Installing serial solar panels

[TeddyDiver]

Originally Posted by ramblinrod

I don't know what you are talking about. One can put 732 breakers and switches on panels in series if they wish to artificially inflate the cost, but I don't really get the point.

There is no reason to put 3 in on the parallel array and only one on the series array.

If one want to be able to isolate the array, for either series or parallel it takes one, if one wants to isolate every panel, for either series or parallel it takes 3.

It was you who defined 3 for parallel and AFAIK having more than one in series is useless becouse it is only one string after all. And becouse I was teasing you being too serious with your opinions..

BR Teddy

[s/v Jedi]

Originally Posted by ramblinrod

What are you talking about?



If one has two 100W panels connected in series, you can't have 2.5 A going through the shaded panel and 5 A going through the non-shaded. They are in series. If one is 2.5 A, both are 2.5 A.



So in theory, if the panels were equipped with bypass diodes in the various series string of cells within each panel, one would expect there to be no significant difference between series or parallel connected panels when it comes to shading.



But please view the video in post 30.



This is a perfect example of my experience between series and parallel connected panels.



In practice, shading absolutely kills panels connected in series, regardless of how many diodes are indicated in the spec sheet.

Really?! What is not clear about strings with their own bypass diode? Where a shaded parallel panel loses 100% power output with even minor shading, in series the panel will still produce 50% or even 66% of it's power. You don't seem to grasp that.
hint: power is not just current, voltage was allowed in the game as well.

[s/v Jedi]

Just to make sure: this is how panels are wired:

[ramblinrod]

Originally Posted by s/v Jedi

Really?! What is not clear about strings with their own bypass diode? Where a shaded parallel panel loses 100% power output with even minor shading, in series the panel will still produce 50% or even 66% of it's power. You don't seem to grasp that.
hint: power is not just current, voltage was allowed in the game as well.

Oh, I think I have a pretty good grasp.

Please explain why when two panels are connected in parallel, and each series cell string is equipped with a bypass diode, the current from the 2 of 3 unshaded strings of cells do not contribute current at the parallel connection node.

Oh by the way, your explanation must comply with the laws of physics vs fairy tales.

Remember that first law of ol' Mr, Kirchoff (no not Chekov, that is something different).

May the electro-motive force be with you.

[DotDun]

Originally Posted by ramblinrod

Oh, I think I have a pretty good grasp.

That's subjective!

Originally Posted by ramblinrod

Please explain why when two panels are connected in parallel, and each series cell string is equipped with a bypass diode, the current from the 2 of 3 unshaded strings of cells do not contribute current at the parallel connection node.

A question like that from one that states:

Originally Posted by ramblinrod

...snip.....
What is the rule about voltage sources connected in parallel?

Oh yeah, THEY MUST BE EQUAL.

....snip....

If you have two voltage sources in parallel, they must be the same voltage. It's the law.
....snip

Do you understand the physics or is this just more blather?

Originally Posted by ramblinrod

Oh by the way, your explanation must comply with the laws of physics vs fairy tales.

Remember that first law of ol' Mr, Kirchoff (no not Chekov, that is something different).

May the electro-motive force be with you.

[Paul Elliott]

Originally Posted by ramblinrod

Please explain why when two panels are connected in parallel, and each series cell string is equipped with a bypass diode, the current from the 2 of 3 unshaded strings of cells do not contribute current at the parallel connection node.

Here's why:
I am looking at specs for an older Shell Solar 140W panel having 72 cells in three strings (each with bypass diodes).

The 72-cell panel puts out 42.8V unloaded. That's about 14.2V per string.
The peak-power voltage is 33V.

If you have one string shaded on a panel, the unloaded output will be about 14.2 + 14.2 - 0.5, or 27.9 Volts. This is the maximum unloaded voltage, which will drop further if you draw current.

If you put this partially-shaded panel in parallel with an unshaded panel having an output voltage of 33V, the shaded panel will be reverse-biased and will not contribute any current.

[ramblinrod]

Originally Posted by DotDun

That's subjective!

Actually, I have a bit of education in and experience with electrical / electronic / electro-mechanical device design, production, and installation.

About 35 years worth.

A pretty good grasp, objectively. ;-)

A question like that from one that states:

Dude, that statement is absolutely correct. The voltage at any node in a parallel circuit can only be one voltage (at least on this planet).

Do you understand the physics or is this just more blather?

Yes, I understand it, at least to this level. As I indicated in a prior post, it is Kirchoff's first law, developed in 1845. Nothing has changed (with respect to this discussion) in 172 years. ;-)

Instead of arguing, prove how the voltage at a single node, can be more than one voltage. It simply is not possible.

If two sources are connected in parallel, they are the same voltage at the connection node. Neither you, nor I, no even Obi Wan can change that.

[ramblinrod]

Do you understand the physics or is this just more blather?

Sorry, in the previous post the sentence above should have been in quotes from Dot Dun. (Unintentional ommision on my part.)

[DotDun]

Originally Posted by ramblinrod

Actually, I have a bit of education in and experience with electrical / electronic / electro-mechanical device design, production, and installation.

About 35 years worth.

A pretty good grasp, objectively. ;-)



Dude, that statement is absolutely correct. The voltage at any node in a parallel circuit can only be one voltage (at least on this planet).

Do you understand the physics or is this just more blather?

Yes, I understand it, at least to this level. As I indicated in a prior post, it is Kirchoff's first law, developed in 1845. Nothing has changed (with respect to this discussion) in 172 years. ;-)

Instead of arguing, prove how the voltage at a single node, can be more than one voltage. It simply is not possible.

If two sources are connected in parallel, they are the same voltage at the connection node. Neither you, nor I, no even Obi Wan can change that.

And yet, Paul just explained what happens when something breaks your coveted LAW! Is Paul a higher entity than Obi Wan??

You are so obsessed with your partial knowledge about the topic, you refuse to accept there is more to the story than what you know.

I hinted to your lack of knowledge when I belittled you about implementations where parallel power sources utilize higher voltages to meet an application (a grid tie inverter being 3v above commercial power). You discarded it as confusing and too different from the topic at hand. That demonstrates (to me) a lack of knowledge of the physics of parallel circuits.

A Paul stated, in parallel power sources, when there is a difference in voltage, the lower voltage source loses the race as there isn't enough potential to push it's current into the circuit (a simple explanation).

Back to topic!

Using Paul's example:

Here's why:
I am looking at specs for an older Shell Solar 140W panel having 72 cells in three strings (each with bypass diodes).

The 72-cell panel puts out 42.8V unloaded. That's about 14.2V per string.
The peak-power voltage is 33V.

If you have one string shaded on a panel, the unloaded output will be about 14.2 + 14.2 - 0.5, or 27.9 Volts. This is the maximum unloaded voltage, which will drop further if you draw current.

If you put this partially-shaded panel in parallel with an unshaded panel having an output voltage of 33V, the shaded panel will be reverse-biased and will not contribute any current.

Paul explained parallel.

If the (2) panels in the example were connected in series, you would lose ~47w plus the power dissipated across the bypass diode, ~2w. (vs. 140w in a parallel configuration) In a series configuration you would still have 231w of output.

Questions?

[ramblinrod]

Originally Posted by Paul Elliott

Here's why:
I am looking at specs for an older Shell Solar 140W panel having 72 cells in three strings (each with bypass diodes).

The 72-cell panel puts out 42.8V unloaded. That's about 14.2V per string.
The peak-power voltage is 33V.

If you have one string shaded on a panel, the unloaded output will be about 14.2 + 14.2 - 0.5, or 27.9 Volts. This is the maximum unloaded voltage, which will drop further if you draw current.

If you put this partially-shaded panel in parallel with an unshaded panel having an output voltage of 33V, the shaded panel will be reverse-biased and will not contribute any current.

Everything was perfect until that last sentence.

All panels block reverse bias current flow (with either internal or external blocking diodes). (Note to kids following this, don't put blocking diodes in series with panels that don't require them, most don't, or you add an unnecessary voltage drop).

When shaded, and connected to an unshaded panel, the connection node voltage is pulled up to the unshaded panel voltage.

Each panel supplies the current produced to the connection node at the connection node voltage.

Has to be.

[TeddyDiver]

Originally Posted by ramblinrod

When shaded, and connected to an unshaded panel, the connection node voltage is pulled up to the unshaded panel voltage.

Each panel supplies the current produced to the connection node at the connection node voltage.

Has to be.

Aaargh

[ramblinrod]

Originally Posted by TeddyDiver

Aaargh

Gentlemen. You can bang your head against a Rick wall all you wish. The voltage at a connection node cannot be two different voltages. By definition, a reverse biased p/n junction cannot pass current. In the circuit under question the only device that can sink current and pull down the unshaded panel voltage is the load (controller).

I respect Paul and nice attempt to try to explain how something that can't possibly happen can, it as explained was seriously flawed and incorrrect.

Teddy, Dot, I think you've bashed your head against brick walls too many times. This is the most basic of circuit analysis guys. You may be smarter than this, and this may be just a temp brain fart, but it is he way it is, and nobody, not even Obi Wan, can change it.

[TeddyDiver]

Is water flowing uphill?

[ramblinrod]

Originally Posted by TeddyDiver

Is water flowing uphill?

Apparently in everyone else's world, and there the sun is rising in the west and setting in the east, and the Easter Bunny comes year round when he isn't messing around with the Tooth Fairy.

[TeddyDiver]

Originally Posted by ramblinrod

Apparently in everyone else's world, and there the sun is rising in the west and setting in the east, and the Easter Bunny comes year round when he isn't messing around with the Tooth Fairy.

Sorry, trying just use simple consepts to make you understand a shaded panel doesn't produce any current while another nonshaded installed parallel with it..

BR Teddy