# Need help on a few things for off grid solar setup

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Registered Users Posts: 53 ✭✭
I have 16 12 volt 130 watt 6.9 amp panels....5.0 sun hours oklahoma.....need to size batt bank...have in mind 12 trojan  225ah I believe by the calculations this is ok...charge controler is my biggest issue....need something to handle all those amps...any ideas would be of much help
thanks

• Registered Users Posts: 48 ✭✭
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what is the system voltage 24-48 volts, you might want to consider that first
edited April 2016 #3
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Just running the math... Assuming those are Vmp~17.5 volt panels (36 cells) and a 24 volt battery bank--5% rate of charge minimum (seasonal/weekend use), 10% full time off grid. And ~13% typical cost effective minimum battery bank, then:
• 16 * 130 Watt panels * 0.77 panel+controller derating * 1/29 volts charging * 1/0.05 rate of charge = 1,105 AH @ 24 volt bank
• 16 * 130 Watt panels * 0.77 panel+controller derating * 1/29 volts charging * 1/0.10 rate of charge = 552 AH @ 24 volt bank
• 16 * 130 Watt panels * 0.77 panel+controller derating * 1/29 volts charging * 1/0.13 rate of charge = 425 AH @ 24 volt bank
I would suggest that >~800 AH battery bank would jump up in bank voltage (i.e., 1,105 AH @ 24 volts to 552 AH @ 48 volt battery bank).

And the sun varies with season...

### Oklahoma CityAverage Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 54° angle:
(For best year-round performance)
 Jan Feb Mar Apr May Jun 3.97 4.23 4.98 5.47 5.38 5.59 Jul Aug Sep Oct Nov Dec 6.03 5.70 5.32 4.79 4.05 3.71
So--Some months are better than 5 hours, other worse... Assuming 5 hours nominal minimum:
• 16 * 130 Watt panels * 0.52 off grid system eff * 5 hours of sun = 5,408 Watt*Hours of AC power (5 hour day, max typical energy)
And I would suggest that you use 25% of the battery storage capacity for 2 days and 50% maximum discharge (for longer battery life). Using the 10% rate of charge bank size:
• 552 AH * 24 volts * 0.85 inverter eff * 1/2 days storage * 0.50 maximum discharge = 2,815 WH per day of "stored energy" for "dark days/over night")
And then there is how much power you can draw from a flooded cell lead acid battery bank (AC loading):
• 552 AH * 24 volts * 0.85 AC inverter eff * 1/20 hour discharge rate = 563 Watt AC load (~5 hours per night, 2x nights. 50% maximum discharge)
• 552 AH * 24 volts * 0.85 AC inverter eff * 1/8 hour discharge rate = 1,408 Watt AC load (continuous for ~3 hours)
• 552 AH * 24 volts * 0.85 AC inverter eff * 1/5 hour discharge rate = 2,252 Watt AC load (short term max continuous)
• 552 AH * 24 volts * 0.85 AC inverter eff * 1/2.5 hour discharge rate =4,504 Watt AC max surge (seconds)
Anyway, those are the numbers as I would take at my first guess.

Questions,

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 53 ✭✭
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wow...some good info....I should tell you the rest of the story to make the setup more understandable...these are used astro power (out of business) ap130 panels...but all working in tip top as far as volts when tested with volt meter...all around 18 volts on an overcast day.. rated voltage is 18.9...open circuit voltage 24.6...the plan was to have them wired in 12 volt because the bulk of the appliances are running off 12 volt....Jensen 12 volt tv..led lighting ect... exceptions are mini fridge/ 8000 btu a/c  ...the system will be wired like a travel trailer for maximum efficiency
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You do want to size the battery bank for your loads... Large loads and 12 volt banks generally do not go well together (you need short 12 volt runs, and/or very heavy cables for longer runs/larger loads).

When you get much more than powering a standard 120 VAC refrigerator (i.e., air conditioning).

With larger systems--Many times, a 120 VAC system + AC Inverter (12/24/48 volt battery bank) can make the overall system design and usage easier.

Do you have a good idea about your loads (Watts/Watt*Hours and/or Amps and Amp*Hours) by device/total loads? That will make designing the battery bank and overall system much easier and (probably) less costly.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 53 ✭✭
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tv 12 volt 150 watt 4 hours in a day...30 12 volt led lights 70 watts total... 4 hours a day....cpap 12 volt 30 watts 8 hours...5volt car phone charger...have no idea on that 2 hours per day...12 volt well pump 96 watts 1/2 hour per day...on the A/C inverter side ...air condition 740 watts 8 hours per day ....fridge 450 watts 6 hours per day avg...this is pretty close...may be a few other things used here and there...but this is ballpark
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Regarding conservation--For a new LED TV, you can probably reduce power usage to 50 Watts or so (vs 150 Watts). CPAP--there are units that use less power (for travel/camping--probably does not use heat to vaporize water/increase humidity).

The rest seem pretty reasonable... Bu the fridge and A/C will drive you to a much larger system (at least 24 volt, if not 48 volt) to manage the high starting surge loads (600-1,000 VA surge for a typical fridge).

Running the math:

TV 150 Watts * 4 hours = 600 WH per day
LED Lights 70 Watts * 4 hours = 280 WH per day
CPAP 30 Watts * 8 hours = 240 WH
Phone Charger ~ 20 WH per day
Well pump 96 Watts * 1/2 hour per day = 48 WH
A/C 740 Watts * 8 hours = 5,920 WH
Fridge 450 WH * 6 hours = 2,700 WH per day (fridge can get new unit down ot ~1,000 WH per day)
===========================================
9,808 WH per day

That works out to about 300 kWH per month. Not a bad level of energy usage for a standard home--And pretty low for a home that is using A/C. But quite a bit more than the ~3.3 kWH per day that I would suggest for a "small/efficient" off grid home aim point--or ~100 kWH per month).

Battery sizing (2 days of storage, 50% maximum discharge--Assume all power is 120 VAC, since most power is AC loads):
• 9,808 WH per day * 1/48 volt battery bank * 1/0.85 AC inverter eff * 2 days storage * 1/0;.50 max discharge = 962 AH @ 48 volt battery bank
For this large of battery bank, I would highly suggest that you stick with 48 volts... A 12 volt battery bank would be 3,846 AH and need almost 400 Amps @ 14.7 volts for charging current--That is a lot).

Two calculations for solar array sizing... One based on size of battery bank (rate of charge) and second based on loads and amount of sun per day.

First rate of charge... Suggest 5% to 13% rate of charge, and 10%+ rate of charge for full time off grid usage (solar panels are cheap, batteries are expensive these days):
• 962 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 3,686 Watt array minimum (weekend/seasonal)
• 962 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 7,371 Watt array nominal
• 962 AH * 59 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 9,283 Watt array "cost effective" maximum
Second based on loads and location. Say that you only need A/C when you have 5+ hours of "summer" sun per day:
• 9,808 WH per day * 1/0.52 off grid system eff * 1/5 hours of sun per day = 3,772 Watts of solar array minimum
Or almost, at a minimum 2x the number of 130 Watt solar panels you have today.

I also made a simplification that you collect power during the day and use it at night/bad weather--Much of that is the A/C system. In theory, if you only ran the A/C during sunny days--You could reduce the battery AH capacity by 1/2 with careful power management

When you add a refrigerator and A/C--The solar power systems are no longer "small". And since they use an AC inverter 100% of the time (usually)--Then you might as well look at powering the rest of your loads with 120 VAC too... Makes wiring (and many times appliance) costs less.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 53 ✭✭
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Well...you took a part of my spirit away....lol...I guess its back to the drawing board...I cannot find any of the same panels that I have and I know better than to mix them so the other option is to buy a separate system just for the AC
• Solar Expert Posts: 6,006 ✭✭✭✭✭
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It's no problem mixing panels, either by finding panels of the same VMP for the string or simply on a separate charge controller.

If you are running your A/C with the sun (hot days are pretty much always sunny) and you aren't trying to run the A/C off the battery much, you can discount the battery size a good bit, maybe 30% less. I know that is the way things work for me in Missouri. You will want a larger array for those needs. I run a window unit of 5200 BTU nearly around the clock (on thermostat) during the summer, only shutting it down for cloudy days.

I, would recommend a 48 volt system. I only have a 24 volt system since I had the battery from a slightly smaller system.

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
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You can mix panels. Just need to watch the rules and or use two or more charge controllers.

I do not want to rain on your dreams. But I try to answer questions as asked.

You look at the energy usage. 3 devices account for the vast majority of your energy usage. You can cut the fridge+tv usage by 1/2 or more.

Water heating can be done at 1/3 the energy usage of standard resistor based heaters. And they "exhaust" cold/dry air. Something you need in Hawaii any way.

Or solar thermal. Really good diy your project (plus plumbing).

A/C you need to look at your home. Is the home insulated or open (tropical) design.

Can you make the home more livable in other ways?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 53 ✭✭
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as far as the cabin goes it is a 16 by 40 lofted but the one bedroom is going to be highly insulated with spray foam insulation walls underneath and the loft above it ....
which will serve like an attic...trying to turn it into an ice chest and this will be the primary room with the air conditioner
• Solar Expert Posts: 6,006 ✭✭✭✭✭
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Well insulated, is important. Also reducing heat gain. So you want to build in the shade if at all possible. You want to keep cooking and refrigeration in another building or at least another room. The 5200 btu A/C cooled my 10x16 cabin fine, I had 6" walls and I built it in the shade. I also build a separate building for a kitchen/bathroom (composting toilets produce heat and function best with a small heater...
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Registered Users Posts: 53 ✭✭
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yes I am absolutely in the shade trees all around me a wonderful spot I guess my other question is I had no idea you could run two solar chargers on One battery bank I was trying to find a charge controller with the highest amps to run it
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Yes, you can run parallel chargers to a single battery bank.

Some higher end chargers will "sync" so that they agree on voltage/current/stage of charging. But this is not required.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 53 ✭✭
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What are some of the less expensive mppt style and best place to buy?
thanks
• Registered Users Posts: 53 ✭✭
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Another question...lets say i go ahead and wire the panels and batt bank in 48 ...will this give me 675 ah @48volts...and will this be an easier or more efficient  set up for the panels to keep charged?...i can re figure the appliances to run off the 48 volt/120 ac inverter....and one more question on the led lights....can i wire them in series of 4 to run directly off the 48?
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First, regarding shading--Solar electric panels do not do well in shading. Their output can fall by 50% to 100% per string (depending on shade/wiring/which panels are shaded). Also, shading of panels in a high voltage string can cause damage/ruin panels (not supposed to do that, but I would try to avoid--The bypass diodes can overheat and fail).

US made MPPT charge controllers are expensive. For a small system, PWM controllers can be OK--But it depends on what solar panels you get (Vmp~18 volt vs Vmp~30 volt). 18 volt panels can work fine with PWM controllers. 30 volt panels (and some other types) really need an MPPT controller for efficinient operation. So save money with 30 volt panel and spend money on MPPT controllers.

There are import MPPT controllers from Asia--But that can be hit or miss. There are a few out there that some folks here are very happy with... And there are others that are marked MPPT type controllers, but are really PWM type (and those have been known to die an early death).

Your best bet is to try several paper designs (18 volt Vmp panels+pwm; and 30 volt panels+mppt) and see what works best for you. For smaller systems (less than 400 watt arrays) a PWM system may be cheaper. For >~800 Watt arrays, generally a MPPT system is more cost effective/easier to wire up.

For larger systems, I suggest running most everything from the AC inverter. There are many energy efficient LED lights and appliances that are almost as efficient as their DC counterparts--And the AC versions tend to be a lot cheaper and easier to find/buy.

Placing 12 volt LED lamps in series for 48 volt battery bank. It depends on the construction of the LED lamp assembly--But I would recommend against it in general. It is better to run them off the "right voltage" (and do not wire 12 volt "battery tap" from 48 volt battery bank--You end up with "unbalanced" battery loads and bad charging of the series batteries).

Also watch "DC appliance" ratings. A 48 volt battery bank can run from ~42 volts (heavy discharge on a near dead battery bank) to 62 volts (or more) when equalize charging. There are not a lot of 48 VDC devices that "like" that wide of voltage range.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 53 ✭✭
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Ok...thanks for the info...I have to make a decision pretty quick on the entire set up and im not against removing the 12 volt leds and moving them to the pole barn to run off a different source..and buying a conventional 120 volt tv.ect....that being said 48 volt system...or 24?...i found an aims 48 volt 2000 watt inverter / charger pure sine around 715.00
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For a 675 ah @ 48volt battery bank--that works well with a larger single MPPT type charge controller (you can get 80+ amp charge controllers). If you wire as 1,350 AH @ 24 volt battery bank, you will need at least two 80 amp charge controllers (if you want ~10% rate of charge), and much heavier DC wiring.

2,000 Watt AC inverter @ 48 volts is fine for that bank (assuming enough solar panels for charging and to support your loads). And if your peak power needs are that low, then a 24 volt battery bank would be fine too...

Which leads us to the question--Do you need such a high capacity battery bank in the first place?

Lastly, the AIMS inverter--Not a very high quality inverter (some posters have reported poor reliability here). Although, a few people seem to be OK with them.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 53 ✭✭
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so lets re calculate a 48 volt....i have 16 12 volt 130 watts at 6.9 amp...wired to 48 volts it gives me 27.6 amps @48 volts if this is correct...then i only need one charge controller to handle the 28 amps right?...if it is correct what is a good battery bank number for this kind of charge using the t105 225ah wired in 48v...sorry if i am being a pain...just trying to change things around to be the most efficient before i invest the money in this equipment
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Yes, you are correct.... Assuming 27,6 amps of charging current and 5%/10%/13% rate of charge (48 volt battery bank):
• 27.6 amps / 0.05 rate of charge = 552 Amp*Hour (maximum battery bank, weekend/seasonal/emergency usage)
• 27.6 amps / 0.10 rate of charge = 276 Amp*Hour (nominal battery bank, full time off grid)
• 27.6 amps / 0.13 rate of charge = 212 Amp*Hour (smallest lead acid battery bank I would suggest for average off grid use)
Keep asking questions--There are lots of factors to juggle here--And, in reality, you need to know/understand your loads so you can have a "cost efficient" off grid solar system that meets your needs.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 53 ✭✭
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Okay so I believe if I wire 8 six volt 225 amp hours batt up to 48 volts and then another set of eight up to 48 volts and then parallel them...I'll get 550 amp hours @48 volts... If this is correct then this is the route I'm going to take for now.... By the way this will be a full time off grid cabin within the next 6 months. I figured I needed to let you know that to make it easier to calculate some of these things
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Yep. Got it right on how to calculate the batty bank capacity.

We have people here that do 5% rate of charge and are happy with the results.

However, they enjoy monitoring the system closely and adjusting loads (sometimes daily) to keep the battery bank "happy".

If you want to have system that you can use and not baby sit so much, then 10%+ rate of charge can really help.

Batteries are expensive and "fragile" if under charged/over discharged.

Solar panels are historically cheap and last 20+ years without any service. So, "over paneling" your system is not the worst mistake to make.

Plus electric loads tend to grow over time.

You could go with a slightly "smaller" solar array and use a genset during dark and stormy weather as a start. And add panels later, if you wish.

Power usage is highly personal. The rules of thumbs are a good place to start. But your needs still need to be understood (most power use at night after home from work, vs daytime loads for home office/shop/irrigation/etc.).

A 10%+ array makes these load questions less important.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 53 ✭✭
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One more question before i go wiring this up....how dangerous is 27 amps @48 volts when the human hand comes in contact with the pos / neg ?...also wiring the battery's with 550 or so amps @48....what kind of precautions if any should i take... i never had an issue with 12 volt but i have only wired up a total of 6 12 volts ....but i have an idea this is something of concern  when expanding to this point
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That would give you 5% rate of charge with the panels you have.

For full time off grid living, I would suggest 1x string of batteries, or 2x strings of batteries with twice as many solar panels (both give you 10% rate of charge).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 767 ✭✭✭✭
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There is no such thing as a cheap mppt controller.
You pay for the  real thing or you get a cheap knock off that is not a real mppt controler.

Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

• Registered Users Posts: 53 ✭✭
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Okay Define cheap because I have no idea which ones are false mppt and which ones are real but they run from around \$89 up. I would like to know some of the brand names that are true mppt Chargers like Morningstar? Like Outback? And maybe a few other brands that are good I would like to know which ones are false flag and what constitutes it what should I be looking for thanks
• Registered Users Posts: 79 ✭✭
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My system is 48 V with one bank of 215 Ah batteries. Found out this winter that low temperatures can cut the battery capacity in half just when your solar charging capacity is at it lowest. My refrigerator fortunately used less due to the lower ambient temperature but if you need electricity for heating like I do using a heat pump, the calculation of the battery capacity for summer and winter should be considered.
Sunpower 3 x 435 watt panels, 48 v 215 AH battery bank (Sam's club), Midnite Kid and WBjr, Fujitsu 9RLS3 split duct AC, Outback FX 3048T + transformer 2000W 120/220V, GrapeSolar Fridge.
• Solar Expert Posts: 6,006 ✭✭✭✭✭
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I hope you have a nice setup, so that your solar array cn have direct sunlight most of the day and your cabin still be in the shade. I know this isn't impossible, I had it! ...but often when figuring this out, it's important to remember that low voltage current drops over distance. a 48 volt system will help if you have large distances between the array and the power center (where your inverter and batteries are)

A 48 volt PWM charge controller for the current array should be inexpensive, and quite effective so long as you don't have long distances to cover (+50 - 60 feet) and might be okay up to a 100 feet with out going to huge gauge wires.

The higher voltage of a 48 volt system, in general, will reduce problems with voltage drop throughout the system. I believe Cotek and Samlex make 48 volt inverters that some would consider a step up from an Aims inverter, yet be in the same cost range. Here's a link to a 1500 watt Cotek at Amazon, our sponser doesn't list either in a 48 volt version.

http://www.amazon.com/COTEK-S1500-148-1500-Watt-Inverter/dp/B00EWBSG2W/ref=sr_1_32?ie=UTF8&qid=1461377951&sr=8-32&keywords=48volt+inverter

Things to look for in an inexpensive inverter that aren't always obvious or even easy to find out;

A voltage range high enough so that high equalizing voltages won't shut down your inverter. in a 48 volt battery  bank, I'd want a range that went up to 61-62 volts minimum.

Also it would be nice to have an inverter that can be 'hardwired' most higher cost inverters can only be hard wired, having no 'outlets' but some come in a one or the other like ProSine. Some have outlets and can be hardwired Exeltech and some Samlex/Cotek

Lastly, but perhaps more of a qualifier. Will the system need to be inspected? by the county to meet code or an electrician for insurance purposes? This will require an inverter that has UL inspected to 1741 (UL 458 is for mobile applications) This will disqualify most of the inexpensive inverters and leave you with Magnum, Outback or Xantrex/Schnieder.

Midnite makes some good MPPT type charge controllers and They were selling a few 'bent and dent' or refurbs on their forum site with a full 5 year warranty. This would be worth checking out. They are great people and if they've sold out it might be worth a call to see what they have around.

If you are new to an 'Off Grid' world, it will take a while to get use to. shifting things around to make best use of the energy when it's sunny out. Example, I ran my water heater today turning it on when I went into work. It's topped off. I did laundry this evening only because I knew it would be sunny all day tomorrow and I'll run my Electric Chain saw and weedeater a good bit and likely want to run my AC in the afternoon when things heat up.

I'll likely come in from outside, turn off the water heater and put a pizza in the Pizzazz pizza oven and take a shower, turning on the AC in the back bedroom. I know I have to run by work for a couple hours in the afternoon and I'll likely pop the water heater back on to top it off... Juggling like this I can live on a somewhat under sized (for my system) inverter and have fully charged batteries at the end of the day. I can run the water heater during the day as I have a second 1100 watt inverter I use with yard tools.

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Registered Users Posts: 53 ✭✭
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Ok thanks for the info...i did a lot of planning and the cabin is almost completely shaded most of the day.....I plan on moving the panels closer to the cabin tomorrow  before i start the 48 volt wiring....the closest i can get to the cabin with the clearing for the panels is going to be about 60 feet...what kind of gauge wire and where am i to get it?
• Registered Users Posts: 53 ✭✭
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By the way...no codes to comply with...no permits....love pushmataha county here in Oklahoma