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diy solar

RV Solar Question

Aaron Noel

New Member
Joined
Oct 23, 2024
Messages
2
Location
Cleveland Ohio
Hello everyone, newbie poster, but longtime visitor and reader on this site and on YT. My question or problem I suppose, is one that has been discussed on here plenty I'm sure. About 3 years ago when many prices started to drop on various solar panels and accessories, I finally took the dive and learned as much as I could about solar. Around that time, I had bought a new RV and was certain a 12v system and 100ah batteries was the best way forward for my needs. Due to some life circumstances, this stuff sat for over 2.5 years before I finally got everything on my RV and working in July of this year. Everything works, except I haven't hooked up all my solar panels. I'd like to know from you experts on here if I am doing things to maximize what I have. Currently I have 9 Renogy 100W solar panels on the roof of a 29' Coachmen TT. It was pre-wired for solar with 10AWG cable. I connected a Renogy Rover 60a MPPT controller with a Vevor 3500w Pure Sine Wave Inverter. I have 5 total Power Queen 100ah LifePO4 batteries and a Renogy battery monitor with shunt that I don't have connected at the moment, because I kept getting odd readings, so naturally thought I messed something up. I have used 4 AWG cable to connect the batteries together in Parallel and have used Will's videos to use proper fuses, breakers and such.

Where I start to get confused is the whole series vs Parallel argument and how much I can connect. I actually have 4 more 100w panels on the roof right now that are not connected, because I'm unsure about voltage, Watts, or pretty much everything being too much. What would any of you change about this current setup (besides going 24v and other upgrades, I get it)? Am I able to run that much solar power through the existing wiring in the RV? This RV is one of those that can go below freezing, so it's pretty much impossible to run any new wiring underneath, unless someone has some ideas on that as well. Thanks so much for reading.
 
Assuming these specs
Panels - Voc = 24.3v, Isc = 5.21a

MPPT - Max input voltage = 140v, max current out 60amps.

at 12v - max wattage outv = 800w

So that means -
you can do

3s3p = 9 panels
3 * 24.3 = 72.9v
3 * 5.21 = 15.63a
72.9 * 15.63 = = 1139w -- overpaneled by a large margin (42%) and with 3 parallel strings you need to fuse all 3 strings

4s2p = use 8 panels
4 * 24.3 = 97.2v
2 * 5.21a = 10.42a
97.2v * 10.42a = 1012.824 watts - still over panels by a bit (26%)

Technically you could do 5s2p but you would be overpaneled enough it would probably damage the MPPT.

So, Your answer is 2 strings of 4 and you have 1 panel left over.

NOTE: check that the specs attached match the panels you have and if they don't report back and we can refigure again.

now that we know what configuration of panels you have we can figure for how much power it could generate -

800w (max the MPPT will put out) * 5hrs = 4000Whrs per day under ideal conditions - if they are mounted flat they will never get more than around 60% of the power... This is where 3s3p might work out by giving you another hundred watts.

So figure you will only get around 480watts into your batteries per hour - 2400Whrs


5 * 12.8v100ah batteries = 6400Whrs

Always compare watthours to watthours when figuring stuff it is easier.

You have 2.67 times more battery than you can charge in 1 day with your panels.

Worked the other way - 6400w /5hrs = 1280watts of actual power produced per day to charge them daily and let you pretty close to drain them at night or on rainy days.

To get more power you need more panels and another MPPT to collect the power and put it to the batteries...They can each take up to 100amps charge current so you won't over do things by adding more MPPT. Most battery MFG come out and say max of 1C charge current which is BMS amps times 1, in this case 100amps ... but they also say for longevity to use a charge current between 0.2C and 0.4C.... So I would add another 60amp or better 100amp charger and more panels

Now you have 5 batteries but Power Queen says no more than 4 in parallel - you can ignore that and be fine if you do it right, or you can find another use for the 5th battery on something else.

To parallel them you need at least a 6 stud bus bar rated at 600amps. Better to have 8 studs for your setup - 5 for batteries - 2 for SCC - 1 for inverter. Signature solar has some nice 12 stud bars that are pure copper and will do the job well, or the Blue sea systems 1000amp bus bars would work. Don't get sucked in by the "600amp bus bars" on Amazon for $30 a pair - they are brass and junk - real copper bus bars will cost you.

I have the both of these - the amazon pair is more expensive but is more compact, the signature solar ones are good, but I think more intended to a home rackmount setup.


The downside of 12v systems is you will need large cables to connect the bus bars to the inverter.

3500w /12.8 = 273amps * 1.25 for safety margin = 341 amps For that I would buy Windy Nation 4/0 cable, or 4/0 from batterycableusa

If you don't already have hydraulic crimpers and this is your only project just buy the pre-made cables from either of those two places. If you are planning to buy crimpers go for the Temco brand and not the cheap crap harbor frieght or AMZCNC brand... all the $50 or less hydraulic crimpers on amazon are metric dies marked in AWG and they tend to make crappy crimps...

Read the link in my signature on tools and I talk about it...

You will want a 350amp class T fuse between the bus bar and the inverter and you will want 125amp MRBF fuses with holders on each positive battery post.

Digest that and come back with questions
 

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Assuming these specs
Panels - Voc = 24.3v, Isc = 5.21a

MPPT - Max input voltage = 140v, max current out 60amps.

at 12v - max wattage outv = 800w

So that means -
you can do

3s3p = 9 panels
3 * 24.3 = 72.9v
3 * 5.21 = 15.63a
72.9 * 15.63 = = 1139w -- overpaneled by a large margin (42%) and with 3 parallel strings you need to fuse all 3 strings

4s2p = use 8 panels
4 * 24.3 = 97.2v
2 * 5.21a = 10.42a
97.2v * 10.42a = 1012.824 watts - still over panels by a bit (26%)

Technically you could do 5s2p but you would be overpaneled enough it would probably damage the MPPT.

So, Your answer is 2 strings of 4 and you have 1 panel left over.

NOTE: check that the specs attached match the panels you have and if they don't report back and we can refigure again.

now that we know what configuration of panels you have we can figure for how much power it could generate -

800w (max the MPPT will put out) * 5hrs = 4000Whrs per day under ideal conditions - if they are mounted flat they will never get more than around 60% of the power... This is where 3s3p might work out by giving you another hundred watts.

So figure you will only get around 480watts into your batteries per hour - 2400Whrs


5 * 12.8v100ah batteries = 6400Whrs

Always compare watthours to watthours when figuring stuff it is easier.

You have 2.67 times more battery than you can charge in 1 day with your panels.

Worked the other way - 6400w /5hrs = 1280watts of actual power produced per day to charge them daily and let you pretty close to drain them at night or on rainy days.

To get more power you need more panels and another MPPT to collect the power and put it to the batteries...They can each take up to 100amps charge current so you won't over do things by adding more MPPT. Most battery MFG come out and say max of 1C charge current which is BMS amps times 1, in this case 100amps ... but they also say for longevity to use a charge current between 0.2C and 0.4C.... So I would add another 60amp or better 100amp charger and more panels

Now you have 5 batteries but Power Queen says no more than 4 in parallel - you can ignore that and be fine if you do it right, or you can find another use for the 5th battery on something else.

To parallel them you need at least a 6 stud bus bar rated at 600amps. Better to have 8 studs for your setup - 5 for batteries - 2 for SCC - 1 for inverter. Signature solar has some nice 12 stud bars that are pure copper and will do the job well, or the Blue sea systems 1000amp bus bars would work. Don't get sucked in by the "600amp bus bars" on Amazon for $30 a pair - they are brass and junk - real copper bus bars will cost you.

I have the both of these - the amazon pair is more expensive but is more compact, the signature solar ones are good, but I think more intended to a home rackmount setup.


The downside of 12v systems is you will need large cables to connect the bus bars to the inverter.

3500w /12.8 = 273amps * 1.25 for safety margin = 341 amps For that I would buy Windy Nation 4/0 cable, or 4/0 from batterycableusa

If you don't already have hydraulic crimpers and this is your only project just buy the pre-made cables from either of those two places. If you are planning to buy crimpers go for the Temco brand and not the cheap crap harbor frieght or AMZCNC brand... all the $50 or less hydraulic crimpers on amazon are metric dies marked in AWG and they tend to make crappy crimps...

Read the link in my signature on tools and I talk about it...

You will want a 350amp class T fuse between the bus bar and the inverter and you will want 125amp MRBF fuses with holders on each positive battery post.

Digest that and come back with questions
I hope I'm not breaking forum rules by posting and planning on coming back to post again. I am going to be busy for a while today and so I can't digest all that without giving it proper time - However, for now, thank you so much! I am some random new person asking a question here (that I need to expand a bit more about), and you gave this tremendous well thought out answer that blew me away at first glance. As soon as I can have some time to sit down and make sense of everything I will reply. Again, thank you for leaving such a detailed answer.
 
Unlikely 900W of panels will produce more than a 60A mppt can handle laying on an rv.
With a maximum voltage of 140V and cold possibilities, voltage is the biggest concern.
5 would be the max i would consider in series.

Please verify the specs of the panels, and the charge controller.
 
Did I read it correctly that you actually have 13 panels on the roof? 9 + 4.???

If that’s the case…. You may want to look at 4s3p array - please verify the specs on the panels. (Plus a spare just sitting there).

Can you get another set of wires from the roof to your batteries (so you can run two solar charge controllers)?

How did you wire the batteries? Show a picture. With 5 batteries they should each go to a bus bar with equal length/size cables.
 

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