Existing RV solar to power an off-grid cabin?

[TripleDave]

Hi, I'd really appreciate some advice. I'll try and keep things short:

This year we plan to build a cabin on woodlot in Nova Scotia. As part of this, we were looking into solar systems. We like to keep things simple so we really liked the look of the all in one units like the EG4 6500ex. Then I thought we could use 2 of the 12v 100AH lifepo 4 batteries in the RV and buy 2 more, exactly the same, so cutting down on the biggest cost (we have a budget for all of this so thinking of clever solutions to that save us money while not affecting us too much appeals) and wiring them for 48v. We have lived in our RV for long periods with our RV solar: 800w on the roof, 60A mppt and the 2 batteries (no inverter) and it has powered the 10cu ft 12v fridge non-stop plus lights, phones, laptops, 12v kettle without a problem. So, we can live quite happily not using much electricity.

We are going to use this cabin when we are not travelling in the RV - maybe up to 6 months of the year. We would like to upgrade the RV solar too as while we are building this cabin it would be good to have the ability to use AC power and have more batteries in reserve. Should point out we also have a duel fuel generator.

This morning, I had an idea. Not sure if it's a good one! I don't like the idea of investing in 2 separate solar systems, especially when they won't be used simultaneously. So, as we have a nice RV with a decent sized solar system (we could out another 1 or 2 panels on the roof and change the brackets so they tilt plus inverter and 2 more batteries) could this be used to power the cabin? Bearing in mind we don't use much power we will just need the same as above plus the occasional appliance and a well pump (no microwave, aircon etc). We plan to use a woodstove only for heat and propane for for cooking, hot water heater. We haven't bought anything yet but can base what we get on what is possible.

The other benefits I thought of is, we wouldn't be leaving an expensive solar setup in the middle of the woods in the winter.
We could skirt the RV and use the propane furnace on the thermostat in the winter.
It's already wired up including for generator use.
Obviously the cost savings could be huge.

Negatives would be, it would be a 12v system (not sure how much of a negative this is for a small system).
Don't know the implications from a permitting point of view.
Not sure how possible / practical it really is.
It would be quite limited in terms of size, especially if we have visitors.

Any help would be greatly appreciated. I'm not great with some of the jargon so laymen's terms would be also be very much appreciated.

Thank you

 

[sunshine_eggo]

Hi, I'd really appreciate some advice. I'll try and keep things short:

This year we plan to build a cabin on woodlot in Nova Scotia. As part of this, we were looking into solar systems. We like to keep things simple so we really liked the look of the all in one units like the EG4 6500ex. Then I thought we could use 2 of the 12v 100AH lifepo 4 batteries in the RV and buy 2 more, exactly the same, so cutting down on the biggest cost (we have a budget for all of this so thinking of clever solutions to that save us money while not affecting us too much appeals) and wiring them for 48v. We have lived in our RV for long periods with our RV solar: 800w on the roof, 60A mppt and the 2 batteries (no inverter) and it has powered the 10cu ft 12v fridge non-stop plus lights, phones, laptops, 12v kettle without a problem. So, we can live quite happily not using much electricity.

EG4 6500EX will likely increase your usage substantially. That inverter has a high idle consumption and will eat 30-40% of your stated 100Ah battery capacity, i.e., 90W * 24h = 2.16kWh => 2.16kWh / (4 * 1.28kWh) = 42%.

The inverter idle draw will likely be about 2X your fridge if not more.

 

[TripleDave]

EG4 6500EX will likely increase your usage substantially. That inverter has a high idle consumption and will eat 30-40% of your stated 100Ah battery capacity, i.e., 90W * 24h = 2.16kWh => 2.16kWh / (4 * 1.28kWh) = 42%.

The inverter idle draw will likely be about 2X your fridge if not more.

The EG4 was what I was considering before. The question is about using our existing RV system for our cabin, with it's existing 60A mppt as well as purchasing a 2/3000w inverter.

 

[sunshine_eggo]

3000W on 12V is rough.

3000/12/.85 = 294A = marine grade 4/0 cable from battery to inverter.

Additional consideration I see is powering a stationary grounded/earthed structure with a mobile one. You would need to have your N-G bonded and earthed at the cabin with the the inverter N-G unbonded.

If you select an inverter with N-G unbonded and able to feed a 30A RV outlet with output terminal blocks (L-N-G terminals, not just a 120V 15A "household" outlet), you could "plug in" your cabin to your RV. You would obviously cut the female end of the cord and attach it to your house panel input.

Does this meet code? I seriously doubt it, but the proper grounding and earthing goes a long way to improved safety.

 

[Rednecktek]

So, just to make sure I'm understanding this correctly...

You have a solar setup in the RV that does what you need it to do, but could probably be a little better...
You have a cabin that needs power but you don't want to leave all those expensive parts laying around all year...

Why not just wire in an exterior outlet on the RV and run an extension cord from the cabin to the plug on the RV? The extension cord would feed a breaker box for your lights and outlets inside.

Seems simple, or I'm missing something.

 

[TripleDave]

So, just to make sure I'm understanding this correctly...

You have a solar setup in the RV that does what you need it to do, but could probably be a little better...
You have a cabin that needs power but you don't want to leave all those expensive parts laying around all year...

Why not just wire in an exterior outlet on the RV and run an extension cord from the cabin to the plug on the RV? The extension cord would feed a breaker box for your lights and outlets inside.

Seems simple, or I'm missing something.

Probably is quite simple! In fact it seemed like a perfect solution, I hadn't heard of anyone else doing it, so thought I was missing something! There are exterior outlets on the RV already. I wasn't sure if a typical extension cord would cut it.

 

[chrisski]

I would not use a 3000 watt 12 volt inverter.

I have a 3000 watt 24 volt inverter I ran at 2000 watts for 6 hours straight.

I hard wired a 30 amp plug into the inverter, which I plug into shore power. You could p pop lug that into your cabin.

Please note a 3000 watt inverter is limited to 25 amps at 120 VAC.

 

[Rednecktek]

Get a nice 10awg cable and you'll be fine.

Sometimes the simple answer is the best, even in solar.

 

[TripleDave]

Get a nice 10awg cable and you'll be fine.

Sometimes the simple answer is the best, even in solar.

I like simple! But, the inverter would therefore have to be on 24/7 right? As there would be things like the fridge to power. And everything would have to be AC. So no 12v fridge. I am guessing I would need a fair amount of sun for 2000w inverter and 800/1000w of panels. Winter might be tough and generator would need a lot of use. Having a separate 12v system sounds messy.

 

[chrisski]

I like simple! But, the inverter would therefore have to be on 24/7 right? As there would be things like the fridge to power. And everything would have to be AC. So no 12v fridge. I am guessing I would need a fair amount of sun for 2000w inverter and 800/1000w of panels. Winter might be tough and generator would need a lot of use. Having a separate 12v system sounds messy.

My 24 volt 4000 watt inverter would pull about 24 watts idle draw, so about 600 watt hours a day. My 12 volt 2000 watt inverter pulled about 15 watts, ao 240 watt hours a day. So, depending on loads, most likely will be an issue in the shorter days of the year for 1000 watts of PV panels.

Any decent inverter will show an idle draw in the specs. I'd be cautious of eco-modes which have a higely reduced draw. It will deliver this with no AC load, but if you have an inverter on, there will always be something drawing power taking it out of eco-mode.

 

[Rednecktek]

Any decent inverter will show an idle draw in the specs. I'd be cautious of eco-modes which have a higely reduced draw. It will deliver this with no AC load, but if you have an inverter on, there will always be something drawing power taking it out of eco-mode.

The other issue is that for inverters to come OUT of eco-mode is a pretty high draw. As an example, when I was planning my initial system for my cabin I realized that if I turned on every light in my cabin it wouldn't be enough to take my inverter out of eco-mode and none of the lights would work.

 

[chrisski]

The other issue is that for inverters to come OUT of eco-mode is a pretty high draw. As an example, when I was planning my initial system for my cabin I realized that if I turned on every light in my cabin it wouldn't be enough to take my inverter out of eco-mode and none of the lights would work.

That is interesting. The only inverter I have an eco mode is a 375 VA and the only load I use is a 230 watt crock pot. The crock pot takes that little inverter out with no problems. Never knew it may not come out of eco mode.

 

[Rednecktek]

I was going to use a 3kw 24v Growatt which needs over 50w to come out of eco-mode. I only have 8 6w bulbs on the 120v line, so even every light on only got me to 48w.

 

[TripleDave]

I was going to use a 3kw 24v Growatt which needs over 50w to come out of eco-mode. I only have 8 6w bulbs on the 120v line, so even every light on only got me to 48w.

Ok, so what if I did this: go with 12v, have 400AH of batteries, 1000w panels, 60A Mppt, then added a 2000w inverter and wired it up to my RV to have all sockets usable. Then, connect a normal extension cord to an outside socket of my RV, ran that 100ft to the cabin where it is wired into the sub panel.

This would then power a normal sized residential fridge (will get an energy star), lights, laptops and phones plus the occasional hair dryer (during the day with nothing else on).

How does this sound? Is there anything that should be changed or done differently? And what are the implications of running a normal 15A extension cord, could it be a 30A RV type cord used and if so would it add any major benefits?

 

[Rednecktek]

That plan would work fine. 100ft is a pretty long run so make sure you get a nice 10AWG cable to minimize loss.

 

[chasingentropy]

I like the idea of powering the cabin from the campers solar system however

1. a single 100ft extension cord will not be able to run a hair dryer on a single 15 amp socket with a 100ft extension cord attached. Assuming you have 3kw+ inverter that wouldnt die under the load; you'd still max out your line before any other load was added and probably will trip the breaker.

2. You will need significantly more power storage (batteries) which will be increasing your dry weight, create additional wear on brakes/engine, greater risk of fire, etc...

 

[Rocketman]

since you are considering keeping everything on your RV - take a good look at Victron. Yes they cost a bit more - but they are great for RV’s. The Multiplus 12/3000 has a low 24/7 wattage needs.

I use it on my MotorHome, has been a great inverter.(on 24/7 for 2-1/2 years).

If you decide to stay on your property into the winter - setup another ground solar array - there is never enough solar in winter in the North. You could mount the SCC in your rig - then you are only leaving your panels when you travel.