Double check my list/design please - 24V Off Grid Cabin

s13gram

New Member
My buddy and I have a 600 sqft 2 br cabin in Northern Georgia that's fully off grid. It's surrounded by national forest and has limited sunlight and limited open space around it and the current solar system is not working well (12V charger, 120V inverter, 100Ah worth of batteries, 100W panel). We drain this system from fully charged in a weekend or less.

Panels will most likely be mounted on the porch roof which is near level with a slight orientation west. Our cabin is in an area that gets poor sunlight and has a good amount of rainfall and overcast days, we definitely need a system that will keep up even if it's cloudy, or is big enough to regularly not get sun for 4-5 days. My one electricity class 15 years ago is completely gone so forgive any mistakes I make.

The cabin is regularly used, mostly for 2-3 day weekends, by 2-4 people at a time. We want to upgrade to something we can use without concern, even though are needs are not super high. It would be nice to be able to charge and run electronics, run the wood stove blower in the winter, 12v water pump, LED lights, bathroom fans, ceiling fans or window fans as needed. We have propane fridge/utilities and a generator for the AC (rarely used) so not looking to run anything super high draw. I would definitely like to be able to plug in our generator and use it to power the cabin as needed and recharge batteries. Based off what I've read and the experiences of people I've talked to, I think I want a 24V MPPT system with LiFePO4 batteries. Don't want to deal with dead batteries constantly like we currently do.

My back of the envelope calculations look like 2000-4500 watt-hours of usage per day, mostly 120V.

I'm thinking 6 300W panels for 1800W, 24V input. Probably 6 of these: https://a1solarstore.com/canadian-solar-cs3k-315ms-solar-panel.html

300Ah of LiFEPO4 batteries, 2x https://www.techdirectclub.com/life...h-220-ah-battery-pack-ev-golf-solar-with-bms/

I want an all in one unit with utility charging from the generator. I'm thinking this one: https://watts247.com/product/hybrid-lv2424/

Am I missing anything obvious here or any reason these wouldn't all work together?
 
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snoobler

Solar Honey Badger
4500Wh = 5.3kWh after inefficiencies

You really need to get a handle on your actual available solar. Check #5 link in my signature.

LV2424 has pretty weak surge, so if you have a lot of items with electric motors, it might be a concern. It might also be limited to the unit's own power even when running on a genny.

300Ah * 24V * 0.8 = 5.76kWh Enough for 24 hours of usage.
 

s13gram

New Member
2.5 (winter) -5.75 (summer) kWh/m2/day roughly, I'm going to average that out to 4 kWh/m2/day * 300W/panel * 6 panels = 7200Wh on a good day.
 

snoobler

Solar Honey Badger
Did you also key in your panel direct and tilt? You should also adjust it based on your actual situation with shading and such.
 

s13gram

New Member
I did. That's on a flat westward facing roof. I don't think I could do more than 6 panels on that section anyways, I'm nearly at the width of the porch. Shading on that section of the roof isn't too bad, I just don't have excess land to put more panels on.
 

snoobler

Solar Honey Badger
If it's going to be used in the winter too, you should factor that in as well - 4.95kWh - sounds like you'll almost meet the 5.3kWh even then - a major upgrade to your current situation.
 

MichaelK

Photon Sorcerer
Utilizing whatever panels you can fit on a roof is going to be limiting. Have you thought instead about using ground mounts? In my attached pics, I've got four 250W grid-tie panels mounted in this mount, that can be adjusted for both time of day, and seasonally.

Wired in series for 120VDC, I can send this power ~125 feet with almost no voltage drop. On a sunny February day when I commissioned a new set of batteries, I produced 6.1kwh of power on the first day by rotating the array left to right across the course of the day.

Having ground mounts spaced away from your cabin might solve your shading problems. By rotating the panels sideways, I could have fit 6 panels. Doing that, you could wire 1500W in either a 3S2P configuration, or a 6S1P configuration. You'll need a good controller though that can handle the 240V+ Voc of 6S1P.

I would NOT recommend an all-in-one unit. All the quality name-brand components are single unit designs. Buying components separately, you can match voltages/power to your particular needs.

Let's say you built the rotating array and positioned it in full sun. Wired in a 6S1P configuration (180VDC), you could send the power 200+ feet with very little loss. Bring that power into a Midnight 250V charge controller. The output of the controller feeds the batteries, and your batteries feed the inverter. Chose a Magnum, Outback, or Schneider. If you want split-phase 120/240VAC, you can get a Magnum or Schneider. You can get a split-phase Outback Radian if you are willing to go to 48V.

What creative ideas can you come up with to deal with the issue of shade?
 

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s13gram

New Member
When I say it backs up to national forest, I mean it literally. I have about 6 feet off the back of the cabin before the trees are marked. Everywhere else is surrounded by 40 foot tall trees I can't touch. Our only land otherwise, aside from the driveway, is deep in a wooded ravine and it would be a disaster to deal with. Ground mounts are not an option without it being constantly in the way or on public land.

Also, I specifically don't want the hassle of sourcing and installing separate components and figuring out how they all work together. Between my day job and grad school, this is an extra project I don't need to be any more complicated than the absolute minimum.
 

Master Dalor

Self made Master
Hello. If you can almost make it through the weekend with 100W pannel and 100Ah battery, maybe flooded lead acid, or agm, witch will give at most 50Ah.
Your installation could be ok.
It means that your new system will give you 18 times the solar power, and 3 to 10 times battery autonomy depending of your old battery real capacity, and the limits of charge, discharge you will set your Lifepo4 charger to.
1800W pannels / 24V can produce 75A in the best conditions, maybe 25A with shadow, bad weather.
300Ah / 25A = 12h to fully charge.
If you need 3 days in the cabin, the system can charge for 4 days, 12h / 4 = 3 hours charge per day.
The charger you choosed can divert the current when the batteries are full, you could power some kind of heater, ( resistor ) in the winter, or cooler, (fans, small airco) in the summer, thermostat driven.
You could also use smaller cheap batteries for your 12V water pomp, led lights, as backup in case of emergency, or main solar problem occuring when you where away.
 
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