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Old 05-07-2019, 08:16 AM   #281
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Mine is a 3 (100w) panels in parallel to a new simple controller feeding 2 old school CG2 wet cell golf cart batteries. No link ups, no history or projections. Just a simple to understand volt/ amp meter . No inverter. If it's 12vdc it's good enough.
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Old 05-07-2019, 08:26 AM   #282
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Originally Posted by Dirtyairhead View Post
Mine is a 3 (100w) panels in parallel to a new simple controller feeding 2 old school CG2 wet cell golf cart batteries. No link ups, no history or projections. Just a simple to understand volt/ amp meter . No inverter. If it's 12vdc it's good enough.
John
KISS works for me too John. Just stick a few panels on the roof, connect them to the Zamp rooftop box on 2017 & up, connect a compatible solar controller between the solar prewire and the busbars and go camping with batteries that get recharged every day. Don't sweat the details. Replace the cheap wet-cell batteries with CG2 batteries when they run out of juice.

Thanks for sharing your simple installation!
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Old 05-07-2019, 09:24 AM   #283
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Originally Posted by AirMiles View Post
......
There's an even bigger determinant of using series-parallel on a 2017 and up Airstream. There are only three inputs in the rooftop box, there is thin 8-10 gauge wire run to the controller, and the curved roof does not work with large wattage panels. Therefore the Airstream prewire is designed for either 200W in parallel, 400W in series-parallel, or 600W in series parallel. .......
Hi

Turns out there is room on the box to drill a fourth hole for another connector. That gets you to the "four in parallel" config on a more or less factory setup. I have empirical data on this ....

======

The whole "series does not work" thing is a bit silly. With a MPPT controller, you actually do not "loose" the whole second string when one is partially shaded. The controller simply moves to a lower operating point on the voltage curve. It works that way because *all* solar panels are series connected internally. They get shaded as part of how the real world works. The good controllers deal with this. The less exotic controllers struggle.

Bob
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Old 05-07-2019, 09:51 AM   #284
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Originally Posted by uncle_bob View Post
Hi

Turns out there is room on the box to drill a fourth hole for another connector. That gets you to the "four in parallel" config on a more or less factory setup. I have empirical data on this ....

======

The whole "series does not work" thing is a bit silly. With a MPPT controller, you actually do not "loose" the whole second string when one is partially shaded. The controller simply moves to a lower operating point on the voltage curve. It works that way because *all* solar panels are series connected internally. They get shaded as part of how the real world works. The good controllers deal with this. The less exotic controllers struggle.

Bob
Great post Bob! Sometime we spat and other times we agree. All in good fun of course. Thanks for sharing this idea.

I just had another idea. Couldn't you just share a Zamp plug with rooftop wires from two panels by connecting the positive's together and the negative's together at the SAE connector? No need to drill, remove the box, rewire the box . . . for those who prefer to use a 400W full parallel configuration.
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Old 05-07-2019, 07:10 PM   #285
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Before sharing more points, I do want to say that this has been a great thread with all the contributions. Theory is one thing, but to Airmiles credit, he has done solid research in informing his strategy and design decisions. There's more than one way to skin a cat. His tests and use shows a well performing and viable system. What's optimal for one person, may not be optimal for others.

Quote:
Originally Posted by Uncle_Bert View Post
I am wondering if anyone, or any systems, use bypass and blocking diodes as described in this link:
https://www.electronics-tutorials.ws...ss-diodes.html
Seems to address some of the potential problems with series-parallel setup raised by pteck.
Yes, it does. To an extent. It's not ideal, but it does salvage some output depending on the type of shading going on. Shade still has the larger impact than what can be mitigated.

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Originally Posted by AirMiles View Post
A 400W series-parallel configuration with four 100W panels is a 400W parallel configuration with two 200W panels. I agree that shading impacts a series pair, but if it also affects the parallel pair, then it would also affect the parallel panels in a full parallel configuration.
4x 100W in series-parallel cannot be modeled the same as 2x 200W panels in parallel.

Internally in a single panel, there are generally multiple paths to conduct current. When one puts 2x 100W panel in series, even though that second panel has multiple internal paths, it is likely to block any current from the first. When you consider the added complexity that the series connected panels are dependent on each other to reach the string "system" voltage, it is even more likely to completely block current.


Quote:
Originally Posted by uncle_bob View Post
The whole "series does not work" thing is a bit silly. With a MPPT controller, you actually do not "loose" the whole second string when one is partially shaded. The controller simply moves to a lower operating point on the voltage curve. It works that way because *all* solar panels are series connected internally. They get shaded as part of how the real world works. The good controllers deal with this. The less exotic controllers struggle.

Bob
MPPT can do awesome things to increase efficiency. What they cannot do is magic however, exotic or not. What they do is choose a voltage point at which there is the most power output.

To maximize both series "strings" in a shaded scenario, there would need to be two independent controllers to allow each to operate at independent voltages. Otherwise the strings are intertwined with voltage dependencies.


I completely understand that I probably went too deep (while trying not to) than some want to comprehend. What I can offer is some videos that might do a better job conveying some of the series shade issues. These however don't address the matrix of compounding issues of two parallel connected series strings, which gets complicated in a hurry.




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Old 05-08-2019, 06:45 AM   #286
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Hi

The basic building block in side every solar cell on the planet puts out < 1V. Unless you are using a system that is set up for < 1V output, you *have* series connected cells. Series is series it's a basic way to do things. If series does not work then your standard panel does not work.

Indeed if you want to *prove* that there is an issue, rig a setup where the controller is almost at dropout voltage. Then the controller will struggle as you drop the volts. That is *not* the case when you wire panels in series. You now have way more than minimum voltage to deal with. The controller does not drop out and ... geee ... it works.

Bob
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Old 05-08-2019, 07:00 AM   #287
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I watched those videos before I installed my series-parallel solar configuration and was concerned that it may not work well. Since it was so easy to self-install solar with the factory pre-wire, I decided to "test" the series-parallel configuration for a couple of months before making the trek to Eugene OR to have AM Solar reconfigure my system to full parallel. What I found when I was "testing" was that the series-parallel configuration met all my solar power needs and there was no need to reconfigure the system to full parallel. Here is a quote from my first post on this thread: My plan is to test this configuration over the summer while traveling across the U.S. from east-to-west and north-to-south and post my results (good, bad, or ugly) on this thread. If the this configuration performs unsatisfactory, it can easily be reconfigured into a full parallel setup with an additional 30' of 10/2, a rooftop combiner box and 30' of 6 awg.

I believe I demonstrated how well the configuration works in a real-life partial shade test in my post #4. With one panel shaded, the series-parallel configuration still output 72% of the amps from when all four panels were in the sun. With two panels shaded, it still output 66% of the amps from when all four panels were in the sun. How much more real life can you get than that?

Theoretically, you stated " - That single shaded panel will effectively reduce output of series connected panel to almost nothing because it's current limited (c) and the other working panel effectively has its generation blocked by the shaded panel. (-200W potential)" So you said output should drop by 50% with one panel shaded, but my real-life test shows its only 28%. Then you went on to say " - The shaded panel also just knocked out 18V on that string as it's not contributing. Reducing it's voltage down to a single panels worth. - Because parallel strings must operate at the same voltage (d), that second string is also brought down to ~18V, making it's potential at best 100W. (-300W potential)" . Therefore, based on your theory, the output should drop by 75% with one panel shaded in a four panel series-parallel configuration. Again it only dropped by 28%, not 75%. Even with two panels shaded under a complete tree canopy, my series-parallel configuration's output only dropped by 66%.

It pretty obvious that your "theory" is flawed. Can we be done with this conversation now? I'm sure everyone's eyes have glazed over by this point.

Thank you Uncle_Bob for your expertise in explaining those videos and that a series-parallel configuration "works". Its amazing that real-life hard facts cannot bust myths that prevail on AirForums.
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Old 05-08-2019, 07:44 AM   #288
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I'll live and let live. We don't have to agree.

Curious for my own edification Air miles, what kind of shading were you applying in you testing?
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Old 05-08-2019, 07:48 AM   #289
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Oops, on the above post I said:

Even with two panels shaded under a complete tree canopy, my series-parallel configuration's output only dropped by 66%.

But the word "by" should have been "to".

What kind of shading? I was using a dense canopy of Florida Live Oak tree shade. You can see pictures of the Airstream under the tree in Post #1 of this thread and post #4. On post #4 you can see the hazy sun conditions when the test was done at 10:30 am. Here is a good picture of exactly the shade I was using that shows how close the tree canopy was to the solar panels. The tree is nearly scraping the Airstream.
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Old 05-08-2019, 08:17 AM   #290
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Originally Posted by AirMiles View Post
KISS works for me too John. Just stick a few panels on the roof, connect them to the Zamp rooftop box on 2017 & up, connect a compatible solar controller between the solar prewire and the busbars and go camping with batteries that get recharged every day. Don't sweat the details. Replace the cheap wet-cell batteries with CG2 batteries when they run out of juice.

Thanks for sharing your simple installation!
Zamp? My youngest trailer is 1999. I work with vintage or just old stuff . I enjoy reading about the high tech and appreciate quality reports on their ways. I learn from others then simplify to my needs. It's good to know I'm not alone.
John
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Old 05-08-2019, 10:40 AM   #291
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Oops, on the above post I said:

Even with two panels shaded under a complete tree canopy, my series-parallel configuration's output only dropped by 66%.

But the word "by" should have been "to".

What kind of shading? I was using a dense canopy of Florida Live Oak tree shade. You can see pictures of the Airstream under the tree in Post #1 of this thread and post #4. On post #4 you can see the hazy sun conditions when the test was done at 10:30 am. Here is a good picture of exactly the shade I was using that shows how close the tree canopy was to the solar panels. The tree is nearly scraping the Airstream.
Interestingly, a series-parallel setup best handles even numbers of shaded panels. Odd...well, I'll leave it at that.

One thing you did well is to locate your panels at the far corners of the Airstream. This physically helps situations where shade may cover only a portion of the trailer.
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Old 05-15-2019, 07:33 PM   #292
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Hi everyone, spring has finally arrived here in upstate NY and I was able to complete my project of relocating the batteries to inside under the bed. I also took the opportunity to rewire just about everything in the electrical compartment. Thanks to all for your recommendations and guidance. If anyone is curious, four 100AH Battleborn batteries do (just barely) fit lengthwise under the bed. Rocking the power now!
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Old 05-16-2019, 07:13 AM   #293
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Up & running....

...with our two 180w Zamps.

Still on the road so the shake down continues.

Well Pleased...👍

Bob
🇺🇸
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Old 05-16-2019, 07:28 AM   #294
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Meddle, Nice install of 400AH of Lithium Batteries, count me in as one of the "jealous".

Robert C., Thanks for sharing your output screens. I just installed the new Victron update with the trend graph. Not sure how useful this graph will be. I leave Sunday for our cross-country summer travels so I will soon learn. Looks like your solar is performing well with 218W of production and 16.2A at 9:30AM. Gotta love it!
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