24v 3k+ Off Grid system

WarrenB

New Member
Joined
Jul 17, 2021
Messages
8
Wow, very glad I found this Forum. I was starting to get a little discouraged trying to research a system I could DIY.

We have land we want to build on in southern Utah with zero utilities. We are going to start with a small container home until we can save enough for our retirement home and I think I might start with a 24v, 3k Growwatts all in one with San tan panels and a pair of 200ah 12v. lead acid. I am hesitant to buy Lithium because it does freeze a lot. I'm not sure how I am going to mount the panels or how many I am going to order. Shipping doesn't seem to bad from Phoenix to Vegas I may go pick them up but that's 8 hours away

Anyway back to researching, If anyone has any suggestions on mounting panels on a 40' container or what you think about anything else that would be great. Thank You to William and all of you for having this great resource.
 

Wibla

Engineer
Joined
Jun 6, 2021
Messages
262
How long do you think it'll be until you start on the retirement home?

Talk to SanTan about how to get those panels to you the cheapest way. Sometimes they can ship them to the closest freight depot. Buy a whole pallet (25-30 panels) while you're at it, sell the excess locally on craigslist, or keep them for later - 25*250W is only 5-6 kWp (depending on degradation). Don't forget that racking isn't free, and look into doing ground mount.

Going 24V with a couple of batteries and a 3k all-in-one and some solar panels is deceptively easy to do, it also means you'll probably find yourself upgrading pretty soon. Go with a 48V system instead, and spend a bit of time thinking about batteries after you've done an energy audit. 200 Ah at 24V is just 2.6 kWh of usable energy, and that means pretty heavy conservation of power during nighttime.
Remember that the inverter uses a fair bit of power even when you have no actual loads (this can be 20-50W, sometimes more - 50W 24/7 = 1.2 kWh per 24 hours, or nearly 50Ah out of a 24V battery bank).

LiFePo4 batteries can be put in an external, insulated battery box with a small heating pad that runs on a thermostat.
You can also expand lithium battery banks a lot easier than lead acid.
 

WarrenB

New Member
Joined
Jul 17, 2021
Messages
8
We wont be finished with home for 5-10 years.

I will look into 48v ,LiFePo4, heated battery box and ground mount. Thank you for the great suggestions. Also would wiring an off grid home with 120v and 12v going to be a good option or should I just run 120v curcuits? will 12v. lighting curcuits save on current draw?

I love how easily you can expand to split phase or even 3 phase down the road with the all in ones.
 

Wibla

Engineer
Joined
Jun 6, 2021
Messages
262
5-10 years is a fair timeframe, it also means "future proofing" gets kind of iffy, since there's so much happening in this field.

With your location, I would probably go with a larger (6+kWp) array, and plan for using an AC or mini-split for the hot season (mini split heatpumps are good heat sources, too, fwiw).

Doing 12V lamps isn't a bad idea, especially for your 40' container. That means you can turn the inverter off at night.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Joined
Oct 29, 2019
Messages
5,780
Location
Rural NE Ontario Canada
I live OFF Grid am Rural & Remote up near Algonquin Park, Ontario Canada.
24V/4000W system, original battery bank was 428AH Heavy Lead (214 Net AH), now backup with New Bank of 1190AH LFP 30.4kWh (LiFePO4).
I started with a 3000W inverter and within a year I upgraded to 4000W, which also meant attery cables from 2/0 to 4/0 which was another ouch. I do not use 240VAC and am wired for 120VAC. My Well Pump is also a GrundFos SQ-5 120VAC Softstart which reach 1100W @ Cutoff point of 52PSI. 260' deep to a 50 Gallon pressure tank then 75' to house and there is neer a noticeable pressure drop.

The general unwritten rule is to not draw more than 250A from a battery bank (excepting surge handling). Stackable inverters and such are another matter handled differently.
12V@250A=3000W (25A AC),
24V@250A=6000W (50A AC),
48V@250A=12,000W (100A AC)
-- for quick reference. The (50A AC) can be 120V/50A out to panel or 240V/25A split phase to panel.
In simple terms. -- AC 120V/15A=1800W, 240V/15A=3600W uncorrected
? 250A. Because it's recommended to be the MAX draw limit for a standard"single" system. Single, meaning non-stacked inverters and similar.
! Inverter Wattage has to support the watts required plus surge capacity. Should never be run at the limit for an extended period of time (that's undersized).

My 24V system, uses a Samlex EVO-4024 4000W Pure Sine Low Frequency inverter that can handle 12,000W surge.
As I sit here writing this I am using 10.2A, turn on coffee maker add 50A for 6 minutes while brewing (no warmer has thermal carafe). Turn on Microware (1200W Panasonic Inverter type) and there's 72A. IF I was running 12V that would be Double the amps drawn, if 48V then it would be Half the amps drawn. I turn on my compressor and get a surge of 200A and then 75A while running (2.5HP, 20gal).

Much more information & details with links to items and devices etc on the "About my System" link at the top of my signature. I'm sure several of your pending questions would be answered there and may create new questions.

HINDSIGHT NOTE:
Looking back, I should have chosen 240VAC as opposed to only 120VAC. Even though I have no "need" for 240V it would have provided more options & flexibility. Notably things like EV Charging (and with the new models being V2G (Vehicle to Grid) / V2H (Vehicle to home) so that could be leveraged for house power as well. What is "today" is evolving for tomorrow so best to be prepared. Even wired for 240VAC to panels, you still get the 120VAC legs so no loss and NOW it's not really more expensive then 120V Only. When I started 240V Inverters cost more than just 120V output. Even so, I wired everything so it can handle 240VAC/200A including the run from Powerhouse to house which is wired with one #6/3 & one #8/3 (I got one heck of a deal on the wire so I could not refuse).

Note that I designed & built my home which is hyper-efficient and very energy frugal. In the "About my System" page, there is a blue spoiler with more detail.

First Rule of Offgridding, conservation is far cheaper than generation & storage.
A well insulated home designed to take advantage of the environment it's in, can work to save costs on heating & cooling while making it far more liveable. IE: Yesterday it was 95F in the shade, with 65% Humidity so "ugh" but in my home was 76F and I no longer own an AC - gave it away a few years ago. In Winter when it's -22F outside my heating system only runs two cycles of 2 hours each to maintain the house at 77F.

The tricks are a Cool Roof system that uses passive convective venting which is a thermal break between roof "skin" and physical roof shell, preventing heat transfer in/out for the roof. The "RainScreen" Siding also provides a Thermal Break between the siding & house shell, that also uses passive convective airflow, preventing ANY dead airspaces. The last trick which is the key, an insulated FPSF Foundation (frost-protected slab foundation) which prevents the slab from losing its heat in winter but also prevents heat gain from "the soil" thereby remaining as the Heat Sink & regulator for the house. During summer my slab remains at a constant 62.6F which keeps the house cooler.

Sea-cans are nefarious for heating & cooling but with external insulation & a rains-screen siding system plus a proper roof to prevent direct sun exposure to reflect & deflect the heat they can work really well. The trick is to prevent the metal from having direct solar exposure and preventing it from heating up.

Some quick & dirty info for you:
53° = 9:12 Pitch which is the nominal angle for year round generation.
1626686846133.png
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Solar Reflectivity, Emissivity, and SRI: (Chart from Tin Roofing manufacturers)
The Highest SRI reflects/deflects solar input. "Natural White" being the most effective, additionally, using a Natural White background in combination with Bi-Facial Panels mounted properly above can leverage maximum production capacity for the space available. "Pure White reflects the "Full Spectrum" which is the best.
1626687795476.png

Simple cool-roof info from a "Dead Site" (owner fell victim to Covid)
Attached info as PDF.
1626688294617.png1626688344698.png

Hope it helps, Good Luck.
Steve
 

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Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
10,609
Here are turn-key systems with lead-acid battery, from DC Solar bankruptcy. That should take care of freezing issue, and if healthy (not dried out) the battery should last the decade until you build a house. Cheaper unit is one 6kW inverter, more expensive is two. You could expand with up to 12kW or 24kW (respectively) of GT PV inverter that does frequency-watts (adjust output as commanded by frequency shift.)



 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
10,609
Forgot to say, if you get only one Sunny Island, output is 120V so need a 120/240V transformer in order to AC couple the 240V Sunny Boys.
If two, they are wired 2s for 120/240V. In that case a transformer is optional, only if you want to run loads with such an imbalance between the phases that it exceeds SI and SB output capability.

My four are wired 2s2p, which allows pass through of 112A at 120/240V from the grid.
If you got 3 SI, they can do 120/208Y 3-phase.

No one has told me yet if these trailers have either a battery shunt or a communication interface for Midnight charge controller. If you use both AC coupled Sunny Boys and DC coupled charge controller, SI needs one of those to know battery current and keep track of SoC.
 

WarrenB

New Member
Joined
Jul 17, 2021
Messages
8
Thanks Hedges there were a few around town a while ago I should have scooped one up. A little Leary of the trailer, though you get a trailer and a system pretty good score if you can find one that fits the bill.
 
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