statement that volts don't drop with shade. That is with the panel totally unloaded. She should have had the voltmeter always connected to the panel and used a switch to turn the load on and off and demonstrated how a load affects the voltage. I think she has confused people into thinking their arrays will maintain the same voltage and only current drops. A schematic diagram of the cell configuration showing which cells are blocked was needed. I kept wondering what she was trying to say. It is hard to make a really good video. I think this was a pretty poor video.

 

[JoeHam]

At what age she died, was natural death, illness or accident?

Cancer sucks, ‘nuff said.

 

[caki]

Amy Beaudet the "Solar Queen" Dies at 55 | altE Blog

Amy was a 14-year veteran of the solar industry, where she was widely seen as one of its best trainers and communicators with her YouTube videos.

www.altestore.com

 

[JoeHam]

I think many are confused by this demonstration and her statement that volts don't drop with shade. That is with the panel totally unloaded. She should have had the voltmeter always connected to the panel and used a switch to turn the load on and off and demonstrated how a load affects the voltage. I think she has confused people into thinking their arrays will maintain the same voltage and only current drops.

Her next video in that series had a constant load, a fan. No switch as you wish but…

And this was before millions of YT videos with increasing production quality. Her stuff was the best at the time IMHO.

See here for the fan loaded video :

 

[JoeHam]

Amy Beaudet the "Solar Queen" Dies at 55 | altE Blog

Amy was a 14-year veteran of the solar industry, where she was widely seen as one of its best trainers and communicators with her YouTube videos.

www.altestore.com

We had a similar thread here but it looks like that, and all of her posts, were removed for some reason.

@SolarQueen was her screen name here also.

Poor choice by this forum IMHO.

EDIT: last night a search on her name came up empty but now stuff is back.

Here is one thread :

Remembering Amy

Amy Beaudet, our very own Solar Queen, has passed away. Amy Beaudet, affectionately known as ‘The Solar Queen’ and a pioneer in the field of renewable energy, passed away on Sunday, May 2, 2021 at Brigham and Women’s Hospital in Boston, Massachusetts. She was 55 years old. AltE has a notice...

diysolarforum.com

 

[120vjohn]

For short, is a trade off between cell size, geometry and shading.
If you split your array in more strings with smaller cells, probability that one equivalent cell to be completely shaded is negligible, if the cell is a long thin strip, probability to be completely shaded is lo.
Smaller cells are expansive to manufacture and wire, cutting larger cells is less expansive but wiring is still a problem, cutting cell in half is a trade off between cost an benefits.
Correct, with no load total voltage almost not changes but under load you lose voltage and power, if only one cell is shaded you lose as least number of cells covered by a bypass diode usually 20 for 60 cells panel or 24 for 72 cells panels.

About cell level bypass diode panels, are not real benefit in multiple cells shading, because those diodes are in series, and voltage drop is hi,they must have standard bypass diodes wiring along cell level bypass.

There are multiple local maximum power points in case of shading, the absolute maximum does not corresponds with higher voltage,that may confuse some MPPT trackers, can lock on a non optimal point.
If you stick to maximum voltage maximum power point you are lees exposed to hotspot problems, shading is temporary, some times maximum voltage maximum power point becomes absolute maximum.
I use a fixed input voltage control, that stick on maximum voltage MPP, this protect panels, and have advantage in changing weather because the loop is very fast.