Off-Grid Cabin - 120v AC and/or 12v DC buildout?

12VoltInstalls

Solar Addict
I vote for the hybrid system - 12vdc as much as possible and invert to 120ac only when necessary if battery is up for it.
I have no cabin and no practical experience (other than my little hobby system where the inverter proved to be a real hog!) but I always thought this was the way to go to avoid inverter losses.

My approach would be:
  • fill the S-facing roof with panels (assuming you don't want to get into ground mounting panels)
  • determine how much power these panels could support
  • reduce expectations and live within the restrictions of available power
I’m with this thought.

I run 12V lights but I use dual diode lensatic flood lights. Multiples (they are inexpensive) but for example just one over the stove is sufficient but others can be turned on by separate switches. If big light is needed I have low profile RV led ceiling lights.
I’d suggest buying to charge at 48V into a 12V bank. Then use as much 12V as possible.

I’m going to break that tradition this winter.
In summer I can run an electric fridge fine. I’m going to add panels and a couple more batteries and try electric fridge this winter. So I’ll need to insure enough for the inverter inefficiency as well as battery headroom and the additional Ah I will need.
I am going to rig a one-wire internally regulated GM alternator with a cheapo HF gas motor for the November/December cloudy period for just in case. That’s 80A of charge availability if I need it- retail generators are terrible at charging 12V imho. Not efficient, low amps.

there’s just so many great 12V items at a decent price from the marine and RV world I’m not ready to jump to all 120AC or 24V battery bank. However I can see how 48V from the panels could be a benefit.
 

pvnick

New Member
I’m with this thought.

I run 12V lights but I use dual diode lensatic flood lights. Multiples (they are inexpensive) but for example just one over the stove is sufficient but others can be turned on by separate switches. If big light is needed I have low profile RV led ceiling lights.
I’d suggest buying to charge at 48V into a 12V bank. Then use as much 12V as possible.

I’m going to break that tradition this winter.
In summer I can run an electric fridge fine. I’m going to add panels and a couple more batteries and try electric fridge this winter. So I’ll need to insure enough for the inverter inefficiency as well as battery headroom and the additional Ah I will need.
I am going to rig a one-wire internally regulated GM alternator with a cheapo HF gas motor for the November/December cloudy period for just in case. That’s 80A of charge availability if I need it- retail generators are terrible at charging 12V imho. Not efficient, low amps.

there’s just so many great 12V items at a decent price from the marine and RV world I’m not ready to jump to all 120AC or 24V battery bank. However I can see how 48V from the panels could be a benefit.

Agree 100%. It would be awesome IMO to have a completely DC system. I strongly considered that when we started building but there were a couple things that held me back:

1) If you're wiring up a full house @ 12V then the voltage drop on the long runs become a concern which means you would often have to up the wiring size ($$)

2) A system like that is deviating very far from a conventional house electrical system. Basically the protection features you'd be required to have (depending on your region ex: GFCI, AFCI) are not *really* interchangeable. So if you commit to it there's pretty much no changing your mind unless you're prepared to go through the massive hassle of tearing out drywall, etc.

3) Even if you get an inspector / electrician to rubber stamp your design, the insurance companies will see that it is not 100% to the letter exactly identical to every other system and ask you to take you your wallet and give them all of your money.

4) There still are some modern conveniences that are difficult to map into the 12Vdc world. For example all the different power supplies you have for phones / tablets, etc.

Like you said though, there is a lot still available in the DC world though. My fridge for example (Unique UGP-470L1) despite being similar (maybe the same) size as my 120 VAC fridge at home appears to be quite a bit more efficient.

tl;dr : Hybrid system FTW!
 

12VoltInstalls

Solar Addict
Agree 100%. It would be awesome IMO to have a completely DC system. I strongly considered that when we started building but there were a couple things that held me back:

1) If you're wiring up a full house @ 12V then the voltage drop on the long runs become a concern which means you would often have to up the wiring size ($$)

2) A system like that is deviating very far from a conventional house electrical system. Basically the protection features you'd be required to have (depending on your region ex: GFCI, AFCI) are not *really* interchangeable. So if you commit to it there's pretty much no changing your mind unless you're prepared to go through the massive hassle of tearing out drywall, etc.

3) Even if you get an inspector / electrician to rubber stamp your design, the insurance companies will see that it is not 100% to the letter exactly identical to every other system and ask you to take you your wallet and give them all of your money.

4) There still are some modern conveniences that are difficult to map into the 12Vdc world. For example all the different power supplies you have for phones / tablets, etc.

Like you said though, there is a lot still available in the DC world though. My fridge for example (Unique UGP-470L1) despite being similar (maybe the same) size as my 120 VAC fridge at home appears to be quite a bit more efficient.

tl;dr : Hybrid system FTW!
I never indicated going DC exclusively. I have a 1200W true sine inverter.

2) the GFCI and AFCI 120V distribution safety elements will work fine on solar- going solar doesn’t mean throwing out the NEC. (In my case the inverter is feeding a panel- GFCI in between. Not “normal” but it added an element of safety I thought was a good idea.)

1) distance losses: for led lights and usb charging ports the distance(s) in a small or normal house are not an issue in practice. The loads are small and the DC is stepped down.

3) what exactly is deviating? Just do it to code. There’s been ul listed dual box/covers for high voltage / low voltage for twenty years. There isn’t any ‘getting an inspector to rubber stamp’ anything differently than any other project they deal with every day.

my point was in the poster’s circumstances I thought handling basic simple things with 12V made sense. Lighting at 12V is often a no-brainer.
 

pvnick

New Member
I never indicated going DC exclusively. I have a 1200W true sine inverter.

2) the GFCI and AFCI 120V distribution safety elements will work fine on solar- going solar doesn’t mean throwing out the NEC. (In my case the inverter is feeding a panel- GFCI in between. Not “normal” but it added an element of safety I thought was a good idea.)

1) distance losses: for led lights and usb charging ports the distance(s) in a small or normal house are not an issue in practice. The loads are small and the DC is stepped down.

3) what exactly is deviating? Just do it to code. There’s been ul listed dual box/covers for high voltage / low voltage for twenty years. There isn’t any ‘getting an inspector to rubber stamp’ anything differently than any other project they deal with every day.

my point was in the poster’s circumstances I thought handling basic simple things with 12V made sense. Lighting at 12V is often a no-brainer.
I think you're misunderstanding me. I was simply saying that I agree with you that a hybrid system makes sense and that there's a lot of DC appliances out there which IMO makes sense to use if you can. I agree with you again WRT the lighting. Mine are on an AC circuit but in hindsight I wish I had got some DC lights instead.

The rest of the discussion I think you were under the assumption that I was accusing you of... something, but I wasn't, I was simply explaining what happened in my situation, and why I ended up with a hybrid system, which it seems we're both advocating for anyway...

To anyone else who understood me as saying that either you should be "throwing out the NEC" or that it is not possible to comply with it for a solar system, that's not at all what I was saying. I was saying that in my region (Canada) if you wanted to wire up a house with 100% DC only (as I was thinking of doing originally) I think you would have a bit of a challenge getting that system to map into what the code requires. One thing I was alluding was with the required safety features, for example, in my area it says that receptacles in bedrooms and living spaces are required to be on an AFCI circuit. I don't know if you can even buy a 12VDC AFCI circuit breaker (maybe you can?) but in my case it seemed easier to wire up the house as a standard AC electrical system and feed the panel from an inverter. I also have some DC circuits on the side for fridge, pump, etc. That's what worked for me and that's why I ended up there.

Since the original question is essentially do I go 120VAC or 12VDC my answer is, I did both, turned out great, so I recommend that.
 

SS294

New Member
We have a 400 sq ft cabin off grid with a 960 watt system. I went with 120v for everything mainly due to the distance from the solar system to the cabin. Solar is installed on a shed roof in a field and cabin is in the woods, Cheaper and easier to run the 200' of cable for 120v ac than 24 v dc. Controller, inverter and battery bank are in the shed. Also easy to just use standard household fixtures and wiring in the cabin. Concerning conversion losses, just put enough panels up so it doesn't matter and don't worry about it. We run a 10.2 cu ft Magic Chef fridge, ceiling fans, small microwave, tv, 120v seaflow waterpump, led lighting and occasional power tools. Doesn't really even tax the system, though we only use the cabin from spring to fall.
 

12VoltInstalls

Solar Addict
10.2 is a good size. What’s the watts?

The retail stores have the stupid government/EPA energy label on their websites which means NOTHING to me.
I did find a 4 CF with a .8A motor label in a store but I really want around 7CF and “345kW Annually” tells me nothing I need to know. Other than ‘maybe’ they think it needs 1000W a day.
 

Q-Dog

¯\_(ツ)_/¯
10.2 is a good size. What’s the watts?

The retail stores have the stupid government/EPA energy label on their websites which means NOTHING to me.
I did find a 4 CF with a .8A motor label in a store but I really want around 7CF and “345kW Annually” tells me nothing I need to know. Other than ‘maybe’ they think it needs 1000W a day.
My refrigerator Energy Star label number, divided by 365, equals 1.21 kWh per day. Running that same fridge through a Kill-a-watt meter for a few weeks also gave me 1.2 kWh average use per day. The Energy Star rating works just fine and is a good place to start.
 

chrisski

Photon Sorcerer
My refrigerator Energy Star label number, divided by 365, equals 1.21 kWh. Running that same fridge through a Kill-a-watt meter for a few weeks also gave me 1.2 kWh average use per day. The Energy Star rating works just fine. What more info do you need?
I gotta ask, do you think that fridge works a lot harder in the summer?

For my usage, I'd expect 1.7 kw in the summer, and .7 in the winter based off temps.
 

Q-Dog

¯\_(ツ)_/¯
I gotta ask, do you think that fridge works a lot harder in the summer?

For my usage, I'd expect 1.7 kw in the summer, and .7 in the winter based off temps.
My refrigerator is inside a house, in conditioned space, so no I don't think the difference between summer and winter is significant. It likely runs harder during the spring when I open windows and the humidity is higher inside the house.
 

Mr.Michael

New Member
Our off-grid farm house runs of 24V LifePo4, 1000W used panels and 2 inverters, 40A MPPT. All continuous loads are on 24V except the DSL modem that is on a step down power supply for 12V. You can find decent 24V LED ceiling lights as well. Our fridges run off 24V, the larger one as a fridge and the smaller one as a freezer. We got a small 150W inverter that is used to charge the power tools and the laptop - only one at a time. This inverter also has 3 USB ports including one fast charge port. We only turn on the larger inverter when needed. The larger inverter is 1500W pure sinewave and is used mostly for the induction cooktop, bread maker and hot water kettle. Basic goals we had:

Lowest possible idle consumption - with DSL modem and small inverter in idle about 20W or 750mA
Sufficient power for induction cooktop and kettle
Low noise
Low cost ($50/panel and used APC UPS as 1500W inverter)
 
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SS294

New Member
10.2 is a good size. What’s the watts?

The retail stores have the stupid government/EPA energy label on their websites which means NOTHING to me.
I did find a 4 CF with a .8A motor label in a store but I really want around 7CF and “345kW Annually” tells me nothing I need to know. Other than ‘maybe’ they think it needs 1000W a day.
I mistyped above. It's the 10.1 Magic Chef you can get at HD. It's rated at 297 kwh per year so about 0.8 kwh per day (divide by 365). I've never put a kill-a-watt meter on it (cause mine is back home in SC), but I would say that rated value is pretty accurate. When we were looking for a fridge for the cabin, I found that this model was as efficient or more efficient than the smaller dorm fridges we checked on. Couldn't see the need to go with a super efficient (and expensive) "solar" rated fridge. PV panels were cheaper. I can tell you that our average electrical use at the cabin is around 1.2 kwh per day for everything this time of year in NY state.
 

12VoltInstalls

Solar Addict
0.8W. That’s great!
I found one 4.5cf in a store that had .8A on the power sticker but 4.5 is tiny. I’m going to look into the one you have. There used to be a 7.2cf single door with freezer that would go on sale @ Home Depot for $250ish but apparently that ain’t a thing anymore. I guess they got a lot of returns because it didn’t defrost. But that would work for me!
My propane RV fridge is fine now that I cleaned dead bugs out of the burner and it’s out there for sale. If it comes down to it the 4.5 is only $167 and I could deal until a 10.2 is on sale.
 

ken morgan

Solar Addict
I have a 900ish square foot cabin that I run totally solar, nothing fancy that I run totally AC with. my first project (10 years ago) was a camper that I ran mixed AC and DC in at the time finding 12 volt items was pricy though I did spring for a 12 volt Engel fridge made by sawfuji electric that, plus lights, water pumps etc were all 12VDC. but my microwave, A/C were both AC on a 2k magnum along with a smaller 300 watt samlex inverter for computer and cell phone charging. I only turned the magnum on for the microwave or the AC. other than that it was the samlex or DC power. you spend as much money adjusting for voltage drop with DC appliances as you do to simply buy a bigger inverter and run it all AC. obviously their are some items where the electrical break even made sense, such as the engal refrigerator. but the cost of the engel was up there so high that the monetary break even was not there. In reality a normal compact high efficiency "dorm" fridge would have been the best bet.

spend more time thinking about ways to save energy... its easier to reduce use than it is to create power. take a high efficiency fridge and surround the sides with 4" foam (except for the heat rejecting side of course), put a small fan on that side or bolt a cheap heat sink to it to make it more efficient. Use LED lights. run yor water pump DC because you can put your pump room next to your power room and use short DC runs to it. (If the cost of the DC pump is not exorbient) and lastly use 48 volt inverters... more efficient and less power wasted, smaller cables are OK. etc.

in a nutshell I dropped my power comsumption at my cabin by 40% over two years of trying and playing around. simple things like better insulation... a wood stove vice gas heat, an on demand propane heater that is indoors but ducts its exhaust out so no need for a heating circuit to keep it from freezing in the winter...little things add up fast and you will have more fun chasing them down then you think.

R

Ken
 

TItreasure

New Member
Hi there - I’ve been searching for more information on 12V solar systems as we recently purchased a small cabin that is entirely wired with 12V DC. Fridge, stove, hot water all run on propane. There is one small inverter box that has the “cigarette lighter” end and then two outlets. We’ve been using that to charge phones, plug in a small TV, etc.

I’ve tried searching the web and this forum and I haven’t had any luck with this specific question. My apologies in advance if this is very basic.

There are several regular/conventional looking outlets around the camp that are labeled “12V DC”. What exactly can be plugged into those? The only inverters I’ve seen are either battery clamps or the cigarette lighter ends. I guess I don’t understand why those were wired in....

Thank you!
 

chrisski

Photon Sorcerer
My GUESS is whoever did your cabin wired those outlets 12 volts. Don't recommend plugging anything in until tested.

You could also test these with a multimeter.

There is no standard for a 12 VDC. With 120 VAC socket, there is. If that's what the prior owner did, I think choosing a 120 VAC socket is a poor idea. Potential to be dangerous when plugging appliances into the wrong socket voltage.
 

chrisski

Photon Sorcerer
Yes. Unless you want to rewire your 12 volt appliances with standard 12- VAC cords, which I think is dangerous. Especially if you lend the cabin out and people don't realize that.

I have a 12 volt line I added to my RV, but I only added USB sockets and direct wired lighting. I think 12 volt appliances have there place, but most are not made for quick disconnect. The cigarette lighter is popular in cars. SAE connectors are another option. That's only if you want to keep them.
 
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