Installing serial solar panels

[OceanSeaSpray]

Originally Posted by ramblinrod

Referring to a solar panel as a voltage source is 100% correct, especially in this case.

No, it is not. Sorry about the schooling. I must be getting tired of seeing two people firing at each other while stating things that are not strictly correct.

The difference between a voltage source and a current source is how they behave under load. Discussing the panel's voltage under no load doesn't make it a "voltage source" and you are just adding confusion.

Your point that the voltages equalise the minute you connect two sources in parallel has been made over and over again (it is rather elementary) and I just explained earlier (twice actually) what happens when the system is then loaded (which was then repeated by aXis).

As far as I can see, no one is pretending that two voltages exist at the parallel connection point. We should therefore be able to move on, hopefully.

[ramblinrod]

Originally Posted by OceanSeaSpray

The difference between a voltage source and a current source is how they behave under load.

Agreed.

Discussing the panel's voltage under no load doesn't make it a "voltage source" and you are just adding confusion.

Any power source, can be described as a current or voltage source as best suits the analysis.

Referring to a solar panel as a voltage source, when considering the voltage in the analysis without concern for the current, is absolutely, 100% correct.

From Wikipedia...

Since no ideal sources of either variety exist (all real-world examples have finite and non-zero source impedance), any current source can be considered as a voltage source with the same source impedance and vice versa.

Quite frankly, anyone with any rudimentary electrical knowledge should be able to answer what the voltage across two voltage sources connected in parallel is.

IIRC correctly, this was covered in high school, Grade 10, Electricity - AC and DC Circuit Fundamentals, the very first day.

[OceanSeaSpray]

Keep splitting hairs, arguing and giving lessons as much as you want. You are long past adding any value.

Solar panels behave as current sources as they are when we buy them and "transforming them into voltage sources with a reconfigured impedance" is primarily useful to fuel your pointless argument. Since you started, you didn't manage to explain a quarter of what I did in two posts. Have a good day, my friend.

[DotDun]

Originally Posted by aXis

It's a physics law. I.e. a physical phenomenon that has been proven to be absolutely true over repeated scientific observations and experiments. You will be unable to produce with a scenario that breaks it.

As state multiple times, if you connect two items with different voltages together, they will equalise to a common voltage. The exact nature of how they achieve this depends on the the characteristics of the devices, but it will happen.

For your example, connecting a 34V/60 cell panel and a 20V/36 cell panel together (with blocking diodes) *will* result in a common no-load voltage of 34V. Internally there will be 20V across the string of cells in the 36 cell panel, and the remaining 14V will appear across the blocking diode. The polarity of the voltage across the blocking diode will cause it to be reverse biased and so no current can flow. The 36 cell panel will be completely useless, effectively isolated and unable to contribute.

If you then apply a load to the system, the common voltage will reduce from 34 volts and the voltage across the 36 cell panel's blocking voltage will also reduce equally. Initially all of the current will be supplied from the 60 cell panel only. If you keep loading it so heavily that the voltage drops to 19.7V or so, the blocking diode will become forward biased and the 36 cell panel can start to contribute weakly.

If you load it further such that the voltage drops down to 13V or so, the 36 cell panel will be contributing it's full rated amps, and the 60 cell panel will be delivering something between rated amps and short circuit amps. This 60 cell panel will be running very inefficiently though.

In practice, if you were to connect this to an MPPT controller you would have variable results. Ones that use a genuine hill climbing algorithm may settle on an intermediate voltage between 13V and 19.7V and allow both panels to contribute, but ones that use the open circuit method would probably settle on about 26V and only the 60 cell panel would contribute.

I do understand. My example is absurd due to not solving any application. My post is a retort to a long standing argument in this thread that starts back at post 57.

What's unclear to me, if the 36 cell panel does not have a blocking diode, will the cells be damaged?

[DotDun]

Originally Posted by OceanSeaSpray

Keep splitting hairs, arguing and giving lessons as much as you want. You are long past adding any value.

Solar panels behave as current sources as they are when we buy them and "transforming them into voltage sources with a reconfigured impedance" is primarily useful to fuel your pointless argument. Since you started, you didn't manage to explain a quarter of what I did in two posts. Have a good day, my friend.

Thanks!

He is a legend in his own mind.

He has moved some, he is no longer stating the 'sources' must be the same voltage, which has been my only argument all along.

It has been somewhat entertaining, kind of like being gummed to death by a duck!

[ramblinrod]

Originally Posted by DotDun

He has moved some, he is no longer stating the 'sources' must be the same voltage, which has been my only argument all along.

Sorry DOT, that is a lie.

What you have been claiming, is that two anything connected in parallel can be two different voltages, from solar panels, to grid tie inverters and mains, to voltage sources, to "devices".

The truth is DOT, when two anything are connected electrically in parallel, they MUST have the same voltage across them, as I have been stating since the start of this thread.

This is defined by Kirchoff's First Law.

So almost 24 hours ago now, I asked you a basic question about voltage in parallel circuits, so you could demonstrate your knowledge of the subject for all here to see.

Most people with a grade school knowledge of electricity can answer this type of question instantly, without even thinking about it.

"Remembering Kirchoff's First Law, if that system had 4 x 100W panels in parallel, and one panel had 15.0 Vdc across it, what voltage would the other panels have across them?"

DOT, here is the correct answer that you have not been able to come up with, long after the bell has rung, and the other kids have left the class room...

15.0 Vdc.

DOT, I am sorry to inform you, that you have failed Electricity 101.

You may repeat the course and try the exam again later if you desire.

Better luck next time.

[Paul Elliott]

Originally Posted by DotDun

He has moved some, he is no longer stating the 'sources' must be the same voltage, which has been my only argument all along.

Again, I think your disagreement is strictly semantic:

"sources are the same voltage" vs "sources are at the same voltage".

The first apparently refers to the open-circuit voltage, or perhaps the mythical internal voltage of a complex voltage source. The second refers to the actual voltage measured at the external points of connection of paralleled panels.

This argument will continue until you both agree to discuss the same thing. As I see it, you're both right.

["complex" in the sentence above means "complicated", not vector-related or reactive.]

Regarding current-source vs voltage-source models for solar cells, yes, a current-source with a few additional components is the more appropriate model. But there are also voltage-source based models that work.

[DotDun]

Originally Posted by ramblinrod

DOT, I am sorry to inform you, that you have failed Electricity 101.

You may repeat the course and try the exam again later if you desire.

Better luck next time.

I'm devastated! I'll send my degrees back!

[ramblinrod]

Originally Posted by OceanSeaSpray

Keep splitting hairs, arguing and giving lessons as much as you want. You are long past adding any value.

Solar panels behave as current sources as they are when we buy them and "transforming them into voltage sources with a reconfigured impedance" is primarily useful to fuel your pointless argument. Since you started, you didn't manage to explain a quarter of what I did in two posts. Have a good day, my friend.

Sorry you didn't get any value from learning that a current source can also be treated as a voltage source and vice versa.

[DotDun]

Originally Posted by Paul Elliott

Again, I think your disagreement is strictly semantic:

"sources are the same voltage" vs "sources are at the same voltage".

The first apparently refers to the open-circuit voltage, or perhaps the mythical internal voltage of a complex voltage source. The second refers to the actual voltage measured at the external points of connection of paralleled panels.

This argument will continue until you both agree to discuss the same thing. As I see it, you're both right.

["complex" in the sentence above means "complicated", not vector-related or reactive.]

Regarding current-source vs voltage-source models for solar cells, yes, a current-source with a few additional components is the more appropriate model. But there are also voltage-source based models that work.

Exactly! No acceptance that both are possible.

[NorthernIsland]

Originally Posted by ramblinrod

Sorry you didn't get any value from learning that a current source can also be treated as a voltage source and vice versa.

Rod - do you agree with OceanSeaSpray that solar panels are pretty close to a current source and not so close to a voltage source?

[ramblinrod]

Originally Posted by NorthernIsland

Rod - do you agree with OceanSeaSpray that solar panels are pretty close to a current source and not so close to a voltage source?

I have tried to already answer this as accurately as I could, but I'll try in a different way.

This is a bit like the classic "chicken or egg" argument.

The best answer I can give, is that the whether a solar panel is best represented as a current of voltage source is situationally dependent.

For the situation I applied it to, it is best represented as a voltage source. For
other situations, it may be best represented as a current source.

Again, for anyone with any degree of knowledge of electrical circuit
theory, this should not cause any confusion or difficulty whatsoever.

For anyone with little knowledge of electrical circuit theory, that this would confuse, well, they would already be confused by electrical theory first principles,
such as Kirchoff's laws or Ohm's law anyway.

[TeddyDiver]

Originally Posted by ramblinrod

For the situation I applied it to, it is best represented as a voltage source.

Just to be precise, what situation you are referring to? Presume unshaded and partially shade panels in parallel..

[Vladis]

Hello,

About voltage or current sources - any linear circuit can be described by an ideal voltage source in series with an impedance or by an ideal current source in parallel with an admittance. These are the Thevenin or the Norton equivalents of a linear circuit. So we can describe a source by a voltage or by a current source. However an ideal voltage source, for example, has not a proper current source equivalent. Example: a 12V ideal voltage source with zero series resistance would translate to a current source with infinite amperes with a zero ohms resistance across.

If panels were ideal voltage sources they would obligatory connected in series. If they were ideal current sources they would need to be connected obligatory in parallel. If they are real sources (current or voltage) they can be connected in both ways. The first concern would be to minimise losses in the internal impedances when there is a mismatch. Then shades and so on.

Sorry if this a bit out of topic but it is only (about) 1/200 of this thread!

Regards, Vladis

[ramblinrod]

Originally Posted by Vladis

Hello,

About voltage or current sources - any linear circuit can be described by an ideal voltage source in series with an impedance or by an ideal current source in parallel with an admittance. These are the Thevenin or the Norton equivalents of a linear circuit. So we can describe a source by a voltage or by a current source. However an ideal voltage source, for example, has not a proper current source equivalent. Example: a 12V ideal voltage source with zero series resistance would translate to a current source with infinite amperes with a zero ohms resistance across.

If panels were ideal voltage sources they would obligatory connected in series. If they were ideal current sources they would need to be connected obligatory in parallel. If they are real sources (current or voltage) they can be connected in both ways. The first concern would be to minimise losses in the internal impedances when there is a mismatch. Then shades and so on.

Sorry if this a bit out of topic but it is only (about) 1/200 of this thread!

Regards, Vladis

I concur 100%.

Whoops, forgot to spoke the rite langwij..

As I be'ed sayin' and a whole bunch of suppository engine ears has be'ed complainin' 'bout. ;-)

Canajun Teknishun