Help planning off grid cabin/tinyhouse solar system

[hornet136]

So, tell me how you would do it.. I have some ideas but want some other perspectives.

We have a few acres of bare ground in the mountains where we have been managing well for years in a run down camp trailer with a single 12v deep cycle marine battery that I charge one or two times a year. It runs the lights, and an RV water pump, nothing more.

I am building an 8'x20' cabin (this size since its on a trailer frame that will, however, not be mobile). Its really more of a glorified tent as it is simply a bed, few chairs, a small stove and a small kitchenette. We will use it 3 seasons and little if any in the winter.

The desire is to have a few lights (4-5), a few 110 outlets for charging laptops, some USB outlets for phone charging, and an RV pump for kitchen sink.

Additional possibilities if we go crazy would be a small 12v fridge/cooler, and maybe the occasional random AC appliance. We don't have TVs or Internet here so an inverter would get used a bit but not on a regular basis.

Since I'm building this myself, should I just wire it up all AC and use an inverter off of solar charged batteries, or should I go with a mixed DC/AC system?

I thought about going with DC lighting, USB charging, and pump for the sink. Then have a run of regular romex and AC outlets on an inverter. It seems however with the limited lighting options for DC I might be able to just do it as a whole AC system and just run off of an inverter.

I currently have the following to start with:
* Crusty first gen Harbor Freight solar system
* 1 12v lead acid (Interstate srm-29) deep cycle marine battery
* Honda eu2000i generator
* Xantrex Xpower 1000 inverter (1000w)

I was thinking about purchasing:
* Renogy 100w 20A kit with bluetooth module OR maybe an MPP 1012LV-MS 1000w 12v MPPT 40A all in one.
* A couple 1'x1' 12v LED panels for the ceiling (35w each)

Aaand thats about as far as I got before I started overthinking it all......

So.. All AC via solar->batteries->inverter or do some mix of AC and DC wiring in the walls. Or other?

Thanks all!

 

[Craig]

I have a similar situation. I chose to do a mix of AC and DC. Honestly I still do not know if it really matters.

Here is what I have

DC

• All lights
• on demand water pump
• all phone charging
• router
• cameras

AC

• Power for Inflatable air mattresses
• Power for instant tank less water heater. uses AC for fan and ignition, gas for fuel
• coffee pot (we used to boil water in a old fashioned perk pot but the electric ones are so much easier.
• occasional large power tools needed for building
• charging cordless tool batteries
• Chest freezer

I can easily run all of this off of a 150Ah 24V battery in the summer fall and spring. In the winter not so much I have quadrupled my solar array and doubled my batteries for winter the main problem I have is I am on wrong side of mountain for winter and get maybe only 1 or 2 hours of sun on a good day.

I have 2 tiny house buildings (glorified tents as well) both 12x16 one has a shower and a kitchen sink the other is a bedroom and storage.
I have led lights everywhere hey hardly use any energy. The only thing I have to be careful with is the Coffee pot but since I added storage and panels this last month I had no more problems

I am not a fan of renogy but if its in your price point I dont hate it either

12v will work fine but if you ever plan on expanding look at 24v as well. I started with 4 wal mart deep cycle batteries that served me well for a few seasons but they do wear down fairly fast and I probably was over using them.

 

[MichaelK]

At my own cabin, I started out similarly, with a 12V Xantrex 1000W, and a couple of Harbor Freight sets. I very quickly observed the limitations of what Harbor Freight is capable of, and quickly upgraded two more 150W panels. This was OK for a couple of years. It kept a couple strings of Trojan T105s fully charged. As more and more finishing work on the cabin was completed, I got it hard-wired for 120VAC and tried connecting the Xantrex to the main electrical panel (see horrid pic). It sort of worked, though I did see flickering at some light fixtures. Don't let an inspector ever see something like this!

Once completed though I upgraded to 48V, and got a very nice Schneider 120/240V inverter that has performed much better. It can handle anything I throw at it, including a toaster oven and my 240V well pump. Unless you yourself have a well pump, I would not recommend going to 48V, though I think you should seriously consider upgrading to 24V once your cabin is complete. Especially if you want to run a refrigerator, you'll have fewer headaches at 24V than 12V.

The best, really serious off-grid components start at 24V. Solar panels have dropped in price to the point that they are now the cheapest component in your system, and I think you'd be better off in the long-run giving up 12V for your cabin, and wiring the whole cabin just for 120VAC. Serveral tier-one companies like Outback, and Schneider make code-compliant 120/240VAC systems that seamlessly wire into the main electrical panels of homes/cabins. That's how my 48V system is now wired. There are a lot of people out there that seem to religiously cling to 12V, but unless you're on wheels, you'll benefit from a voltage increase.

 

[OffGridIdaho]

Off grid tiny cabin (650sf) North Idaho for 5 years now. After trying a lot of stuff that didn't work (and doing a ton of research!!!) I can tell you what my system will be when I get the cash. Our current system is in my nfo.

Morningstar Tristar MPPT 60A CC (made for government remote mountain top sensor locations---BULLETPROOF) Programmable
Magnum 4000w 24/48v Inverter/charger (feeds main panel in cabin for 110v to house)
6 or 8 x 350w solar panels (we have clouds so I need extra wattage) Run in series and parallel
Midnite combiner box (allows me to flip breakers for added panels during clouds and rain)
10g solar wire
Midnite breaker box
LIPO battery bank 24/48v
Grundfos SQ well pump (only draws 7.5a start and run)
1200 gallon Cistern (Mono tank with lid not split tank with seam half way)
80g Pressure tank for pressurized water filled from cistern by grundfos
12v aux out usb bank to use as charging station for phones/tablets
Jetboil coffee press system (makes 2 cups of fresh hot coffee with no drain on my batteries early AM)
Englander 2000sf wood stove (massive firebox and 1/4 inch steel retains heat for 5hrs) We burn a small fire to warm the stove and then enjoy residual heat for hours.

 

[Stiffmeister]

It was mentioned that solar panels are the cheapest component. I have an Outback 7.2kw inverter and the so called experts said that 24x300w panels is the correct match. Well panels never make their rated numbers. Now I'm running a Midnight Solrar MNPV12 with 36x300/310/330 watt panels using two Outback FlexMax80 charge controllers. The charge controllers will protect themselves maxing out at 80 amps so you do the math with your voltage setup. I'm now a firm believer of extra panels because they are cheap. The expensive part is the pure sine wave inverter. Now that I have the Outback 7.2kw...I may try to clone what they did on their pre-wired setup. Oh, batteries are the ShunBin LiFEPO4 batteries off Amazon.

OffgridIdaho, did you do your research on that Grundfos SQ well pump? I need one but have not started comparing yet. How does the pressure tank work? I need to solve this problem. Down in Cabo San Lucas and these construction guys don't really know much about solar/efficiency/etc.

 

[OffGridIdaho]

It was mentioned that solar panels are the cheapest component. I have an Outback 7.2kw inverter and the so called experts said that 24x300w panels is the correct match. Well panels never make their rated numbers. Now I'm running a Midnight Solrar MNPV12 with 36x300/310/330 watt panels using two Outback FlexMax80 charge controllers. The charge controllers will protect themselves maxing out at 80 amps so you do the math with your voltage setup. I'm now a firm believer of extra panels because they are cheap. The expensive part is the pure sine wave inverter. Now that I have the Outback 7.2kw...I may try to clone what they did on their pre-wired setup. Oh, batteries are the ShunBin LiFEPO4 batteries off Amazon.

OffgridIdaho, did you do your research on that Grundfos SQ well pump? I need one but have not started comparing yet. How does the pressure tank work? I need to solve this problem. Down in Cabo San Lucas and these construction guys don't really know much about solar/efficiency/etc.

Grundfos are one of the best well pumps made. I have mine sitting on its side about 12" off bottom of cistern. For now we haul water from a local free well in the town. The cistern lasts 1 month of conservative water use and 3 weeks of gardening and animal water.

So in a nutshell.......

Cistern has grundfos internally. Cistern is down 9 ft below surface at bottom and 1ft at top. Cistern never freezes. Water line is down 8ft below surface and runs to our cabin. Pump has backflow checkvalve and I also installed an inline checkvalve to prevent back flow.
Pump feeds pressure tank in house that has a pressure switch. When pressure hits 30lbs water tank fills till it hits 50psi then shuts off. Its a standard well system. Most wells fills a cistern then the pressure tank. Outherwise the well pump would have to run all the time and that wears them out. Pumps and installing them is $$$$$$$$$$$$$$$$$.

So my tank is connected to my plumbing and it feeds all water supply. I have drain frees at garden and side of house for animals. They dont freeze.

The grundfos sq is AC and the sq-flex is ac/dc.