LiFePO4 batteries? Solar panels?

[Kirk W]

23 minutes ago, Lou Schneider said:

Solar panel current is almost perfectly constant regardless of output voltage

5 minutes ago, rbertalotto said:

I'm confused by this.

Me too. Did they repeal ohm's law for solar?

[Lou Schneider]

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Edited April 17, 2022 by Lou Schneider

[Kirk W]

34 minutes ago, Lou Schneider said:

Not at all, except solar panels are constant current devices so that part of the equation stays constant.

So are you saying that if you apply the output of a solar panel to a pure resistance load, the current through that load will remain constant, even if the resistance increases? I have read several explanations online and none of them address this question. The foundation of ohms law that I was taught is V=IR.

[oldjohnt]

 Kirk, DITTO yeppers Ohm Law is still valid last I heard !!! While it's been years since I was in EE school one never forgets the basics and Ohms Law (talk about EE101 or even High School science) still rings true as far as I know. I recall a theoretical IDEAL CURRENT SOURCE which pumped out a constant current regardless of the load and the other theoretical IDEAL VOLTAGE SOURCE which similarly maintained constant voltage regardless of the load  NEITHER EXISTS WELL DUH and a Solar Panel is NOT an Ideal source.

 A battery or a solar panel is NOT an IDEAL SOURCE and doesn't produce constant current or constant voltage ABSOLUTELY REGARDLESS OF THE LOAD. The power (V x I) a solar panel can deliver is not infinite and varies of course based on the intensity and angle of the sun plus its efficiency and temperature. Its unloaded open circuit voltage will decrease as more and more current is drawn from it.   If you short it out the voltage of course drops drastically... As Power = Volts x Amps ifffffffffff it were to remain constant yet V or I changed, so must the other right ???  

 That all being said in sunlight the panels are delivering current down to the solar charge controller and the bigger the conductors (IE less resistance) the less line voltage drop and less wasted I Squared R heat energy losses. I DONT SEE ANYONE HERE DOUBTING THAT I HOPE ??? As you add more panels and increase the current pumped down to the charge controller you likely need bigger less resistance conductors to reduce line voltage drop and heat losses.   

 Soooooooooo that's all I have to say about "Ohms Law" (I know it and agree with Kirk) I'm NOT commenting on the voltage and current curves of a solar panel versus sunlight intensity and angle and load etc., but I bet the manufacturers have that information available ... 

 Fun discussion yall, Thanks Kirk we agree yayyyyyyyyyyyyyyy

 John T  Longgggggggg retired n rusty Electrical Engineer but believe Ohms Law remains valid...and a Solar Panel IS NOT AN IDEAL SOURCE 

 

 

Edited April 16, 2022 by oldjohnt

[DanZemke]

Here's an explanation:

https://www.learningaboutelectronics.com/Articles/What-is-a-constant-current-source.php

 

Edited April 16, 2022 by DanZemke
Chaged "exclamation" to "explanation"

[Lou Schneider]

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Edited April 17, 2022 by Lou Schneider

[Kirk W]

23 minutes ago, Lou Schneider said:

Take a look at the Voltage vs. Current curve in this article.

Like every solar advocate that I have met, you didn't answer the question asked. Perhaps your next career might be in politics? Once more, are you saying that if you apply the output of a solar panel to a pure resistance load, the current through that load will remain constant, even if the resistance increases?  The answer is either yes or no.

 

[Lou Schneider]

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Edited April 17, 2022 by Lou Schneider

[Kirk W]

2 minutes ago, Lou Schneider said:

No above it.

So it is not a true constant current situation, as I have long tried to make a point of. It is in fact constant current within specified parameters. It still requires an increase in voltage or a drop in current flow if you change the resistance of the load. 

[DanZemke]

Let's move on - please

[rbertalotto]

I find this thread very interesting and educational....Carry on!

 

[DanZemke]

hemsteadc: My 'solar ready' wiring was #10, which was good to about 350w at nominal voltage.  I added more panels and wired them in series so I didn't have to rewire anything.

Lou Schneider: Solar panel current is almost perfectly constant regardless of output voltage, so the power loss will be the same ...

-------------------------------------------------

IMO, the issue being discussed, in this sub-thread is: what are the trade-offs of adding more solar panels via parallel or serial connections?

My impression is that Lou was saying: with an MPPT controller hemsteadc could have added more panels in parallel, using the same wire size.  And the efficiency would be about the same.

Lou - please correct me if I've misunderstood.

[Kirk W]

4 hours ago, DanZemke said:

Let's move on - please

Sorry if you don't agree, but I started the thread looking for some answers. I think that the key to the operation is in the controller and a pure restive load probably doesn't happen in practical applications.  

Edited April 17, 2022 by Kirk W

[oldjohnt]

15 hours ago, Kirk W said:

It is in fact constant current within specified parameters. It still requires an increase in voltage or a drop in current flow if you change the resistance of the load. 

Kirk (based on my training and 50 years experience as an electrical engineer) you are correct. A Solar Panel has ONLY limited capacity, it's NOT any Ideal or infinite energy source and Power (such as for example a 100 Watt Panel) still = Volts x Amps..It may be capable of supplying X number of amps into a given resistance load, but if the loads resistance changes in order to deliver the same current Voltage has to change WELL DUH....Power = V x I and I = V/R....

The key, controlling and accurate portion of your post above is when you state  "constant current within specified parameters"   If the resistance drops yet current is to remain constant VOLTAGE WOULD HAVE TO CHANGE... if a Panel out there can deliver X constant continuous amps regardless of the attached load WHERE CAN I BY ONE LOL

As everyone knows the output of a Panel is not constant, it changes with different sunlight intensity,  angle, temperature and efficiency. It cant provide constant current regardless of the loads resistance and regardless of the sunshine IT CAN HOWEVER PROVIDE CONSTANT CURRENT AS KIRK STATES WITHIN "SPECIFIED PARAMETERS" 

Again I do not have the voltage and current curves of any certain panel and they surely exist Im NOT commenting on those curves ONLY THAT I BELIEVE KIRK IS CORRECT REGARDING OHMS LAW. 

PS the load placed on solar charging system is dependent upon the State of Charge of the batteries. If they are depleted more power will be drawn from the solar charging system but once they are at 100% SOC they require less charging amps suppled by the solar system. SO THE LOAD CHANGES and isn't constant. 

Hope this helps everyone yall have a Happy Easter now take care and God Bless

John T  Long retired Electrical Engineer but believe Ohms law is still true

Edited April 17, 2022 by oldjohnt

[Kirk W]

30 minutes ago, oldjohnt said:

Hope this helps everyone

That is very helpful. I guess the next step for me is to see what I can find about the solar controllers, what they do, and how they do it. 

[oldjohnt]

1 hour ago, Kirk W said:

I guess the next step for me is to see what I can find about the solar controllers, what they do, and how they do it

I likewise could learn more about them. In a nutshell as I'm sure you already know, it's my understanding (No warranty I'm NOT an expert) the solar controller regulates and provides so called "Smart" charging of the battery bank utilizing the energy provided by the solar panels. If the battery SOC is low the controller uses all energy (depends on sun intensity and angle) the panels can provide (high load on panels) but once fully charged they go to a small maintenance trickle charge level (low load on panels).  I've monitored my MPPT controller charging my Lithium battery bank (has Bluetooth monitoring) and after a nights use when my batteries are discharged (needs max power panels can provide) once the sun shines bright the controller starts pumping max available charging current into my batteries, but after some time and my monitor nears 100% SOC (less panel power is needed) the controller slows way down and despite full bright sunshine only pumps a few amps into the batteries.  The load on the panels varies (NOT a constant) depending on the SOC of my batteries and their V x I  Power depends on the sun. I see BOTH my battery BMS  PLUS  the Solar Charge Controller having a part in providing the proper charging. I see NONE of this disputing Ohms Law, its always there and I see the solar panels load varying based on the battery SOC and its power based on the sun AND THOSE TWO ARE EVER CHANGING.   The panel has very limited power and again NOT any ideal infinite energy or current source and as its Power (based on sun) = V x I  iffffffffff the power were a constant ???? if the output current changed so must the Voltage  IM STICKIN TO THAT !!!!!!!!!!!!

Thats my story n Ima stickin to it. If incorrect it wont be my first time and Id appreciate an expert educating me of where I went wrong grrrrrrrrrrr lol  

Fun sparky chatting with you Kirk and I apologize for boring the others

Again, Happy Easter everyone

John T

[hemsteadc]

17 hours ago, DanZemke said:

My impression is that Lou was saying: with an MPPT controller hemsteadc could have added more panels in parallel, using the same wire size.  And the efficiency would be about the same.

Lou - please correct me if I've misunderstood.

I hope Lou wasn't saying that, because it's incorrect.  Since he's checked out, I thought I'd answer.

Edited April 17, 2022 by hemsteadc

[Kirk W]

John, I’m hoping that this is helping other folks who might be considering both solar and lithium batteries. And your latest at least gives me a starting point. At the point in life I am it is doubtful that I will move to solar but I am looking at it partly because I have a son who is an RVer and another one starting to look. 

[Zulu]

42 minutes ago, Kirk W said:At the point in life I am it is doubtful that I will move to solar but I am looking at it partly because I have a son who is an RVer and another one starting to look. 

Though I’m several years younger than you, I’m still getting up there. Nevertheless, I’m doing my 4th (and most likely last) RV solar install . . . and this last install is probably the most important.

We’ll be making our last cross country trip next year. Long trips are wearing and expensive for us, so we’re back to doing shorter trips like when we stared RVing.

Anyway, we live in CA and want to camp on ocean campgrounds with hookups. These are verrrrrrrrrrrry difficult to book (see Bots Booking Campsites). Even with years of booking experience, I’m usually left with a handful of basic (no hookups) sites available.

Enter solar.

With a roof full of solar panels we now have many more site options.

[Randyretired]

I have been watching with interest the posts on this.  I don't really know enough about MPPT controllers to add anything.  I have seen charts that seem to indicate these controllers maximize the panel power but how that relates to optimal battery charging power I am not sure.  How all of this manipulation after voltage loss might change things is a mystery to me.

[oldjohnt]

Yo hemstead, if I understand you correctly, it appears to me if you add more panels IN PARALELL,,,,,,,And since current adds when using panels IN PARALLEL,,,,, The current will be greater from the PARALLEL combination of multiple panels !!!!!!!! IM CONFIDENT THATS CORRECT. Given that as you increase current (due to multiple panels in parallel) you increase line voltage drop and I Squared R heat energy losses UNLESS you increase cable size.... IE it IS NECESSARY to increase wire size when adding multiple panels (subject to what size was originally used) in parallel or else there's more line voltage drop. NOTE that's true regardless of each panels output being any finite fixed amount regardless of load which I doubt anyway.

Example if one panel was pumping out say 5 amps and you added another identical panel in parallel, I hope all agree you now deliver 10 amps down to the controller. If the SAME wire was used you obviously increase the line voltage drop as it's a function of wire size, current, and distance.. WELL DUH 

While NOT a Solar expert, just an old retired EE, I firmly believe the above is accurate...But hey I've been wrong before grrrrrrrrrr 

John T

Edited April 17, 2022 by oldjohnt

[Zulu]

1 hour ago, oldjohnt said:

 . . . since current adds when using panels IN PARALLEL,,,,, The current will be greater from the PARALLEL combination of multiple panels !!!!!!!! IM CONFIDENT THATS CORRECT.

Yep. And some controller manufacturers supply online calculators to help you figure out how to wire PV panels, like this one from MidNite Solar. Keep in mind it's designed with MidNite's controllers.

[hemsteadc]

1 hour ago, oldjohnt said:

Yo hemstead, if I understand you correctly, it appears to me if you add more panels IN PARALELL,,,,,,,And since current adds when using panels IN PARALLEL,,,,, The current will be greater from the PARALLEL combination of multiple panels !!!!!!!!

Oh yes, that's correct.  Small wire handles higher voltage much better than amperage... up to a point of course.. as long as your controller can handle it.  We're not talking 400 volts or higher here.  And wiring panels in series is so much simpler.

Edited April 17, 2022 by hemsteadc

[Kirk W]

8 hours ago, Zulu said:

With a roof full of solar panels we now have many more site options.

That is what makes solar and Lithium batteries so appealing. With the health issues of my wife and the increasing age factors, it is questionable if upgrading to something with solar is economically wise for us as we are at a point where we start each season with the concern that this could be our last one. It is all so dependent on health related issues. Mobility is becoming an issue for her and since we have been pretty much joined at the hip for so long we just can't imagine not sharing. I have difficulty spending what would be required when it might not get used for long but remain envious of those who have it. 

[Randyretired]

Kirk, My wife also gas some mobility issues and I have taken over the daily chores.  One of my reasons for solar and lithium is to make sure she is comfortable.  We still like to spend time in our RV and specifically like to boondock.  As long as I can keep up we hope to do some limited travel.  Like you we also are day by day.  If that day is sooner rather than later than somebody else will get more use out of the solar unless one of our children want the components.