Solar Off grid for 2 campers

First off forgive me if I'm asking what has already been asked in a different post.  I'm feeling a bit overwhelmed and hoping someone can point me in the right direction (maybe hold my hand a little).  Feel free to post links instead of explaining what has already been explained.

My Story: My family and I have been working to move to the country for awhile and haven't had much luck finding land that we can afford yet.  We have a friend that is letting us move onto his land until we find a place of our own.  We are setting up 2 campers (both 30 amp) in his barn (it's a big barn) for the winter.  It has electricity.  We want to move the campers to a different spot that if my research is correct will cost several thousand to run electrical to so I'm exploring solar options.  My thought was to build a single ground array to hook both of them up to in order to share the battery bank.  Each camper will have a fridge and furnace.  I would like to use the AC, but it's not necessary at the moment.  I can grow into that.  We are working on changing all lighting to led.  NO microwave. Light laptop and mobile device recharging.  I will have a Desktop with large monitor that I will be using for work during the day.  Any tools can be kept and used at the barn.  There might be some kitchen appliances like a mixer or instant pot that we'll want to use (probably during the day)  I'm thinking I'll at least want a 24V system.  Will I need a 48V?  I can tell you how much I use now, but I don't feel like it will be an accurate comparison.  Also do I bother trying to hook up directly to the DC side of the campers or go ahead and convert all to AC so it can turn around and convert it back to dc for some of the lighting?

I probably forgot to tell you something.  Teach me wise ones. Please?

solar seems to be unique to every place and environment.

One thing to figure out is your use. What are you going to need to store? What is your solar range? How many days of storage will you need.

Fridge's and furnaces will draw quite a large amount of power depending on their size. Maybe consider using 12v fridges.



Here is a tool for figuring out your usage. https://diysolarforum.com/resources/system-energy-audit-and-sizing-spread-sheet.128/download


24v would be fine for what you want to do.

Most of the lights in your camper are probably already wired for 12v i would guess.... You can use DC-DC converters to get the 24v to 12v.


Gotta start at what your usage will be. than the rest can be sized.

I could help you fast-track this a bit by telling you what I'm consuming at my own cabin.  I have a 18cuft frig, lights, TV, computer like you want to run, and I'm finding that my typical daily consumption is in the range of 3000-3500Wh of power.  That's 3.0-3.5kWh of power.

Let's say you round that to 4.0kWh, so you can plan on using 4.0 + 4.0kWh of power for both campers.  First you need to look at the number of sun hours your location receives between December and June, and then decide how many days of autonomy you want.  That is how long your battery needs to support your needs if a storm blows through and you have no incoming solar.

For the sake of doing the math, let's say you get 2.5sunhours (sh) in December, and 5.0sh in June.  Plan for the worst day of the year, not the best.  You also should include a fudgefactor to compensate for panels almost never putting out their rated output.  I usually use 85%.  So, let's do some simple math to see what you need.

(8000Wh/2.5sh)/85% (0.85) = 3765W of panels.  That's quite a bit.  Those are for panels on fixed mounts facing South.  What I've personally found is that you can basically double the effective sunhours by placing the panels on a rotating mount, that can track the sun from East to West.  Look at the pics of the simple rotating mount I made.  It does not have a motor.  You have to rotate the array by hand.  I call that hillbilly solar tracking.  It's simple, and cheap.  It works.  My mount shows 4 grid-tie panels in the portrait orientation.  It could hold six in the landscape orientation.

So, make a rotating mount that can hold six 300W panels, and you can make 8000Wh of power in December.  Double that for a fixed mount.

Now, the battery.  If you go with lead-acid, you want to avoid draining the batteries more than 50% for longest life.  Here is where you need to decide on your battery voltage.  I agree it should be at least 24V.  Let's do the math for 24V, assuming you want two days of autonomy for stormy weather.

(8000Wh X 2 days X 2fold battery supply)/24V = 1333Ah.  That's a really BIG battery.  They make them, but you need two guys to lift one, and you'd need twelve 2V batteries to make 24V.
Let's try 48V
(8000Wh X 2 days X 2fold battery supply)/48V = 666Ah.  That's still big, but along the lines of what I have (Rolls 8 CS 17P).

Let's say you will skip the 2 days of extra supply and start a generator to charge the batteries during a storm.  Keeping with 48V that would be....
(8000Wh X 1 day X 2fold battery supply)/48V =333Ah.
That number looks a bit more reasonable, and lines up nicely with Trojan's 6V L-16 RE-B battery at 377Ah.  You need eight of those for a 48V system.

Now, you need a charge controller to handle that incoming power.  You need to pay attention to both the maximal number of amps, and also the maximal volts.  For 1800W/50V charging = 36A, you don't need to have the very biggest controller.  At 24V, charging at 25V, you need double that, or 72A.  You want to select a controller that can handle at least 36A and as much as 72A.  Now the voltage.  Let's say that you wire your six panels in two strings of three panels in series.  We write that as 3S2P.  Let's assume your 300W panels have a Voc of 48V?  48V+48V+48V in series = 144V.  So, you don't want a controller that has a Voc of 100V, and maybe not one that's limited to 150V.  Go with a 200V controller.  Take a look at Epever's 8420AN.
https://www.ebay.com/itm/373089155693?_trkparms=ispr%3D1&hash=item56ddd8ba6d:g:gdwAAOSw5ERe7dLv&amdata=enc%3AAQAGAAACoPYe5NmHp%252B2JMhMi7yxGiTJkPrKr5t53CooMSQt2orsSafTQYbq3L7RBVAMi0K9cw65cFKT8taILJPii5gx%252BlmATWbYqiUHXOW5Mtatn4lC%252BD3YEaRNOiIr9GB7G7QXGHyBSDnm5TPpcexshOLzFUOKUkcRHQ6p9iyynapgmlyh5N92mvvr%252BhaIT996da%252B%252BAX1QjryZ%252FhGRK0Pj5Vi6zWVDkfU4ntn1Y6VGs8Y44FLf7sgfvOK3AOuBLCcEbbOiPsr6k03toAU2SGWC91%252FBuiOSlQKODww2AhqZBUOEdcZ6of%252FG0qz9ov0bCo8fdH%252FL6yLOFrxA8tn0RMWGpLV5SDbCoMOj1oPqY1a98lO%252BoyAeYqw%252FwB0AJ1BLGmwwOZ5bPgcjIqAG3XWeM%252Bhn8IRLVEtFgajoMM0Ii2NN89gMObbd9r%252FcAg07SXBbXlAPyQv56cZ36YZXl892Dz6nU1rC9u6IzGsPMtA0LqAoHyWjArkbnBIL7ygep7FX9UUBOhDBIcV0mmkvLHWyOZFo8%252FbxbIYFa61%252Boj6%252B7JrNWxI0YSKBVnn9622baycjE8PPvAQvhsy0ow%252F%252FDoLF6R03t8V%252F6cc7qlOBEP%252B2OY8r9gQHBoi1sFGWNauPJrbx7YMkOD5UbeHhVZscIqV7FxouNLr3zftQ7E1wVzoBMUb%252FTr3hRKMqA%252F9HxWfP3YSt1B1G5QKuGBD%252FdaH7obVS%252FRwEB%252BMPGh7IOFEwJEudS1tWa%252BajojaQxYwc16K4YqHJdd8Xkiivx%252FU7U%252BUSNzCLO78zYFv6AzrxdYCYic9%252FRSIb%252FW3lkw0fN72iLexBYBB5dGEJObTs49QMIwSwL21w%252BrnEgfDO4xiCIxbR%252Fb102DecfVT6Q%252FIQTWbWpen5HThtKnVPMJ9k5jw%253D%253D%7Cclp%3A2334524%7Ctkp%3ABFBM2KiMn9Jf

Finally, there's the inverter.  You do NOT want a square-wave, or modified square-wave inverter if you run anything with an electric motor, such as your refrigerator.  Anything besides sine-wave will cause the motors to overheat, and quickly fail.  Here are a couple of nice 48V inverters, that feature both split-phase 120V/240VAC, and direct generator charging.
Magnum: https://ressupply.com/inverters/magnum-energy-ms4448pae-sinewave-parallel-inverter
Schneider Conext: https://ressupply.com/inverters/schneider-electric-conext-sw4048-120240-invertercharger
Outback: https://ressupply.com/inverters/outback-gs4048a-01-radian-invertercharger

If your RVs are already running everything at 12v, I would recommend building the system that way too. Your charge controller can take higher incoming voltage and convert it to 12v, so panels that are strung in series could be generating current using 100-150v, and thus use thinner/cheaper wire. Then you size thicker wire once you're past the CC. Will each RV have its own batteries, or would you build a battery storage shed that can be kept warm/cool that you'd park next to?

Otherwise if you wire your batteries at 24v, then you have to convert that back to 12v and there is a loss from conversion. So I would minimize that by staying at 12v DC, but you could still use 24v and convert to 12v, or pick up DC bulbs that handle both. I was looking at bulbs that can handle 12/24/36/48v DC, they are like $15-20 for 4-6 packs on Amazon. Converting to AC should only happen for devices that are AC only, definitely not for lights that are already wired 12v DC. You will lose 10-15% each time you use an inverter, perhaps as little as 7% depending on how much you spend and how often you are converting at the most efficient rate.

The Rolls CS (5000 series) are great batteries, they will easily hit 5000 cycles if you take care of them. My coworker uses them and confirmed he has had them in service 15+ years before replacement but he sticks to the heavier plates you get in the 2v-6v range. The batteries are heavy, you can go over 200# each pretty fast based on AH. So if you have the batteries on the RVs, that is a lot of weight. But lithium batteries are about triple the cost and don't last any longer than the Rolls CS batteries. Unlike Rolls, I wonder what kind of warranty support the always-changing shops offering affordable lithium setups will have. Maybe that's unfair, but since I don't have a mobile use like you I haven't tried lithium yet. Used Tesla battery packs have been used too, but DIY on something which has the potential to catch fire if not done right makes me very wary.

You might also want to look at these batteries:

https://ironedison.com/shop/batteries/nickel-iron/nickel-iron-ni-fe-battery/

YES, much more expensive, but, prorate those costs over a 20 year period and see that it actually will be the cheaper cost in the long years of use of your batteries.

You can also see information on these at:    Nickel-iron battery - Wikipedia
[Search domain en.wikipedia.org] https://en.wikipedia.org › wiki › Nickel–iron_battery
The active materials are held in nickel-plated steel tubes or perforated pockets. It is a very robust battery which is tolerant of abuse, (overcharge, overdischarge, and short-circuiting) and can have very long life even if so treated. It is often used in backup situations where it can be continuously charged and can last for more than 20 years.

Not what you asked for, and maybe you've done all this already: reducing use will be your friend: If you have the option, site your campers so you can get solar gain in the colder months but not bake in the warm/hot months. Are there large deciduous trees to take advantage of? Orient campers with side with most windows facing south. Skirt your campers. When it is cold and you are heating you can use outdoors as refrigeration (so you won't be having both high-use appliances drawing during the same seasons). Actually I find it very doable to live without a running fridge (I use one that is not running to help food and seeds avoid temperature changes/extreme heat and cold), wind and shade can keep things cooler in hot weather.

Barbara Kochan wrote: I find it very doable to live without a running fridge.

This is a bit off-topic but back in my camping days, I used to stand my jug of milk in a plant saucer half full of water and drape a piece of paper kitchen towel or wet cloth over it, dipping into the water all round. The water on the cloth evaporates, extracting the latent heat of evaporation from the milk, thereby cooling it, and is replaced by more water wicking up the cloth. It works just fine and I always had good milk for my cup of tea after a long day's hill walking.

You'll need to experiment with different cloths to find the one that works best. You might be able to extend the system to a box containing perishable food standing in a tray with a cloth draped over it, perhaps with water dripping onto it. Good use for that leaky bucket! Maybe a cedar wood box would work? You just have to remember to keep the water topped up.....

It warms the cockles of my heart to see just how much trouble folks are willing to go to in sharing their knowledge and experience to help someone else find a solution to their problems. This is a great community!

Not sure I parsed all your wants/needs correctly ...
 - things are fluid/mobile, and there is a move to permanent land at some point
 - two campers, 30-amp ea
 - no idea of constraints from current landowner
 - possibly living in barn until ready to get out on landowner's land, or on other permanent land

1. Get a (small) trailer, upon which everything will be mounted (generator, inverter/charger/mppt gear, solar panels, propane tank)
 -  see all kinds of designs for this, but keep it mobile & safe from elements
 - look into "sound-proof enclosures" for genny, for ideas on how to hold everything in the trailer
 - could be a very inexpensive HF 4x8, depending on your handyman skills

2. add generator & propane
 - inverter/generator, anywhere from honda 2200 on up to predator or duromax (as much KW as you can afford)
 - 100-lb propane tank (this is temporary, until you get to land where you can have propane installed)

At this point, you have power; if necessary, pair two of these gennies together for more power, or again, buy as much KW as you can. Generator will run all the time you need power, but all it cost at this stage was a gennie and propane tank. If no trailer, get the tank with wheels.

3. add 24v inverter/charger & two lifepo4 batteries
 - 24v inverter/charger (magnum or similar)
 - ampere time 100ah, 200ah, or 300ah lifepo4 (whatever you can afford) ... at least two

At this point, now the genny isn't running all the time; it is only to refill the batteries, which, being lifepo4 (very lightweight), will last you many 1000's of cycles. Easy to hook up to campers, and a splitter can power both. An electrician or similar knowledge will help you set everything up.

4. add solar panels/mppt
 - as many panels as needed to fit your mobile lifestyle (and mppt), and will become permanent when land is found

The trailer is key to being mobile, until you don't need to be any longer. You can then either keep things on the trailer, move them to a utility shed, or do whatever is necessary when things become more permanent, all without losing too much of your investment.

Scale the solution up or down (12v, 24v, etc.) to fit requirements and budgets, but always buy more than you need, so you can grow into it (or reuse it elsewhere at permanent land). Avoid 12v if at all possible; more of a camping solution than a permanent solution. Inverter/generators are expensive, so if possible, utilize an open-frame genny (more KW, less cost); just can't tell what "stealth" options will be needed.

As there is a landowner involved, verify at every step of the way that there is no grief from them. Trailer can be made to support "silent operation", so landowner doesn't know/complain too much, and can safely be out of the way while still routing power to campers (not in the barn with you), and still protected from the elements.

If all fails (landowner boots you out, and this has high potential), just hit the road with campers & trailer to next location. Haven't lost any investment, and all can be expanded upon at final location.

Hope this helps ...