Help me build my off grid system... dont know which direction to go.

2000tranzam · April 2020

Hello all...

So I just bought 6x of the lion energy UT 1300 batteries (had them on sale from costco for 700 a piece).
Ive got it in a little travel case so its portable in the event I need to move it around the house or another location.
Ive already purchased the 8420AN model of MPPT charge controller from Epever but after contacting their support they said that model doesnt support Lifepo4 batteries, so I will be returning it.

So these batteries are rated at 1344 watt hours at 12.8 volts, or 105 amp hours or so... for a total of 8064 watt hours @ 12 volts.

I also purchased this AC charger as it was recommended by Lion energy : https://www.amazon.com/gp/product/B0030G7YXC/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1

Im really worried about potential power outages with all this shit going on around the world... and here in phoenix it gets 118+ during the summer, so the last thing I want to do is be without air conditioning or a way to keep food in the fridge/freezer cool.

I purchased 4 of these Jinco 400 watt solar panels (brand new) from a local company : https://www.santansolar.com/product/jinko-400w/
They are 24 volt and was told to run 2 sets of 2 panels in series together and then run them all in parallel at 48 volts to the charge controller.

I already have a 1000 watt 12 volt pure sign wave inverter that I was going to be using, however I dont know if its correct for my application.

So basically the questions that I have are what direction do I go regarding getting a new charge controller... should I stick with Epever and get one that is good for Lifepo4 batteries? Or should I get a victron and spend a bit more money on that one? Secondly, with the battery bank that I have, should I keep it as a 12 volt setup or would it have any benefit in wiring them to a 24 volt setup? I dont mind buying another larger inverter but does it make sense based off the purposes of what Ive listed? The 8k btu ac that I would use is about 650 watts when I plug it into the Kill a watt power meter. Im not sure what model for victron or epever I would need...

Or should I plan to get something like the 24 volt mpp solar hybrid charge controller/inverter combo?

Another question I had is when I have the whole system set up including the solar array, when I have something consuming power from the inverter... does it pull power from the battery and the solar array recharges the battery (assuming power created and power consumed are equal) or does it use specifically whatever the array can produce, thus extending the life of my batteries by not discharging them?

Sorry for all the questions, it just seems impossible to find anyone solar related that not a grid tied company that can give advice on this.

Thanks in advanced, much appreciated.

P.S. Pics for reference of the setup :

https://imgur.com/JxOcRNQ
https://imgur.com/tCzCfh1
https://imgur.com/E5ZqaiQ

mike95490 · April 2020

You need to see / check with battery mfg, if you are allowed to wire the batteries in series for a 24 or 48V system

Your inverter will need to be able to start the air con compressor, and that is more easily done with a 48V system (lower amps=less loss)
but the inverter size needs to be carefully balanced for both starting ability AND low idle consumption.

2000tranzam · April 2020

I wasnt planning on using an air compressor... im curious what that has to do with it? And yes, I can go in series or parallel up to 48 volts, or 1000 amp hours/1000 amps :

"You can increase the voltage from 12V on a UT up to 48V total by connecting them in series (4 batteries connected together via + to - posts). You can increase the Amps (A) and Amp Hours (Ah) up to 1500A and 1000Ah by connecting them in parallel (+ to + and - to -). "

Would a 24 volt inverter be best for 630 amp hours worth of battery?

Photowhit · April 2020

2000tranzam said:
The 8k btu ac that I would use is about 650 watts when I plug it into the Kill a watt power meter. Im not sure what model for victron or epever I would need...

2000tranzam said:

I wasnt planning on using an air compressor... im curious what that has to do with it?

Air conditioners use a compressor to help return the gas to a liquid (I think) anyway that is the compressor he is talking about.

2000tranzam said:
Im really worried about potential power outages with all this shit going on around the world... and here in phoenix it gets 118+ during the summer, so the last thing I want to do is be without air conditioning or a way to keep food in the fridge/freezer cool.

To understand your needs, it is important we have both the momentary power needs, perhaps the 8K tbu air conditioner and a standard fridge, AND the legnth of time you want to power them.

With 8kWhs or batteries and a 1600 watt array, you will not be able to power them 24/7, but with a full battery you will likely be able to go 4-16 hours depending on ambient temperature and time of day.

Your 1000 watt inverter is not likely to start your 650 watt air conditioner reliably.

2000tranzam said:
Another question I had is when I have the whole system set up including the solar array, when I have something consuming power from the inverter... does it pull power from the battery and the solar array recharges the battery (assuming power created and power consumed are equal) or does it use specifically whatever the array can produce, thus extending the life of my batteries by not discharging them?

It pulls from the system, it will charge the batteries at the same time as providing power so long as there is enough energy to do both.

petertearai · April 2020

Compressor is the compressor within the air conditioner . If you can go 48 volts to start with i think best . Don't think anyone regrets going with the higher voltage . Plenty regret staying at 12 or 24 volts .

mike95490 · April 2020

> air con compressor
Air Conditioning compressor motor, and it also has 2 fan motors, all of which come on at the same time and have surge requirements, in addition to poor power factor. There is a chance the inverter is not going to be large enough to start the motors, and you may need to exchange for a larger one.

2000tranzam · April 2020

I understand the requirements of watt hours and that I can only run certain appliances a certain amount of time as Im limited with battery life... that is fine.

So the general consensus would be to wire my batteries into either a 24 or 48 volt system? From what I understand 24 volt is much safer to work with regarding shock and what not correct?

Lets assume I go with a 24 volt setup. Based off that I would wire the 2 sets of 3 batteries in series and then run those 2 sets in parallel to create a 24 volt, 315 amp hour setup? Does that sound about right?

Assuming that part is set up, then what charge controller and what inverter would you guys suggest? I want something reliable but nothing ridiculously expensive.

BB. · April 2020

I am Mr. Conservative regarding design... Particularly for the Paper Design Q&A.

You sort of "jumped the gun" by making purchases before you really had a system design first.

For example, your battery purchase of 6x (very nice) 12 volt Lithium Ion batteries. Since the only configuration that you can use all of those batteries is in 1x series x 6 parallel (12 volt @ 105 AH) for a 12 volt @ 630 AH battery bank. Or 2x series x 3 parallel strings (still 6 batteries) for a 24 volt @ 315 AH battery battery bank.

Note that the 12 and 24 volt configuration above still store the same amount of energy--(P=V*I)... If you double the voltage and 1/2 the AH capacity, the answer is the same:

6 x 12.8 volt * 105 AH = 8,064 Watt*Hours total (less losses, conservative charge/discharge, etc.).

If you wanted to make a 48 volt battery bank, that would be 4x series x 1 string (4 batteries total) for a 48 volt @ 105 AH battery bank--With 2x batteries "left over". Or, you would have to purchase 2x more batteries to make a 4x series x 2 parallel for a 48 volt @ 210 AH battery bank.

Choosing between 12/24/48 volt battery banks is a combination of how much power you want, and what XX Voltage Battery Bus components you want to purchase (typically 12 volts are for "lower power" loads, and 48 volts are for higher power loads).

My first cut suggestion is 12 volts for (roughly--All solar rules of thumbs are "rough" numbers) is for ~1,200 to 1,800 Watt maximum loads. 24 volt for ~2,400 to 3,600 Watt max loads. And over that look at 48 volt bus.

And there is the battery bank Amp*Hour capacity... I suggest that if your battery bank capacity is over ~800 Amp*Hours, then go to the "next higher bus voltage" (12 volts @ 800 AH -- Go to 24 volts at 400 AH, etc.). When you get over ~100 Amps of bus current (loads/charging), you have to use very heavy copper cables to carry that current. Also, 12 volt systems can only tolerate (again roughly) a 0.5 volt drop in the wiring (nominal). It makes it very difficult to send 12 volt power any distance without a "crazy" amount of $$$ copper cable (heavy cable for more than 10 feet or so).

The other suggest I make is to keep your battery bank to 1-3 parallel parallel strings. You can do more parallel strings (12 volts would be 6x parallel strings, 24 volt would be 3x parallel strings)--But it is something I try to steer people away from if they don't need it.

You can look at how to parallel wire your battery bank at this website:
http://www.smartgauge.co.uk/batt_con.html

If you design the system properly, you charge (and pull current from the panels as loads/battery state of charge dictate) when the sun is up, and use battery power when the sun is down (or if you have "high surge" current from starting heavy motors, etc.). Sort of like your car's battery+alternator+loads... Everything works "transparently" until you demand more than the system can supply (running your loads without the engine running, something breaks, etc.).

Normally, I would suggest measuring/defining your loads, and design the system to support those loads. Another way is to break down what you have (battery bank where your $$$ is), and estimate the available power per day from the system.

Li Ion batteries are "nicer" that Lead Acid... You can use more of the "Range" of the batteries without damaging them. Lead Acid, if you leave them 1/2 charged or cycle them too deeply, lose life).

The typical "off grid" system assumption. Your battery bank will run your loads for 2 days of "no sun" (stormy weather, near zero solar harvest). You can also plan for 1 day of storage (such as dark day/overnight loads), and plan on second "dark day" to not power loads, use genset to recharge/run loads, etc... For this design, I will assume that you will want the battery bank to supply 2 days of energy. And run from 20-90% state of charge for the battery bank ("don't push" the batteries to where they could be damaged/shutdown unexpectedly):

6x 12.8 volts * 105 AH * (90%-20% state of charge) = 5,645 WH of "useful storage" (conservative)
5,645 WH / 2 days of stored energy = 2,823 WH of DC energy per day
2,823 WH * 0.85 AC Inverter eff = 2,400 WH per day of 120 VAC energy

Then there is sizing the AC inverter vs your battery bank capacity... Your Li Ion batteries can supply 100 Amps peak each--That is 600 Amps * 12.8 volts or 7,680 Watts peak... And most quality AC inverters can supply ~2x rated output for surge current, then the "maximum" AC inverter on this bank would be

7,680 Watt peak DC bus power * 0.85 AC inverter eff * 1/2 surge derating = 3,264 Watt "max" AC inverter (for your 6 battery bus)

And if you limit your discharge rate to 5 hours (C/5)--Typical maximum I would suggest for any battery bank (although, if you had specialized high power/surge loads, we could talk more):

12.8 volts * 630 AH * 1/5 hour discharge * 0.85 AC inverter eff = 1,371 Watt suggested "high nominal" AC inverter rating

And then even a little more conservative, C/8 hour discharge rate:

12.8 volts * 630 AH * 1/8 hour discharge rage * 0.85 AC inverter eff = 857 Watt "conservative nominal" AC inverter rating

OK--Lots of math and numbers, but I would be siding towards the 857 Watt to 1,3871 Watt AC inverter--And at that level, a 12 volt battery bank is perfectly OK. It is easy to "overbuy/oversize" the AC inverter--But you don't want to do this--Large AC inverters have higher losses (tare losses) when just being "turned on"---Something like 20-40 Watts is typical for larger inverters. Smaller inverters can be down in the 6-12 Watt Tare loss range--You don't want to "waste" energy on smaller systems.

So--Looking at AC inverters in the 12 and 24 bus voltage range, and find the brand/model/features that you would like (suggest remote on/off, and "search mode"--Low power "standby" which "turns on" the inverter with >~8 Watt AC loads).

Your last post, Just to clarify--If you want a 24 volt battery bus, 2x 12 volt batteries in series (for 24 volt battery bus). And 3x parallel strings (for 3*105 AH) for 315 AH--6 batteries total.

12 or 24 volt is both a "valid choice". You might find more (1,200 watt or smaller) AC inverters that meet your needs in 12 volts. The selection of 24 volt "small" AC inverters may be a bit thin.

For the battery bank wiring, I would like to suggest 24 volts--3x parallel strings and the smaller AWG wiring is a nice feature. 6x parallel strings is a lot of heavier copper and connections/fittings--But would work too.

I will stop here right now... I want to confirm my power estimates (for loads). The next choice is to "pick" the 12 or 24 VDC inverter that you would like (features/price).

Our host (NAWS--Northern Arizona Wind & Sun) has a nice selection of quality AC inverters for your initial search--But feel free to look around elsewhere too:

https://www.solar-electric.com/residential/inverters/off-grid-inverters.html

-Bill

MichaelK · April 2020

You can NOT use the phrases 12V and air conditioning in the same sentence. It's not going to work. Well, it will work, for minutes at least. Even at 48 volts, 1600watts of panels is at the very, very low end. A 1000watt inverter? Hope you can get your money back? With 3000-4000 watts of panels, a 4kw to 8kw inverter, and 500+amphours of 48V storage, I'd say you can make it work. Between 10k to 15k dollars should make a functional system.

2000tranzam · April 2020

Ok thank you so much for all the information... based off of your information, as Im not able to run a 48 volt setup with 6 of these batteries ill just bite the bullet and buy another 2 and run 2 strings of 48 volts in parallel with each other... I returned the solar charger along with the AC charger and decided to go with this all in one system... : https://www.ebay.com/c/6018155965 Seems to have good support, made in the US and is a decent price. So ya, im basically building the system based off $$$ available rather than trying to calculate a load that I might need...

So new setup will be that all in one charge controller/ac charger/3kw inverter, 8x Lion energy 1300 UT batteries, and thats about it. Gonna get ready to order the 2 other batteries, just want to confirm with you guys that everything should be ok based off the description I gave prior to spending another 1800 on batteries.

2000tranzam · April 2020

MichaelK said:

You can NOT use the phrases 12V and air conditioning in the same sentence. It's not going to work. Well, it will work, for minutes at least. Even at 48 volts, 1600watts of panels is at the very, very low end. A 1000watt inverter? Hope you can get your money back? With 3000-4000 watts of panels, a 4kw to 8kw inverter, and 500+amphours of 48V storage, I'd say you can make it work. Between 10k to 15k dollars should make a functional system.

No way will I have enough space to fit that many batteries in the travel case to create 500amp hours of 48 volt storage... the idea of this is to be able to take it on camping trips too... they arent just sitting on a shelf somewhere.

BB. · April 2020

Assuming 8x 12 volt @ 105 AH batteries for a 48 Volt @ 210 AH battery bus... The battery specs:

https://lionenergy.com/products/lion-safari-ut-1300

And a bit more information for the AC inverter:

https://usa-mpp-solar.com/manuals/gw/Growatt%20SPF%203000TL%20LVM%20Datasheet.pdf

A 3kWatt inverter would draw (at max load, 2x that for surge):

3,000 Watts * 1/0.85 AC inverter eff * 1/42 volts battery cutoff = 84 Amps

Your batteries can output up to 100 Amps each, 2x parallel strings is 200 Amp max rated.

205 AH (48 volt battery bank) / 84 Amps (3kW inverter/AC load) = 2.44 Hours to "battery dead" (lots of wiggle room, but close enough for this discussion)

The Growatt inverter is also an MPPT solar charge controller... 60-115 VDC input (Vmp-array-std rating????).

According to the EBay listing, this inverter is made in China (in the details). Pretty typical for electronics these days.

And you have 4x 400 Watt solar panels. From your link:

Specifications:

Rated Power: 400W
Open circuit voltage (VOC): 49.5 V
Max power voltage (VMP): 41.7 V
Short circuit current (ISC): 10.36 A
Max power current: 9.60 A

It looks like you would put 2 panels in series (Vmp-array=83.4 volts) by 2 parallel strings--Works with the Growatt input (it looks like). And room to grow with more panels, if you wish later.

Assuming you are around Phoenix, AZ, panels mounted flat to roof of RV:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Phoenix
Average Solar Insolation figures

Measured in kWh/m2/day onto a horizontal surface:

Jan	Feb	Mar	Apr	May	Jun
3.20	4.07	5.45	6.62	7.37	7.52
Jul	Aug	Sep	Oct	Nov	Dec
6.78	5.97	5.45	4.48	3.50	2.95

Toss bottom 3 months (use less power, use genset, and/or tilt array for better sun):

1,600 Watt array * 0.61 AC off grid system eff with Li Ion batteries * 4.07 hours of sun per day (Feb average) = 3,972 WH per day

Does look a pretty capable system (I don't know anything about the components--I am not in the solar business).

Before you buy the AC inverter, I would try to get the Owners/Installer's manual and make sure that everything you get works "nicely" together (don't see any major issues--Other than that is a pretty big AC inverter for the battery bank+solar array--But if it does what you want....)

So, it can work... Is it "useful" for you. As always, trust but verify the information I have here and from the Mfgs.

-Bill "in my humble opinion".

2000tranzam · April 2020

BB. said:

Assuming 8x 12 volt @ 105 AH batteries for a 48 Volt @ 210 AH battery bus... The battery specs:

https://lionenergy.com/products/lion-safari-ut-1300

And a bit more information for the AC inverter:

https://usa-mpp-solar.com/manuals/gw/Growatt%20SPF%203000TL%20LVM%20Datasheet.pdf

A 3kWatt inverter would draw (at max load, 2x that for surge):
3,000 Watts * 1/0.85 AC inverter eff * 1/42 volts battery cutoff = 84 Amps
Your batteries can output up to 100 Amps each, 2x parallel strings is 200 Amp max rated.
205 AH (48 volt battery bank) / 84 Amps (3kW inverter/AC load) = 2.44 Hours to "battery dead" (lots of wiggle room, but close enough for this discussion)
The Growatt inverter is also an MPPT solar charge controller... 60-115 VDC input (Vmp-array-std rating????).

According to the EBay listing, this inverter is made in China (in the details). Pretty typical for electronics these days.

And you have 4x 400 Watt solar panels. From your link:
Specifications:
Rated Power: 400W
Open circuit voltage (VOC): 49.5 V
Max power voltage (VMP): 41.7 V
Short circuit current (ISC): 10.36 A
Max power current: 9.60 A
It looks like you would put 2 panels in series (Vmp-array=83.4 volts) by 2 parallel strings--Works with the Growatt input (it looks like). And room to grow with more panels, if you wish later.

Assuming you are around Phoenix, AZ, panels mounted flat to roof of RV:
http://www.solarelectricityhandbook.com/solar-irradiance.html
Phoenix
Average Solar Insolation figures
Measured in kWh/m2/day onto a horizontal surface:
Jan Feb Mar Apr May Jun
3.20
4.07
5.45
6.62
7.37
7.52

Jul Aug Sep Oct Nov Dec
6.78
5.97
5.45
4.48
3.50
2.95

Toss bottom 3 months (use less power, use genset, and/or tilt array for better sun):
1,600 Watt array * 0.61 AC off grid system eff with Li Ion batteries * 4.07 hours of sun per day (Feb average) = 3,972 WH per day
Does look a pretty capable system (I don't know anything about the components--I am not in the solar business).

Before you buy the AC inverter, I would try to get the Owners/Installer's manual and make sure that everything you get works "nicely" together (don't see any major issues--Other than that is a pretty big AC inverter for the battery bank+solar array--But if it does what you want....)

So, it can work... Is it "useful" for you. As always, trust but verify the information I have here and from the Mfgs.

-Bill "in my humble opinion".

Bill, you are the man. Thank you for all your input and quick responses. I calculated to have approx 5 hours of sunlight on the lower end to use as a baseline figuring I would get more hours during any time it is not winter. So I figured 5 hours at 1600 watts would be about 8000 watts that were replenish-able during the day. I did not realize you need to multiply that number by .61

My concern is we either have rolling blackouts or some how complete outages due to not enough people in the workforce keeping the grid on. I know the chances of that are horrifically unlikely but my motto has always been better to have it and not need it then need it and not have it.

Main components I would be running that would consume electricity are the deep freeze and air conditioning unit to keep a room cool so we dont die from heat exhaustion. I think its about 700 watts each give or take, and I know I should be able to run the freezer intermittently to keep it cool enough to prevent food from going bad. Figure maybe the AC could run from 10 am to 6 for 30 min intervals on and off, so that would use about 2800 watt hours (although might let it run throughout the day since its a heavier load and we have free energy during that time). The 700 watts from the freezer is actually peak wattage usage so Ill have to see what it actually uses. Do I just let it run for 24 hours then divide by the 24 to get average hourly usage?

So lets just say it uses an average of 350 watts per hour. I figure I can prob run it for 12 hours, so thats about 4300 watt hours. so between the 2800 and 4300 we've got about 7100 watt hours. Lets assume I replenish 4k watt hours from solar. that means that I would have about 3100 less watt hours from the total capacity? So if its 1344 per battery x 8 batteries = 10752 watt hours... and you remove the loss @ 85% you get 10752 x .85 = 9139 watt hours. Then you subtract the 3100 from that 9139 to get 6039 total watt hours available after those loads are imposed? If my math is wrong please correct me, Im trying to learn.

Thanks again and I appreciate all the guidance.

Oh, P.S. Another question I had... for that hybrid controller unit, for the output it was mentioned to get an extension cord, cut it, and just wire it in directly to the unit using the ground, hot and neutral line... would I be able to use a surge protector that has multiple outlets instead of a single prong plug? I figure I would be ok as long as Im under the 15 amp fuse load or whatever it is?

BB. · April 2020

The 0.61 derating factor... I was a "bit conservative" on that number... Things get a bit more complicated if you harvest/use more power during the day (directly from solar panel), plus power at night--Because there are multiple deratings. Also, Li Ion batteries are almost 100% efficient--So have less losses than AGM or Flooded cell and Li Ion do not have the Day vs Night derating factor difference.

Some estimates would be (not too conservative, but not "optimistic" numbers):

0.81 derating for "hot panels" (vs standard test conditions/marketing numbers from Solar Panel companies)
0.95 Efficiency of MPPT solar charge controllers
0.85 Efficiency of AC inverters
0.80 Flooded Cell Battery eff
0.90 AG Battery eff
1.00 LI Ion battery eff...

So, the end to end charging efficiency factor for your Li Ion based system with AC inverter

0.81 Panel * 0.95 MPPT charge controller * 1.0 Li Ion battery eff * 0.85 AC inverter eff = 0.65 end to end eff (not 0.61 I used above)

And example for Flooded Cell Battery (charge during day, discharge at night):

0.81 panel * 0.95 MPPT controller * 0.80 FLA battery * 0.85 inverter eff = 0.52 end to end FLA system (AC+Day/Night usage)
0.81 panel * 0.95 MPPT controller * 0.85 AC inverter = 0.65 Day Time only system eff (direct from Solar to AC inverter)

Note that I use 0.77 derating (or 0.75 used by some other here) for Solar Panel + Charge Controller derating. For properly designed solar systems, both MPPT and PWM have pretty much the same "deratings" (of 0.77) in warm to hot climates. MPPT controller only "outperform" PWM systems in cold to subfreezing climates. Panel Vmp "falls" as panels get hot. MPPT controller "get more efficient" as solar cell temperatures fall (typically in subfreezing conditions) vs PWM "efficiency" which stays (typo) the same over temperature (PWM controllers cannot "take advantage" of rising Vmp as temperatures fall).

There are other variations, AC inverter efficiency depends on output loading... Many are close to 95% efficient at mid range loading. At very low loading (big inverter, small AC loads) and very high loadings (100%), they can fall to 85% eff (full loading) to well below 85% when very low AC loads (i.e., 30 Watt load and 30 Watt Tare loss, ~50% eff).

With solar power--Any power numbers/estimates that are within 10% of measured values are pretty much "dead on". There are lots of variations--Both in weather conditions, hardware, how it is operated and even with the accuracy of the measuring equipment.

Most of the time, the above (relatively conservative numbers and fudge factors) are close enough for 90% of the operational time/most installations. For those times when the system is operating in dead of winter, yes yout get a "bonus" in energy harvest with MPPT based controllers.

-Bill

Photowhit · April 2020

2000tranzam said:

No way will I have enough space to fit that many batteries in the travel case to create 500amp hours of 48 volt storage... the idea of this is to be able to take it on camping trips too... they arent just sitting on a shelf somewhere.

So is this going to be a mobile array mounted on the roof of a camper?

2000tranzam · April 2020

BB. said:

Assuming 8x 12 volt @ 105 AH batteries for a 48 Volt @ 210 AH battery bus... The battery specs:

https://lionenergy.com/products/lion-safari-ut-1300

And a bit more information for the AC inverter:

https://usa-mpp-solar.com/manuals/gw/Growatt%20SPF%203000TL%20LVM%20Datasheet.pdf

A 3kWatt inverter would draw (at max load, 2x that for surge):
3,000 Watts * 1/0.85 AC inverter eff * 1/42 volts battery cutoff = 84 Amps
Your batteries can output up to 100 Amps each, 2x parallel strings is 200 Amp max rated.
205 AH (48 volt battery bank) / 84 Amps (3kW inverter/AC load) = 2.44 Hours to "battery dead" (lots of wiggle room, but close enough for this discussion)
The Growatt inverter is also an MPPT solar charge controller... 60-115 VDC input (Vmp-array-std rating????).

According to the EBay listing, this inverter is made in China (in the details). Pretty typical for electronics these days.

And you have 4x 400 Watt solar panels. From your link:
Specifications:
Rated Power: 400W
Open circuit voltage (VOC): 49.5 V
Max power voltage (VMP): 41.7 V
Short circuit current (ISC): 10.36 A
Max power current: 9.60 A
It looks like you would put 2 panels in series (Vmp-array=83.4 volts) by 2 parallel strings--Works with the Growatt input (it looks like). And room to grow with more panels, if you wish later.

Assuming you are around Phoenix, AZ, panels mounted flat to roof of RV:
http://www.solarelectricityhandbook.com/solar-irradiance.html
Phoenix
Average Solar Insolation figures
Measured in kWh/m2/day onto a horizontal surface:
Jan Feb Mar Apr May Jun
3.20
4.07
5.45
6.62
7.37
7.52

Jul Aug Sep Oct Nov Dec
6.78
5.97
5.45
4.48
3.50
2.95

Toss bottom 3 months (use less power, use genset, and/or tilt array for better sun):
1,600 Watt array * 0.61 AC off grid system eff with Li Ion batteries * 4.07 hours of sun per day (Feb average) = 3,972 WH per day
Does look a pretty capable system (I don't know anything about the components--I am not in the solar business).

Before you buy the AC inverter, I would try to get the Owners/Installer's manual and make sure that everything you get works "nicely" together (don't see any major issues--Other than that is a pretty big AC inverter for the battery bank+solar array--But if it does what you want....)

So, it can work... Is it "useful" for you. As always, trust but verify the information I have here and from the Mfgs.

-Bill "in my humble opinion".

Bill, you are the man. Thank you for all your input and quick responses. I calculated to have approx 5 hours of sunlight as on the lower end to use as a baseline figuring I would get more hours during any time it is not winter. So I figured 5 hours at 1600 watts would be about 8000 watts that were replenish-able during the day. DIdnt realize you have to multiply that by .61

My concern is we either have rolling blackouts or some how complete outages due to not enough people in the workforce keeping the grid on. I know the chances of that are horrifically unlikely but my motto has always been better to have it and not need it then need it and not have it.

Main components I would be running that would consume electricity are the deep freeze and air conditioning unit to keep a room cool so we dont die from heat exhaustion. I think its about 700 watts each give or take, and I know I should be able to run the freezer intermittently to keep it cool enough to prevent food from going bad. Figure maybe the AC could run from 10 am to 6 for 30 min intervals on and off, so that would use about 2800 watt hours (although might let it run throughout the day since its a heavier load and we have free energy during that time). The 700 watts from the freezer is actually peak wattage usage so Ill have to see what it actually consumes. Is the best way to plug it into the kill a watt meter and just let it run for 24 hours then divide by 24 to get hourly average?

Lets be overbearing and say it uses 350 watts per hour... so lets say its running during the day when the suns out for 12 hours, and the other 12 hours its not running. So thats about 4300 watt hours (350x 12). So between the 2 appliances its around 7100 watt hours. So if I am able to replenish an average of about 4000 watts per day, that means Id only be about 3100 watts below my full battery level correct? And we calculate my total available being 1344watt hours per battery x 8 = 10752 watt hours@12 volts. So subtract the 3100 to get approx. 7650ish watt hours, which you multiply that by .85 from loss in inverter which = 7504 approx. watt hours of usage left over for time not being charged from the sun?

Just trying to understand the math so I know how to use what available power is there. Thanks again for all the help.

Estragon · April 2020

The freezer and air loads would be estimated as roughly running watts x duty cycle. A "normal" duty cycle might be 1/3 but running in high ambient temps might be higher.

Eg a 700w load might be 700w x 24hr x 1/3 duty = 5,600wh/day. For inverter losses, divide by 0.85 = 6,588. Multiplying by 1/.85 is the same as dividing by .85.

Running a freezer intermittently likely won't save much and may be a problem if it causes a defrost cycle to run more. Better to just adjust the thermostat up a bit if practical so it cycles normally. Avoid opening it and don't put warm stuff in while on solar/battery power. Better insulation can help a lot, providing you don't block the external heat dissipation (some use the metal skin for this).

2000tranzam · April 2020

Photowhit said:

2000tranzam said:

No way will I have enough space to fit that many batteries in the travel case to create 500amp hours of 48 volt storage... the idea of this is to be able to take it on camping trips too... they arent just sitting on a shelf somewhere.

So is this going to be a mobile array mounted on the roof of a camper?

No, with this setup Im just gonna lay out the panels in the back yard in a non fixed location, like on top of my hot tub cover so I can move them around if needed. Or if I go camping I can always throw them in the truck with the rest of the setup.

706jim · April 2020

(I haven't read every post in this thread.....)

Just suggesting that if you're going to move panels around stick with smaller ones. a 1 x 2 meter panel is awkward to move with one person.

2000tranzam · April 2020

706jim said:

(I haven't read every post in this thread.....)

Just suggesting that if you're going to move panels around stick with smaller ones. a 1 x 2 meter panel is awkward to move with one person.

Im planning on building retractable wheels with leg stands for each panel so I can just roll it around... I know they are heavy, big and awkward but they are just mainly gonna be used for testing and if SHTF. Maybe camping.

softdown · April 2020

Like BB said - six batteries doesn't work for your plans. Neither does running full time A/C in Phoenix without spending more serious money.
Thinking 48 volt system with 3.5 kW (3500 watts) inverter or better - the better ones can support surge loads for a certain period of time.

You are thinking of extended power outages. Phoenix is not where I'd want to be in that case. So I may focus on portability. Which 400 panels don't fit very well.

A swamp cooler could make things bearable while using a sustainable amount of energy. They can work well in dry environs like Arizona. It is still too hot to be comfortable - the goal is survivability.

Welcome to do-it-yourself off grid solar. Where everybody makes major miscalculations the first time around.

Costco will take the batteries back. Get eight of their $90 golf cart batteries for this application.

Oh boy - investing in a big off grid solar system in case the power goes out for good in Phoenix. I guess we all have our monsters to fight.

If the grid goes down for months/years - hot cities will not be the place to be. At all. Unless you have a shooter for literally every window I would think. We can't seem to make our own face masks now. The grid going down would literally be hell on earth. Years to have our Asian manufacturers replace our transformers. Some of them only accessible by railway spurs that no longer exist. Long term planning is not our forte. Now "mining the moon" (putting nuclear missiles on the moon)? Yep - on that.

2000tranzam · April 2020

softdown said:

Like BB said - six batteries doesn't work for your plans. Neither does running full time A/C in Phoenix without spending more serious money.
Thinking 48 volt system with 3.5 kW (3500 watts) inverter or better - the better ones can support surge loads for a certain period of time.

You are thinking of extended power outages. Phoenix is not where I'd want to be in that case. So I may focus on portability. Which 400 panels don't fit very well.

A swamp cooler could make things bearable while using a sustainable amount of energy. They can work well in dry environs like Arizona. It is still too hot to be comfortable - the goal is survivability.

Welcome to do-it-yourself off grid solar. Where everybody makes major miscalculations the first time around.

Costco will take the batteries back. Get eight of their $90 golf cart batteries for this application.

Oh boy - investing in a big off grid solar system in case the power goes out for good in Phoenix. I guess we all have our monsters to fight.

If the grid goes down for months/years - hot cities will not be the place to be. At all. Unless you have a shooter for literally every window I would think. We can't seem to make our own face masks now. The grid going down would literally be hell on earth. Years to have our Asian manufacturers replace our transformers. Some of them only accessible by railway spurs that no longer exist. Long term planning is not our forte. Now "mining the moon" (putting nuclear missiles on the moon)? Yep - on that.

So like I said before, I ended up getting 2 more of those batteries, and got them all setup in my container, which is relatively portable considering the power it provides : https://i.imgur.com/wQrKObw.jpg

I understand the panels are a bit big but if shit ever does hit the fan I can totally manage them all myself i needed. I ended up getting this hybrid 3000 watt inverter/charger : https://i.imgur.com/GuCbqfz.jpg

The plan is just to get through summer if things did go south as most everyone would be trying to leave at the same time... so Ive got food and water that would last me a bit. Just dont want to get stuck with everyone else. Once fall/winter comes I can reassess the situation.

But as far as my output that connects to it, can I use a multi outlet surge protector or does it have to be a single output cord?

BB. · April 2020

Of course, you don't have to follow codes... But I would suggest that if you wish to use the full capacity of that 3,000 Watt AC inverter, that you break the output into to 2x 15 amp circuits (or whatever meets your needs). 3,000 Watts, nominally:

3,000 Watts / 120 Volts = 25 Amps max continuous output

Get a small subpanel from Home Depot (or there are construction J-boxes that can be used too). Nominally, 2x 15 Amp circuits of 14 AWG (minimum wiring) getting power from 2x 15 amp breakers.

The "standard" household 120 VAC plug is rated for 15 amps (you can get 15/20 amp rated receptacles too).

What you don't want to do is supply 25 Amps to your 15 amp rated power strips/extension cords (for example).

You can find temporary pre-wired/configured power boxes:

https://www.homedepot.com/p/Midwest-Electric-Products-70-Amp-Temporary-Power-Box-with-GFCI-and-50-Amp-Outlet-Top-Feed-U055GP/100187107

Or you can get a small sub panel and build your own to meet your needs:

https://www.homedepot.com/p/Square-D-QO-100-Amp-6-Space-12-Circuit-Outdoor-Main-Lug-Load-Center-with-Cover-QO612L100RBCP/100071456

Or even setup a transfer switch (source: AC mains / Solar Inverter / etc.):

https://www.homedepot.com/p/Reliance-Controls-30-Amp-6-Circuit-Manual-Transfer-Switch-306A/206499418

There are just so many choices--And to a degree code/danger. Improperly connected transfer switches back to the main house wiring--Code/danger of fire/damage to genset/inverter, danger to linemen, etc...

You can just run extension cord(s) from outside into the house to your loads that needed backup power--That is a pain (did that with a small genset when California shut down utility power because of high winds in parts of the state (including some urban areas too).

Doing it right can be a bit of a pain, and can be expensive (my need to hire a licenced electrictrician, may need building permit, etc.). And if you choose to hardwire some existing circuits in the home so you can supply backup power easily (refrigerators, some lighting, a few outlets around the home, etc.)... A sub panel, transfer switch, etc...

Lots of ways of doing this (and I am certainly no electrician or contractor).

-Bill

softdown · April 2020

In retrospect the lithium batteries offer many advantages in longevity and portability. You are getting ti done. Since this is for emergencies that may never happen - I might evaluate two 12 AWG well insulated extension cords with surge protected multi-outlets. Keep it mostly stashed away yet readily accessible should the need arise.

And a campers toilet and a lot of good water. I had considerable chagrin about my extensive prepping - then suddenly everyone started prepping. Yet demonstrated a high degree of purely emotional reactions.

The toilet paper syndicate won.

softdown · April 2020

Costco sells two 50' 12 AWG extension cords for about $35. 100' ext. cords are very prone to bothersome tangles if one packs them away.

2000tranzam · May 2020

Ok so I actually ended up building the setup and it works great... however I did a load test and use a power meter to determine how much KWH usage I actually got. The battery was fully charged to about 53.5 volts give or take, then seemed to shut off around 50.1 volts (which doesnt make sense because the inverter charger I used has a low voltage cut off of 48 volts. Total KWH usage was about 4.434, which seems really low. I mainly did a test on my freezer to see how efficient things were. The freezer was able to run for about 4.5 days on this system alone without any other devices connected. Seems quite a bit lower than I was expecting... am I supposed to be only able to use 40% of the 10+KWH system? Am I doing something wrong? After the battery died, I shut the inverter off, turned it back on and started charging it again... however Soon as the system came back up it looked like the voltage said it was around 38 volts which makes no sense. How can it go from 50.1 volts to 38, and why didnt it run down to 48 volts to give me more usage?

Sorry for the delayed responses but thank you for any input.

Also I want to add this 12 volt addition so I can have access to usb ports and 5 volt cig lighter accessory... but Im pretty sure I need to have a fuse or breaker in between it and the battery bank for the power leg. https://www.amazon.com/gp/product/B0741CHQ49/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

What size fuse/breaker would I need to put in line for this?

Thanks again.

BB. · May 2020

Not sure why the 38 volts... Can you tell us what your final system ended up being (array, charge controller, AC inverter, battery bank, etc.)...

Setting to 48 volts LBCO--That is still sort of high... And if you have any surge current (starting fridge/freezer/well pump/etc.), the short surge could take 50 volts down to 48 volts for a few seconds or longer.... Some LBCO shutdown imediatly at xx volts, others will need to see less than XX volts for y minutes or such.

Regarding the 12 volt panel... How do you plan on getting 12 VDC to the panel? You do not want to take 12 volts from your 48 volt battery bank... You will have 12 volt battery section under charged/over discharged, and the other 36 volt section full or over charged (you are "unbalancing the battery bank". This is very hard on FLA battery banks, and something that should never be done on AGM or Li Ion banks.

The two standard options for 12 VDC from 48 VDC battery bank... One is to get a DC to DC down/buck mode switching converter/power supply:

https://www.amazon.com/s?k=dc+to+dc+step+down+converter

Another option is to setup a separate 12 volt battery bank and use a DC to DC battery charger or AC to DC battery charger...

-Bill

2000tranzam · May 2020

BB. said:

Not sure why the 38 volts... Can you tell us what your final system ended up being (array, charge controller, AC inverter, battery bank, etc.)...

Setting to 48 volts LBCO--That is still sort of high... And if you have any surge current (starting fridge/freezer/well pump/etc.), the short surge could take 50 volts down to 48 volts for a few seconds or longer.... Some LBCO shutdown imediatly at xx volts, others will need to see less than XX volts for y minutes or such.

Regarding the 12 volt panel... How do you plan on getting 12 VDC to the panel? You do not want to take 12 volts from your 48 volt battery bank... You will have 12 volt battery section under charged/over discharged, and the other 36 volt section full or over charged (you are "unbalancing the battery bank". This is very hard on FLA battery banks, and something that should never be done on AGM or Li Ion banks.

The two standard options for 12 VDC from 48 VDC battery bank... One is to get a DC to DC down/buck mode switching converter/power supply:

https://www.amazon.com/s?k=dc+to+dc+step+down+converter

Another option is to setup a separate 12 volt battery bank and use a DC to DC battery charger or AC to DC battery charger...

-Bill

Ok so I ended up having 4 x 400 watt 24 volt panels, 2 will be wired in series, and then those 2 will be wired in parallel. Here are the panels : https://store.santansolar.com/product/jinko-400w/
Rated Power: 400W
Open circuit voltage (VOC): 49.5 V
Max power voltage (VMP): 41.7 V
Short circuit current (ISC): 10.36 A
Max power current: 9.60 A
Maximum system voltage: 1000V IEC
Power Tolerance: 0~+3%
Fuse Rating: 20 A
Frame: Anodized silver aluminum alloy
Weight: 49.6 lbs
Dimensions: 79.06″ x 39.45″ x 1.57″

I havent actually connected, ran and test charged from the panels yet cause they are big mofo's and I havent had time to clear an area out to try them yet.

Here is the charger/inverter/controller https://usa-mpp-solar.com/manuals/gw/Growatt%20SPF%203000TL%20LVM%20Datasheet.pdf

Here are the batteries, I ended up going with 8 total : https://lionenergy.com/products/lion-safari-ut-1300

I also ran 2 100 amp breakers on each power line from each of the "2" 48 volt lines, and from there ran to a distribution block, and then ran directly to the inverter as seen here :

Regarding the shutdown from the LBCO, since it was connected to a freezer i know it does have surges up to approx 597 watts, but this inverter should be good for 3000 watts minimum, prob close to 6000 peak. From what the battery company suggested, they suggested cutting power at 48 volts to be safe... I thought it should be a bit lower, like closer to 44 or 46 volts from what Ive been reading... or is that not safe for the life of the batteries?

Regarding my 12 volt situation, I already bought one of these guys... so I would just run the positive wire from the 48 volt part of the converter regulator to the red power distribution block that has both 48 volt 4 gauge wires already ran to it, so it would be reading off 48 volts, not 12. And then I figure I need a fuse or breaker on the power line from the 12 volt portion of the converter regulator to the 12 volt panel, but what size?
https://www.amazon.com/gp/product/B0756T983Q/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1

2000tranzam · June 2020

bump

mike95490 · June 2020

I've got nothing to add. You seem to have painted yourself into a corner.

You HAVE to understand the battery operating range and how in intersects with the inverter voltages and amp draw of your loads

Photowhit · June 2020

2000tranzam said:

Ok so I actually ended up building the setup and it works great... however I did a load test and use a power meter to determine how much KWH usage I actually got. The battery was fully charged to about 53.5 volts give or take,

It would be good to check your battery spec's, from the link you provided for the battery, which doesn't understand spec's IMHO, since this info is not under Spec's;

53.5 volts represents about 13.4 volts in a comparable 12 volt system. So perhaps around 50-60% (dumb guess)

Since Lithium batteries need very little voltage above the existing voltage to charge, I'd assume 14.6 x 4= 58.4 or there abouts to be fully charged. I would ask them for a discharge curve, it may be that it has a very steep knee (which I think Lithium do in general) and it went from 51 to 38 volts with only a minimal discharge.

What You Need To Know About LiFePO4 Batteries - Off Grid Ham

I'd suggest losing the ring posts and buying some power distribution blocks, (you're throwing a ton on money at this, might as well build it right IMO)

Hope this helps.

Help me build my off grid system... dont know which direction to go.

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Help me build my off grid system... dont know which direction to go.

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Specifications:

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Phoenix
Average Solar Insolation figures

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