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Small Cabin Forum / Off-Grid Living / HELP! Solar system for off grid small cabin
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# Posted: 27 Oct 2020 10:13

Hello All,
I’m putting together a solar system for my Off grid 700sq ft cabin. I have 6 panels rated 295 watts/ 45.4 VOC that I got a deal on from Craigslist and a 6000 watt diesel generator. I’m looking for a charge controller, Inverter and battery bank that can power small fridge and small A/C system using both sources of power. I’m looking to purchase an Epever 100a MPPT controller rated for 150v and 7500w. Next question is am I matching panels and charge controller and how to best wire panels For maximum efficiency. they will be approximately 100 ft from battery bank. Any help in this matter wold be greatly appreciated

# Posted: 27 Oct 2020 10:39

Start with figuring out what the total load is going to be. Use a calculator like one below to add up your power usage in a 24 hour period, that should help you size batteries you'd need to run for 1 day. Then you can decide how many days of reserve storage you'd like and add batteries from there.

The fridge is probably doable but even small AC systems can use up a lot more power than you'd think. Check the user manual or maybe the sticker on the back to see what the running wattage is.

# Posted: 27 Oct 2020 10:40

Disclaimer: I aint an expert!
Fwiw, my system is 600W (6 panels in 3 banks of 2) series wired to 50W mppt CC, 12v battery bank inverted to 120vac.
And math will be your friend before you spend any more money on stuff that wont work together.
You will need (NEED) to define your total usage; there are lots of 'solar calculators' online. Make your best, most device inclusive list and at least up the est. by 50%, better to even double it. The biggest problem Ive seen is people new to solar that grossly underestimate their power needs and way over-est. the solar array output (ie, most places will give you about 4, 5 Max hrs of real usable sun per day/24hrs. and your system will only make about 70% of its 'potential output').
Go with a min 24v system, 48 would be far better. For what you have said already do not consider a 12v system at all.
The Mppt charge control that matches (well, exceeds) the panels VOC times 1.25 for cold weather spike protection.
Wire panels in series, the mppt will maximize the volts and amps output and any shadowing on panels wont be as much a problem as when paralleled. Also, parallel requires lots of fuses at panels/combiner boxes and far more wires/complication.
But the big thing is the series will allow much longer wire runs from panels/array to the CC; ie, the voltage drop over distance can kill you for wire size and cost. Parallel is only suitable for close runs, imo.
Batteries will be many and expensive, most likely the most expensive part of this project. Dont think you can just parallel a bunch of 'marine deep cycle' 12v bats together. My rule of thumb is no more than 2 batteries parallel. You will need to know about and understand 'series/parallel' battery bank concepts.
Imo, wire the structure per normal, and code, for 120vac, c/w the proper Circuit Breaker box. With the big genny you will probably need a fancy auto transfer box, perhaps an inverter-charger that incorporates the transfer internally.
Dont bother with anything less than a quality Pure Sine Wave inverter.

# Posted: 27 Oct 2020 11:54

Thanks, I know that a/c will draw more power than I can generate with array I have as it will have to be 2 zone 220V system and that’s where generator will have to be used. The cabin is 2 story and top floor is closed from bottom floor other than staircase. I intend to use generator for hot days when I’m using a/c and when cloudy. That’s good information and should help me. Looks to me like the 6 panels might be more than charge controller can handle

# Posted: 27 Oct 2020 12:39 - Edited by: gcrank1

What we have discovered is that with solar and a bat-bank we have had to downsize our expectations and elec power use; probably easier for us than many as the 'new' cabin is one room, 16x24ish, rustic (more a hunting cabin that a fancy 'finished cabin/cottage'). Totally off-grid and dry.
We have a 3kw pull start 'construction' gen, a fancier elec start 5kw at home if needed, but our current fav (by Far!) is the 1700/2000max kw Champion inv/gen (think 'generic Honda EU2kw). The weight of a big suitcase, quiet, economical and will start & run, with care, our old 5000btu window air cond. Mostly we use fans inside.
My norm procedure is to start the Lil' Champ of a morning to run the microwave or toaster and it is hooked up to the bat-bank 2/10/20 amp smart charger to top the bats whenever the gen runs. This is the bulk recharge right away from the night use and the solar tops 'em through the day.
Really, the big thing for us is having the wonderful 120vac LED lights. What a diff from the old Edison base RV bulbs we used to use in the old cabin (we built in '83-84). And the fan(s) in the hot, still summer with some little use from a 12vdc water pump for transfer.
Btw, our utility water is completely satisfied with a 30gal. black plastic rainwater 'pickle barrel' with a first flush filter, all diy from online tips last winter while recovering from quad bypass surg.
I prefer ground racks for service and maintenance of the array. Old guys shouldnt go on roofs, even ladders are iffy, imo. Note I said 'shouldnt'.....sometimes a guy just has to do what he shouldnt. I really think it through now!
A friend in Alaska made a great suggestion (great to me anyway), get an EV, get to the cabin and plug the car into the cabin to power it. Gotta make sure you dont run the car bat-bank too far down but easy-peasy. Im waiting for the affordable EV mini pick-up truck though a std IC truck with a big, portable bat-bank in the bed Think 'power bed' rather than 'power wall') to recharge at home would be a treat. No solar at all but maybe only a very small scale 200-400W 12v on site.
I gave up on running refrigerator, ac, even microwave (high draw stuff) on solar, to me the costs ($ and time/effort of being my own power company) dont add up. Doing it all over, knowing what Ive learned, I would start out completely as a std house wiring powered by a gen; ie, all up and running well, then start adding in some solar to augment it/play with.

# Posted: 27 Oct 2020 13:19

I live Off-Grid, 400 square foot hyper insulated cabin.
PumpHouse-Powerhouse combo building 75' from cabin, solar racking 35' from powerhouse (fixed ground mount). I run with only 120V, 240 is unnecessary.

Water Pump is a Deep Well Submersible GrundFos SQ-5 120V Stoft Start (starts at 500W and ramps to 1100 Watts before pressure cutoff @ 50 PSI. It's 260' deep, pushes to a 50 Gal pressure thank, then to cabin through dual filters. never notice pressure drop or change.

System in Use:
- 8X Canadian Solar CS260P 4 in series, 2 parallel sets)
- Midnite Solar Classic 200 Solar Controller.
- Samlex EVO-4024 4000W Pure Sine Low-Frequency Inverter / Charger (Dual AC IN) only using Genset In (no grid power here).

New Battery bank is DIY LiFePo4 910AH/21.84 kWh, my old bank was Lead Acid 428AH/10.272 kWh. usable.

I can run my Mig Welder, 3HP Heavy Compressor etc BUT I leave those nasties for my Generator. NO point in stressing out my solar gear for that....

BEFORE ANYONE CRIES LITHIUM IS DANGEROUS / EXPENSIVE ! Give it up, LiFePo4 does NOT catch fire or Explode like other Lithium Based CHemistres and it is NOT expensive... They are now on Par or Lower cost than New Heavy Deep Cycle Lead.

I will provide this one Link to a Known Good Vendor which has supplied many people in my other group with thousands of cells without issue.
Luyuan Tech Alibaba

Example 24V/280AH/6.72 kWh
, straight 8S battery pack is attached below.

Free Shipping to USA & 8Pcs 3.2V 280Ah US $938.36 Delivered DPP (Duty Taxes paid)
1X FUSE per Battery. MRBF's are $25.00 USD.
1X 8S-BMS (Battery Management System) from $150 and up depending on type, features & functions.

These are Grade-A Commodity Cells, meaning they are not Matched, Batched & Binned (that adds up to $50 to a cells cost) But they meet the factory Grade Spec and tested as such. They will need to be Top Balanced at minimum prior to assembly.

Dangerous VS Safe Lithium (YT Video)
24V Basic LFP Prismatic Configs
24V Basic LFP Prismatic Configs

# Posted: 27 Oct 2020 23:02

Quoting: Steve_S
System in Use:
- 8X Canadian Solar CS260P 4 in series, 2 parallel sets)

So 2080w of solar panels is enough for your needs in our northern winter solar exposure?

# Posted: 28 Oct 2020 08:09

In my particular case it "just barely" did it with the FLA Battery Bank (limited to only 428AH / 10.272 kWh) which required me to run genset after 2-1/2 days of non-generation. With LFP 910AH / 21.84 kWh sitting there I don't think I'll be needing genset much. Won't know till I get through the winter.

I am NOT a power hog. Even now as I sit here typing this I am pulling 6.5A off the 24V bank, if the fridge kicks on, I go up to 9.5A, Radiant heating kicks on, that's another 1.5A. My 3 Big Draw Devices are Water Pump, Microwave, Coffee maker (uses a thermal carafe, no warming element), none of which gets much significant use through a day.

No problems in summer as the heavy lead would be fully charged on or about noon pretty much every sunny day.

Canadian Solar released 660W Panels yesterday. The game is changing and fast !

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