48v residential total off grid system

bushi12

Solar Enthusiast
Joined
Sep 19, 2021
Messages
94
Building my first 48v residential total off grid system. looking at 10-13kwh day. Planning on doing the 13kwh system Will did on his video. My main question is the size of the battery(lithium) and number of solar panels. I am figuring 3 days storage. If I'm doing it correctly I need about 2000ah. Is this correct? Would 20 of the 450w bifacial panels that are in his video be sufficient. I would rather get what I need once so I only cry once. thanks for your input!! North Central Texas area 4-5hrs sun from what I've seen.
 

Roswell Bob

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Joined
Dec 5, 2020
Messages
450
Location
Warner, NH
Yes, it seems the usual rule of thumb is 3x your daily usage in kWh for cell storage. I suppose a 16S2P array of the 280Ah cells would be good. Maybe split into 2 systems would be good. If one go down you have another. I think 2000Ah is about 100kWh at 50v so maybe too big for your needs. For 5 hours of sun you would need near 3kW in panels. I have similar system and use 4kW worth of panels. It is nice to not have to run backup generator. So I think maybe 8-10 panels may be good for you. I have split my solar array into 2 independant systems with their own charge controller for some redundancy. You may want to do that.
 

bushi12

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Joined
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Messages
94
Yes, it seems the usual rule of thumb is 3x your daily usage in kWh for cell storage. I suppose a 16S2P array of the 280Ah cells would be good. Maybe split into 2 systems would be good. If one go down you have another. I think 2000Ah is about 100kWh at 50v so maybe too big for your needs. For 5 hours of sun you would need near 3kW in panels. I have similar system and use 4kW worth of panels. It is nice to not have to run backup generator. So I think maybe 8-10 panels may be good for you. I have split my solar array into 2 independant systems with their own charge controller for some redundancy. You may want to do that.
I suppose a 16S2P array of the 280Ah cells would be good. Sorry for my Lack of knowledge but I don't know what this means.
If I'm understanding you I could get by with 10 panels split into 2-5 series systems. What Ah would be sufficient? 600, 800 or 1000?
 

bushi12

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Sep 19, 2021
Messages
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I suppose a 16S2P array of the 280Ah cells would be good. Sorry for my Lack of knowledge but I don't know what this means.
If I'm understanding you I could get by with 10 panels split into 2-5 series systems. What Ah would be sufficient? 600, 800 or 1000?
Sorry I googled it and see your talking about building a battery. I'm really knew to this. That shows to by 560Ah so 600 would answer my question about that. I really appreciate your help!!!
 

chrisski

Photon Sorcerer
Joined
Aug 14, 2020
Messages
2,383
In my signature block there is a solar calculator for off grid that will help you determine Your needs. My guess is you probably need more power in the summer when there’s more sun than in the winter when there’s less. Which is a good thing.

Also in my signature block is another one (Same System, Different Areas, huge difference) about determining the size of the array and battery bank based off the days from the calculator. I think Texas is more like AZ in that example which is perfect for solar, versus Cloudy Seattle Which is much worst.

You do need to take your 13 kWh requirement and figure how many days to go without the sun before firing up a generator to recharge. This may up your requirement to 26 kWh or even 39 kWh. If you review the link I mentioned above, you really get to see a lesser power requirement in the winter months with those shorter days helps with how much back up you need. Usually AC will drive that high summer requirement.

Depending on the Ah of your 48 volt bank, that may take you outside the type of generator you get at Home Depot. I’m going to 24 volts, and will have the capability to recharge a 580 ah bank at 35 amps, with a generator you get from Home Depot, but if battery bank really depleted, that generator will be on all night long and that won’t recharge the battery bank, maybe 70% recharged. The guys with forklift batteries for 48 volt systems need a lot more to recharge. I think they say thinks like 10kw diesel generators.
 
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bushi12

Solar Enthusiast
Joined
Sep 19, 2021
Messages
94
In my signature block there is a solar calculator for off grid that will help you determine Your needs. My guess is you probably need more power in the summer when there’s more sun than in the winter when there’s less. Which is a good thing.

Also in my signature block is another one (Same System, Different Areas, huge difference) about determining the size of the array and battery bank based off the days from the calculator. I think Texas is more like AZ in that example which is perfect for solar, versus Cloudy Seattle Which is much worst.

You do need to take your 13 kWh requirement and figure how many days to go without the sun before firing up a generator to recharge. This may up your requirement to 26 kWh or even 39 kWh. If you review the link I mentioned above, you really get to see a lesser power requirement in the winter months with those shorter days helps with how much back up you need. Usually AC will drive that high summer requirement.

Depending on the Ah of your 48 volt bank, that may take you outside the type of generator you get at Home Depot. I’m going to 24 volts, and will have the capability to recharge a 580 ah bank at 35 amps, with a generator you get from Home Depot, but if battery bank really depleted, that generator will be on all night long and that won’t recharge the battery bank, maybe 70% recharged. The guys with forklift batteries for 48 volt systems need a lot more to recharge. I think they say thinks like 10kw diesel generators.
Okay when you say increase to 26 or 39 kWh are you meaning adding another LV6548 6.5KW - 120v Solar inverter 8kW -2 x 4kW 250V MPPT to the 2 that i'm already planning on using? Or you mean increasing my solar panels and battery bank?
 

chrisski

Photon Sorcerer
Joined
Aug 14, 2020
Messages
2,383
Okay when you say increase to 26 or 39 kWh are you meaning adding another LV6548 6.5KW - 120v Solar inverter 8kW -2 x 4kW 250V MPPT to the 2 that i'm already planning on using? Or you mean increasing my solar panels and battery bank?
That would be battery storage. Even here in Sunny Arizona, we have 65 cloudy days a year. Some of these are over a three or four days. The cloudy days I have been set up, my panels have made 1/6 th the normal power. I'm only an RV set up with maybe 3.5kwh a day of production. Once fully charged, I have about 2.5 kwh of usable battery power.

When that cloudy day charging drops to 500 or 600wh a day, I have enough battery to make it through one day with little sun, but I start running the generator that night.

I'm increasing battery capacity in my RV a bit to 10 kwh useable, and that way I can wait another 48 hours until I turn the generator on. I plan for two entire days with no sun. Most times I can last weeks, but its the cold nights the propane blower motor for the heater comes on that I use the 3.5 kwh of power. Most days my power usage are much less, some 400 watt hours of power. So I built my new battery pack so it would hold more than 7 kwh of useable power, or two days of no sun. Most times I don't use heat, but I have to plan my battery pack for my worst case.

It really comes down to how much you're willing to run the generator, or hook to the grid. Each 16 cells of 280 ah eve gives you about 10 kwh of energy off a 48 volt battery. Each of those is at least $5k to assemble. One of those batteries will last you through the night, and if there's enough panels and sun, you'll make it through the next day fully charged at sun down. Its when its been a cloudy day where its a problem. A single Aims 120 volt charger will charge batteries at 18 amp hours, so leaving the generator on all night will get you though the night and provide about 4 kwh of total power.
 

OffGridInTheCity

Solar Addict
Joined
May 23, 2021
Messages
448
Location
Southern Oregon
Building my first 48v residential total off grid system. looking at 10-13kwh day. Planning on doing the 13kwh system Will did on his video. My main question is the size of the battery(lithium) and number of solar panels. I am figuring 3 days storage. If I'm doing it correctly I need about 2000ah. Is this correct? Would 20 of the 450w bifacial panels that are in his video be sufficient. I would rather get what I need once so I only cry once. thanks for your input!! North Central Texas area 4-5hrs sun from what I've seen.
I have a 12.8kw PV array and 81kwh battery bank in an off-grid configuration - and nearing 3 years of operation - so I have good solid numbers as follows:.
*The array produces 18,000kwh/year or 49kwh/day. I get 15,000kwh/year of usable power - e.g. 83% overall efficiency and 41kwh/day. Note: I have AIMS ETL inverters and this is the biggest loss of efficiency in my system.
*Spring/summer I get 2000kwh/month of useable power
* Winter is 500kwh/month - about 25% of summer.
* My average consumption is 3000watts/hour over 5,000hrs per year. This is an average of 13.7hrs/day @ 3000w = 41kwh/day of solar power.
* My average DOD on my 81kwh battery bank is 40%.


Building my first 48v residential total off grid system. looking at 10-13kwh day. My main question is the size of the battery(lithium) and number of solar panels.
By extrapolation, to get 13kwh/day (on average) of useable power at 80% DOD you'll need at least 32% of what I'm running which is:
1) 4.1kw PV array
2) 13kwh battery

If you want this thru winter - e.g. 13kwh/day, you'll need
1) 10.3kw PV array
2) 33kwh battery
but of course you'll have 39kwh to 50kwh/day in summer - e.g. significant excess over 13kwh in winter.


I am figuring 3 days storage. If I'm doing it correctly I need about 2000ah. Is this correct?
13kwh/day * 3 days = 39kwh/day of useable battery. At 80% DOD that's 50kwh of battery. 48v@2000ah = 96kwh of battery - e.g. more like 13 * 6 days.


Would 20 of the 450w bifacial panels that are in his video be sufficient.
20 * 450w = 9kw PV array. My estimate is 10.3kw - so this is in the ball park.

I would rather get what I need once so I only cry once. thanks for your input!! North Central Texas area 4-5hrs sun from what I've seen.
Suggest PVwatts https://pvwatts.nrel.gov/ web site as a way to compare your area to my numbers for adjustments.
If you run PVwatts for your location on 9kw PV array you can get a percent of 18,000kwh/year that I get and adjust from my numbers and be pretty close. Here's the breakdown of how my numbers add up to 18,000kwh/year of PV production.
1632116900808.png

**Best advice: If you can - start at your 20 (or whatever you decide) panels but try to leave room for more - more panels, more charge controllers / inverters, more wiring, more batteries, more everything for future expansion. Once you get a system running - its SOOOOO COOOOL - you may very well want to expand it. That's what I did. Started with 24 panels and 30kwh of battery and expanded to 45panels and 81kwh of battery :)
 
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bushi12

Solar Enthusiast
Joined
Sep 19, 2021
Messages
94
That would be battery storage. Even here in Sunny Arizona, we have 65 cloudy days a year. Some of these are over a three or four days. The cloudy days I have been set up, my panels have made 1/6 th the normal power. I'm only an RV set up with maybe 3.5kwh a day of production. Once fully charged, I have about 2.5 kwh of usable battery power.

When that cloudy day charging drops to 500 or 600wh a day, I have enough battery to make it through one day with little sun, but I start running the generator that night.

I'm increasing battery capacity in my RV a bit to 10 kwh useable, and that way I can wait another 48 hours until I turn the generator on. I plan for two entire days with no sun. Most times I can last weeks, but its the cold nights the propane blower motor for the heater comes on that I use the 3.5 kwh of power. Most days my power usage are much less, some 400 watt hours of power. So I built my new battery pack so it would hold more than 7 kwh of useable power, or two days of no sun. Most times I don't use heat, but I have to plan my battery pack for my worst case.

It really comes down to how much you're willing to run the generator, or hook to the grid. Each 16 cells of 280 ah eve gives you about 10 kwh of energy off a 48 volt battery. Each of those is at least $5k to assemble. One of those batteries will last you through the night, and if there's enough panels and sun, you'll make it through the next day fully charged at sun down. Its when its been a cloudy day where its a problem. A single Aims 120 volt charger will charge batteries at 18 amp hours, so leaving the generator on all night will get you though the night and provide about 4 kwh of total power.
Okay thanks for the info I'd rather have a cushion of power for cloudy days.
 

bushi12

Solar Enthusiast
Joined
Sep 19, 2021
Messages
94
I have a 12.8kw PV array and 81kwh battery bank in an off-grid configuration - and nearing 3 years of operation - so I have good solid numbers as follows:.
*The array produces 18,000kwh/year or 49kwh/day. I get 15,000kwh/year of usable power - e.g. 83% overall efficiency and 41kwh/day. Note: I have AIMS ETL inverters and this is the biggest loss of efficiency in my system.
*Spring/summer I get 2000kwh/month of useable power
* Winter is 500kwh/month - about 25% of summer.
* My average consumption is 3000watts/hour over 5,000hrs per year. This is an average of 13.7hrs/day @ 3000w = 41kwh/day of solar power.
* My average DOD on my 81kwh battery bank is 40%.



By extrapolation, to get 13kwh/day (on average) of useable power at 80% DOD you'll need at least 32% of what I'm running which is:
1) 4.1kw PV array
2) 13kwh battery

If you want this thru winter - e.g. 13kwh/day, you'll need
1) 10.3kw PV array
2) 33kwh battery
but of course you'll have 39kwh to 50kwh/day in summer - e.g. significant excess over 13kwh in winter.



13kwh/day * 3 days = 39kwh/day of useable battery. At 80% DOD that's 50kwh of battery. 48v@2000ah = 96kwh of battery - e.g. more like 13 * 6 days.



20 * 450w = 9kw PV array. My estimate is 10.3kw - so this is in the ball park.


Suggest PVwatts https://pvwatts.nrel.gov/ web site as a way to compare your area to my numbers for adjustments.
If you run PVwatts for your location on 9kw PV array you can get a percent of 18,000kwh/year that I get and adjust from my numbers and be pretty close. Here's the breakdown of how my numbers add up to 18,000kwh/year of PV production.
View attachment 65455

**Best advice: If you can - start at your 20 (or whatever you decide) panels but try to leave room for more - more panels, more charge controllers / inverters, more wiring, more batteries, more everything for future expansion. Once you get a system running - its SOOOOO COOOOL - you may very well want to expand it. That's what I did. Started with 24 panels and 30kwh of battery and expanded to 45panels and 81kwh of battery :)
Wow I really appreciate the detailed explanation. I'll look further into my plan and try and get more accurate numbers. I definitely want room for expansion! Would it be better for me to build my battery bank or buy one? Cost wise. One person said a 10kWh battery bank would cost 5k I'm finding ones to buy cheaper.
 

OffGridInTheCity

Solar Addict
Joined
May 23, 2021
Messages
448
Location
Southern Oregon
Would it be better for me to build my battery bank or buy one? Cost wise. One person said a 10kWh battery bank would cost 5k I'm finding ones to buy cheaper.
Building you're own is cheaper, and sometimes *much much* cheaper BUT... it can be huuuuuge amount of work. I'm 18650 (second hand cells) and paid around $200-$250/kwh for 81kwh(s) after all was said and done but I'm retired and worked it part-time for several years.

Looking at https://bigbattery.com/ (as just one example) and dividing things out I see
48v@5.3kwh (LifePo4) for $2438 which would be $460/kwh
48v@2.1kwh (MNC) for $699 which would be $333/kwh
but with these, if you build a large battery bank with 10 of 1st or 25 of the 2nd - you have too many individual BMSs... and it may not be practical as they weren't designed to be part of a large battery bank.

For an example of something that can scale (cooperative BMSs) to 20, 30, 50kwh you can 'buy off the shelf', See @DavidPoz youtubes on EG4 (2nd generation Gyll) - https://shop.signaturesolar.us/products/48v-100ah-lifepower4-battery-by-eg4 48v@5.1kwh for $1500 would be $292/kwh. BUT it may be difficult to order them as they have been hard to get. But still - its a useful price comparison of what may be coming.

You may get comments on price/kwh. In my case - I bought high quality (90%, 95% original capacity) used cells from Battery Hookup and Battery Clearing House kind of thing - which cost $. If you had a source for second hand cells where you can get them free/cheap - then it dramatically changes the price / kwh.

Bottom line, in my opinion, there is huge potential for big big $ savings on DIY battery builds IF you can afford the time/effort. Its one of those things where you *actually* can save money thru DIY. But if you can't afford the time, don't beat yourself up, be patient, and there are deals to be had :)
 
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bushi12

Solar Enthusiast
Joined
Sep 19, 2021
Messages
94
Building you're own is cheaper, and sometimes *much much* cheaper BUT... it can be huuuuuge amount of work. I'm 18650 (second hand cells) and paid around $200-$250/kwh for 81kwh(s) after all was said and done but I'm retired and worked it part-time for several years.

Looking at https://bigbattery.com/ (as just one example) and dividing things out I see
48v@5.3kwh (LifePo4) for $2438 which would be $460/kwh
48v@2.1kwh (MNC) for $699 which would be $333/kwh
but with these, if you build a large battery bank with 10 of 1st or 25 of the 2nd - you have too many individual BMSs... and it may not be practical as they weren't designed to be part of a large battery bank.

For an example of something that can scale (cooperative BMSs) to 20, 30, 50kwh you can 'buy off the shelf', See @DavidPoz youtubes on EG4 (2nd generation Gyll) - https://shop.signaturesolar.us/products/48v-100ah-lifepower4-battery-by-eg4 48v@5.1kwh for $1500 would be $292/kwh. BUT it may be difficult to order them as they have been hard to get. But still - its a useful price comparison of what may be coming.

You may get comments on price/kwh. In my case - I bought high quality (90%, 95% original capacity) used cells from Battery Hookup and Battery Clearing House kind of thing - which cost $. If you had a source for second hand cells where you can get them free/cheap - then it dramatically changes the price / kwh.

Bottom line, in my opinion, there is huge potential for big big $ savings on DIY battery builds IF you can afford the time/effort. Its one of those things where you *actually* can save money thru DIY. But if you can't afford the time, don't beat yourself up, be patient, and there are deals to be had :)
Okay can't thank you enough for the details. I'm not knowledgeable enough right now to do what sounds like is required to DIY. It maybe better to buy. Time is also a factor as well.
 

Pyrofx

Flux capacitor builder
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Jul 27, 2020
Messages
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Location
Oatman Az
DIY is not hard. 13kwh is doable for about 2600. Using cells from amy in texas and chargery bms.
Just ask lots of questions before buying stuff. To many people buy the wrong parts then say ah crap.
 

bushi12

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Joined
Sep 19, 2021
Messages
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DIY is not hard. 13kwh is doable for about 2600. Using cells from amy in texas and chargery bms.
Just ask lots of questions before buying stuff. To many people buy the wrong parts then say ah crap.
How do I get in contact with cells from amy in Texas?
 

toms

Solar Addict
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Messages
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If you are able to run a generator, including it in your system plan will be the most cost effective.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,409
How do I get in contact with cells from amy in Texas?

Check out Ghostwriter's new love.
She has lots of experience buying cells.

 

bushi12

Solar Enthusiast
Joined
Sep 19, 2021
Messages
94
Check out Ghostwriter's new love.
She has lots of experience buying cells.

Will do thanks!
 

bushi12

Solar Enthusiast
Joined
Sep 19, 2021
Messages
94
Will do thanks!
I looked into this and am very interested in building a battery bank from them. I can drive to their Houston warehouse and get them. My question is how many do I buy for a 30kWh storage? Would it be like building 4 16s strings at 280ah?
 
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