40ft RV want to go off grid if possible needing advice on sizing the system

Hello everyone I am purchasing a 39ft toy hauler and want to get it 100% off grid if possible it has a 50 amp plug for shore power.
been watching tons of videos etc. still have no idea how big I need to go.
I watched 1 guy had 2500 watts on roof and 20 battle born batteries $$$ OUCH. I will build my own batteries after watching all the videos I can pull that off no problem. I know they need padding between and under for vibration dampening of traveling on the road.
Panasonic makes some nice panels that produce 340watts and 71 volts thinking 8-9 of them, there supposed to be good for RV roofs as far as durability from the research I have done.
any suggestions I will be happy to listen to people that have experience as I have zero knowledge.

I am thinking 280AH lifepo4 48v system would be best.
not sure of size this was what I thought would do it 2 - 48v x 16 bank batteries was what I was thinking of course I have no clue if that's enough power.
as far as inverters/chargers/BMS same issue not sure what I need. what should I get??? I do want it all to have a nice control board that shows me all power and where it is going like the Victrons panel
Have looked at the Victron quattro but that may be overkill and not even what I need.

doing calculations gets confusing for me on this stuff with inverter power loss & conversion from 48v to 110AC power so there for I am here to ask for HELP PLEASE.
Here is what i have figured on total power consumption pretty sure I am going over.
it will have 2 roof air units that pull 1500 watts AC without surge each as well fridge I am thinking 400 watts AC, 150watts TV another 200watts misc modem router & LED lights.
I looked at putting Soft Starts on the Air units as well to help the compressor start load this will make a big difference.
most times 2 air units would not be needed at the same time and only run 8-10 hrs a day max but would like to build the system to accommodate them both just in case but not really needed.

thank you everyone for your help I am grateful. have a nice day & be kind to your fellow man.

Welcome to the forum.

Panasonic is getting out of the solar panel business by 2022 I believe.

Your solar and batteries are dictated by:

1) your solar availability (link #5 in my signature).
2) your usage (link #1 in my signature for an energy audit).

If you neglect either of those details, you're just guessing. You either design a system that falls short, or you grossly over-spend. Sometimes both.

My recommendation is you don't get mired down in component selection. Determine the overall parameters of the system and then design it.

Additional things to consider:

1. A/C use is brutal. Since you plan to use A/C, plan on covering your entire roof and possibly carrying additional panels you can deploy as a ground array.
2. Absorption fridges are absurd on AC power use. Your typical 8 cu-ft fridge can burn 5kWh/day of juice. That's about 5-6X more than a residential fridge of the same volume. 5kWh/day is 1000W+ of panels alone - if you get great sun. If your fridge can run on propane, run on propane. If you truly want to be all electric, swap out the whole fridge or swap out the cooling unit.
3. 30/50A input. 50A power is 120/240VAC split phase. 30A power is 120VAC only. The 50 to 30A adapter for plugging into 30A power jumpers the lines so you get 120V on both legs, but they are 0V to each other. Running with a generator or plugging into shore power requires scrutiny in this area. Very easy to design a system locked into 30A or 50A input, but if you want the flexibility to plug into either, it's more complex. Easy to overcome, just more details.

Do you have a generator on your rig? How much will you need the A/C’s?

I have a MotorHome - with a Multiplus 12/3000 (and lots of other Victron stuff). I am adding a self built Lithium battery this spring. (Eight 272Lishen cells - 12v500ah usable). I figure I run one of my A/C’s for about 3 to 4 hours before the battery is too empty to make it through the night.

Currently with 800 watts of solar - it is enough to run my rig (no A/C, LP for heating & cooking & absorption fridge- although in good sun I will run the fridge on A/C while the sun is out and batteries full- using excess solar).

For solar - look at 200watt panels - I think they are the best for size/rigidity of glass.

Don’t start the process looking at 48v - 24v may be overall better.

snoobler said:

Running with a generator or plugging into shore power requires scrutiny in this area. Very easy to design a system locked into 30A or 50A input, but if you want the flexibility to plug into either, it's more complex. Easy to overcome, just more details.

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can you elaborate more on this? The details and caveats.

DerpsyDoodler said:

can you elaborate more on this? The details and caveats.

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Unfortunately, no. There are threads on this forum that document it. I can't find them at the moment. It depends on which way one structures their system.

10 hours a day on a 1kw+ AC unit is over 10kw of energy. Could be more for larger units. If you plant to run AC off the grid, the first step is to evaluate the efficiency of your rooftop AC units. Most RV style units are inefficient garbage. Not to mention loud. To make this feasible without running a generator is hard enough with high efficiency units. You can look at high efficiency mini splits, which are a better option, but cost more.

Most RVs also have garbage for insulation. They leak air like mad as well. This makes heating and cooling very energy intensive. No one here can estimate what your RVs needs are, you will need to measure them yourself to see whats feasible.

Start a spreadsheet stared, you MUST do a good job breaking down your usage/needs. You are not going to be successful with some scattered thoughts and randomly selected parts. Get a kill-a-watt and measure the energy usage of each 120V appliance. Then work out energy usage based on the number of hours used in a typical day. For DC devices convert amps to watts, and estimate their usage or duty cycle.

If you are talking about making your own 48V battery pack, I suggest stopping right now and taking a hard look at your capabilities and knowledge. Custom higher voltage systems, especially ones with big energy storage, are not to be taken lightly. Fire risk, safety, etc, will all be your responsibility. If in doubt, hire a pro to consult.

It sounds like you are totally new to this. Do you have a strong background in DC and/or AC power systems? Lots of cash to spend? Have you ever done any similar projects? What you are asking for costs $$$$ for a pro to design, don't expect random folks on the internet to do the leg work for you. If you want to tackle yourself in a safe manner without blowing tons of cash, you need to educate yourself. This means a lot more than some Youtube videos.

FWIW, my RV A/C uses 1500W according to Victron.

Most toy haulers have an on-board generator (mine does). It's a lot less expensive to run the generator for air conditioning than to build battery/solar to run the air conditioning. Yes, it CAN be done, it's just a lot of work and a lot of money.

You can put in a 48v system, but you'll still have a lot of high amp 12v loads that need to be addressed.

Luthj said:

10 hours a day on a 1kw+ AC unit is over 10kw of energy. Could be more for larger units. If you plant to run AC off the grid, the first step is to evaluate the efficiency of your rooftop AC units. Most RV style units are inefficient garbage. Not to mention loud. To make this feasible without running a generator is hard enough with high efficiency units. You can look at high efficiency mini splits, which are a better option, but cost more.

Most RVs also have garbage for insulation. They leak air like mad as well. This makes heating and cooling very energy intensive. No one here can estimate what your RVs needs are, you will need to measure them yourself to see whats feasible.

Start a spreadsheet stared, you MUST do a good job breaking down your usage/needs. You are not going to be successful with some scattered thoughts and randomly selected parts. Get a kill-a-watt and measure the energy usage of each 120V appliance. Then work out energy usage based on the number of hours used in a typical day. For DC devices convert amps to watts, and estimate their usage or duty cycle.

If you are talking about making your own 48V battery pack, I suggest stopping right now and taking a hard look at your capabilities and knowledge. Custom higher voltage systems, especially ones with big energy storage, are not to be taken lightly. Fire risk, safety, etc, will all be your responsibility. If in doubt, hire a pro to consult.

It sounds like you are totally new to this. Do you have a strong background in DC and/or AC power systems? Lots of cash to spend? Have you ever done any similar projects? What you are asking for costs $$$$ for a pro to design, don't expect random folks on the internet to do the leg work for you. If you want to tackle yourself in a safe manner without blowing tons of cash, you need to educate yourself. This means a lot more than some Youtube videos.

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I have a good background in AC power 110/220 , 35 years in DC batteries etc with rc cars and drones but ZERO in converting power and solar knowledge .
budget 10-15k
I will be getting a voltage 3615 toy hauler 38.11 length so lots of space for panels.
yes on generator 5.5kw onan so I can charge them fast if need to vs having the gen set running for entire time.
the fridge is gas and electric wahoo just found out so I can take that you of the power draw.

as well now I just want to be able to run 1 ac unit ,tv & wifi during sunny days off the battery bank and solar this is basically what I saw 1 guy in a video doing. his 2500watts on roof was making more then it was using from batteries? is this called floating the batteries?
he had 12 battle born batteries was running everything I mention, so I know it can be done. .https://www.youtube.com/watch?v=roa2kRjNknw
now how long it will run a A/C unit after sun goes down is a matter of battery bank if I can get at least 6 hours of Air conditioner I would be happy

I appreciate the advice on 48 VS 24V the kill-a-watt meter will be my 1st purchase to see what I consume on the daily before buying solar panels and chargers. looks like 24v is the way to go.
I do like the Victron units for the display and showing what's going on with power 24/3000/70 multi plus is the units I am looking at and a mppt controller all Bluetooth for sure.
I am learning just thought more power less conversion would be better & last longer but I do not want to blow up m rig either.
last night I was checking out some of the batteries recommended on the site here and saw these 300AH

Cold Temperature 12V 300Ah KiloVault or the Ampere Time units.​

this seems much simpler/safer saves me time & the pain of making the battery dealing with BMS etc, just wire up as many as can handle weight wise??.
thank you for your input I am grateful for any help this is going to be a fun project I am sure.

Marc B.

A 7.6cu-ft propane/electric absorption fridge will burn up to 5kWh/day in warm weather. They are horribly inefficient. If you have one of the big double units, count on 7-9kwh/day. Absorption fridges use 5-6X the electrical energy of a comparably sized residential compressor fridge.

38' 11" of trailer length is a lot of roof. But is it useable roof? The RV manufacturers don't layout objects on the roof (vents, skylight, AC, etc) in a way that makes for good solar panel deployment.

I wouldn't buy any panels until you have a detailed, measured, drawing of your RV's roof. I created a CAD drawing of my roof so I could virtually install panels to see how they fit.

snoobler said:

A 7.6cu-ft propane/electric absorption fridge will burn up to 5kWh/day in warm weather. They are horribly inefficient. If you have one of the big double units, count on 7-9kwh/day. Absorption fridges use 5-6X the electrical energy of a comparably sized residential compressor fridge.

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well crap I thought it was residential at first but then found out it is a dual unit it's 18cubic foot .
I am surprised they consume so much power, I mean propane is simply heating ammonia & propane is cheap.
for 12v it's low due to heating a element for the ammonia assuming that at least /110 I guess is using a real compressor 6.61 amps ouch.
well i just found the specs it uses very little power & research says most fridges will only cycle maybe 4-6 times a day for 15 minutes max to keep temp set. all depending on how much door is opened.

I will keep researching and getting a idea of total load.
Once I have a KILL-A-WATT I might hit up the dealer before I purchase it to turn on everything and see what it is going to take.

thank you for the information knowledge is key I had no idea they used so much 110v power.

looking like 12 - 100AH batteries minimum and 2500 watts of panels might be enough but I am not spending a dime till I know what I truly need for my use.
I will be going by a solar shop in town and speaking with them about my plans so I don't take up everyone's time on here.

HRTKD said:

38' 11" of trailer length is a lot of roof. But is it useable roof? The RV manufacturers don't layout objects on the roof (vents, skylight, AC, etc) in a way that makes for good solar panel deployment.

I wouldn't buy any panels until you have a detailed, measured, drawing of your RV's roof. I created a CAD drawing of my roof so I could virtually install panels to see how they fit.

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I will not spend a dime $$ till I know power needs etc I know better.
should be getting on roof soon at the dealership and plotting like you said it even before I buy it .
going to probably make a rack system from uni-strut steel that's heavy or L track/airplane seat track aluminum & light weight ? ? I have bed of my truck lined with it for strapping in any location with 1 inch points of movement. if it is done correctly I should be able to hit the main frame structure for roof or possibly go all the way from 1 side to other to attach to outer frame. I figure thats the most solid mount I can get.
after seeing everyone with simply dicor and tape holding brackets through the wood roof yet holding on is amazing. Oklahoma winds are like hurricane winds 25-40 typical then add on 70mph driving. I will be making a air dam to get it up and over them.

have a nice evening Marc B

I think 1200ah of batteries is probably more than you need .
I figure I will be able to run the A/C for a couple of hours just on batteries (500ah12v battery). If I need more than that then the generator will go on to run both A/C’s and recharge the battery. Then repeat.

Good luck with your project. Also do lots of research on building your own bank.

For racking look at 8020.net - extruded aluminum. There is good (but expensive) stuff there.

motomarc said:

after seeing everyone with simply dicor and tape holding brackets through the wood roof yet holding on is amazing. Oklahoma winds are like hurricane winds 25-40 typical then add on 70mph driving. I will be making a air dam to get it up and over them.

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Not all of us are living on the edge like that. My panels each have six brackets and each bracket has at least one screw that is in the roof truss.

If they run on propane, they're absorption. They will run about 16 out of 24 hours per day in warmer weather whether on propane or electric. Your low end use will be 7kWh/day and 9kWh for a high.

The 12V is the control circuit and the propane valve. It will not heat off 12V.

The kind of cycling you reference is how a residential compressor fridge runs.

The norcold 2118 is the same as I have in my Momentum 5th wheel, and the fridge uses 7.9kwh per day during the winter ? (checked with a kill a watt meter)

I have started using the propane instead.

You are also in a similar position and similar direction im going through, im going to be doing an all in one solar/inverter/charger unit in the next few weeks. Im getting a 16s 48v 280ah diy battery than im putting together, a 6500watt inverter, and roughly 1000watts on the roof of the RV (i can fit almost 3200watts as my RV is 45', but I dont need it) and 5-7kw solar panels on the building I park next to.

DerpsyDoodler said:

can you elaborate more on this? The details and caveats

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The only thing I can add is a 50 Amp connection is 240 volts and a 30 Amp connection is 120 volts. @Cinerg may have touched on that subject on his thread or one of his videos. The caveats are many.

Ampster said:

The only thing I can add is a 50 Amp connection is 240 volts and a 30 Amp connection is 120 volts. @Cinerg may hav touched on that subject on his thread or one of his videos.

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Careful with that, it's technically still 120v, not 240v once it goes into the trailer.

The 50 amp has 2x 120v 50 amp legs (commonly referred to as split phase 120/240), and instead of combining them to make 240v, it gets split to 2 separate 110v sides of the breaker panel.

Only reason I bring it up is because I've seen people put actual 240v through their trailers and fry everything in the rig.