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Old 01-13-2020, 06:01 AM   #1
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Any solar installs on FC28 with 2 AC units?

Anyone install solar on an FC28 with two AC units? Ours came with a 2nd AC which was a welcome option here in TX.


However the two natural 'solar' spots in the back of the trailer now would be flanked by an AC unit. I had been planning on a setup similar to Airmiles (series-parallel with the opposing panels in series) but I'm rethinking it.



My options:
- Only have two panels in the front, in parallel. These would be something like the Grape Solar Mono units, 180W each. They look great!
- Proceed with the series-parallel anyway and hope for the best. If the sun shines from the back or front, I'm ok. If from the side, the back string is impacted.
- Try to cram the 2nd string between the AC units. Not sure if any of the other rooftop devices in that middle area are in the way...


This is not our trailer but it's the same layout
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Old 01-13-2020, 06:43 AM   #2
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Why not just put 4 100 watt panels all parallel?
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Old 01-13-2020, 07:24 AM   #3
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I think dual A/C's will cause more shading issues with series-parallel. Both of my installs were with single A/C's. 400W series-parallel on single A/C models works great. I now have 600W series-parallel with one panel flanking the A/C. I have not had good weather to test this setup and I've only used it for 30 days to date. My initial impression is that having a series-parallel panel flanking an A/C is not ideal. I do try to position my Airstream with the front facing North or South so that at mid-day all six panels are not shaded. With dual A/C's, you may want to either install four 100W panels in parallel, or the two 180W panels in parallel on the front to avoid potential shading issues. If you are careful keeping the Airstream parked north-south, it probably wouldn't make much difference whether in parallel vs. series-parallel. But when parked east-west, the A/C shading would likely have a significant affect on pairs flanking the A/C.

As you can see on my 27' layout, parking north-south or curb-side south works well. Parking the curb-side north would definitely have the greatest shading impact.
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Old 01-13-2020, 07:56 AM   #4
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Originally Posted by GMFL View Post
Why not just put 4 100 watt panels all parallel?
I guess I could. But then I'd likely need to upgrade the wiring, was hoping to use the factory wires.

Here's the other side - note the huge vent in the middle

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Old 01-13-2020, 08:28 AM   #5
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Originally Posted by Kalashnikov View Post
I guess I could. But then I'd likely need to upgrade the wiring, was hoping to use the factory wires.

Here's the other side - note the huge vent in the middle

You can use the factory prewire with 400W in parallel! Just wire it up that way and share your results on the Solar Show and Tell thread so we can compare my historic 400W series-parallel performance to your 400W full-parallel performace. I am certain you will be completely satisfied with 400W in parallel on the factory prewire. The prewire can handle 30A with less than 5% loss. You will rarely see 30A, so your losses under average conditions will be much less. You won't even notice the losses and your batteries will stay fully charged most of the time. Just do it, you'll be satisfied.

P.S. Looks like you could do 600W with the same layout as my 27'. With 600W, you would have to use series-parallel like mine above. I would suggest buying a solar controller capable of at least 600W, like a Victron 100/50 even if you plan to install only 400W. Solar panels are addicting, you will soon be adding the additional 200W. Then you'll wish you did series-parallel so you can still use the solar prewire. Therefore, consider doing 600W series-parallel. Again, I am certain you will be satisfied. Sure, occasionally, you will suffer some panel shading. But you'll probably never notice the shading. I wish I had a full summer of data to share with you about 600W on the solar prewire with shading. We'll just have to wait until summer 2020 for these results. But I'd take 600W with potential shading issues over 400W. I've seen low 500W output in less than ultimate conditions which is better than 400W can produce in any conditions. So consider doing 600W right away.
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Old 01-13-2020, 08:47 AM   #6
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Originally Posted by AirMiles View Post
You can use the factory prewire with 400W in parallel! Just wire it up that way and share your results on the Solar Show and Tell thread so we can compare my historic 400W series-parallel performance to your 400W full-parallel performace. I am certain you will be completely satisfied with 400W in parallel on the factory prewire. The prewire can handle 30A with less than 5% loss. You will rarely see 30A, so your losses under average conditions will be much less. You won't even notice the losses and your batteries will stay fully charged most of the time. Just do it, you'll be satisfied.
Yes, but per Victron their controllers don't fire up unless there's a rather high voltage on the outside. I'm concerned that an 18v panel wired in parallel may not be enough:
Quote:
The mppt won't fire up until it sees >5V difference between the panel Voc and Vbat. In production that Voc changes to Vmp, and that can be a big step down in poor morning light, even as much as halving the Voc. Then the difference becomes only 1V for it to keep working. But if it can't maintain that it will falter and drop out.
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Old 01-13-2020, 08:55 AM   #7
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Yes, but per Victron their controllers don't fire up unless there's a rather high voltage on the outside. I'm concerned that an 18v panel wired in parallel may not be enough:
PTECK and I have completely hashed out this issue. I firmly believe series-parallel is slightly better overall, but would not hesitate to do full parallel with 400W. The voltage jumps all over the place with solar. It will bounce to Vbatt+5 and the controller will fire up. Then it only needs Vbatt+1 to stay on. You will be just fine at the lower voltage of full parallel.
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Old 01-13-2020, 09:04 AM   #8
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Then you have my setup, which only has room for three panels. I’m stuck with parallel connections because I don’t have the roof area to get 4 panels up there. If I could, I would do 4 and go series/parallel as an experiment. At the moment I have no issues keeping my batteries well charged out here in SoCal.

I do have the advantage of heavier wire from the combiner box than the factory pre-wire, which I never did find.
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Old 01-13-2020, 09:12 AM   #9
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Quote:
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Yes, but per Victron their controllers don't fire up unless there's a rather high voltage on the outside. I'm concerned that an 18v panel wired in parallel may not be enough:
I have 400watts full parallel and All Victron components no problem with them not running at lower voltage.
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Old 01-13-2020, 09:20 AM   #10
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Its easy to overthink all this stuff . . . solar, batteries, hitches, tow vehicles, generators, tires . . . That's what keeps us all entertained here on AirForums. We all want perfection for our pride-and-joy Airstreams. But most of the time "perfection" is an expensive and unnecessary goal. You just need to determine when "good enough" will meet your needs. 400W in parallel will work good enough as will 400W in series-parallel. 600W in series-parallel will work good enough too, and possibly better than 400W in parallel. But all this stuff is debatable. The challenge is deciding whether good enough will meet your needs or whether to spend the money on perfection. I share my performance results so others can make that determination on whether my low-cost factory-prewire self-installed solar configurations are good enough for their needs.

I think you need to decide if you may want to go to 600W in the future and if you would want to use the factory prewire with 600W. If you might go 600W on the factory prewire, wire the 400W in series-parallel and buy a Victron 100/50. If you think 400W is all you will ever need, wire it up parallel. I don't think you will be disappointed in whichever configuration you decide.
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Old 01-13-2020, 10:27 AM   #11
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All good point AirMiles! I'm certainly not shooting for perfection but OTOH don't want to shoot myself in the foot.

Found this great looking 200W panel for just $185. With the KISS principle I may just lay down two of these at the front of the trailer and call it a day:
- Cost for panels is equal or less than 4x100W scenario
- Less mounting, less wiring
- Voltage is high, no doubt about driving the Victron 100/30
- Plenty of space left on the roof for future expansion

Brand is Hightec, don't know anything about it, but it's a Mono

https://www.continuousresources.com/...iABEgI-JfD_BwE

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Old 01-13-2020, 10:39 AM   #12
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Originally Posted by Kalashnikov View Post
All good point AirMiles! I'm certainly not shooting for perfection but OTOH don't want to shoot myself in the foot.

Found this great looking 200W panel for just $185. With the KISS principle I may just lay down two of these at the front of the trailer and call it a day:
- Cost for panels is equal or less than 4x100W scenario
- Less mounting, less wiring
- Voltage is high, no doubt about driving the Victron 100/30
- Plenty of space left on the roof for future expansion

Brand is Hightec, don't know anything about it, but it's a Mono

https://www.continuousresources.com/...iABEgI-JfD_BwE

26.75" wide could be an issue. Notice the skylight on my 27' is not centered. Make sure there is room for that wide panel.
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Old 01-13-2020, 12:25 PM   #13
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AM Solar has a pic on their website with another solution when installing 4x100W panels - they are offset based on available space. Do I care? Sort of - but in the end performance matters more than looks

Note that although this is a 28' with two ACs it's still a different floorplan compared to the FC 28 (the large silver vent is in a different location compared to mine)

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Old 01-13-2020, 04:58 PM   #14
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Sometimes I question how AmSolar chooses to place their panels. For example, this install: https://amsolar.com/solar-panels-for...ewmar-essex-45 1400W of panels, but hardly a panel that will not get serious shading. I wonder how well some of these installs work??? I guess they just install them and hope for the best.
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Old 01-13-2020, 09:29 PM   #15
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Any solar installs on FC28 with 2 AC units?

I’ve got 800w in parallel on my 30’ with some room to spare. 4ga wire from panels to my victron 150/85 controller. No problems. I get about 60amps to the batts in June / July midday.

Note that if you use extended feet from AM solar you can mount the panels over top of the bathroom and shower vents, and still be able to open / operate the fans. As you can see the only vent you cannot cover is the aluminum fridge vent, everything else is under the panels.

This maximizes the number of panels you can fit and also orients them flat on the roof so all panels receive sun at the same angle, with the ability to tilt if desired.

I’ve experimented with series - parallel configurations on my last trailer, but prefer full parallel for this level of wattage. Just personal preference.
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Old 01-14-2020, 04:23 AM   #16
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Great idea to use the extended feet wulfraat! Then I guess I could easily fit two panels in the front and two more in the middle while staying away from the air conditioners.

I'll have to get up there and do some measuring. After coaxing from AirMiles I'm now leaning toward a 600W system instead of settling for 400W. However this could be two sets of 2x150W panels in series-parallel instead of doing 6x100W. (There are a TON of options these days when it comes to panels )
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Old 01-14-2020, 07:19 AM   #17
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Go with high-quality narrow panels at 100 W. You’ll easily be able to get six if not seven panels on that roof.

My air conditioners really don’t kick off much if any shade based on how the panels are positioned and installed... and you can always tilt.

My opinion is do this once - go for as many panels as possible.
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Old 01-14-2020, 08:18 AM   #18
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Agree totally with Wulfraat on putting as many panels as possible on the roof. If using the factory prewire, that means 600W. I also agree with Wulfraat that you want to use 100W compact panels. The Renogy 100W compact panels are really small and narrow. Look at that small panel next to the A/C in the post #3 picture. That is a Renogy 100W compact panel. Because it is skinny, it stays farther away from the A/C unit than would the other 100W panels on my roof. My other panels are AmSolar SP100's which are identical to Renogy Eclipse 100W solar panels. For about $1500 you can self-install 600W of solar on your roof. Here is a link to the parts list I used for my 600W installation: http://www.airforums.com/forums/f448...ml#post2288463 Also read the post following that link which added the SikaFlex and SAE Adapters with links.

I wish I had some wonderful performance results to show from my 600W of series-parallel configured solar on the factory prewire. But I have only used this configuration for a 30 period starting Sept. 17, 2019. That was the most overcast thirty day period I have ever experienced since documenting my solar's performance. There was rarely anything but overcast. The one day where 2Kw was produced was only sunny for a few hours in the morning before overcast rolled in for the rest of the day. Here is how the 600W on the factory prewire performed over a challenging 30-day period.
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Old 01-14-2020, 11:40 AM   #19
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I asked Marvin at PrecisionRV.com since I knew he had done a 28 recently. Depending on the location and heights of the vents 600W and possibly 800W. Cut a bunch of cardboard templates. As an alternative get an overhead aerial photo of your rig. Print it into Visio or similar program. Using a known dimension from the roof it is easy to mock up panel sizes and do what if arrangements. That has worked pretty accurately in my last 4 setups from an FC25 to a 45ft motorhome.
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Old 01-14-2020, 12:27 PM   #20
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500W on a dual AC 28 foot

On a dual AC unit, there is no problem installing 500W without covering any vents. True the AC units may shade one or the other panels depending on the direction of the sun, but with 5 panels, wired in parallel, there is always a sufficient number of panels to keep the batteries full. My reasoning was, panels are cheap, cover as much real estate as you can.
Here are pics of both sides of the trailer.
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