Off grid rv help

dwd902

Hello all. I have been reading this forum for awhile now and am starting to set up my system. Before I get started I wanted to get some insight and make sure I am not messing anything up. I bought land and am living in the RV on the land until my house is built. The house will be completely off grid so connecting to shore power isnt an option ( about 3000 feet to closest utility pole).  I have purchased 2 Trina Solar 280W 20V Solar Panel, Black TSM-DD05A.05-280. Ohh I only plan on using the propane heater and water pump. No TV or anything Fancy. Assuming my 4 amp heater is running 24 hours a day I was thinking 300 amp hour battery on a 12 volt system will do. I will use 6 volt batteries. I'm not the greatest with math but my understanding is with this system I would need a 60 amp charge controller. I also read which could be wrong that you can use a lower amp charge controller it just wont charge past that limit of whatever amp it's at. I would love some input or thoughts if anyone has to share. Am I missing anything? I dont plan on getting an inverter. I will charge phone with my car on my way to work. Thank you in advanced. 

mcgivor

To start with, never buy components without a design, the design starts with anticipated loads, the battery needed is determined by this, the PV required to maintain a sufficient charge is based on battery requirements. Reverse engineering is problematic, start with the loads, since you already have panels, this will define the system to some degree, accurate load calculation is the best point to begin the venture.

Estragon

So assuming a 4a load 24 x 4 is 96ah/day.  300ah is a bit of an odd size (GC would be ~225ah, L16 ~350), but using 300ah, that would give you ~ 1.5 days to 50% charge.

2 x 280w rated panels will likely produce ~ 280 x 2 x .75 = ~420w with proper tilt in full sun.  420w ÷ 12v = 35a.  A 40a controller would likely do, but a 60a would be better for catching a bit of available production in cloud-edge events etc.

At 50%, 150ah plus losses plus loads is needed to get the bank back to full.  35a - 4a load leaves 31a.  Charging is pretty efficient up to ~80%, so about 4hrs full sun to get there, and 2-3 more to get full.  In most locations, you might get full in one day in summer, but likely not in fall/winter.  Most places get runs of gloomy weather, so you'll likely need a generator anyway.

dwd902

mcgivor said:

To start with, never buy components without a design, the design starts with antisapated loads, the battery needed is determined by this, the PV required to maintain a sufficient charge is based on battery requiments. Reverse engineering is problematic, start with the loads, since you already have panels, this will define the system to some degree, accurate load calculation is the best point to begin the venture.

Sorry I should have included when I tried to figure it out I got roughly 112 amp hours of use per day with using heater full time and a few lights and even though the fridge is propane it still uses some electricity and a few other things like water pump. Its bare minimum. Sleep in and that's basically it. I have a propane stove I'll cook on.  The battery I just doubled my daily use so I had extra if needed. Sorry.  

dwd902

Estragon said:

So assuming a 4a load 24 x 4 is 96ah/day.  300ah is a bit of an odd size (GC would be ~225ah, L16 ~350), but using 300ah, that would give you ~ 1.5 days to 50% charge.

2 x 280w rated panels will likely produce ~ 280 x 2 x .75 = ~420w with proper tilt in full sun.  420w ÷ 12v = 35a.  A 40a controller would likely do, but a 60a would be better for catching a bit of available production in cloud-edge events etc.

At 50%, 150ah plus losses plus loads is needed to get the bank back to full.  35a - 4a load leaves 31a.  Charging is pretty efficient up to ~80%, so about 4hrs full sun to get there, and 2-3 more to get full.  In most locations, you might get full in one day in summer, but likely not in fall/winter.  Most places get runs of gloomy weather, so you'll likely need a generator anyway.

Sorry  I just took the 112 amp hours per day and rounded up for 2 days plus  I could make by with less. This is a bare m il minimum use. I am selling my house and can still shower and stuff there but want it empty for the most part to help sell and so it can get fixed  does that make sense. 

dwd902

dwd902 said:

Estragon said:

So assuming a 4a load 24 x 4 is 96ah/day.  300ah is a bit of an odd size (GC would be ~225ah, L16 ~350), but using 300ah, that would give you ~ 1.5 days to 50% charge.

2 x 280w rated panels will likely produce ~ 280 x 2 x .75 = ~420w with proper tilt in full sun.  420w ÷ 12v = 35a.  A 40a controller would likely do, but a 60a would be better for catching a bit of available production in cloud-edge events etc.

At 50%, 150ah plus losses plus loads is needed to get the bank back to full.  35a - 4a load leaves 31a.  Charging is pretty efficient up to ~80%, so about 4hrs full sun to get there, and 2-3 more to get full.  In most locations, you might get full in one day in summer, but likely not in fall/winter.  Most places get runs of gloomy weather, so you'll likely need a generator anyway.

Sorry  I just took the 112 amp hours per day and rounded up for 2 days plus  I could make by with less. This is a bare m il minimum use. I am selling my house and can still shower and stuff there but want it empty for the most part to help sell and so it can get fixed  does that make sense. 

Also sorry it have a generator and the thing to charge batteries with the alternator  

Estragon

In that case, I'd probably just go with a pair of GC batteries.  I did that with just a generator (no solar at all) for a few years while working on the cabin.  Solar would have been a bonus not having to run the genny every day

Estragon

If the panels really are 20v, maybe a controller like:
https://www.solar-electric.com/trts12vochco.html

Reasonable price with enough capacity to handle the panels.  Can be used for higher voltage banks, so might be useful in eventual house system, and fanless design might be preferable for use in RV.

dwd902

Estragon said:

In that case, I'd probably just go with a pair of GC batteries.  I did that with just a generator (no solar at all) for a few years while working on the cabin.  Solar would have been a bonus not having to run the genny every day

What are GC batteries? Just good quality?  Sorry  originally I was going to rely on the generator but figured I'd get a better understanding of solar and hook up the RV before the cabin  

dwd902

Estragon said:

If the panels really are 20v, maybe a controller like:
https://www.solar-electric.com/trts12vochco.html

Reasonable price with enough capacity to handle the panels.  Can be used for higher voltage banks, so might be useful in eventual house system, and fanless design might be preferable for use in RV.

So 45 amp charge controller will work. Might sound stupid but the display seems like it would be nice for a newbie. Then again if I dont understand most of it, it might be pointless. Also OneSolar is that a reputable brand and legit a mppt controller? I've read that there is a lot of fake mppt controllers  

Estragon

GC = Golf Cart batteries.  They're generally ~225ah@6v.  A pair in series is 225ah@12v.  Roughly the size of a large-ish car battery (a bit taller) and reasonably easy to handle.  Widely available, true deep cycle, and reasonably priced (~$100-125ea), so good for learning batteries.  I'd go with a single string (pair) and work them harder, but you could add a second string if need be.

They're a good choice as long as the relatively small capacity doesn't mean needing more than two strings to handle required loads.  Bigger banks (> 450ah@12v) would be better off with bigger 6v, or individual cell 2v L16 sized batteries.

dwd902

Estragon said:

GC = Golf Cart batteries.  They're generally ~225ah@6v.  A pair in series is 225ah@12v.  Roughly the size of a large-ish car battery (a bit taller) and reasonably easy to handle.  Widely available, true deep cycle, and reasonably priced (~$100-125ea), so good for learning batteries.  I'd go with a single string (pair) and work them harder, but you could add a second string if need be.

They're a good choice as long as the relatively small capacity doesn't mean needing more than two strings to handle required loads.  Bigger banks (> 450ah@12v) would be better off with bigger 6v, or individual cell 2v L16 sized batteries.

Thanks  I'll check out the batteries. Another question. Do I need fuses between solar and charge controller and charge controller and battery?

mike95490

You need a fuse at the largest power source (battery) to protect the wires.  When a charge controller fails it can sometimes short, so a fuse at the battery is good.  Size the fuse to protect the wire (10ga = 30A,  12ga=20A) and size the wire to carry the required amps

Estragon

As Mike said, definitely between controller (and anything else connected to battery, eg inverter) and battery.  Between controller and panels, only really needed if more than two panels or strings in parallel, but a breaker can be handy as a disconnect in any case. 

I prefer breakers to fuses as they work out to similar cost (w/holders and spare fuses), and breakers double as disconnects.

Tecnodave

GC Golf cart batteries come in two flavors!

GC-2 are 6 volt and are for older golf carts which are 36 volts and used 6 of them in series. 6X6 is 36 volts

but modern golf carts are not 36 volts!

GC-8 are 8 volt 4 cell batteries for modern golf carts  6 batteries at 8 volts....48 volts.


david

BB.

And, of course, 3x 8 volt batteries gives you a 24 volt battery bank.

Why I always suggest lots of paper design work at the beginning to give you options before you lay out your hard earned $$$$ or €€€€ or  £££, etc.

-Bill