Best set up for my RV solar project

[hazed]

New to the forum but have used it to help answer questions and get ideas in the past. However, I wanted to try to get some specifics from knowledgeable people in this forum. I have wired my own new construction house from the service to every outlet, so I have some decent experience, however, sometimes it is good to run questions by folks that know solar, as it is new to me.

Anyhow, I have a Thor motorhome and it has a 12v 100 watt panel on the roof. I ordered 6 more 12v 100 watt panels to add to that. After reading my overall goal, I will need to know if the original panel has slightly different specs, if it will truncate the panels it is hooked to, power-wise. I am looking to hook 4 panels together and 3 panels together at 12 volts each to bring 24v into the solar controller as lithium likes 14+ volts for better charging.

I am looking to purchase 3 Lifepo4 12v batteries that are 280-300ah each to have 840-900ah total.
I have a 3000w pure sine invereter with 6000w surge.
I will have to change my factory charger controller to a lithium compatible one.

Since I have yet to buy any other items or wires, can some of you help me with the specs on wire size or any equipment.

What do you recommend for wiring the panels together besides 2-1 connectors for 3 sets of panels and another set for the other 4 panels?
Wire size to solar controller?
Wire size from solar controller on?
Wire sizes anywhere else?
60 amp MPPT solar controller? Or, is that overkill if my motorhome from the factory only came with 30 amp service?
Any other thoughts or suggestions or quick sketch???

I am planning on being able to charge from the onboard generator or shore power, if necessary, so the new charger controller should have a built in transfer switch or I can use the factory standalone Southwire 30 amp transfer switch. With that said, I don't believe any wiring from the generator or otherwise will need replaced??? I do plan on running everything off of the inverter, as most things in the RV are 12v to include the refrigerator. There will be 110v for the microwave, water heater and mini split, but most of those will not ever run at the same time. The mini split is an inverter style, 9k btu's and runs about 716w on high at 110v.

I would like to find the best options to charge the batteries the fastest with solar and hopefully be able to run the mini split, likely not on high but auto at less watts, and find a happy medium to have the batteries maintain a charge while supporting the climate control.

I do not have a factory inverter, so I am not sure if my pure sine inverter will suufice, or if I should go with an inverter charger, or if that matters with solar.

Guessing something like the attached photo is what I am looking for but want the proper size wire for the least resistance.

Thank you very much in advance and I am sure there will be some additional back and forth!!

 

[time2roll]

With a solar controller it is just a battery charger. Will run along with any other charging system or loads that are present.

3000w on 12v is about the practical maximum and works well for many people. Will need a transfer switch to wire the inverter into the electric system.

I would stick with the existing converter while building the system. Replace only if there is an issue. Stock converters will not hurt the lithium battery. For example my converter is disabled as the solar does all I need.

 

[Rocketman]

I am a Victron fan, used lots of it in my MotorHome.

Get a shunt based battery monitor to fit the lithium batteries- I would recommend a Victron Smartshunt or BMV712.

Get two mppt solar charge controller-
Array1 four panels 2s2p Victron smart mppt 100/30
Array 2 3s either 100/20 or another 100/30 (could you add a fourth panel to this array?).

With 7 panels it is probably best to go two arrays, with 8 panels you could go 2s4p or 4s2p (maybe need more info) or goto 9 panels and 3s3p (whenever putting more than three strings in parallel you need to fuse each string - there are MC4 fuses for that. Also look at larger panels you may save money with fewer solar mounts. I used 200w panels, my dad got used 250w panels.

Solar wire 10awg is what is usually used, but you need to watch it if you have three+ strings in parallel (it can only handle 30amps.

From the mppt to the batteries/bus bar - you need to size for the solar charge controller. I like going one size larger if there is any distance involved:

20a - 12awg (I would use 10awg)
30a - 10awg
40a - 8 awg
50a - 6 awg
60a - 4 awg
(Don’t remember off the top of my head the larger sizes).


I believe you are mis-understanding the amps in your RV.
Your 120v service is 30a coming in from Shore.
Your 12v system will be using much higher amps. To run a 3000w inverter will take:
3000w / 12v = 250amps - that will be 85 amps from each battery and will need 4/0 wire to the inverter.

You must match the battery voltage to the inverter voltage.

Keep asking questions.

 

[hazed]

With a solar controller it is just a battery charger. Will run along with any other charging system or loads that are present.

3000w on 12v is about the practical maximum and works well for many people. Will need a transfer switch to wire the inverter into the electric system.

I would stick with the existing converter while building the system. Replace only if there is an issue. Stock converters will not hurt the lithium battery. For example my converter is disabled as the solar does all I need.

Thanks for the reply. I heard that lifepo4 need 14v plus, to fully charge to 100%, or otherwise? I just want to make sure I am getting the most from the system. I am going to look at the factory transfer switch to see if it has the option to wire an inverter into it as well. As for the stock converter, I didn't know if it needed to be lithium compatible specific or not. I could be overthinking things!?!?

 

[hazed]

I am a Victron fan, used lots of it in my MotorHome.

Get a shunt based battery monitor to fit the lithium batteries- I would recommend a Victron Smartshunt or BMV712.

Get two mppt solar charge controller-
Array1 four panels 2s2p Victron smart mppt 100/30
Array 2 3s either 100/20 or another 100/30 (could you add a fourth panel to this array?).

With 7 panels it is probably best to go two arrays, with 8 panels you could go 2s4p or 4s2p (maybe need more info) or goto 9 panels and 3s3p (whenever putting more than three strings in parallel you need to fuse each string - there are MC4 fuses for that. Also look at larger panels you may save money with fewer solar mounts. I used 200w panels, my dad got used 250w panels.

Solar wire 10awg is what is usually used, but you need to watch it if you have three+ strings in parallel (it can only handle 30amps.

From the mppt to the batteries/bus bar - you need to size for the solar charge controller. I like going one size larger if there is any distance involved:

20a - 12awg (I would use 10awg)
30a - 10awg
40a - 8 awg
50a - 6 awg
60a - 4 awg
(Don’t remember off the top of my head the larger sizes).


I believe you are mis-understanding the amps in your RV.
Your 120v service is 30a coming in from Shore.
Your 12v system will be using much higher amps. To run a 3000w inverter will take:
3000w / 12v = 250amps - that will be 85 amps from each battery and will need 4/0 wire to the inverter.

You must match the battery voltage to the inverter voltage.

Keep asking questions.

7 panels is pushing the real estate space on the roof, but i will check to see if i can add 1 more. Panels are in hand, so likely stick with what I have. Understanding that an odd number of panels makes uneven everything. However, I am hoping to find a wiring plan that I could use the existing wiring from the roof top to the solar controller. But, if not, I have no problem wiring larger wire down through the roof to the controller. Is there an option for one controller?

I have a welding shop I like to buy wire from for other projects and cut and swedge ends on to what I need. Correct, 30 amp shore power. My RV is around 25 feet long. Probably 12 feet from the roof inlet to the current controller. Batteries to charger controller is 6 feet and batteries to transfer switch is 10 feet at most.

 

[time2roll]

Thanks for the reply. I heard that lifepo4 need 14v plus, to fully charge to 100%, or otherwise? I just want to make sure I am getting the most from the system. I am going to look at the factory transfer switch to see if it has the option to wire an inverter into it as well. As for the stock converter, I didn't know if it needed to be lithium compatible specific or not. I could be overthinking things!?!?

Yes 14.2 - 14.4 volts is faster than 13.6 volts. However lithium is far different from lead-acid where we have long needed these high voltages for several hours to get a tip top 100% charge to maintain capacity. 100% charged lithium is a bit overrated. 98% is fine and discharge to 20% every day works great and would kill a lead-acid. Yes the lithium will take a few extra hours to get 100% on 13.6 volts. If running the air conditioner 24/7 the generator will also be running similar, same for plugged in... lots of time to charge. Without the air running the solar will get the battery to 100% faster with the programmed voltage. All things maximum all the time is not necessary.

 

[Rocketman]

re transfer switches.

You will need a transfer switch for the inverter to power stuff in the RV.

I have seen four different approaches.

#1 inverter only 120v outlets. You run new outlets - these outlets are powered by inverter only, no other outlets are powered. (My dad did this, needed inverter power at night near the bed - worked for him and his needs).

#2 transfer switch built into inverter. My Victron Multiplus inverter/charger has this. This opens up lots of other options too - power assist,etc. everything just works…

#3 adding an additional transfer switch, near your other transfer switch- I have not heard of an automatic transfer switch with three inputs - shore, generator, and inverter. But you can add another one, then when you turn on the inverter everything is powered. Caution- figure out your system for the battery charger- you do not want a “perpetual loop” (charging batteries with inverted power that comes from the batteries).

#4 plug inverter into the shore or generator cord. Some people will manually plug the inverter into their shore or generator cord. Beware the perpetual loop here too.

My favorite is#2 with my Victron Multiplus- but your needs may be different than mine.

Remember you are the system engineer- it is your responsibility to build something that works and is safe. KISS - Keep It Simple and Serviceable (somehow I seem to always mess up the Serviceable ).

Good Luck

 

[featherlite]

putting more than three strings in parallel you need to fuse each string

I think you meant to say "three or more" (i.e., "more than two").

 

[Rocketman]

I think you meant to say "three or more" (i.e., "more than two").

Yep - I blame the keyboard for not outputting what my brain was thinking.

 

[Mattb4]

Not sure if OP understands that so called 12v panels are actually ~22Voc and 18Vmp. 7 in series would give ~154Voc for the SCC to handle.

3 12vDC LiFePo4 batteries at 300ah ea. or 900ah is likely to want 90a charging and at that rate it would take about 2 days worth of solar production without loads. 90a X12vDC =1080w from panels. 7- 100w panels will only deliver ~600w peak so more like 50a to charge batteries with. Thus 3 days of PV production at 5 hour average.

I would rethink this if I was you.

 

[Rednecktek]

Or you do like I did in my camper and take the converter completely out in favor of an AIO and a breaker box.



I just used a 12v 2Kw AIO for my charging and 120v, ran a line for the 12v stuff, and mounted DIN rail breakers in a box. 120v AC breakers on the left, 12v DC breakers on the right.

 

[hazed]

Not sure if OP understands that so called 12v panels are actually ~22Voc and 18Vmp. 7 in series would give ~154Voc for the SCC to handle.

3 12vDC LiFePo4 batteries at 300ah ea. or 900ah is likely to want 90a charging and at that rate it would take about 2 days worth of solar production without loads. 90a X12vDC =1080w from panels. 7- 100w panels will only deliver ~600w peak so more like 50a to charge batteries with. Thus 3 days of PV production at 5 hour average.

I would rethink this if I was you.

Understood on your reply. I may be able to squeeze another panel up there, for a total of 8 x 100 watts. Do you suggest larger watt panels as another wiser one in this post did? I should add that this is a motorhome and will be moving down the road often, so it will be rechaging through the alternator too, as it should be doing from the factory?? My main goal is to have enough power supply to run the mini split as needed and if I need a boost from the engine or generator, then I have that too. What would be the amount of solar I would need to meet my demands or get close with the limited amount of roof space I have.? Maybe that is not entirely possible with my rig but I haven't mounted anything as of yet.

 

[mikefitz]

4 panels together and 3 panels together at 12 volts each to bring 24v into the solar controller

A typical 100 watt panel will have max power volts at aound 18 volts and open circuit volts around 22 volts, max current just over 5 amps.
A MPPT controller will have a maximum input voltage, several panels at 22 V oc gives a total of 154 volts, too high for a typical 150 volt rated controller.
You could have 6 in series, or two strings of three In parallel. Note, providing the solar input volts is a few volts or higher, ( up to the controller limit), that battery volts, the controller converts input power to a suitable voltage to charge the battery
With 6 panels you need a controller rated at 45 amps,
Example,

SmartSolar MPPT 150/35 & 150/45 - Victron Energy

Maximize the energy-harvest, driving it intelligently to achieve full charge in the shortest possible time using the SmartSolar MPPT. Learn more now.

www.victronenergy.com

With 8 panels, arrange as two parallel strings of 4 panels. Victron 150/60

SmartSolar MPPT 150/60 up to 250/70 - Victron Energy

Maximize the energy-harvest, driving it intelligently to achieve full charge in the shortest possible time using the SmartSolar MPPT. Learn more now.

www.victronenergy.com

 

[hazed]

A typical 100 watt panel will have max power volts at aound 18 volts and open circuit volts around 22 volts, max current just over 5 amps.
A MPPT controller will have a maximum input voltage, several panels at 22 V oc gives a total of 154 volts, too high for a typical 150 volt rated controller.
You could have 6 in series, or two strings of three In parallel. Note, providing the solar input volts is a few volts or higher, ( up to the controller limit), that battery volts, the controller converts input power to a suitable voltage to charge the battery
With 6 panels you need a controller rated at 45 amps,
Example,

SmartSolar MPPT 150/35 & 150/45 - Victron Energy

Maximize the energy-harvest, driving it intelligently to achieve full charge in the shortest possible time using the SmartSolar MPPT. Learn more now.

www.victronenergy.com

With 8 panels, arrange as two parallel strings of 4 panels. Victron 150/60

SmartSolar MPPT 150/60 up to 250/70 - Victron Energy

Maximize the energy-harvest, driving it intelligently to achieve full charge in the shortest possible time using the SmartSolar MPPT. Learn more now.

www.victronenergy.com

Either way, the existing solar wiring from the roof to the current controller would need to be a larger gauge to handle either 6 or 8 panels, correct?

 

[hazed]

Or you do like I did in my camper and take the converter completely out in favor of an AIO and a breaker box.

View attachment 198654 View attachment 198656

I just used a 12v 2Kw AIO for my charging and 120v, ran a line for the 12v stuff, and mounted DIN rail breakers in a box. 120v AC breakers on the left, 12v DC breakers on the right.

This is intriguing. I'm a firm believer in the K.I S.S. model with the S on the end holding the traditional meaning we used to use in the military which usually is followed by me saying DUH, after a little thought. Anyhow, what does this eliminate from anything else? I believe if I remove my winter guard Wi-Fi rooftop booster I can add an additional panel to give me a total of eight. Does your system allow you to keep Shore and generator power as well through a dedicated transfer switch? Or are you relying totally on solar? I have no problems rewiring everything in the controller from the roof and go a size higher for peace of mind.

 

[Rednecktek]

Does your system allow you to keep Shore and generator power as well through a dedicated transfer switch?

Nope, the shore power cord wires right into the inverter and it is set to prioritize shore power over battery power. I can plug into a generator as well as the inverter just treats it like shore power.

Anyhow, what does this eliminate from anything else?

I have more DC circuits available which let me split the loads as the factory had the water pump, the heater, the DC of the fridge, and all the lights on a single circuit which didn't work for me wanting to feed a small inverter and multiple USB-PD and other DC outlets. I don't have to worry about my converter not charging a LFP battery correctly as well. What I sacrifice in space housing that inverter more than makes up in utility for me.

I have no problems rewiring everything in the controller into something else but I guess I'm a little perplexed by utilizing the existing solar wires coming from the roof into the charger controller and if I can do that in any way with the amount of solar panels I have on top. I'm guessing the answer is no?

The wires from the factory are probably undersized to begin with so if you want to keep them you'll have to arrange your panels in series to get the voltage up really high and keep that amperage down. While this keeps the physical wire diameter small, and therefore re-usable, in series any panel that gets shaded nerfs the entire string. With 7 panels there's no good way to split them up (prime numbers are a pain) unless you can get that 8th panel involved. With a 4s2p your wires would probably be just enough to pass the 88v and 10a through, but shading is going to easily halve your potential power.

 

[hazed]

Nope, the shore power cord wires right into the inverter and it is set to prioritize shore power over battery power. I can plug into a generator as well as the inverter just treats it like shore power.


I have more DC circuits available which let me split the loads as the factory had the water pump, the heater, the DC of the fridge, and all the lights on a single circuit which didn't work for me wanting to feed a small inverter and multiple USB-PD and other DC outlets. I don't have to worry about my converter not charging a LFP battery correctly as well. What I sacrifice in space housing that inverter more than makes up in utility for me.


The wires from the factory are probably undersized to begin with so if you want to keep them you'll have to arrange your panels in series to get the voltage up really high and keep that amperage down. While this keeps the physical wire diameter small, and therefore re-usable, in series any panel that gets shaded nerfs the entire string. With 7 panels there's no good way to split them up (prime numbers are a pain) unless you can get that 8th panel involved. With a 4s2p your wires would probably be just enough to pass the 88v and 10a through, but shading is going to easily halve your potential power.

Thanks for the input! As the Victron fan offered his advice, I will ask you the same. If it comes down to $500-1000 or so, one way or the other, I will do what it takes to have the better setup over another. I found out today, if I remove my Winegard 2.0, I can add another panel for 8 total. With that said, what would you suggest for wiring, wire size from roof to controller and size of controller. Like I said, this is new to me and doing my best to learn from the pros!

 

[Rednecktek]

Thanks for the input! As the Victron fan offered his advice, I will ask you the same. If it comes down to $500-1000 or so, one way or the other, I will do what it takes to have the better setup over another. I found out today, if I remove my Winegard 2.0, I can add another panel for 8 total. With that said, what would you suggest for wiring, wire size from roof to controller and size of controller. Like I said, this is new to me and doing my best to learn from the pros!

Well, first question is "Is shading an issue where you go?" In my case I live in trees so I ended up going 4p through a combiner box so I can keep each panel running independent from each other, but it was no big deal for me to run 8awg wire down the size to my distribution box. With 8 panels up top you can either go 4s2p or 2s4p quite easily. Being mounted flat on a roof you're always going to take a hit in production because unless you're on the equator at solstice, the sun is shining at an angle on the panels instead of straight on.

You can see my process and what I did on my camper in my other thread. It might be informative.

OK, so let's do some napkin math with rough numbers:

100w panels are usually in the region of 22Voc, 20Vmp and 5a, so we'll use those numbers for the guesstimates. The rule of thumb for 12v systems is you need 10a of SCC per 100w of panel, so you're going to need somewhere in the 60-80a range. 60 would probably be fine which are pretty available.

8s: 176Voc, 160Vmp, 5a is pretty light load so 16awg would work, 14awg would be better. This lets you re-use the wire coming through the walls without having to re-fish anything. Down sides are that you'll need a really expensive MPPT to take advantage of that high voltage, and if a single panel gets shaded your whole system is nerfed to the lowest panel's production. Works fine in the desert, pretty worthless anywhere else.

4s2p: 88Voc, 80Vmp, 10a so 14awg would be fine, 12awg would be better. You Might have that size already in the wall so you can re-use that wire. No combiner box needed, just a Y-splitter which makes wiring easy. Pretty much any half decent brand of MPPT controller will work well with those specs. Downside is that if a single panel gets shaded by a branch or anything, half your panels are nerfed and not producing squat.

2s4p: 44Voc, 40Vmp, 20a so you'll need at least 12awg wire, 10awg or 8awg preferred. You'll need a combiner box or a stack of fuses (which introduces multiple points of failure) which adds about $100 or so. Again, any half decent brand of MPPT will play nicely with those voltage and amperages. The plus side is if a single panel gets shaded, 3/4 of your strings are still plugging along just fine. The down side is the requirement for an extra piece of hardware (the combiner box or fuses) and the extra cost of the thicker wire.

8p: 22Voc, 20Vmp, 40a, so 8awg really good silicone wire, or 6awg thicc boy wire. You'll have to fish expensive thick wire through the walls, you'll need an 8 position combiner box ($$$!!) but if a single panel gets shaded you're other 7 are plugging right along. May have problems reaching starting voltage in cloudy weather. Just don't.

3s/4s for 7 panels: you'll have to run another set of wires through the roof and get a 2nd SCC involved because you can't get 7 panels to parallel up. At that point you have 2 arrays, a 3s and a completely separate 4s array with their own wires and their own controllers. That's why everyone is trying to get you into that 8th panel.


OK, those are how the different configurations work out with each other using example math. Does that help make sense?

 

[Mattb4]

Your wire size depends on how many amps it has to carry. The panels will list amperage but if you know the watts it is no big deal to figure. Watts= Volts X Amps. When wired in series, panels add voltage and the amperage stays the same. In parallel, panels voltage stays the same and adds amperage.

Using an example of a 100w panel at Imp at 18vDC. of 5.56a. All 7 or 8 in series means the wire must carry 5.56a. You could easily get by with 16awg wire rated for 10a. lets say you run a 4S2P arrangement of 8 panels. 4 times the voltage and twice the current. With 11.2a you would need 14awg wire rated for 15a.

Your SCC must be rated to carry the max possible voltage which is expressed by panel Voc rating. Say it is 22Voc per panel, a 4S2P setup means that your SCC must be rated to withstand 88Voc and a bit more for cold conditions likely 100Voc minimum.

 

[hazed]

Well, first question is "Is shading an issue where you go?" In my case I live in trees so I ended up going 4p through a combiner box so I can keep each panel running independent from each other, but it was no big deal for me to run 8awg wire down the size to my distribution box. With 8 panels up top you can either go 4s2p or 2s4p quite easily. Being mounted flat on a roof you're always going to take a hit in production because unless you're on the equator at solstice, the sun is shining at an angle on the panels instead of straight on.

You can see my process and what I did on my camper in my other thread. It might be informative.

OK, so let's do some napkin math with rough numbers:

100w panels are usually in the region of 22Voc, 20Vmp and 5a, so we'll use those numbers for the guesstimates. The rule of thumb for 12v systems is you need 10a of SCC per 100w of panel, so you're going to need somewhere in the 60-80a range. 60 would probably be fine which are pretty available.

8s: 176Voc, 160Vmp, 5a is pretty light load so 16awg would work, 14awg would be better. This lets you re-use the wire coming through the walls without having to re-fish anything. Down sides are that you'll need a really expensive MPPT to take advantage of that high voltage, and if a single panel gets shaded your whole system is nerfed to the lowest panel's production. Works fine in the desert, pretty worthless anywhere else.

4s2p: 88Voc, 80Vmp, 10a so 14awg would be fine, 12awg would be better. You Might have that size already in the wall so you can re-use that wire. No combiner box needed, just a Y-splitter which makes wiring easy. Pretty much any half decent brand of MPPT controller will work well with those specs. Downside is that if a single panel gets shaded by a branch or anything, half your panels are nerfed and not producing squat.

2s4p: 44Voc, 40Vmp, 20a so you'll need at least 12awg wire, 10awg or 8awg preferred. You'll need a combiner box or a stack of fuses (which introduces multiple points of failure) which adds about $100 or so. Again, any half decent brand of MPPT will play nicely with those voltage and amperages. The plus side is if a single panel gets shaded, 3/4 of your strings are still plugging along just fine. The down side is the requirement for an extra piece of hardware (the combiner box or fuses) and the extra cost of the thicker wire.

8p: 22Voc, 20Vmp, 40a, so 8awg really good silicone wire, or 6awg thicc boy wire. You'll have to fish expensive thick wire through the walls, you'll need an 8 position combiner box ($$$!!) but if a single panel gets shaded you're other 7 are plugging right along. May have problems reaching starting voltage in cloudy weather. Just don't.

3s/4s for 7 panels: you'll have to run another set of wires through the roof and get a 2nd SCC involved because you can't get 7 panels to parallel up. At that point you have 2 arrays, a 3s and a completely separate 4s array with their own wires and their own controllers. That's why everyone is trying to get you into that 8th panel.


OK, those are how the different configurations work out with each other using example math. Does that help make sense?

I can add the 8th panel, so which wiring would you recommend the majority should go with? And, on the AIO, can one wire the existing transfer switch I have for shore and generator into it? Would the AIO think it's just a single source of power and cut off the battery supply?