N1ESE's 2023 Cabin Build

[N1ESE]

Hi new friends.

Five years ago, I moved to the Missouri Ozarks to begin living an off-grid lifestyle in the woods. Up until September of 2021, I was living a very primitive off-grid existance on some very remote 5 acres that was difficult to access. It was fun and I finally upgraded from living outside to living in a cabin with a 12V 600W solar system with a roughly 420Ah battery bank using 6V golf cart batteries wired series-parallel. However, I wasn't truly happy on this property and moved back to town a year ago. Now, after a year, I've finally rebooted myself and have purchased new land closer to town, with much easier access, and a much larger clearing already established for better solar potential. I'm going to learn from my mistakes of the past and build smarter this time around.

My cabin is going to be roughly 192 sq. ft. and I plan to insulate it very well (probably spray foam), top to bottom, and use quality windows. Heat will be from a wood stove.

Three key requirements I did not think I needed last go around but definitely want this time:

• 7 to 10 cu. ft. freezer
• Smaller refridgerator (milk, egg, butter, some veggie storage)
• Air Conditioning

I'd been debating air conditioning for quite awhile but I think it's going to have to be a requirement. At the new place, my cabin will be out in the sun a lot more than my old property. This past summer has been hotter than my previous years in Missouri, we had several long spells where we stayed above 100F degrees. Although I'm still thinking about a 9,000 BTU mini-split, I am currently leaning towards a Midea 8,000 BTU inverter window AC, Will Prose has one and really likes it. I like the idea of a mini-split in a tiny cabin but I don't need the heat portion and, if I wanted to heat with it, I'd have to size my solar system much larger than it would need to be for just cooling in the summer.

Most of the remaining electrical requirements will be mostly ham radio and tiny computer gadgets and some lighting with some small, low voltage, water pumps here and there. No microwave oven, no toaster, no air fryer or hair dryer, none of that crap. I've lived without that stuff for awhile, don't need it going forward.

My current dilema is trying to figure out what size battery bank to go with. I use the ham radio and computer gadgets 8 to 10 hours a day and all of it runs off of 12V or 5V at very low current draw. A large capacity 12V bank would seem to make sense until I factor in the fridge, freezer, and/or AC during the summer and I don't know if I want to run a handful of DC-DC coverters for all of my low voltage stuff.

Would appreciate any thoughts/advice about anything above. I'm going to try and keep this thread going as a journal as I start building the cabin over the next couple of months.

 

[Rednecktek]

Well, I'll start the default answer to these questions and we can work from there. Here's you To-Do list:

1: Power audit! This will give you some important information on how big your inverter needs to be as well as how much battery capacity you'll need. There is a link in the FAQ section (I think, or someone here will post it shortly) so fill in the blanks and see what it comes up with. You'll probably need some sort of Kill-A-Watt to get accurate measurements. Are you going to be running a 12v system? 24v system? 48v system? What are the specs on your solar panels? VoC? Vmp? Being as this is a new build, throw together a wish list of what you want and estimate on the high side.

1a: Where do you live? Speccing out a system for Scotland is a LOT different numbers than Arizona due to the amount of light you actually get. Someone here can post the link to the PVwatts.com or JCR Solar Uber-Sun-Hours calculator sites to help figure out how much you'll have to work with. That will be a box in the Power Audit form.

2: Parts list: You don't need a make & model list, just a parts list to start from for reference. You'll need an inverter, a MPPT charge controller, fuses, shunt, buck converter, batteries, wire, etc. Once you have a basic list it can be fine tuned to make & models after that. If you're looking at the All-In-Ones check for correct voltage outputs (120v or 240v Split Phase for North America, 220v Single Phase for European type areas) and make sure it has enough capacity for a little bit of growth and fudge factor.

3: Budget!: Steak is great but doesn't mean anything if your wallet says hamburger. Figure out what you're able to spend now vs what you'll have to cheap out on now and upgrade later.

4: Tape measure! Figure out where you're going to stick all the stuff you'll need. A dozen 3000AH batteries sounds great until you're sleeping on the floor because there's no room left for a bed. Is there a compartment that can house all this stuff? Will the server rack batteries fit? Are you going to have to make space? Physics can be pretty unforgiving.

5: Pencil out what you think you need and throw it at us so we can tell you what you've missed (because we ALL miss stuff the first go-round ) and help figure out which parts and pieces you're going to want to get.

 

[N1ESE]

Well, I'll start the default answer to these questions and we can work from there. Here's you To-Do list:

Did you read my post? lol This isn't my first rodeo, been here with a lot of this stuff before. I am in an early pre-planning stage, the cabin is still being planned out on graph paper.

 

[Rednecktek]

Yup, but my advice still stands. Having a correct-ish power audit and a tape measure seem to be the two biggest factors at this point, and knowing how big your inverter is going to need to be are really really important, especially with the AC involved. By the sounds of it a 3Kw system should provide plenty of power and startup surge capability for your cabin, but since you're still planning it all out you can still easily factor in the physical aspects of where you're going to stick everything.

If you have the space AND environmental stability for LFP batteries then going with a 48v system is going to be your best bet. However, if your cabin is anything like mine it gets well below freezing at times and you'll need to go with some flavor of lead acid which is going to take up a LOT more space for similar capacity. At less than 200 square feet you don't have a lot of space to play with unless you plan in a utility shed or the like.

Speaking of which, what's your water situation going to be like? Do you need to plan in for a well pump or shallow jet pump? 120v or 240v?

As to the air conditioning, I just spent 3 weeks at my cabin during a "record heatwave" and my 300sq ft cabin was kept pretty nice with a cheapie 8k BTU unit, so I think a 9k would be plenty. If you can spring and fit a mini-split the power efficiency will make up for itself pretty quick. My cabin was using about 6Kwh/day keeping that window unit going as a point of reference.

So yeah, I'd say shoot for a 48v setup if you can fit it, a 3Kw inverter, all the solar you can fit in the yard, and a mini-split. As for how much capacity, that's going to entirely depend on what the power audit has to say.

 

[N1ESE]

Speaking of which, what's your water situation going to be like? Do you need to plan in for a well pump or shallow jet pump? 120v or 240v?

Mostly rainwater collection and hauling in from a couple miles down the road for the first few years while I'm still young enough to deal with the hassle. A well is planned to be drilled maybe five or six years down the road.

I think I'm pretty much settled on a saddle style window AC unit. Either the Midea 8,000 BTU (about 725W) which uses inverter technology so the initial surge current is very low or there is the Soleus 6,000 BTU unit (about 500W) but it's going to have a higher surge requirement. Here in Missouri, I'll mostly be running it during the day when the sun is out unless it's super humid at night when I may only run it in "dry" mode. The Midea is $400 and the Soleus is $550.

 

[Rednecktek]

Either of those units should be well within the limitations of a 3Kw inverter so good to go there. Once you get around to the well portion of the place, plan on finding something like a Groundfoss that is going to be solar friendly and you should still be good to go.

If you go with a 48v setup right out the gate then if in the future you find that your well is super deep and needs 240v it's easy enough to get another inverter or upgrade the one you have rather than having to change out charge controllers and battery banks and the like.

The physics is still going to be an issue though, a utility shed to house all the stuff and then just feed AC to the cabin might be a viable option. As for the DC-DC converter, just getting 1 large capacity one for a 12v bus system should be plenty. I'm doing the same thing at my cabin to feed all my 12v stuff and it wasn't all that expensive to just get a single large converter and take it between the DC and the fuse block.

 

[MichaelK]

Based on the experiences in my own cabin, I'll fast-track things a bit and tell you I think you'll need ~3-4kWh of power per day, excluding air-conditioning. Add air-conditioning and that number basically doubles.

Since there's the discussion of the future well, and needing a well-pump, then 48V is the best choice. I could envision an incremental upgrade path, with adding extra panels, larger batteries, ect as time goes by.

Starting small, you could go with a 48V bank of 6V golf-cart batteries. Assuming you don't want to drain more than 50% that's 210Ah X 48V X 50%= 5040Wh, or 5 kWh of power. That might get you through a day of cloudy weather before the batteries get seriously low.

To adequately charge that size battery, you want to charge at 1/8th of C. The math works out to be (210Ah/8) X 50Vcharging X 1.175FF = 1542W of panels. The FF stands for fudgefactor, with 1.175 being the reciprocal of 85%, which is what I've measured most panels real-world production at. So, six 250-260W grid-tie panels will put out that level of power. I can get those for 75$ each right now. They could be wired 3S2P to work with any 150V charge controller. A 50A controller could handle that power level effertlessly, but allow for future expansion. Look at Epever's 5415AN, or 6415AN.

So, assuming you get 2.5sunhours in winter, and 5 sunhours in summer, that will give you ~3.75 to 7.5 kWh of power between winter and summer.

Instead of a window air-conditioner, I'd recommend you look at wall-mounted units. That what I did for my own cabin. My wall unit is 8000BTU, and draws about 750W at startup. The wall unit is better than the window, because on evenings when it cools down, you can simply shut off the AC, and open the windows. That's harder to do with a window-mounted unit.

As time goes by, you can increase the size of your battery, either by adding parallel strings of the same make/model, or turning them in for a bigger size. You want to upgrade your solar first, BEFORE you upgrade the batteries. Don't add a parallel string to batteries that are more than 1 year old. Then the new batteries will get dragged down to the performance level of the old string. Better to trade them in for a bigger size, say Trojan L-16s.

Now the inverter. With everything besides the well-pump, you really only need a 1500-2000W inverter. With the well-pump, maybe a 4000-5000W inverter. You might get by with a Samlex PST-1500W for a while. To run a well-pump though you need a low-frequency transformer-based inverter. A Conext SW4048 could power a 240V well-pump as large as 1/2hp. It has split-phase 120/240V AC, can surge to 7000W for 5 seconds, and has a built-on generator charging circuit.

Once you are consuming more power, you can add a duplicate set of another 1500W of panels if you like. Bringing your array to 3000W will generate a lot of power for you.

 

[N1ESE]

Since there's the discussion of the future well, and needing a well-pump, then 48V is the best choice. I could envision an incremental upgrade path, with adding extra panels, larger batteries, ect as time goes by.

Instead of a window air-conditioner, I'd recommend you look at wall-mounted units. That what I did for my own cabin. My wall unit is 8000BTU, and draws about 750W at startup. The wall unit is better than the window, because on evenings when it cools down, you can simply shut off the AC, and open the windows. That's harder to do with a window-mounted unit.

I'm not even going to begin thinking about the well at this point. It is too far off in the future and may not even happen at all.

Regarding window AC units, your comment is why I'm looking at saddle style units like the Midea, Soleus, or GE Clearview so I can still open the window. I also really like the Midea because of it's inverter compressor.

 

[littleharbor2]

I may have missed it while reading through but I have to ask. With such a small structure will you have enough room on the roof for the amount of solar panels you will need? Being a remote cabin, I can't imagine a ground mount array. About the only way I can see to have enough roof would be to build a single plain south facing shed roof.

 

[N1ESE]

I may have missed it while reading through but I have to ask. With such a small structure will you have enough room on the roof for the amount of solar panels you will need? Being a remote cabin, I can't imagine a ground mount array. About the only way I can see to have enough roof would be to build a single plain south facing shed roof.

There's plenty of open field for ground mounted panels.

 

[JoeHam]

I would suggest a 48V nominal system for general power needs and a 12V nominal system for ham radio needs.

I do that myself and have been happy with it. A 12V 100 Ah battery with a cheap panel and MPPT should run the radio shack fine. I even take that portable for Field Day etc.

You will definitely want a 48V system to run an Air Conditioner and other AC loads IMHO.

I’ve found that a buck converter on 48V wastes too much power and it’s so easy to have an additional 12V setup.

Just another way to skin that cat.

 

[littleharbor2]

There's plenty of open field for ground mounted panels.

No worries with getting the panels stolen?

 

[N1ESE]

I would suggest a 48V nominal system for general power needs and a 12V nominal system for ham radio needs.

Yeah, I've been thinking about this as well. Thanks

 

[N1ESE]

Adding this data here for cabin planing and future reference. * Sun hours based on south facing and year-round 30 degree tilt.

Your optimal year-round tilt angle:
30.1° from horizontal
Your optimal tilt angles by season:

• Spring: 30.1°
• Summer: 15.1°
• Fall: 30.1°
• Winter: 45.1°

Your optimal tilt angles by month:

• January: 40.1°
• February: 35.1°
• March: 30.1°
• April: 25.1°
• May: 20.1°
• June: 15.1°
• July: 20.1°
• August: 25.1°
• September: 30.1°
• October: 35.1°
• November: 40.1°
• December: 45.1°

Your annual average:
5.25 peak sun hours per day
Your monthly averages:

• January: 3.95
• February: 4.32
• March: 5.2
• April: 5.72
• May: 5.91
• June: 6.44
• July: 6.45
• August: 6.36
• September: 5.75
• October: 5.11
• November: 4.29
• December: 3.45