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

I am in the planning stages for a 400 sq ft off grid cabin in the central Washington mountains. Summers days are long and Sunny. Winters are short and cloudy for days.
There is no electrical grid. I want to go with a 24v system. I have been reading through the forum and still not sure whether it is beneficial to push all the solar generated electrical through an inverter and just use 120v power throughout. Or a hybrid of 12v lighting, USB power points and whatever appliances I can get. 120v, outlets around for the random plugin.

I don't have a TV or microwave. Heating will be wood or propane stove. Hot water via On-demand system. I will need a water pump to get water out of the water tank. I do have a gas generator to top off batteries to support low solar or high usage.

My main concern is the efficiency of converting DC to AC.

Would love to hear pro's and con's of all 120v or hybrid 120v/12v

Thanks,

Don Miller

Welcome to the forum Don. You’ll likely get a few opinions and here’s mine ?.

With the relatively low cost of solar panels I think many folks would just add enough solar production to cover the inefficiency of using 120v for everything. That makes for a much simpler installation.

In a mobile situation with limited solar it’s a different situation.

Being a former Cougar, I am familar with your area. My vote would be forget 12V completely and go with a pure AC system. Am in complete agreement with JH. Large grid-tie panels are now so cheap per watt that very large off-grid systems can be inexpensive.

Take a look at Schneiders 4024 Conext. It makes split-phase 120/240VAC. With a decent sized battery, and about 1500W of panels, you can have a totally comfortable 21'st century lifestyle. Maybe it won't be your first inverter, but it will likely be your last.

I run 12V at my camp and have 2KW inverter just for the fridge when it runs and a 700W for the dishwasher/kitchen appliances. No inverters run all the time. I run a few extra panels and run most things only during the day. Running dual voltages does take some thought.

Diemjoe said:

I am in the planning stages for a 400 sq ft off grid cabin in the central Washington mountains. Summers days are long and Sunny. Winters are short and cloudy for days.
There is no electrical grid. I want to go with a 24v system. I have been reading through the forum and still not sure whether it is beneficial to push all the solar generated electrical through an inverter and just use 120v power throughout. Or a hybrid of 12v lighting, USB power points and whatever appliances I can get. 120v, outlets around for the random plugin.

I don't have a TV or microwave. Heating will be wood or propane stove. Hot water via On-demand system. I will need a water pump to get water out of the water tank. I do have a gas generator to top off batteries to support low solar or high usage.

My main concern is the efficiency of converting DC to AC.

Would love to hear pro's and con's of all 120v or hybrid 120v/12v

Thanks,

Don Miller

Click to expand...

I've been living off griddle for 7 years partially for economic reasons partially to save the planet and partially because the challenge of achieving self sufficiency is a gas.

As I use and grow my solar farm I find that I do most everything with my 120vac inverter and standard 120 volt appliances.

My next step is to increase the DC battery voltage to a more powerful 24 or 48 volts to power a 240vac, (aka split phase), inverter to feed my cabin electrical panel with the same type of power that is provided by the grid.

24 to 12 vdc voltage reducers are available but also use power in the conversion.

90 to 95% efficiency seems to be a good rule of thumb regarding the efficiency of inverting 12 vdc to 110vac.

Regards OG.

Thanks,
I ordered the MPP Solar Inverter yesterday per Will's video. As usual, I learned I saw a video a bit later that raised the concern about its wattage usage. I am still going to go with it though. The money I saved will just go to another panel. I do thnk I am going to go 120v as I sit here. The lumens for 12v ceiling lights seem to have a hard time getting over 300.

JoeHam said:

Welcome to the forum Don. You’ll likely get a few opinions and here’s mine ?.

With the relatively low cost of solar panels I think many folks would just add enough solar production to cover the inefficiency of using 120v for everything. That makes for a much simpler installation.

In a mobile situation with limited solar it’s a different situation.

Click to expand...

Thanks, I have already done a small test shed with both running. Haven't hooked up the 120 yet but the 12v led ceiling lights are a bit dim for my eyes. Are to find low priced higher lumen lights in 12 v. The thing that has slowed me down with the 120v is connection the 2 circuit dist panel to the inverter. Just haven't had the time to dig into doing it safely. The time is near thouogh.

efficientPV said:

I run 12V at my camp and have 2KW inverter just for the fridge when it runs and a 700W for the dishwasher/kitchen appliances. No inverters run all the time. I run a few extra panels and run most things only during the day. Running dual voltages does take some thought.

Click to expand...

I have a small shed that is designed with dual voltages but haven't gotten around to connecting the inverter to the small distribution panel. Just want to do it right and my internet bandwidth is very limited for the research. I think it is pretty easy but just want to make sure.

JoeHam said:

Welcome to the forum Don. You’ll likely get a few opinions and here’s mine ?.

With the relatively low cost of solar panels I think many folks would just add enough solar production to cover the inefficiency of using 120v for everything. That makes for a much simpler installation.

In a mobile situation with limited solar it’s a different situation.

Click to expand...

Yep, I think I'll just add another panel when the time comes. I have gotten used to 12v life but it might take some getting used to any longer term visitors. I am really leaning towards 120v.

MichaelK said:

Being a former Cougar, I am familar with your area. My vote would be forget 12V completely and go with a pure AC system. Am in complete agreement with JH. Large grid-tie panels are now so cheap per watt that very large off-grid systems can be inexpensive.

Take a look at Schneiders 4024 Conext. It makes split-phase 120/240VAC. With a decent sized battery, and about 1500W of panels, you can have a totally comfortable 21'st century lifestyle. Maybe it won't be your first inverter, but it will likely be your last.

Click to expand...

I am on the sunny side of the cascades so solar power is abundant. Especially in the Summer. The short days of Winter will be a challenge but so far, it is a 3 season camp. Maybe someday I'll have it built out for winter.

efficientPV said:

I run 12V at my camp and have 2KW inverter just for the fridge when it runs and a 700W for the dishwasher/kitchen appliances. No inverters run all the time. I run a few extra panels and run most things only during the day. Running dual voltages does take some thought.

Click to expand...

I have a small Cosco cooler that runs off of 12v. I have never tested its power consumption but I am pretty sure the cobbled together solar that I do have isn't enough. I run my bigger trailer fridge on propane and I get about 1 month per bottle. I don't think it runs 12v but haven't checked the manual to confirm.

I was tempted to build out the cabin with all trailer appliances and lighting but so far that is looking like an expensive solution compared to added capacity.

I think 120 volts AC is needed. I think 12 or 24 volts would be fine until you mentioned water heater.

I don’t find low voltage DC a good choice for high wattage appliances both for wire size and for an arcing risk. I think that’s the big reason there’s not an on demand 12 volt heater available. A quick search of “12 volt on Demand Water Heaters“ on Amazon turns up many 240 VAC heaters, but not 12 volts. I didn’t think there was an on demand 120 VAC water heater. The 240 VAC heaters tend to be around 4.5 kw, which 120 VAC is limited to around 2.4kw at 20 amps.

There’s some low voltage DC heating elements for tank heaters, but they might not live up to their advertising.

If you want electric hot water heater on demand, I think you need to design the syste,m around a 4.5 kw 240 VAC heater.

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

chrisski said:

I think 120 volts AC is needed. I think 12 or 24 volts would be fine until you mentioned water heater.

I don’t find low voltage DC a good choice for high wattage appliances both for wire size and for an arcing risk. I think that’s the big reason there’s not an on demand 12 volt heater available. A quick search of “12 volt on Demand Water Heaters“ on Amazon turns up many 240 VAC heaters, but not 12 volts. I didn’t think there was an on demand 120 VAC water heater. The 240 VAC heaters tend to be around 4.5 kw, which 120 VAC is limited to around 2.4kw at 20 amps.

There’s some low voltage DC heating elements for tank heaters, but they might not live up to their advertising.

If you want electric hot water heater on demand, I think you need to design the syste,m around a 4.5 kw 240 VAC heater.

Click to expand...

Thanks, for covering the hot water heater. I havent dug deep into that effort yet. I was assuming the 12v was just to light the propane but need to look again at what's on offer out there.

I thought you wanted to do an electric heating element. The 12 volt lighting element for the propane heater uses negligible power.

WAIT BEWARE of LPG Ignitors.
There are two types used. LPG Appliances can use Pilot Lights (BAD) or Piezo type ignitors which is best. LPG Ovens can have both of those OR a Lighting Element (very power hungry) and fortunately less common and limited to older applianes mostly.

I am OFF-Grid Year Round rural & remote near Algonquin Park Ontario Canada. My System is 24V and 120VAC Only, I use two On-Demand Water heaters (1 dedicated for Radiant Heating a Takagi TH-3M DVP & 1 dedicated for Hot Water only an Eccotemp FVI-12 and my Cookstove is a Unique Classic offgrid range. All of these have ignitors and therefore no wasted energy. The cookstove actually has a "D" Cell to operate it's ignitors !

Money Saving Tips:
There are many very good 12V & LPG appliances in the RV & Boating world, which when brand new can be ridiculously insane in pricing. BUT people wreck the things all the time and insurance companies write them off pretty quick when damaged. Example; I have a separate Power/Pump house which houses my battery banks & solar gear but also my Wellhead & 50 Gallon pressure tank, so it has to be heated in winter which is set to 10°C/50°F. I bought a Suburban NTS-20 12V/LPG Direct Vent furnace which NEW costs about $750 + bits & fittings, for $350 with all the bits, fitting and even the Regulator from a written off wrecked 4 year old RV. (furnace had never actually been used). Cookstoves, Cooktops, Ovens, Fridges, Furnaces for RV's & Boats can work amazingly well. Locate the local RV Sales, Repair & Service centres and see what they got laying around, you may just be in for a Huge Surprise.

REF Links:

Hope that helps, Good Luck

I'd like to add another voice to those recommending the 120v option. I've been off-grid here in Wyoming for three years now and have zero regrets with my decision to to go that route (120vac vs 12vdc). Yes, you will lose a small amount of efficiency passing through the inverter, however, you will be able to widen your choice of appliances and other electrical items available to (less expensively) outfit your dwelling.
My system consists of 2400 watts of paneling, a Midnite Classic 200, 280ah of Lifepo4, and a Schneider Conext SW4024. This provides me with all I need to run a modern, comfortable home. Yes, we do need to be aware of our usage of electricity in the evening but we don't dwell on it to the degree that it's the focus of our existence. We usually have at least a 75% SOC remaining in the morning.
I looked into 12v appliances/lights etc... when preparing for our move off-grid and did not like what I found. I just could not justify the much higher cost and inconvenience of sourcing these items.

chrisski said:

I thought you wanted to do an electric heating element. The 12 volt lighting element for the propane heater uses negligible power.

Click to expand...

Good timing. I was going to take an off-grid break and putting together my Google research list for the coffee shop this morning.

My 2 cents would be to have a hybrid system and get the best of both worlds. There are a surprising number of the "big" appliances that run off of 24V directly like water pumps and fridges. My cottage is a 24V system and my biggest loads more or less are the fridge (which is 24V) and the water pump (which is also 24V). There are a few things which are 12V for which I use a 24V - 12V buck converter to power (like the wireless router, and cellular modem, etc). The rest of the cottage is wired up like a regular house with the panel driven by a 3000W inverter. When I leave, I just flip the inverter off (avoid the standby power loss) and leave the rest of the DC system running. Might not be for everyone but works great for me.

I guess my point is, if you have appliances that can run directly off the batteries, or can easily get those appliances then in my opinion it makes a lot of sense to run those directly off the batteries and get a smaller inverter instead.

Diemjoe said:

I am in the planning stages for a 400 sq ft off grid cabin in the central Washington mountains. Summers days are long and Sunny. Winters are short and cloudy for days.
There is no electrical grid. I want to go with a 24v system. I have been reading through the forum and still not sure whether it is beneficial to push all the solar generated electrical through an inverter and just use 120v power throughout. Or a hybrid of 12v lighting, USB power points and whatever appliances I can get. 120v, outlets around for the random plugin.

I don't have a TV or microwave. Heating will be wood or propane stove. Hot water via On-demand system. I will need a water pump to get water out of the water tank. I do have a gas generator to top off batteries to support low solar or high usage.

My main concern is the efficiency of converting DC to AC.

Would love to hear pro's and con's of all 120v or hybrid 120v/12v

Thanks,

Don Miller

Click to expand...

This is new and I like it. Have older system but if it ever breaks this is the way I'll go next. Just add panels & batteries

45North said:

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

Click to expand...

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.

12VoltInstalls said:

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.

Click to expand...

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!

RStone13 said:

This is new and I like it. Have older system but if it ever breaks this is the way I'll go next. Just add panels & batteries

Click to expand...

Sorry forgot to include link.

pvnick said:

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!

Click to expand...

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.

12VoltInstalls said:

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.

Click to expand...

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.