Off Grid Solar - learning more from DIY users

pastera

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Batteryhookup discloses the source of the cells they sell. For a while, they had 18650 cells from Ring cameras that were brand new cells just in a plastic housing you had to crack open. The green cells in my latest pack were surplus from a manufacturing run. They are grade A cells that met specs, just not enough of them for anyone to use them in a new product (at least that's my guess).

The 32650 cells in my other pack were manufactured for batteryhookup and so far I have had zero issues with them. Time will tell on how long they last. A lot of DIYers are using them and have not reported any issues. Even if a cell goes bad it should be pretty easy to fix. Word of advice on these: I'm fairly sure the 5AH and 6AH cells are identical! The only difference is grading...the 6AH cells tested above 6AH and are being sold for more. Personally, I bought the 5AH versions which test out at well over 5AH and are IMO a better deal.

Historically, I've used golf cart batteries in my systems. Those are about $225 for 200 amp hours. These are crappy consumer batteries that work ok for a while but degrade quickly. Some of that is probably my lack of maintenance and the rest is that they are just shit. My gut feeling is that a 100AH LiFeP04 pack will perform as good or better than a pair of golf cart batteries over time. If your application is large drain over a long time then of course the lack of capacity hurts you. Off grid power is seldom that kind of load. It's running the microwave for 3 minutes, full sunlight for 4 hours, some lights for a few hours, more full sunlight, etc etc. In the typical off grid power profile shit grade golf cart batteries become unusable after 24 months. My feeling is that LiFerP04 packs will easily last 24 months and probably longer. The only issue is charging in low temperatures...they need to stay warm to accept a charge (my BMS has low temp cuttoff). An unheated cabin up in northern NH will need some lead acid cells to give you power while the place warms up.

Random thoughts....
You state low temperature charging - There aren't battery temperature controllers available?
Quite easy to use the energy that you would throw away to heat the enclosure up to a safe charging temperature.
 

xtry51

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My understanding is LiFePO4 batteries should not be charged under 24F. Doing so will cause chemical degradation and create free Lithium which will reduce efficiency and eventually shirt the cells internally.

This was part of reason I was going to solar heat the shed with vacuum tubes and super insulate it. I also see people mounting batteries up high and above the inverter to capture that heat as well. So maybe a battery "loft" and 2x6 or full double walled 2x4 construction.
 
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My understanding is LiFePO4 batteries should not be charged under 24F. Doing so will cause chemical degradation and create free Lithium which will reduce efficiency and eventually shirt the cells internally.

This was part of reason I was going to solar heat the shed with vacuum tubes and super insulate it. I also see people mounting batteries up high and above the inverter to capture that heat as well. So maybe a battery "loft" and 2x6 or full double walled 2x4 construction.
I have my BMS set to not charge at less than 32 degrees.

There are people using insulated boxes with self-regulating heating pads used for plant germination. Connect a PV panel to the heater and at some point, the battery will be warm enough to take a charge.
 

Duxprep

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My understanding is LiFePO4 batteries should not be charged under 24F. Doing so will cause chemical degradation and create free Lithium which will reduce efficiency and eventually shirt the cells internally.

This was part of reason I was going to solar heat the shed with vacuum tubes and super insulate it. I also see people mounting batteries up high and above the inverter to capture that heat as well. So maybe a battery "loft" and 2x6 or full double walled 2x4 construction.
Correct - You can discharge in the cold, just not charge.

You asked about battery brands. Battleborns are nice, WAY over priced for the energy produced today but they are a great option for people in the RV community who want a 24F sized battery to replace their AGMs and drop a ton of weight- They're about 18 months behind in terms of the Amp hours being provided in LifePo batteries. At that time 100AH was the norm but now it's more than double that - They haven't increased their capacities and have kept their price high

At the end of the day ALL LifPo4 batteries are made in China. US based manufacturers then assemble them here. They all have a significant upcharge given the low Amp hours provided but they do have warranties. With a DIY you get way more power for a LOT less money, but no warranty or support. You can also buy used batteries as they usually have 80% power left so they are a great value

Gomer buys from Battery hookup and they have great deals on used cells and sometimes new. Mostly cylindrical. (18650's and others) or automotive pull outs. Sometimes they have used batteries from solar farms. Building a battery with 18650's is pretty straightforward as the voltages and configurations work to allow for a standard BMS - You will usually need a spot welder though. The pull outs however can be problematic as they usually had propriety BMS's that are no longer included or they may operate at different voltages.

One of the most popular builds today is to use Aluminum cased Prismatic Cells (rectangular), People buy these from Ali express, add a BMS, bus bars and you have a battery. It can be very sketchy buying from Ali express as your dealing direct with Chinese companies - sometimes you're getting grade B cells sold as Grade A new, and support would be limited or non existent. Sometimes the sellers are great though. If you get on Diysolrforum.com and check out the Lishen and Xuba build threads you'll see what people are doing. They have a guy who is coordinating a group buy now on Lishen 272ah cells.

Consider that a 100ah (1200 watts) 12 volt battleborn is $999. I can build 272ah (3264 watts) DIY 12 volt Battery with a BMS for $500 and get nearly 3x the power.

If you really didn't want to build them yourself, I might consider the 300ah Kilo-Vault batteries from the Alt-e- store (house brand) These have a built-in heater and you're getting 300Ahs for $2245. But remember you'll need at least 4 of these for a 48 volt system - (14,400 watts of power) Depending on what your expected daily use is as well as how many days of cloudy whether you want to cover for you might need to double that. (nearly $18,000 for 600Ah's or 28,800 Watts) If you built this with DIY cells you could build 3 48 volt 272AH batteries (816 AH's or 39,000 watts) for a little over $5000....decisions decisions
 
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xtry51

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Yeah I'd say building sounds better. I watched a few videos today and last night. I think I'm good with using prismatic cells, but I'm not feeling the spot welding cylindrical myself. I can spot weld that's not an issue. Just seems like a lot more labor. I have friends who can cut bus bars from copper for me (waterjet) so that's a simple low effort solution for me if I pic a battery type and go all in on a single purchase. I'd rather have 3 day backup with spare cells on a shelf than 1 day and a warranty.
 

xtry51

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So here's our power usage by month. A fair amount of the winter cost is we finished the loft in garage for boys, but we currently are heating it with an electric space heater. It's killing our bill. YoY we're up 50% Feb '20 vs Feb '21. I'm gonna do a mini-split and insulate the underside of the floor this summer.

20210223_184823.jpg

So what do you think a system would cost to supply 70kwh per day in Jan in NH would be? 🤣
 

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So here's our power usage by month. A fair amount of the winter cost is we finished the loft in garage for boys, but we currently are heating it with an electric space heater. It's killing our bill. YoY we're up 50% Feb '20 vs Feb '21. I'm gonna do a mini-split and insulate the underside of the floor this summer.

View attachment 454103

So what do you think a system would cost to supply 70kwh per day in Jan in NH would be? 🤣
lol - I just started doing the math and said holy shi% when I saw the last line of of your post. Is there a Hot tub there as well? I think there is a lot of saving you do with better/fewer appliances, heating and cooking methods, Lighting etc. Then figure out what's whats really needed. Get well below 50kwh /day. The good news for you is you're doing a ground array. You can and likely will make that massive. Even on a sunny day, in the winter you get like 2-3 hours of full sun AND the sun is so low in the sky your production is crap. Think like 10% of summer production - If it's sunny. You need to panel the hell out of your system to make up for it. You could also set up arrays to favor winter and summer sun positions. Come March and through September, you'll be making enough power to charge your entire battery bank as well as run your entire house and likely be leaving power on the ground. The interesting thing about solar is that if there is no load calling for power, the panels don't generate it and they just sit there. If you have a big enough battery bank then the panels will have something to during the day by charging it back up.

Winter is another story though. Lets do some back of the napkin figuring:
Remember that at night you're not generating ANY solar and are entirely off battery. if your loads are say 50Kwh/day thats about 2083 watts /hr. For the sake of argument lets say there is no taper off at night. During the winter you stop making any real solar around 2pm and don't start again until about 9AM. That's 19 hours with no solar production and you're consuming. 39kwh! That takes a LOT of battery power to support that much usage just for one night. This is why you not only need a big battery bank but also ton of solar panels - and of course to lower your consumption. When you look at the solar radiance charts for New England they give you daily average. In my area that's around 4.5 hours of sun/day average. That's full production sun -the max capability your panels could produce. That average though is comprised of 1-2hrs or nothing in winter and 8+ hrs in the summer.

That said you need to plan for the lack of solar production in winter.
 

xtry51

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Yeah it's insanity. We do have some things we just have to live with. Like I have an electric stove and dryer. I can't use propane/NG because my wife has severe allegories and sulfur is a big one. Like she goes unconscious for half a day.

Also this house is not where the solar will be going. And currently we have two teenagers here as well who will both be gone soon, one in 1.5 years and one in 5 years.

I'm exploring ideas for certain things. Like maybe I get a big standby gen to support my garage and the dryer. They I just run it when needed. I don't know for sure. I do know I want to start with solar for lighting, water and fridge/freezers. And I'm definitely going to grow it from there.
 

Duxprep

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My gut feeling is that a 100AH LiFeP04 pack will perform as good or better than a pair of golf cart batteries over time. If your application is large drain over a long time then of course the lack of capacity hurts you. Off grid power is seldom that kind of load. It's running the microwave for 3 minutes, full sunlight for 4 hours, some lights for a few hours, more full sunlight, etc etc. In the typical off grid power profile shit grade golf cart batteries become unusable after 24 months. My feeling is that LiFerP04 packs will easily last 24 months and probably longer. The only issue is charging in low temperatures...they need to stay warm to accept a charge (my BMS has low temp cuttoff). An unheated cabin up in northern NH will need some lead acid cells to give you power while the place warms up.

Random thoughts....
Some thoughts here. Lead acid batteries can generally only be discharged down to about 50% State of charge or half their rated capacity. They require a long time to recharge as they have a bulk , absorption and float phase to become fully charged - Like all day long. Unless they are AGM they need to be vented as well as stored upright. Their lifepsan is relatively short measured in the hundreds of cycle - A cycle being a full discharge - so for Lead acid two 50% discharges is a full discharge. Lastly their discharge profile lends itself to voltage sag as the batteries lose power. This means they are pushing lower and lower voltage to the loads as the batteries are discharging.

Lifepo4 on the other hand can be fully discharged to 0% without damaging the battery - Good practice is to not exceed 80%. As a result you're getting much more usable power from a similar rated battery vs lead acid. This chemistry can be cycled 3-5000 times. Thats 3-5,000 FULL discharges. if you were to discharge your battery 100% each day (you wouldn't) you'd get a minimum of 10 years worth of 100% capacity cycles. When you reach the 3-5000 limit you now have 80% of the battery's original capacity. These last a LONG time. Note: not all lifepos are the same some are less - but most can do this many cycles

LifePo4 has a nearly flat discharge curve. As a result they don't suffer from voltage sag and will deliver full voltage to your loads pretty much right until they run out of juice. They have extremely low internal resistance and are able to deliver massive loads of power upon request. A single 12 volt Lifepo can usually provide 100-150Amps continuous power (whatever the BMS allows) until the battery is empty. Lastly they charge extremely fast and don't require and absorption or float. Some may disagree - and that is a topic that requires deeper conversation than this discussion
 
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namedpipes

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We already use wood heat and the new location will also be primarily wood heated likely with oil for when we are on vacation.

I'm also considering coal instead of wood given coal is easy to store in large quantity.

Will your property have the ability to connect to the grid for electricity?

I wonder if there is a charge controller that can keep the batteries charged up using the most appropriate source of power.

First preference is solar, then the grid, then a generator.

In an extended cloudy weather event you're still enjoying fully charged batteries.

If the powerplant or the rest of the state got nuked you'll still have power for your fridge

Same generator can power heavy duty equipment that would be difficult to run on the batteries. Like a Bridgeport...
 

xtry51

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The Schneider inverter can back charge the batteries using grid or gen hardwired to it.

I have an Enco now and a few welders. I plan on having another Bridgeport, a cnc and at least two more lathes. So having something other than solar is a necessity. I'm definitely going to have grid power available. The question is how do I limit my use of it.
 
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lol - I just started doing the math and said holy shi% when I saw the last line of of your post. Is there a Hot tub there as well? I think there is a lot of saving you do with better/fewer appliances, heating and cooking methods, Lighting etc. Then figure out what's whats really needed. Get well below 50kwh /day. The good news for you is you're doing a ground array. You can and likely will make that massive. Even on a sunny day, in the winter you get like 2-3 hours of full sun AND the sun is so low in the sky your production is crap. Think like 10% of summer production - If it's sunny. You need to panel the hell out of your system to make up for it. You could also set up arrays to favor winter and summer sun positions. Come March and through September, you'll be making enough power to charge your entire battery bank as well as run your entire house and likely be leaving power on the ground. The interesting thing about solar is that if there is no load calling for power, the panels don't generate it and they just sit there. If you have a big enough battery bank then the panels will have something to during the day by charging it back up.

Winter is another story though. Lets do some back of the napkin figuring:
Remember that at night you're not generating ANY solar and are entirely off battery. if your loads are say 50Kwh/day thats about 2083 watts /hr. For the sake of argument lets say there is no taper off at night. During the winter you stop making any real solar around 2pm and don't start again until about 9AM. That's 19 hours with no solar production and you're consuming. 39kwh! That takes a LOT of battery power to support that much usage just for one night. This is why you not only need a big battery bank but also ton of solar panels - and of course to lower your consumption. When you look at the solar radiance charts for New England they give you daily average. In my area that's around 4.5 hours of sun/day average. That's full production sun -the max capability your panels could produce. That average though is comprised of 1-2hrs or nothing in winter and 8+ hrs in the summer.

That said you need to plan for the lack of solar production in winter.
totally agree with you on PV power production in the winter. Based on real-world experience it's more like 3 hours of peak production AND you need to adjust your PV panels angle. This is where LiFePo4 shines because they charge quickly...you can just fire up the generator for a couple of hours and top them off. Lead-acid takes forever.

Another thing from experience is you never want to be using a single 12V panel into your charge controller. You want a MPPT charge controller and at least 2 (12 volt) panels wired in series. This really helps during the winter when low light conditions are the norm. I went from an old PWM charger with 100W 12V panels parallel wired to a MPPT charger with panels in series and harvested at least 20% more power...very noticeable (and no it was not cabling losses).
 

Vermonster

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totally agree with you on PV power production in the winter. Based on real-world experience it's more like 3 hours of peak production AND you need to adjust your PV panels angle. This is where LiFePo4 shines because they charge quickly...you can just fire up the generator for a couple of hours and top them off. Lead-acid takes forever.
Based on my experience working at an off-grid research station, these few sentences contain some really important points.
#1: Don't overestimate winter power production in New England; it can be very poor. Low sun angle. Short day. Snow/ice on panels some days you can't brush off. Many consecutive days of zero sun. NEVER fixed angle panels (roof or ground mount)--we adjust panel angles in October and April. If panel cost is low, consider over-paneling and having panels point in slightly different directions (we are currently planning to add a second array pointing slightly east of south).
#2: Generator run time to avoid destroying lead acid batteries is insane in the winter. You will never get enough sun in winter to complete the required charge cycle, then you will need to run the generator frequently for hours to avoid sulfation. LiFePo4 does not have this problem; you can use the generator for just a short period to fill deficit.

The previously mentioned issue with cold weather charging of LiFePo4 cells is a real problem off-grid. We run an insulated battery box with self-regulated heating mat. It runs ALOT. We ran the numbers this year and think we will be better hyper-insulating the solar equipment room and running a propane direct-vent heater (Empire direct vent no-electric, or similar) with electric mat for backup.

We also run a completely separate, and simple, 12v panel/charge controller/lead acid battery system to start the backup generator. And we keep replacement parts on site. On at least one occasion we have had something go completely haywire on the main solar side (turned out to be a failed breaker feeding the battery bank) and being able to start the generator and run on generator while we fixed things was huge.

For those thinking of being truly off-grid (no grid tie whatsoever), you need to realize that your life WILL need to change and system maintenance becomes very important (especially if you have lead acid batts). You will likely have equipment that you just have to run a generator to use (welder, large compressor, etc.). We have a problem with crews coming back in the late afternoon that need to charge a high volume of cordless tool batteries. We found it was better to run a dedicated small generator (Honda 2200) for a few hours each day to facilitate this rather than draw down a day's worth of solar charge.

IMHO. At present, if you can grid-tie, even if you have to pay $10K to run the lines, you will end up financially ahead of solar. Technology is changing rapidly; I'm not sure I would experiment with equipment today and expect that will be the best solution in 5 years. If a location will become your primary residence, tax credits for solar install can also be really important, and you often can't access those for a second home.
 

xtry51

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Well it seems like LiFePO4 is a certainty unless we see some other new tech in next 24 months.

I am going to design and build the panel mounting myself, so making it adjustable for angle and rotation to track by season is easy.

Maybe the big picture solution is I overbuild just one system for the "needs" grid/array and just stack an insane number of batteries. Then instead of doing multiple grids I go super generator backup with mass underground fuel storage to supplement. I could probably store several years of diesel/gas/propane...

I'm not set on any one plan since I don't know the lay of the property (or where exactly it will be). I am 100% sure I want lights and water on solar because those are key and I think with how efficient LED lighting is now its insanity to not build a house that is at least exclusively lit by solar power systems. The total power needed even in a big house or on a farm is so small as a total its a no brainer to me.
 
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