Reply
 
Thread Tools Search this Thread Display Modes
 
Old 08-09-2018, 01:50 PM   #1
1 Rivet Member
 
1965 26' Overlander
penn valley , Pennsylvania
Join Date: Jan 2018
Posts: 5
Designing a solar system

No, I am not God and I won't be making a sun and planets...just designing a small solar system to power an old Airstream.
I'm a new owner of an old Airstream...a 1965 26' Overlander.
It was gutted by the previous owner so I have a blank slate to start from scratch. No issues with pre-wiring because there is none.
In anticipation of this project I have four purchased four "peel and stick" flexible solar panels that are rated at 135Watts@ 24V output. I made that choice because it was the maximum number of panels that would fit on the roof of my trailer.
I am also intending to use LiFePO4 batteries in spite of their initial high cost because they seem to be very efficient at recharging and deep discharge, and with their high cycle capacity should last for many years.
So my question how to appropriately size the components of the system?
I may be hooking up to shore power on occasion, and I do have a 3200W generator that I would be carrying just in case I needed it.
I will be powering 12V DC equipment and 110V AC appliances.
I am thinking of setting my 4 panels up in a Series/Parallel to send 48VDC to the solar controller (to ease the stress on the inverter and reduce the wire gauge necessary for a safe installation) and set up 4 12V batteries in series to provide 48v to the 110/AC inverter but I also need to have 12v DC available for lights and brakes as well as equipment designed for 12v on a trailer, for example pumps, fans and air conditioner
Any thoughts?
__________________

solst1ce is offline   Reply With Quote
Old 08-10-2018, 12:46 PM   #2
Rivet Master
 
2015 30' Classic
Pleasanton , California
Join Date: Jan 2015
Posts: 709
Let's first discuss your first decision. Why did you purchase flexible panels and who's the manufacturer? Reports that I've read show that the reliability of flexible panels is terrible - making replacement of the panels a difficult and messy undertaking. One reason I've heard for their early demise is that the outer skin of the airstream doesn't conduct the heat away from the solar panels on hot days and we know heat shortens the longevity of solar cells.

I'm a big fan of reusing the existing 10 AWG wiring but in your case you have a clean slate, so I would run heavier gauge wire and plan on wiring all panels in parallel.

In a new installation like yours, I would probably go with all Victron components, including the LiFePO4 cells and take a systems approach. If all the components are from the same manufacturer then you can be assured there will be fewer to no incompatibilities.
__________________

__________________
Al, K6IV
2015 30' Classic, "Chez Nu"
2014 RAM 2500 w/Cummins Diesel
ProPride Hitch, 400 W Solar
alano is offline   Reply With Quote
Old 08-10-2018, 01:01 PM   #3
Rivet Master
 
TheGreatleys's Avatar

 
1974 27' Overlander
Baltimore , Maryland
Join Date: Mar 2016
Posts: 760
I'm not a big fan of flexible panels, but let's assume you go ahead with them.

Why do you want to use 48 volts DC? I don't see any advantage, and it would add unnecessary complexity to the system. You aren't going to have any super long wiring runs that would make fat DC solar wiring impractical from your array to the controller. Why not just wire your panels in parallel and use an MPPT controller capable of serving a 12V battery bank with a 24 volt array? Then you don't have to convert again to 12V for your DC electrical system and you can use standard RV components.
TheGreatleys is offline   Reply With Quote
Old 08-10-2018, 03:06 PM   #4
Half a Rivet Short
 
2017 30' Classic
Carlisle , Pennsylvania
Join Date: May 2017
Posts: 5,966
Hi

Ok, I agree that flexible panels would not have been my choice, you have them so let's move on ....

135W x 4 = 540W. A 24V panel nominally runs around 32 to 36V. You will have roughly 17A out of them if run in parallel. If they are all in series, you will get a bit over 4A at almost 150V. A Victron MPPT 150/60 solar charge converter would match that up fairly well except for the full series combo. I would not risk the potential for over voltage.

If you go for parallel, number 10 wire will do the trick with very minimal losses. You could get away with number 12 and still not be doing anything crazy. I don't see a big need to put them in series (or even series / parallel).

Battery voltage wise, you *could* go with a 48V system. That's going to be a pain if you need 12V for various loads. The normal approach is to stick with a single voltage for everything. Wire is cheap and reliable. DC/DC converters waste energy and break from time to time. ( We go nuts about a 1.2% drop in a wire, but ignore a 10% loss in a DC/DC .... why? .... no idea ...).

The big question is: how much DC load will there be? If you plan on getting 3KW out of an inverter then there will be a pretty substantial DC load. That means (even with lithium) a lot of battery capacity. Simple answer to the wire issue (in that case) is to keep the inverter right by the batteries.

3KW of 120v run from 12V at 90% efficiency is up around 280A. I'd suggest that around 600AH of lithium battery is about as small as you should go for that sort of load. It's also not a bad match for about 600W of panels.

Inverter wise, the Victron MultiPlus 3000 would be about right.

All this is making about a thousand wild guesses. There's a lot more to designing a system than randomly guessing. So:

1) How much inverter (3KW above....) ?

2) How much battery ( 600 AH above...) ?

3) Any other loads ?

One biggie under "other loads" would be the trailer break away power. That needs 12V and running it on a DC /DC ... maybe not so much ....

Bob
uncle_bob is offline   Reply With Quote
Old 08-10-2018, 09:20 PM   #5
Rivet Master
 
TouringDan's Avatar

 
1966 24' Tradewind
1995 34' Excella
Lynchburg , Virginia
Join Date: Sep 2009
Posts: 2,825
Sounds like complete overkill to me. Seems like youíre going to be spending a ton of money on a huge solar power system with lithium batteries and an inverter. Do you really need that large of a system. We boondock and do fine with 2 golf cart batteries, 200 watts of solar and a 1,000 watt inverter.

Dan
TouringDan is offline   Reply With Quote
Old 08-10-2018, 11:35 PM   #6
Rivet Master
 
2015 30' Classic
Pleasanton , California
Join Date: Jan 2015
Posts: 709
Quote:
Originally Posted by uncle_bob View Post
Hi

Ok, I agree that flexible panels would not have been my choice, you have them so let's move on ....
Huh... he can't return them?
__________________
Al, K6IV
2015 30' Classic, "Chez Nu"
2014 RAM 2500 w/Cummins Diesel
ProPride Hitch, 400 W Solar
alano is offline   Reply With Quote
Old 08-11-2018, 10:03 AM   #7
Half a Rivet Short
 
2017 30' Classic
Carlisle , Pennsylvania
Join Date: May 2017
Posts: 5,966
Quote:
Originally Posted by TouringDan View Post
Sounds like complete overkill to me. Seems like youíre going to be spending a ton of money on a huge solar power system with lithium batteries and an inverter. Do you really need that large of a system. We boondock and do fine with 2 golf cart batteries, 200 watts of solar and a 1,000 watt inverter.

Dan
Hi

That's the basic gotcha about guessing at everything in the "requirements" side of the design. Maybe there's a need for 3KW of AC for 12 hours a day. Maybe the biggest thing that ever runs on AC is a television at < 100W for < 1 hour a day. Maybe the solar panels can be returned, maybe they can't.

A better way to do a design:

1) This is what I need to do

2) This is what I would *like* to do if I can afford it

3) I can stretch the budget this far ... maybe further ....

4) This is how much space I'm willing to give up for this project

5) I'm willing (and able) to do some / all / none all of the work myself.

6) It absolutely positively needs to be done by this date ... errr ... maybe longer ..

7) I want the latest and greatest / old but well proven / simple and close to stock stuff in the design.

Yes, this requires input from the OP. Not just a little input, but quite a bit of input. One would *assume* that much of the above was considered before the solar panels were purchased. I would freely admit that when I did this the scope changed a bit as the project moved on .....

Bob
uncle_bob is offline   Reply With Quote
Old 08-11-2018, 11:09 AM   #8
2 Rivet Member
 
1971 27' Overlander
Kansas City , Kansas
Join Date: Jul 2018
Posts: 64
Not sure why you would ever wire solar panels parallel these days? Use an MPPT controller and run the supply to the controller as high as you can. You can then run smaller wires if needed and experience less voltage drop.

I have a similar system to yours. With an electric fridge its about the minimum size you'd ever want. I thought about running a 48v battery bank. But for the minimal gains, a 12v bank made more sence.

The great joy of lithium is the charging rate. I can pump 60 Amps into them with my generator in 1 hour. That's enought power to last me 24hrs, even if it's cloudy all day

It is also very common for people to go crazy oveboard with wire sizes. Use a voltage drop calculator and use the size that is required. Running huge wires through your roof leads to a higher risk of chafing and when you get to the end of your build. You might find that the space in your roof is fast running out of room for all those new wires you're running to everyrhing
Shermy1987 is offline   Reply With Quote
Old 08-11-2018, 08:44 PM   #9
1 Rivet Member
 
1965 26' Overlander
penn valley , Pennsylvania
Join Date: Jan 2018
Posts: 5
staring from scratch

unfortunately, I think I will be staring from scratch because the flexible panels I bought are too long for the tubular length of my trailer. I don't want to even try to wrap them around the end caps... it wouldn't be pretty.
I am bummed because I was hoping to go with panels that would be low profile and applied directly to the skin.
I am measuring 16 feet between end caps. One 3' section and one 6' section in between the two fantastic fans and Dometic AC unit are clear.
I'm shopping for new panels.
solst1ce is offline   Reply With Quote
Old 08-11-2018, 11:23 PM   #10
Rivet Master
Commercial Member
 
New Borockton , Alabama
Join Date: Sep 2002
Posts: 1,528
Images: 21
Flex panels are a drag and sorry you wasted your and others time. Zamp slim lines work well.
__________________
Randy...Converters, Inverters, Trimetric, Surge Protectors, Zamp, Smartplug, AGM Batts
888-828-1893
www.bestconverter.com
68 Overlander is offline   Reply With Quote
Old 08-12-2018, 12:02 AM   #11
Rivet Master
 
TheGreatleys's Avatar

 
1974 27' Overlander
Baltimore , Maryland
Join Date: Mar 2016
Posts: 760
Quote:
Originally Posted by Shermy1987 View Post
Not sure why you would ever wire solar panels parallel these days? Use an MPPT controller and run the supply to the controller as high as you can. You can then run smaller wires if needed and experience less voltage drop.
A parallel array tends to perform far better than a series array when one or more cells are shaded, which is a very common occurrence on an RV roof.

In my view, there's very little benefit to being able to use small wires for such a short distance unless you're stuck with a factory solar prewire.

Quote:
Originally Posted by Shermy1987 View Post
Running huge wires through your roof leads to a higher risk of chafing and when you get to the end of your build. You might find that the space in your roof is fast running out of room for all those new wires you're running to everyrhing
There's an inch and a half of space between the skins. That's plenty of room to run 6awg or 4awg wires from the roof along with all your other wiring, with plenty of room left for insulation.
TheGreatleys is offline   Reply With Quote
Old 08-12-2018, 09:33 AM   #12
2 Rivet Member
 
1971 27' Overlander
Kansas City , Kansas
Join Date: Jul 2018
Posts: 64
Thanks TheGretleys, This never crossed my mind.

It will be interesting for me to cut my array in two, and run 24 volts from each side and monitor my results.
Shermy1987 is offline   Reply With Quote
Old 08-13-2018, 07:58 AM   #13
Half a Rivet Short
 
2017 30' Classic
Carlisle , Pennsylvania
Join Date: May 2017
Posts: 5,966
Quote:
Originally Posted by Shermy1987 View Post
Thanks TheGretleys, This never crossed my mind.

It will be interesting for me to cut my array in two, and run 24 volts from each side and monitor my results.
Hi

Running the panels independently (so you can monitor each of them) gets you into two solar charger converters. That's not a good way to go.

With only two 24V panels, just wire them in seres into any of the Victron converters and move on. Anything from number 12 wire up to 1.5" cross section bus bar will work for the wiring. Anything you pick will be "within measurement error" in terms of losses.

If losses really are a big deal, test your panels and pick the two best ones. Panels vary by more than the loss numbers we seem to get crazy about.

Bob
uncle_bob is offline   Reply With Quote
Old 08-13-2018, 09:17 AM   #14
Full time Airstreamer
 
SCOTTinNJ's Avatar
 
2014 30' FB FC Bunk
Anywhere , USA Living.Somewhere.Yonder
Join Date: Jan 2014
Posts: 1,315
Quote:
Originally Posted by uncle_bob View Post
Running the panels independently (so you can monitor each of them) gets you into two solar charger converters. That's not a good way to go.

Not suggesting it makes a whole lot of sense in this situation, but if one wanted to split the four panels into two separable arrays you can wire them through a switch such as this. Then select the arrays individually or combined.



__________________

__________________
@living.somewhere.yonder | Instagram
SCOTTinNJ is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Can a portable solar panel be added to a factory solar system? larry9000 Generators & Solar Power 7 10-14-2017 05:35 PM
if I were in designing Airstreams, I would ... Roamin Cat General Interior Topics 27 08-07-2008 03:31 PM
Designing a new instrument panel 74Argosy24MH Mechanics Corner - Engines, Transmission & More... 21 09-05-2003 09:00 PM
Custom Designing Cat Cabinets, Counter Tops & Furnishings 0 07-22-2002 03:09 AM


Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 03:13 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.