Help on skoolie build

[Arkangel111]

I'm starting my build soon. despite hours of research I am still lost on what to do. I essentially picked items from various websites that explain what to get, but when it came to panels I could not find the size I was looking for, for any reasonable price. I ended up with 10 x 240w panels (36v) (from a wholesaler) I grabbed a MPPT charge controller that is listed as "60 amp 12V/24V/36V/48v DC 150V PV Input MPPT Solar Charge Controller". I grabbed 5 x batteries that are LiFePo4 12v 200ah rated, however after further review of the description it mentions you can only put 4 in series or 4 in parallel. I'm currently trying to figure out if doing a mixture of the 2 (parallel and series) will let me utilize my battery bank as planned or if I need to return at least one of my batteries. My goal was 2400w of solar and 1000 ah of batteries. But now after further review I am not sure if any of this is gonna work.
I ultimately planned to run a mostly 12v system with the exception of a computer, fridge, and some kitchen appliances. Now I think I have majorly messed this whole thing up and way over purchased. Things were on sale so I grabbed what I could while they were on sale. Basically I have run into a wall and am second guessing myself at every turn. Any help would be greatly appreciated.

 

[WindWizard]

Since you do not mention an inverter yet then you could still salvage your situation. You could purchase an additional battery and go with a 36 volt system using 3S2P for the batteries. The panels you could configure as 2S5p which should give enough voltage to charge your batteries and your charge controller could handle most of the panels okay. (2160 watts). For a 12 volt system you would need to return a battery and go with a 800 amp system. 4p for the batteries and 3p for the panels for a 12 volt. Unfortunately most of your panels would not be able to be used. Your mppt charge controller would be limited to around 720 watts of panels at 12v. (60 amps times 12 volts = 720 watts). Read the information on your MPPT Charge Controller to see the specifics on how much solar panel power it can handle.

 

[camelCase]

A 60 amp controller can pass about ~800 watts if charging current to the batteries at 12v or ~1600w at 24v. Check and see if your batteries can be installed 2s2p for a 24 system. You would only use 4 in that configuration, obviously.

A lot of controllers are OK with over paneling, so the extra panels could be of use in the winter time. Since you are probably going to mount these panels flat, you'll likely never get 200w out of them anyway even in ideal conditions. Another idea is to add a second charge controller in parallel to handle the excess SA wattage.

As to being over spec'ed, solar is like money, there's no such thing as too much, though I get along fine with 200ah of lead acid batteries, but I have propane appliances.

 

[GLC]

I'm starting my build soon. despite hours of research I am still lost on what to do. I essentially picked items from various websites that explain what to get, but when it came to panels I could not find the size I was looking for, for any reasonable price. I ended up with 10 x 240w panels (36v) (from a wholesaler) I grabbed a MPPT charge controller that is listed as "60 amp 12V/24V/36V/48v DC 150V PV Input MPPT Solar Charge Controller". I grabbed 5 x batteries that are LiFePo4 12v 200ah rated, however after further review of the description it mentions you can only put 4 in series or 4 in parallel. I'm currently trying to figure out if doing a mixture of the 2 (parallel and series) will let me utilize my battery bank as planned or if I need to return at least one of my batteries. My goal was 2400w of solar and 1000 ah of batteries. But now after further review I am not sure if any of this is gonna work.
I ultimately planned to run a mostly 12v system with the exception of a computer, fridge, and some kitchen appliances. Now I think I have majorly messed this whole thing up and way over purchased. Things were on sale so I grabbed what I could while they were on sale. Basically I have run into a wall and am second guessing myself at every turn. Any help would be greatly appreciated.

Go back and re-read that statement.
"it mentions you can only put 4 in series or 4 in parallel."
This could possibly mean 4 in series and 4 in parallel? Meaning a max of 48 volts which is common but normally putting batteries in parallel is not an issue. I am currently running 2 parallel banks of 6/12 volt batteries in series to make 24 volts which is 12 batteries.

 

[Ranger Rick]

I'm starting my build soon. despite hours of research I am still lost on what to do. I essentially picked items from various websites that explain what to get, but when it came to panels I could not find the size I was looking for, for any reasonable price. I ended up with 10 x 240w panels (36v) (from a wholesaler) I grabbed a MPPT charge controller that is listed as "60 amp 12V/24V/36V/48v DC 150V PV Input MPPT Solar Charge Controller". I grabbed 5 x batteries that are LiFePo4 12v 200ah rated, however after further review of the description it mentions you can only put 4 in series or 4 in parallel. I'm currently trying to figure out if doing a mixture of the 2 (parallel and series) will let me utilize my battery bank as planned or if I need to return at least one of my batteries. My goal was 2400w of solar and 1000 ah of batteries. But now after further review I am not sure if any of this is gonna work.
I ultimately planned to run a mostly 12v system with the exception of a computer, fridge, and some kitchen appliances. Now I think I have majorly messed this whole thing up and way over purchased. Things were on sale so I grabbed what I could while they were on sale. Basically I have run into a wall and am second guessing myself at every turn. Any help would be greatly appreciated.

Assuming your PV’s VOC is 36v, you’ll need to factor in your coldest temperature coefficient (@1.25x) that equates to ~ 48v per panel. Your SCC allows 150v so 3 in series is close. That would allow for a 3S3P (=9 PVs). 10 PVs could be 2S5P with proper fusing.
You didn’t say what Inverter you have. 2k watts is safe for 12v systems (imo). But pushing 5 200Ah batteries in parallel is doable. If you added a 24-12v converter, you could go with a 24v system and have better options with a sixth battery. Not sure where you get the 4 battery limitation.

 

[John Frum]

@Arkangel111
Did you start with an energy audit?

 

[Arkangel111]

Thanks for the quick replies.
First off, I got the 4 limit from the company website and I confirmed it means 4 and 4 limit.
Second there was some questions about inverter so, I have 'SUNGOLDPOWER 3000W Peak 9000W Pure Sine Wave Power Inverter DC 12V AC 120V with Battery AC Charger Solar Wind Power Inverters LCD Display Low Frequency Solar Converter' from Amazon. Not sure if links are allowed so that is a copy paste of the description if you need to look it up.
If that inverter works I'll grab the extra battery and do a 3s2p setup as suggested. Other than the MPPT and inverter is there going to be other parts I need to throw into my system to make the 12v portion work? Any major pitfalls or hazards to be aware of? (Experienced aircraft electrician so I understand the normal hazards)

 

[WindWizard]

Probably the first thing to decide is if you want to stick to the idea of a 12 volt system. A 12 volt system limits you in a number of ways. You will need to add additional Mppt Controllers to utilize your 10 panels. You will need to have a larger wire size due to ohms law. Higher voltage lower wire size. 48 volt systems are just more efficient and the time to decide is before you actually purchase your inverter. Mppt controller can handle any voltage but the higher the system voltage the more power it puts out. You get four times the power out of a MPPT controller at 48 volts vs 12 volts. 60 amps x 48 volts vs 60 amps x 12 volts.

I was originally going to go with a 12 volt system. I even have two Xantrex 1kw inverters collecting dust. I realized that it just was not going to work for what I needed. I am glad that I went with a 48 volt system myself.

 

[Arkangel111]

I was under the impression that I needed a 12v system. My lights are 12v, led is 12v, and I've really only seen recommendations for 12v systems for skoolies. We're going to be leaning pretty heavy on the inverter since my wife ideally wants AC (not likely I know), a fridge and freezer (5 kids), heating, an induction cook top and daily used blender.
I'll go with whatever best fits what I already have to be honest. Just every resource for the DIY skoolie seems to assume 12v and 600w Solar or less. I know we need more than that so I tried to upsize where possible in order to future proof the build. I originally had some 12v panels lined up but got a great deal on some 36v ones and that's where everything got messed up.

 

[camelCase]

You can get an efficient 24v or 48v to 12v buck converter to take care of low voltage needs.

https://www.amazon.com/48-12-volt-converter/s?k=48+to+12+volt+converter

 

[camelCase]

Heavy inverter loads make a 48v system all the more advantageous. 3000w \ 12v = 250 amps which is a lot of potential heat and a lot thicker cabling required.

 

[Ranger Rick]

If the 36v is the panel’s VOC rating found on the panel’s specs or on the specs sticker on each panel’s back side, your panels will work. I would look more info on going with a 24-volt battery bank and a step down 24to12v converter to tie into your 12v distribution panel. A 24v RV system is safer than a 48v one (Google it).

 

[Supervstech]

You want to potentially operate AC, microwave, induction cooktop, refrigerator/freezer, AND HEATING! 12V stuff can easily be operated off a converter.
Heating, and cooling are the hardest off a mobile solar system… heating means heavy demands, when the sun is at its shortest supply… I recommend diesel or propane heat…
AC is doable with an efficient inverter drive minisplit unit. And, while they do heat, the solar is 1/3 light available, and heating takes more watts…

 

[acdoctor]

If you already own the the 12 volt inverter and can’t upgrade it to a 24 volt one what you have will work. Battery manufacture recommended 4 in parallel because of charge/ discharge balance issues so you will need to be extra careful setting those up. You will need the correct buss bars. Properly sized wires and fuses.
As mentioned above solar charge controllers on 12 volts will only accept 800 watts so you will need at least 1 or 2 more to use all of the panels. I recommend mounting at least some of the panels to be tilted.
I have a 7kw LFP battery in a conversation trailer. In the winter heading with mini split over night low of 28 deg f. my battery is used up heating and 11 cf. fridge. From full charge. I have 2 kw panels, 1 kw is tiltable to 45 deg. If all were flat I would only recover about 1/3 or the battery in a day.

 

[Bobert]

I'm starting my build soon. despite hours of research I am still lost on what to do. I essentially picked items from various websites that explain what to get, but when it came to panels I could not find the size I was looking for, for any reasonable price. I ended up with 10 x 240w panels (36v) (from a wholesaler) I grabbed a MPPT charge controller that is listed as "60 amp 12V/24V/36V/48v DC 150V PV Input MPPT Solar Charge Controller". I grabbed 5 x batteries that are LiFePo4 12v 200ah rated, however after further review of the description it mentions you can only put 4 in series or 4 in parallel. I'm currently trying to figure out if doing a mixture of the 2 (parallel and series) will let me utilize my battery bank as planned or if I need to return at least one of my batteries. My goal was 2400w of solar and 1000 ah of batteries. But now after further review I am not sure if any of this is gonna work.
I ultimately planned to run a mostly 12v system with the exception of a computer, fridge, and some kitchen appliances. Now I think I have majorly messed this whole thing up and way over purchased. Things were on sale so I grabbed what I could while they were on sale. Basically I have run into a wall and am second guessing myself at every turn. Any help would be greatly appreciated.

I set up my rv using 10 240 watt panels and 5 lifepo4 batteries (100ah in my case) the batteries have the same limit of 4 series or 4 parallel. I use a 48v AIO inverter I connected 9 of the panels to the AIO 3s2p as it has a 145v limit on PV input voltage. I use the 5th 12v battery to run my 12v loads and a smaller scc and the remaining solar panel to charge the individual 12x battery. That configuration works quite well. If we need to conserve power I turn off the inverter at night and the single 12 volt has no problem making it through the night. On sunny days now that the sun is out longer and at a more favorable angle I am fully charged and wasting all my solar by 10 or 11 am. I use 2 diesel heaters to keep warm in winter. Down to 10 degrees one works fine but we get -30 and then some where I live so it takes 2 to maintain 65 degrees at that temperature. I use the cheap Chinese heaters and I wouldn’t recommend them if you are not handy they are pretty persnickety. I set my rig up this way in part because of financial limitations but primarily because I had very little space I could devote to batteries and equipment. With a little creativity I’m sure you can use what you have to make a system that works. Design your system on paper trying all the possibilities think outside the box sometimes buying a major component will save you money especially with today’s wire price. Above all be safe no one is going to inspect your setup like a house installation so it is entirely on you to make sure your system works properly and you and yours are safe.

 

[circus]

Seeing you already have a bunch of 12v devices the simplest solution is stay 12v, buy more mppt's and make several separate systems that share only the batteries.

 

[Bobert]

I would leave some room for flexibility. You may find you use power a lot differently than you expect. It’s a bit different for every person and each rig. We found we used a lot more ac power than we anticipated. That’s not something we could have accurately calculated without actually boondocking for a period of time.

 

[Arkangel111]

Ok been doing a bunch more research. I am leaning towards Wind wizards suggestion of the 2s5p solar array with the 3s2p battery bank. This does mean buying another battery but that's fine. My new questions however are:

1. My panels have a Voc listing of 37.2 which puts it up for a nominal voltage of ~20V. According to the research I found its fine going through a MPPT with the 2s5p to ultimately charge a 24v system, with the battery recomendation of 3s2p that is a 36V battery bank and 400AH. Since my panels are good for a 24V system shouldn't it instead be a 2s3p setup for the 24V 600AH setup?

2. how do you determine the inline fuse size? I keep seeing many systems recommend an inline fuse but not how they determine the size needed.

 

[GLC]

Ok been doing a bunch more research. I am leaning towards Wind wizards suggestion of the 2s5p solar array with the 3s2p battery bank. This does mean buying another battery but that's fine. My new questions however are:

1. My panels have a Voc listing of 37.2 which puts it up for a nominal voltage of ~20V. According to the research I found its fine going through a MPPT with the 2s5p to ultimately charge a 24v system, with the battery recomendation of 3s2p that is a 36V battery bank and 400AH. Since my panels are good for a 24V system shouldn't it instead be a 2s3p setup for the 24V 600AH setup?

Why do you make the statement that your VOC of 37.2 is a nominal voltage of 20 volts to charge a 24 volt system? If you have a 24 volt controller, a lot of controllers will handle up to 150 volts and X number of amps and watts. I guess I don't under stand your statement its not like you are using a 24 volt PWM where it will only handle 24 volts. Besides your 2s3p setup is pushing appx 74 volts which is fine. And then you bring up 36 volt battery bank? Can you explain your reasoning for all of your statement in #1.

 

[Arkangel111]

I found a chart, it mentions nominal voltage and explains how to setup your system. My panels don't mention nominal voltage but did have Voc listed. The chart showed a Voc of ~38 is typically listed for nominal at 20V. The article says 20V can charge a 12V system just fine or if using 2 in series with an MPPT a 24V system.
Since it was suggested I use a 2s5p panel setup I was wondering why the suggested 3s2p battery setup instead of 2s3p?