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Old 08-03-2021, 05:33 PM   #1
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How Many Solar Panels?

Hi All,

We have a 2021 GT 25FB with two AC units. How many solar panels can I fit? What configuration and wattage? Pics would be great!

Thanks,

Bruce
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Old 08-03-2021, 06:39 PM   #2
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Get up on thy roof and look with a tape measure. The cut cardboard to the size you want
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Old 08-03-2021, 08:00 PM   #3
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Agree your best course of action is to identify the panels (brand/model) that you prefer to use and then make some cardboard templates of the actual size of the panel(s). It will be tight and there are many items on the roof already. I have a 25’ 2015 flying cloud RB (twin) with single A/C and I was able to get 5 full sized zamp obsidian panels on my roof (480w total) but you might have different obstacles than me. 3 of them are 100w panels, the other 2 are 90w each. I could squeeze in a little more but I wanted human space around the A/C so I can get up there without removing solar panels, if needed. I don’t think 2 A/C will be the limiting factor but it most likely comes down to the way you want your roof to be arranged.
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Old 08-03-2021, 08:25 PM   #4
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Typically 600Watt is max for a 25’ Airstream.
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Old 08-03-2021, 08:50 PM   #5
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As has been mentioned, it will depend on the layout of existing obstacles on the roof.

My installer, AM Solar in Springfield, Oregon, laid out templates for my chosen panels (Zamp 100W Obsidian) and was able to fit 4 without interfering with the various vents. One difference between your 2021 GT and my 2020 25' GT is that I have an absorption frig with it's associated chimney and yours is a compressor frig which I don't believe has a chimney; you may have more roof real estate to work with.

In the end it worked out fine for me because I didn't want to commit all of my panels to the roof anyway. I also have a 180W Zamp portable which gives me some flexibility for those times when the trailer might be parked in shadier locations.

This setup has worked out extremely well keeping our 400Ah lithium battery string topped up.
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Old 08-04-2021, 12:15 AM   #6
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Quote:
Originally Posted by mikeinca View Post
As has been mentioned, it will depend on the layout of existing obstacles on the roof.



My installer, AM Solar in Springfield, Oregon, laid out templates for my chosen panels (Zamp 100W Obsidian) and was able to fit 4 without interfering with the various vents. One difference between your 2021 GT and my 2020 25' GT is that I have an absorption frig with it's associated chimney and yours is a compressor frig which I don't believe has a chimney; you may have more roof real estate to work with.



In the end it worked out fine for me because I didn't want to commit all of my panels to the roof anyway. I also have a 180W Zamp portable which gives me some flexibility for those times when the trailer might be parked in shadier locations.



This setup has worked out extremely well keeping our 400Ah lithium battery string topped up.


Thanks mikeinca. I also got a 2020 GT 25fb and you layout was extremely helpful
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Old 08-04-2021, 06:58 AM   #7
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Quote:
Originally Posted by mikeinca View Post
As has been mentioned, it will depend on the layout of existing obstacles on the roof.

My installer, AM Solar in Springfield, Oregon, laid out templates for my chosen panels (Zamp 100W Obsidian) and was able to fit 4 without interfering with the various vents. One difference between your 2021 GT and my 2020 25' GT is that I have an absorption frig with it's associated chimney and yours is a compressor frig which I don't believe has a chimney; you may have more roof real estate to work with.

In the end it worked out fine for me because I didn't want to commit all of my panels to the roof anyway. I also have a 180W Zamp portable which gives me some flexibility for those times when the trailer might be parked in shadier locations.

This setup has worked out extremely well keeping our 400Ah lithium battery string topped up.
I have the exact roof layout and even with a compressor frig the chimney is still there (June 2021 build). What I had not considered is removing the existing factory 90W panels and replacing them. Looks like a great solution as I wanted to get at least 400W of solar on the roof. Anyone looking for Zamp 90W panels? I'll soon have 2 available

Thanks for the pic Mike!

Cheers,
Bruce
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Old 08-04-2021, 09:18 AM   #8
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Obsidian has AS specific panels which I'm having installed now.
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Old 08-04-2021, 09:25 AM   #9
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Hi

Keep in mind that AS seems to love changing things part way through a year. I would certainly trust what's been said in the posts above. I also would verify that the roof layout on this or that specific trailer *is* able to do this or that before ordering panels.

Bob
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Old 08-04-2021, 09:59 AM   #10
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We were able to fit nine 100 Watt AmSolar branded panels on the roof of our 2014 Classic with room for one more. They are feeding a 600 amp hour lithium that is under the front sofa/hide a bed. We have five of the same panels on the roof of our 2015 23D International Serenity feeding a 315 amp hour lithium battery located just in front of the street side wheel well and under the sofa with no lost of storage or the pull out bed.

Do not order any panels until your trailer is actually on the dealership lot as Airstream often gets a burr under their saddle and re-arranges stuff on the roof. Then think outside the box. We replaced a crank up TV antenna with a round antenna freeing up space for another solar panel.
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Old 08-04-2021, 10:00 AM   #11
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The question

Fellow AS solar panel people- I installed two 130 watt flexible panels and a new controller last year and the bit of boondocking I have done since was fine. I installed those on the advice of the shop owner who has been installing similar systems in chalets here in Switzerland, for the past 20+ years.

I too based part of my decision on space available.

What I do not see in any discussions so far is the most basic one- what do I need? It seems the default questions are about how much real estate does one have, and maybe the cost of the panels plus the batteries.

I saw someone posted a figure of 600 watts. It seems a bit like horsepower in your tow vehicle. More is better. But what do we need?

When not connected, I need some power plus propane for heating, cooking, fridge, fans, and charging phones and gadgets, but all of those together are not much, if you have moderate temperatures and sunlight to use them.

What is your take?

Btw, my shop guy mentioned a study done recently at a local university which showed that maintaining over 50% battery charge extends their life by double years. So that’s a good reason to go with more- longevity. I can get more specs on that if you want.
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Old 08-05-2021, 07:31 AM   #12
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This is a somewhat related question. Our recently acquired 2016 FC25FBT came with factory installed solar, one panel. The panel and controller are from Go Power. No paperwork indicates watts for that single panel. Is it safe to presume 100? Secondly, I’d like to consider installing a second panel. Does that panel have to be the same brand, and would I have to consider a replacement control panel? Thx!
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Old 08-05-2021, 07:51 AM   #13
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Hi

Solar is never a "constant" kind of thing.

One might get 5 peak energy hours a day in one area and 11 hours (wow !!) in another area. Mount the panels "flat" on a trailer roof and you could cut both of those by >30%, even in the best case parking location.

Now toss in campgrounds deep in the woods and solar becomes a very iffy sort of thing. Since there are a lot of definitions of "deep woods" there is some variability here as well. There are places that very little sun gets to this or that campsite.

If you have bad weather (heavy clouds) for a day, that's not to unusual in most parts of the country. It's pretty common to look at solar plus battery as being able to handle this sort of thing. Yes, you can go on for several days. It's unusual to go that deep when planning solar.

How much does your trailer or van use when just sitting there? On a modern AS with a control system that could be 3A. It also could be up around 5A. That's without turning anything other than the fridge on. "Typical 24 hours" usage would be higher.

So, if my RV pulls 5A, that's 120AH a day. Call it 1800 W needed after losses are figured in. . If you are getting an effective 3 peak hours a day, 600W may not be enough. Toss in the "lose a day to clouds" and 1200W may not be enough. All this just to support the static drain while doing nothing in the trailer ....

Even getting 600W on most vans / trailers is a challenge. Going much over 1,000W gets into the very complicated / impossible category. On these fancy new RV's there really isn't a way to put on "to much" solar.

Bob
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Old 08-05-2021, 03:17 PM   #14
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Integrating fixed and portable solar panels

Hi folks,
Hope this fits in with this thread.

A friend would like to know how to combine factory installed roof panels with a portable panel?

Also, after our stock batteries died, an AS dealer set us up with 2 Lifeline grp 31 AGMs, a 160w Zamp suitcase model, and a Zamp Solar Port connected directly to the batteries.
I'd like to add panels on our roof. Should they be wired separately to the batteries? Can they be used simultaneously with the portable?


Thanks,
Dave

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'13 FC28
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Old 08-05-2021, 03:46 PM   #15
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There are really three elements that need to be aligned in order to get a well designed system:

1/ Size of your panels
2/ Size of your batteries (and technology)
3/ Expected energy consumption

In general, you want to make sure your solar panels can charge your batteries fully in 1 day. If not, your batteries will slowly drain until they're empty.

I have 4 panels of 100W each (400W total), and 2 100Ah LiOn batteries (200Ah total, or 2.4 kWh of energy). Because they're LiOn, I can drain them to close to zero, so my panels need to be able to provide 2.4kWh of energy per day in order to keep the batteries fully charged. This assumes I get 6 hours of peak sunlight with my 400W system. That's a lot! It shows that my system is slightly underpowered. It would have been better to have 500 or 600W of solar power.

Then there is the expected energy consumption. My motorhome consumes about 90W in idle state. That's because of the Victron system (inverter, control system, DC stabilizer) and the automation servers I installed (Raspberry Pi, ethernet switch, LTE Model, Wifi AP). That's about 2.2kWh per day. This again shows that I'm underpowered with my solar panels. I really need at least 600W of solar panels to comfortable cover the expected consumption.

Hope this helps.
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Old 08-06-2021, 08:26 AM   #16
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Originally Posted by callmedave View Post
Hi folks,
Hope this fits in with this thread.

A friend would like to know how to combine factory installed roof panels with a portable panel?

Also, after our stock batteries died, an AS dealer set us up with 2 Lifeline grp 31 AGMs, a 160w Zamp suitcase model, and a Zamp Solar Port connected directly to the batteries.
I'd like to add panels on our roof. Should they be wired separately to the batteries? Can they be used simultaneously with the portable?


Thanks,
Dave

'13 GMC 2500 D-Max
'13 FC28
Hi

Portable panels get their own solar controller to convert the solar panel output down to battery voltage. Roof panels get a separate controller to convert their output to battery voltage. The "solar port" the dealer put in is simply a pair of wires going to the battery. There's nothing magic or exciting about it.

Running both roof and portables means running two controllers into the same battery. Neither one knows what the other is doing. As the battery charges up, they will "fight" with each other. Part way through the cycle, one is likely to shut down. The rest of the charge cycle will get done by just one of the panel sets.

You can get controllers that can be networked. You normally also need a "hub" to manage them. This is an "all from the same outfit" kind of thing. To say that it's an expensive solution to the problem is an understatement ....

So:

Best bet is to put the panels on the roof. Put as many up there as will fit. Wire then to a good ( = MPPT ) controller. Get that worked out and running. If you want to fiddle with portable panels, that's fine, but understand the limits in doing so.

Bob
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Old 08-07-2021, 07:20 AM   #17
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Originally Posted by uncle_bob View Post

Running both roof and portables means running two controllers into the same battery. Neither one knows what the other is doing. As the battery charges up, they will "fight" with each other. Part way through the cycle, one is likely to shut down. The rest of the charge cycle will get done by just one of the panel sets.

Bob
So, would it then make sense to go with unregulated portable panels and wire them into the MPPT controller?
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Old 08-08-2021, 07:37 AM   #18
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So, would it then make sense to go with unregulated portable panels and wire them into the MPPT controller?
Hi

If you set up multiple panels, you really would like them to all be "same / same" as much as possible. Unless you know how this or that outfit puts their panels together (which is tough information to dig up ) buying them all from the same outfit in the same size is the practical answer.

The other answer is to bite the bullet and go for networkable controllers plus a hub.

The whole "fighting" thing is a bit more of an issue with lead acid than with lithium. Going over to lithium would help some, but is not a 100% solution.

Bob
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Old 08-08-2021, 08:11 AM   #19
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Originally Posted by david.steed View Post

What I do not see in any discussions so far is the most basic one- what do I need? It seems the default questions are about how much real estate does one have, and maybe the cost of the panels plus the batteries.

I saw someone posted a figure of 600 watts. It seems a bit like horsepower in your tow vehicle. More is better. But what do we need?
At the rally in Lebanon, one of the discussion sessions was about solar and boondocking. The speaker at the session offered a rough approximation that for simple/basic boondocking needs you should plan 200w to 250w of solar panel per 100ah of battery. As mentioned previously, solar from one day to the next is a huge variable, you need clear sunny sky with sun directly above the panels to see the max rated watts of output and that rarely happens.
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Old 08-09-2021, 07:20 AM   #20
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Hi

The problem with any quick "this much solar for that many batteries" number is that it immediately starts getting all sorts of footnotes.

You might get 50% of the amp hours as usable on this or that lead acid and 100% on this or that lithium. Camping up by the Great Lakes is "low solar" compared to the Gulf Coast. You then look at the Arizona desert and .. wow ... that's a lot of sunshine ... Now factor in temperature .....

Lots of variables. Just based on the stuff above you are past a 5:1 spread. Way more footnotes than most folks are going to sit still for. Yes, you can tweak things by adding "usable amp hours" and "in this immediate vicinity" to the estimate. Those qualifiers rarely survive the first edit ....

Crazy !!!

Bob
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