100% off-grid system from the ground up, literally.

Skysthelimit

New Member
Greetings Experts: It's time for me to get serious about creating a power station for my soon to be built barn style home in Southern Utah. I understand a bit about the differences between a 12, 24, and 48 volt system so I've settled on a 48 volt system. I am in the process of drawing out the various circuits and determining the inverter type, wattage, and number. What I have not settled on yet is which cells to use to build my system and what BMS to use. There are so many to choose from and I've watched so many great videos that I'm overloaded with information and there's no clear leader in the industry, at least to my knowledge.

I would sure appreciate some input from anyone who has experience building with raw cells and BMS to make a 48 volt system suitable to power my barn/home that will have a living area of 20 x 40' (2 bedrooms, bathroom, and kitchen/dining/living area) with an equal sized basement right below. Along side that there's a RV garage that's also 20 x 40' and above that there's a loft, again, 20 x 40'. Another 20 x 40' garage is next to the RV garage but it won't need too much in the way of power, at 1st.

Your advice would be much appreciated. George
 

Craig

Watts are Watts!
Staff member
Moderator
If you can keep them warm enough to charge in the winter (above freezing) I think your best option will be to use the 280AH eve cells they are about $110- $125 each delivered in the quantities you want. this would give you 13kw for every 16 cells you need for your 48v system I would get 32 if it is in the budget and you should have plenty of power with extra for the long cold winter days. I like the Chagery BMS but it has its flaws but once you set it up properly its pretty much takes care of itself.
 

Skysthelimit

New Member
If you can keep them warm enough to charge in the winter (above freezing) I think your best option will be to use the 280AH eve cells they are about $110- $125 each delivered in the quantities you want. this would give you 13kw for every 16 cells you need for your 48v system I would get 32 if it is in the budget and you should have plenty of power with extra for the long cold winter days. I like the Chagery BMS but it has its flaws but once you set it up properly its pretty much takes care of itself.
Craig,

Thank you very much for your response and advice. One of the main reasons we are having a basement dug is to put all the electrical components into it so that the battery cells stay above freezing. I'll look into the 280AH eve cells and the Chagery BMS. Have you used these components yourself?
 

Samsonite801

New Member
Craig,

Thank you very much for your response and advice. One of the main reasons we are having a basement dug is to put all the electrical components into it so that the battery cells stay above freezing. I'll look into the 280AH eve cells and the Chagery BMS. Have you used these components yourself?
I live in Utah as well, planning an off-grid home in a Self-Reliance community North of Delta, I just bought a LiFePO4 battery system from Treeline Power Systems: https://www.treelinepowersystems.com/LiFePO4-48V-512v-280ah-14kWh-Battery-System-wIth-BMS_p_37.html They come with the 280 ah cells. I just received the shipment a couple days ago. I ordered 2 of the 14 kW/h 48v banks which is 32x cells total (which came with 2 BMS, one per bank, I got the 200a BMS option with mine). It came to $6548 shipped. The guy, Randy from there (Colorado) was very friendly and answered all my beginner questions and I felt good about getting from them. I was originally looking into buying direct from a China company, but the turnaround was something like 50 days doorstep to doorstep. This guy took about 2 weeks to assemble, test, and get them to me. The ones I got here don't come with any case or anything, just the cells and BMS units, all pre-wired, tested, and unconnected for transport. I haven't reconnected all the BMS and tested myself yet, since I am still planning my solar install soon, so maybe later I could report about how well they work. Hoping to try them soon, supposedly this should provide 28 kW/h with 2 48v banks in parallel. The guy said these BMS do balance on discharge, and have full over-voltage/under-voltage cutoff, and over-temp/under-temp cutoff, so they are fully protected. One reason I also decided to go with a local US supplier, is this guy says he will do advance replacement, so if I get a failed cell ever, he says he can ship new one first. He also said they do advance replacements on other parts they sell too. This is my first purchase from them but maybe I will look into other stuff from them later. He doesn't sell Sol-Ark though, so I am holding out, because I think I want a Sol-Ark 12k EMP hardened inverter once I have it in my budget. For now, I will only use my Victron 250|100 and DC only loads until a bit later when I can afford a Sol-Ark. I have 16x 400w solar panels, these batteries, Victron MPPT charger, combiner boxes, all the cables and connecting hardware, hopefully enough to run a 48v 20,000 BTU DC heater I bought, and some LED DC lights, enough to get me through Winter and keep the Motorhome warm so the pipes don't freeze. I think 28 kW/h should allow me to run a couple nights with that size 1200w heater. Eventually I want to get the 48v mini-split heat pump to heat and cool.
 
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Hedges

Photon Sorcerer
Something like this might serve you well, nice pre-assembled bundle at a good price:


I don't know much about using the Sunny Islands to charge DIY lithium (e.g. from AC coupled GT inverters or grid/generator input to Sunny Island), but I understand the Midnight charge controller can do it.
 

Skysthelimit

New Member
I live in Utah as well, planning an off-grid home in a Self-Reliance community North of Delta, I just bought a LiFePO4 battery system from Treeline Power Systems: https://www.treelinepowersystems.com/LiFePO4-48V-512v-280ah-14kWh-Battery-System-wIth-BMS_p_37.html They come with the 280 ah cells. I just received the shipment a couple days ago. I ordered 2 of the 14 kW/h 48v banks which is 32x cells total (which came with 2 BMS, one per bank, I got the 200a BMS option with mine). It came to $6548 shipped. The guy, Randy from there (Colorado) was very friendly and answered all my beginner questions and I felt good about getting from them. I was originally looking into buying direct from a China company, but the turnaround was something like 50 days doorstep to doorstep. This guy took about 2 weeks to assemble, test, and get them to me. The ones I got here don't come with any case or anything, just the cells and BMS units, all pre-wired, tested, and unconnected for transport. I haven't reconnected all the BMS and tested myself yet, since I am still planning my solar install soon, so maybe later I could report about how well they work. Hoping to try them soon, supposedly this should provide 28 kW/h with 2 48v banks in parallel. The guy said these BMS do balance on discharge, and have full over-voltage/under-voltage cutoff, and over-temp/under-temp cutoff, so they are fully protected. One reason I also decided to go with a local US supplier, is this guy says he will do advance replacement, so if I get a failed cell ever, he says he can ship new one first. He also said they do advance replacements on other parts they sell too. This is my first purchase from them but maybe I will look into other stuff from them later. He doesn't sell Sol-Ark though, so I am holding out, because I think I want a Sol-Ark 12k EMP hardened inverter once I have it in my budget. For now, I will only use my Victron 250|100 and DC only loads until a bit later when I can afford a Sol-Ark. I have 16x 400w solar panels, these batteries, Victron MPPT charger, combiner boxes, all the cables and connecting hardware, hopefully enough to run a 48v 20,000 BTU DC heater I bought, and some LED DC lights, enough to get me through Winter and keep the Motorhome warm so the pipes don't freeze. I think 28 kW/h should allow me to run a couple nights with that size 1200w heater. Eventually I want to get the 48v mini-split heat pump to heat and cool.
Thank you very much for the info on your system. With so many options out there and so many different ways to go, it only makes it harder for me to settle on any specific set of components. It sounds like we have very similar needs. I had never heard of Treeline before but I’m guessing you did some research before settling on them for this large purchase. At this point, I’m collecting some of the cheaper components Like solar panels, 40 x 100 watts so far, but I’ll have to make a decision on batteries, BMS, inverters, and the rest, shortly. I have a local builder who should be breaking ground on our barn/house soon, at least I pray that’s the case, so as soon as that’s started, the countdown begins as to when I’ll need the components. Buying all the additional components right now is not in my budget either, especially since I’ve got similar desires to you and want top notch components. I would really appreciate any updates on your system, installation, and how it’s working for you. Thanks again for the info.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Thank you very much for the info on your system. With so many options out there and so many different ways to go, it only makes it harder for me to settle on any specific set of components. It sounds like we have very similar needs. I had never heard of Treeline before but I’m guessing you did some research before settling on them for this large purchase. At this point, I’m collecting some of the cheaper components Like solar panels, 40 x 100 watts so far, but I’ll have to make a decision on batteries, BMS, inverters, and the rest, shortly. I have a local builder who should be breaking ground on our barn/house soon, at least I pray that’s the case, so as soon as that’s started, the countdown begins as to when I’ll need the components. Buying all the additional components right now is not in my budget either, especially since I’ve got similar desires to you and want top notch components. I would really appreciate any updates on your system, installation, and how it’s working for you. Thanks again for the info.
PLEASE STOP BUYING ANYTHING !
You need to have a Plan and stick with it. Impulse buying ahead of it is wasteful and will not make you nor spouse happy ! ABSOLUTELY GUARANTEED ! Failure to Plan is a Plan to Fail !

Step 1) Those 100W panels = JUNK ! a waste of money. There are 500W panels out there ! A Typical 60-Cell/300W panel will output 24V-30V depending on brand.

- The amount of panels is determined by the Solar Controller Capability in as much as how many Volts, Watts & Amps they can accept.
- Sizing the Solar System (Panels & Solar Charge Controller [SCC] ) is reliant on the Battery Bank size in Amp Hours. a 200AH bank will require less capacity to charge than a 500AH or 1000AH bank and how fast you want to be able to charge the depleted battery bank.
- Then you have to factor in the Maximum Sun Hours per day (mid summer) and Minimum Sun Hour Days (December 21) and then you have to work it out or charging.
- Mounting Type: Ground Mount Fixed or Adjustable, Roof Mount (as you are building now, Orient your buildings to maximize solar gains and profile. In other words, have Good clean SOUTH Exposure by having rooflines run true East to West. This will also affect how much power can be generated over the course of a year.

Look here for Solar Panels, New & Used: https://store.santansolar.com/product-category/solar-panels/
Compare, look at the specs and consder it.

On 48V Battery Bank. That would be the good way to go for you.
But you will NEED TO KNOW how much power you will be using daily, how much power you will want in reserve (autonomous days without any generation at all). Additionally what kind of loads that will be expected... How many Watts/Amps will the system have to be able to deliver at any given point in time. MOST IMPORTANTLY: Conservation is FAR CHEAPER than Generation & Storage, therefore the more energy efficient the home is, the appliances within etc all add up and it is very significant.

Last... Devices like Hot Water Tanks, Electric Stoves Electric Dryers, AC Systems are KILLER POWER HOGS ! There are very efficient electric appliances such as Inverter Microwaves, Induction Cooktops, On-Demand water heaters, On-Demand Radiant Heating (very efficient) and more... We have the Collective Knowledge to share here...

You're not ready to assemble a solar system anyways, you need to build your house first, so you have time on your side for all of this to do research, come up with a plan and then to execute it. DO NOT RUSH or get carried away, NO IMPULSE BUYS !!!

HERE IS AN EXAMPLE of Battery Info
48VDC battery pack requires 16 LFP cells, an 16S-BMS and a fuse of course.
Example:
Free Shipping to USA & 16Pcs 3.2V 280Ah Total US $1,706.72 (DPP Duty/Taxes paid) Link to Lyuan 280s (Xuba Sister Company)
These are NEW, Grade-A Commodity Cells and very popular with many of us here.
A respectable BMS $225 USD +/- depending on features, functions & capabilities.
An MRBF Fuse $26.00 a pop with Block & Fuse: https://www.ebay.com/itm/Bay-Marine...-Single-Fuse-Holder-Kit-30-300A-/174059623226
1,706.72 + 150 + 26 = $1,857.75 USD plus whatever you decide for a case.
This will give you One Battery Pack @ 48V/280AH/13.44kWh for $1,857.75USD (kWh calculated at 48V)

Kwh are a bit tricky. A 48V Battery Pack ranges from 40V (2.50V per cell or 0% SOC) to 58.4V (3.65V per cell or 100% SOC)
40V@280AH = 11.2 kWh. 58.4V@280AH = 16.352 kWh. NORMALLY we leave 5-10% at the bottom and 5-10% from the top to maximize lifecycles of the packs and to keep them as happy as possible.
 

Skysthelimit

New Member
PLEASE STOP BUYING ANYTHING !
You need to have a Plan and stick with it. Impulse buying ahead of it is wasteful and will not make you nor spouse happy ! ABSOLUTELY GUARANTEED ! Failure to Plan is a Plan to Fail !

Step 1) Those 100W panels = JUNK ! a waste of money. There are 500W panels out there ! A Typical 60-Cell/300W panel will output 24V-30V depending on brand.

- The amount of panels is determined by the Solar Controller Capability in as much as how many Volts, Watts & Amps they can accept.
- Sizing the Solar System (Panels & Solar Charge Controller [SCC] ) is reliant on the Battery Bank size in Amp Hours. a 200AH bank will require less capacity to charge than a 500AH or 1000AH bank and how fast you want to be able to charge the depleted battery bank.
- Then you have to factor in the Maximum Sun Hours per day (mid summer) and Minimum Sun Hour Days (December 21) and then you have to work it out or charging.
- Mounting Type: Ground Mount Fixed or Adjustable, Roof Mount (as you are building now, Orient your buildings to maximize solar gains and profile. In other words, have Good clean SOUTH Exposure by having rooflines run true East to West. This will also affect how much power can be generated over the course of a year.

Look here for Solar Panels, New & Used: https://store.santansolar.com/product-category/solar-panels/
Compare, look at the specs and consder it.

On 48V Battery Bank. That would be the good way to go for you.
But you will NEED TO KNOW how much power you will be using daily, how much power you will want in reserve (autonomous days without any generation at all). Additionally what kind of loads that will be expected... How many Watts/Amps will the system have to be able to deliver at any given point in time. MOST IMPORTANTLY: Conservation is FAR CHEAPER than Generation & Storage, therefore the more energy efficient the home is, the appliances within etc all add up and it is very significant.

Last... Devices like Hot Water Tanks, Electric Stoves Electric Dryers, AC Systems are KILLER POWER HOGS ! There are very efficient electric appliances such as Inverter Microwaves, Induction Cooktops, On-Demand water heaters, On-Demand Radiant Heating (very efficient) and more... We have the Collective Knowledge to share here...

You're not ready to assemble a solar system anyways, you need to build your house first, so you have time on your side for all of this to do research, come up with a plan and then to execute it. DO NOT RUSH or get carried away, NO IMPULSE BUYS !!!

HERE IS AN EXAMPLE of Battery Info
48VDC battery pack requires 16 LFP cells, an 16S-BMS and a fuse of course.
Example:
Free Shipping to USA & 16Pcs 3.2V 280Ah Total US $1,706.72 (DPP Duty/Taxes paid) Link to Lyuan 280s (Xuba Sister Company)
These are NEW, Grade-A Commodity Cells and very popular with many of us here.
A respectable BMS $225 USD +/- depending on features, functions & capabilities.
An MRBF Fuse $26.00 a pop with Block & Fuse: https://www.ebay.com/itm/Bay-Marine...-Single-Fuse-Holder-Kit-30-300A-/174059623226
1,706.72 + 150 + 26 = $1,857.75 USD plus whatever you decide for a case.
This will give you One Battery Pack @ 48V/280AH/13.44kWh for $1,857.75USD (kWh calculated at 48V)

Kwh are a bit tricky. A 48V Battery Pack ranges from 40V (2.50V per cell or 0% SOC) to 58.4V (3.65V per cell or 100% SOC)
40V@280AH = 11.2 kWh. 58.4V@280AH = 16.352 kWh. NORMALLY we leave 5-10% at the bottom and 5-10% from the top to maximize lifecycles of the packs and to keep them as happy as possible.
Wow, thanks for your passionate response. I appreciate your advice. The reason I bought the 100 watt panels is because of a few reasons.
1. They are pretty cheap, per watt, that is.
2. They are pretty cheap, to replace, if they are damaged by the elements or something falls on them.
3. They are pretty easy to replace since they are a bit smaller than the bigger panels.
4. I will have several off-grid projects on my property so I can easily use these smaller watt panels with things like a one battery surveillance camera or my battery operated property gate opener, or 12 volt pumps.
I don't know if there's much of a savings per watt if you buy a 300 watt panel vs a 100 watt panel as I've never shopped for them that way. I know I'm gonna need at least 3-8 kw's worth of solar so that's why I'm stocking up now, little by little.
When you say my 100 watt panels are "junk", are you saying that because they are only 100 watt each or what? Does the "quality" of the panel go up as you buy bigger ones?
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
The "Junk" means it's ancient tech that is not going anywhere.... the low watts/power and amps are fine for small uses (RV / Camper Tops) or small space installations but not for real solar use. Every connection is a potential point of failure, as an EE you know that. 1 panel doing the job of 3-4 small ones is only one pair of wires versus 6 or 8 pairs.

Standard Panels are tough... I've helped people convert WoodMizer Saw Mills to Electric & Solar, put up greenhouses and I live offgrid solar and help folks implement it around here too... There is little to no use case for small panels other than those I noted above. Use them for remote monitoring / bush cams and such, even Yard Lighting (barn compounds etc). When you do the math and roll in the BOS you'll be spending at least 2X for teh 100W panels... wires, fuses, combiners etc... all add up and fast.
 

Skysthelimit

New Member
The "Junk" means it's ancient tech that is not going anywhere.... the low watts/power and amps are fine for small uses (RV / Camper Tops) or small space installations but not for real solar use. Every connection is a potential point of failure, as an EE you know that. 1 panel doing the job of 3-4 small ones is only one pair of wires versus 6 or 8 pairs.

Standard Panels are tough... I've helped people convert WoodMizer Saw Mills to Electric & Solar, put up greenhouses and I live offgrid solar and help folks implement it around here too... There is little to no use case for small panels other than those I noted above. Use them for remote monitoring / bush cams and such, even Yard Lighting (barn compounds etc). When you do the math and roll in the BOS you'll be spending at least 2X for teh 100W panels... wires, fuses, combiners etc... all add up and fast.
I appreciate the clarification. I'll keep everything you've said in mind as I move forward.
 

Samsonite801

New Member
Yeah, I bought my 16x Trina 400w panels from SanTan Solar in AZ as they were on sale for $180 panel (960 lbs shipped on a pallet), best bang for the buck I thought. My end plan is to get a Sol-Ark 12k all-in-one inverter as these are the only ones on the market which can be ordered as EMP-hardened (saving more money to afford it), but to get me through this Winter on DC-only power, I bought the Victron 250|100 charge controller (mainly so I can string every 4 panels in series (around 200v open-circuit voltage), while 4 strings of 4 will be paralleled and can charge the 48v battery banks. Bought prefab 8 awg solar cables on Amazon in 5ft, 10ft, and 30ft (with MC4 ends to plug into the panel factory connector and the Eco-Worthy PV combiner panel which has all the string fuses and main DC breaker and surge protection built-in).

As far as Treeline, I stumbled across them just searching Google, was a bit skeptical, but after chatting with him on a contact us message thread for awhile, it became obvious that he was very technical, knows battery stuff very well, and his prices seemed good and the parts like cells and BMS are all tested and balanced, good quality 200a BMS (from Bellhope Technology), and he sent me all of the high quality battery cables and everything. I decided to drop the hammer on the order with fingers crossed, and they eventually came after a couple weeks. Again, the main reason I liked this guy is he offered advanced replacement on warranty stuff, and offer a full 7 year performance warranty ( > 80%) on the battery packs, and even sent me a Treeline baseball cap. I did look up their address on maps.google.com and looks like they're a smaller startup in a business park in Westminster, CO or something. I'm happy with my purchase. I could've easily built a pack like this myself, but decided to go with this just to try it as it was a bit more turn-key.

Now I am just looking into solar mountings lately... Maybe Sinclair Sky-Rack 2.0 or Power Peak, still looking into these, a bit spendy, or I could build one out of wood and Home Depot hardware...

EDIT: The best info on the Sol-Ark inverters I like is from Practical Preppers, Engineer775 on You Tube: https://www.youtube.com/c/PracticalpreppersLLC/videos

He does a lot of Sol-Ark installs.
 
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Samsonite801

New Member
Forgot to say, I want to work with the idea of EMP hardening in my system, as per my reasoning for wanting to go Sol-Ark, but keep in mind, there are no BMS on the market that are EMP hardened, so many people will stick with Lead Acid, AGM, PCC or similar when going for EMP hardened full solution. In my case, I am going Lithium all the way, but will eventually just buy a few spare BMS units and keep them in a faraday bag, inside of a faraday can, so if there ever was a big EMP, and it blew out the BMS, can fix it. The Sol-Ark EMP hardening costs $1500 bucks extra, and it also comes with surge protection devices to wire into the Solar array. Also doesn't hurt to keep some spare blocking diodes handy for the solar panels in case they blow in an EMP.
 
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Hedges

Photon Sorcerer
Electronics, and especially batteries, have limited lifespan. Even suitably protected, their benefit will be short lived.

Chemical refinement, mass spectrometry, all technological society which made their development and manufacture possible would be gone if we return to the stone age.
Bronze edged tools certainly have some value, but I think a quality steel axe is something you could pass on to your grandchildren, giving you and them a technological advantage for decades, even centuries to come.
 

Samsonite801

New Member
Electronics, and especially batteries, have limited lifespan. Even suitably protected, their benefit will be short lived.

Chemical refinement, mass spectrometry, all technological society which made their development and manufacture possible would be gone if we return to the stone age.
Bronze edged tools certainly have some value, but I think a quality steel axe is something you could pass on to your grandchildren, giving you and them a technological advantage for decades, even centuries to come.

Yes of course this is true, part of this transition to an off-grid lifestyle of self-reliance for me means a plan in parallel to reduce my dependency on electricity as well. I am designing a passive house which will not require HVAC solution, and have lots of other ideas for making a homestead which can operate as passively as possible. My choice for lithium batteries also has to do with the fact that they offer a lot of cycles, maybe even up to 5000 cycles, so they should last long enough for me to figure out what are the next steps beyond that... All we can do is do our best and have some faith in the rest. Whenever it seems hopeless, there is always another solution around the corner...
 
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Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
Forgot to say, I want to work with the idea of EMP hardening in my system, as per my reasoning for wanting to go Sol-Ark, but keep in mind, there are no BMS on the market that are EMP hardened, so many people will stick with Lead Acid, AGM, PCC or similar when going for EMP hardened full solution. In my case, I am going Lithium all the way, but will eventually just buy a few spare BMS units and keep them in a faraday bag, inside of a faraday can, so if there ever was a big EMP, and it blew out the BMS, can fix it. The Sol-Ark EMP hardening costs $1500 bucks extra, and it also comes with surge protection devices to wire into the Solar array. Also doesn't hurt to keep some spare blocking diodes handy for the solar panels in case they blow in an EMP.
I was Tempest Certified & Cleared till I retired, so have some familiarity on this point you might say.
I have yet to see any Solar Gear that is Hardened against EMP.

BUT, a Solution that is possible... A Sea Container mounted onto a NON-GROUNDED - Isolated base (6x6 Pressure Treated works fine for that) can provide you a Faraday Cage if you setup properly. You do have to ensure that the ground below is hard, packed, covered with ground cloth (Commercial weed barrier works) & gravel with good drainage on top, then put 6x6's & Sea Can.

Put a "Shed Roof" (with the correct "Average Angle") structure on top and you can cover them over with Solar Panels while protecting the top of the sea can from the elements as such.

HOW TO PUT A ROOF ON ?
One Way is here below but there is potential for more... There are similar products and variations. Additionally, many folks do not realize it but there are "Awning" type kits that can be mounted on Sea Can Side and locked to the mounting brackets built into the sea cans. Even more interesting, is some are motor driven and can be raised / lowered...
check out some options here: https://www.discovercontainers.com/container-accessory-attachments/

 

Trukinbear

Solar Enthusiast
I wholeheartedly agree you should have a really good plan before you start buying equipment. Sad to say some things are hard to estimate without actually doing them, your off-the-grid lifestyle might change your estimates in ways you can't anticipate. My situation was odd, I thought I was just temporarily without store-bought power - I scrounged and built 3 different systems from used parts (except the batteries), and learned a lot along the way. Sure, you can record your on the grid power use, but once you start having to really watch what you do (after you are off the grid) your behavior will likely change. Once I realized my situation wasn't just a temporary blip in my life was when I got serious and started buying new equipment and putting together a system that will last. 48V all the way, but since you aren't doing FLA you might even think of a higher system voltage than that. Think about future changes and leave some room for expansion. In my case, I thought - what is the worst thing they can do to me after I've put in my expensive off-grid solar system? - let me have power again, and/or MAKE me have it, so I designed my system to have the capability to do grid-tie even though I have no intention (chance) of hooking back to the grid, so the worst-case scenario is I make the meter spin backward all summer and use them as my battery in the winter. Left myself room for 50% more panels without having to add any more equipment. I know had I tried to do all this from the start my end result would have been vastly different, so I'm grateful for my 'learning' systems along the way.
 

Samsonite801

New Member
I wholeheartedly agree you should have a really good plan before you start buying equipment. Sad to say some things are hard to estimate without actually doing them, your off-the-grid lifestyle might change your estimates in ways you can't anticipate. My situation was odd, I thought I was just temporarily without store-bought power - I scrounged and built 3 different systems from used parts (except the batteries), and learned a lot along the way. Sure, you can record your on the grid power use, but once you start having to really watch what you do (after you are off the grid) your behavior will likely change. Once I realized my situation wasn't just a temporary blip in my life was when I got serious and started buying new equipment and putting together a system that will last. 48V all the way, but since you aren't doing FLA you might even think of a higher system voltage than that. Think about future changes and leave some room for expansion. In my case, I thought - what is the worst thing they can do to me after I've put in my expensive off-grid solar system? - let me have power again, and/or MAKE me have it, so I designed my system to have the capability to do grid-tie even though I have no intention (chance) of hooking back to the grid, so the worst-case scenario is I make the meter spin backward all summer and use them as my battery in the winter. Left myself room for 50% more panels without having to add any more equipment. I know had I tried to do all this from the start my end result would have been vastly different, so I'm grateful for my 'learning' systems along the way.

Yeah I respect this approach a lot, it is a learning curve for me as well (even with all the planning I thought I knew how to do, some things still went sideways to a certain degree and I'm not even deployed fully yet). I decided to plan with using the 48v DC in my initial solar setup, but my RV already uses a 12v 6-battery setup (with a Magnum inverter, and a few tiny solar panels on the roof with a pmw charger), and also has an Onan 6.5 kW propane generator I wish could be good for charging the 48v or something. Then my Toyota Prius has a 207.2v DC hybrid lithium traction battery setup where I added in an APC rackmount 240v/120v 3.5kW / 5.2 kW surge UPS/inverter connected to it (for backup generator function), however, I have not found an easy way to interface all these system voltages together, other than use a 240v AC output on the Prius APC/UPS to potentially run a generator input on an a Sol-Ark all-in-one or something. Or one guy used a midnight classic MPPT solar charge controller to convert his Prius Hybrid battery 207.2v DC directly, to charge his solar 48v battery bank. For the most part my 48v system should be pretty scaleable by itself, but I wish I could tie some of these systems together to the RV and the Prius, so I could move DC power around in the most efficient way. Then there's all the EMP resistance planning as well (thanks to Steve_S for all that info as well), I plan as much as possible, but as I learn more things evolve and change in my plan. So far not too bad though. Will try to run as many things off raw 48v as possible, and if I get a Sol-Ark later, it will only be a luxury item really, to use AC sparingly, like for power tools, air compressors, and such where DC doesn't make sense. My particular off-grid location has no electricity for 45 miles, so have to build a solid system. If I add in more solar panels later, I would use the MPPT chargers in the Sol-Ark I'd plan to get, to scale out and add those in. For now though I wish I had a way to get more solar to the RV 12v system, might need to buy more panels, since it isn't easy to move power around.
 
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JoeHam

Photon Sorcerer
For now though I wish I had a way to get more solar to the RV 12v system, might need to buy more panels, since it isn't easy to move power around.


Many Solar Charge Controllers can handle different batteries.

I routinely charge 12v and 48v nominal LFP batteries from the same panel array with the same SCC.

Obviously not at the same time 😎
 

Hedges

Photon Sorcerer
What I have not settled on yet is which cells to use to build my system and what BMS to use.
This indicates you have settled on Lithium.

That is a popular option, but not the only choice. There have been several chemistries used. Lithium has become extremely popular for portable devices in recent years due to weight, energy density, and discharge rate, but those aren't a benefit for powering a home.

Consider lead-acid. It costs less per Wh of capacity (perhaps excluding DIY lithium batteries assembled from cells sourced out of certain overseas countries.) It wears out in fewer deep discharge cycles. It doesn't need a BMS and doesn't represent a severe hazard due to improper charging (which a BMS tries to prevent for lithium).

If this is to be an off-grid home using batteries for power every night, a common suggestion is to size batteries to last through 3 days of little to no sunlight. Lithium has a cycle life of thousands of deep cycles (enough to fully cycle every night for 10 years.) But if you size for 3 days autonomy, you're only going to give it 3500 cycles to 17% depth of discharge, with occasional 60% to 100% DoD. So with lithium you've paid extra up front for cycles you're never going to use. (For a vehicle driven to 80% DoD 5 days a week, lithium could be ideal.)

With lead acid, such as FLA wet cell forklift battery or AGM sealed battery, you could size similarly and its life expectancy should be 10 years with typically discharging 17% per night, but occasionally discharging deeper.

Capital cost of lead-acid is lower than lithium, and I think lifetime cost is also lower for an oversized bank you normally only discharge partially. If you right-size battery bank for daily usage and use a "range extender" (fossil fuel generator) to get through periods of low PV production, then lithium could be less expensive. (for similar reasons I say plug-in hybrid is a better use of resources than pure EV.)
 
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