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[C&K]

Hi, we are a semi-retired couple, age 63, that bought a 2,700 sq ft lake home on 1,000 acres when we retired from 38 years of farming. Our home does not have utility power and came equipped with a turn-key off-grid power system. We have twin Schneider Electric 6048 inverters that were installed in April 2013. A 10KW solar array with four MPPT60 charge controllers. The inverters are powered by a 1700ah forklift battery that is 10 years old. And we have two diesel generators, a 25KW Caterpillar prime-rated unit, and a smaller 6KW Perkins standby/peaking unit that assists the inverters in overload. The battery is charged by the bigger generator, both generators are controlled by Schneider AGS units with the Cat hooked to the utility AC inputs in the inverters and the peaking generator hooked to the gen inputs in the inverters.

We call ourselves "semi-retired" since we still help the kids out on the farm (6,500 acre cash grain operation) and we have a small firewood processing business producing about 300 face cords/year of seasoned oak, ash and maple firewood. We don't consider ourselves to be "green", we are more of a product of necessity because of location and we love our retirement home.

We do not have regular internet - only cellular on our iPads and iPhones and a 'mobile hotspot' for our computer. So we don't spend a lot of time on the internet and only check in on it quite infrequently. We spend most of our time in the winter either moving snow or processing firewood with the track loader. In the summer we spend a lot of our time fishing. Spring and fall we spend a lot of time helping out on the farm driving semi's, combines or whatever is required.

We have lived here since May 2020, purchased the place from an estate of a doctor that had built it, and while our system works fine we know that it will eventually require upgrades or repairs. I came across this forum on the internet and it looked like a good source of information and ideas for those future upgrades and/or repairs. So we look forward to learning more about how to keep our power system running in the long term, as it did not come with an 'owner's manual'. I was not sure of the proper procedure for new member introductions, so this area of the forum seemed to be the best bet.

 

[MisterSandals]

The inverters are powered by a 1700ah forklift battery that is 10 years old.

I would first make sure that these are properly maintained. You can test the specific gravity of cells to get an idea what condition they are in (and locate any problems).

 

[RussNM]

We don't consider ourselves to be "green", we are more of a product of necessity because of location and we love our retirement home.

??? Not all of us on this forum are tree huggers. I do this simply because Im fascinated with solar and have a small system for "just in case". Welcome.

 

[C&K]

I would first make sure that these are properly maintained. You can test the specific gravity of cells to get an idea what condition they are in (and locate any problems).

Hi, thanks for that. Our battery has been doing ok so far. It is not 100% capacity anymore but all 24 cells are still even when I check them with a hydrometer. The solar can keep up with it in the summer and the Cat generator never runs from about middle of April to around middle of October. In the dead of winter in Dec and Jan the Cat runs about 8 hours every three days to bulk charge it at 180 amps, and partially absorb it. Then we switch to the small generator to finish absorbing it once the amp load to the battery gets down to about 80 amps where the little generator can handle it. It exits absorb at 50 amps and we never float it with the generator.

The water consumption is still within reasonable limits and it doesn't get excessively warm during charging. So we're hoping it has a couple years left in it yet. However, we are putting considerably more amp-hours into it than we're getting out of it at its age and my rough guess is that charging efficiency is less than 88%.

During summer it maybe uses 12% of its capacity during the night, and the solar easily re-absorbs it and floats it most of the afternoon on most days. In the winter, however, it's being cycled completely, average every 3 days, so it gets roughly 50 deep discharge cycles on it during the winter months. GB Industrial claims 1,500 cycles on these batteries but it will never make that many for an off-grid system because even the slight daily discharge during summer, and re-absorbing it, constitutes a charge cycle. And that is actually harder on it than the deep discharge cycles in the winter time.

So our current plan is, that based on what we're seeing this winter, we can probably get one more winter out of it. Then we'll trade it two summers from now on a reconditioned battery while it still has some decent core value. The battery weighs a little over two tons, and it was originally set in the utility room with an excavator. My John Deere track loader will lift it, but we'll have to drag it to the door with a chain where I can get the pallet forks under it to lift it. And then figure out how to get the new one back in place in the utility room - probably roll it on the floor on some 4" sections of pipe. We're not looking forward to the day we have to replace it. But we realize it is one of the consumable replacement items for these types of power systems. While there is newer battery technology that might be better, we are told that these big traction batteries are still the cheapest per kWh over their useful life.

There is other options too, like going with individual 2V cells that can be handled with a dolly cart. But then we don't have the welded interconnects between the cells and have a bunch of battery cables to maintain. So when time comes we'll probably just go with another forklift battery, and GB Industrial has their own delivery trucks and will bring the battery right to you, and take the core away. You just have to have the equipment on site to handle it when they get there with it.

 

[Don B. Cilly]

Sounds absolutely great.
I live completely off-grid too. 70 sqm (say 700 sqft) little house, a bit less than 4 acres.
1.2kW PV, 1.3KWh LFP batteries. Stihl chainsaw ;·), heat house with wood, cook and heat water with gas, so plenty power.

One thing I would look into is LFP batteries. Expensive (compared to lead-acid) but... hey. The no-worry factor is really quite impressive, not to mention the higher efficiency and useful life. Low temperatures are not really a problem, there are many ways around that.
You can easily sell the big generator to offset the cost and come out ahead :·)
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[C&K]

Sounds absolutely great.
I live completely off-grid too. 70 sqm (say 700 sqft) little house, a bit less than 4 acres.
1.2kW PV, 1.3KWh LFP batteries. Stihl chainsaw ;·), heat house with wood, cook and heat water with gas, so plenty power.

One thing I would look into is LFP batteries. Expensive (compared to lead-acid) but... hey. The no-worry factor is really quite impressive, not to mention the higher efficiency and useful life. Low temperatures are not really a problem, there are many ways around that.
You can easily sell the big generator to offset the cost and come out ahead :·)
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What is LFP batteries? I am not familiar with those.

For us, the big generator serves a second purpose. The cooling system on it is hooked into my 40 x 80ft shop building and heats it with a Modine heat exchanger in the winter. After an 8 hour run it's 68 degrees in the shop and it stays pretty nice in there for two days even at 20 below, as long as I don't open the overhead door. We heat the house with wood, we have a brick fireplace upstairs in the middle of the house. And we have a forced air Daka furnance in the basement that evens the heat out in the house. And we also have electric baseboard heaters for backup that are powered by the big generator. So that Cat is kind of necessary since it provides power and heat for the shop, and battery charging and backup heat for the house.

And this is also why I say we're not necessarily "green". Seven months of the year solar works fine. The other five months it is primarily diesel power.

 

[Don B. Cilly]

LFP is Lithium-Iron-Phosphate. LiFePO4. A much better technology than lead-acid.
I've lived for many years on lead-acid. LFP definitely improved my quality of life.

Look it up. Which reminds me, I also use mobile for internet access. I have a little antenna on the roof and an amplifier. I get really decent speed (10-40 Mb/sec, depending on... not sure what, it just varies). The cell is some 10 Km. away. I have a pretty much unlimited (120GB/month) plan for some €20/month, which includes two SIM cards (with the same number) so I keep one as a hotspot and the other in the phone.

On heating, you might want to check out the link in my signature.
I also have a generator. I only use it for the air compressor, cement mixer and such.
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[ShaneC]

Assuming that 1700ah battery is at 48v then it'd cost a small fortune for 81.6kwh of LFP. I think server rack batteries run about 40c/kwh at best so you're looking at $35k. You can save money by going DIY with raw LFP cells bringing costs down to about 20c/kwh but what I'm saying is if it ain't broke don't fix it. Some day you'll have to and LFP is currently the best choice when buying new, who knows what it will be in a few years when you do need to change batteries. This is definitely the right place to ask though.

 

[C&K]

Assuming that 1700ah battery is at 48v then it'd cost a small fortune for 81.6kwh of LFP. I think server rack batteries run about 40c/kwh at best so you're looking at $35k. You can save money by going DIY with raw LFP cells bringing costs down to about 20c/kwh but what I'm saying is if it ain't broke don't fix it. Some day you'll have to and LFP is currently the best choice when buying new, who knows what it will be in a few years when you do need to change batteries. This is definitely the right place to ask though.

Yes, it is a 24 cell 48v battery in a steel tray. And very heavy, around 4,300 lbs. It is 1105ah at 6hr rate and 1742ah at 20hr rate. It is available from GB Industrial for $10,240 new or $7,860 remanufactured with good core exchange. New or remanufactured is the same as far as warranty on it, they take these batteries apart and rebuild the plates to new spec in a remanufactured one. The only difference is if you don't have a battery you have to buy new, if you already have one you can get the exchange price. New or remanufactured, they have mobile service technicians that will come to your location and replace a defective cell at no charge in the first 7 years. The battery is designed for the Caterpillar M80 lift truck.

I believe it is actually 66.8 kWh since it is designed for 1,500 cycles at 80% discharged. So our price would be the $7,860 plus $250 delivery charge and you are expected to have the equipment on site to unload the replacement battery and load the core into GB Industrial's delivery truck. I do not know how that compares to the LFP type, but it seemed to be pretty reasonable and since we already have GB Industrial's auto watering system on it we don't need to buy that again.

 

[MisterSandals]

1742ah at 20hr rate.

I believe it is actually 66.8 kWh

51.2V nominal x 1742Ah = 89.19kWh

 

[C&K]

51.2V nominal x 1742Ah = 89.19kWh

51.2 would be at-rest fully charged voltage. Nominal is 48V. 48 x 1742 = 83.6kWh. Of which 80% is usable, or 66.8kWh actual stored power.

According to the chart that came with the battery, nominal voltage is 48.0V at rest, at which point the battery is 50% SOC and should not be recharged yet. It's designed to be discharged to 20% SOC before being recharged. It says at 46.6V at-rest with no load, 46.0V @ 30 amp load, 44.8V @ 50 amp load, or 44.0V @ 70 amp load, it is 80% discharged. So the trigger in the AGS is set to start the Cat generator if the battery is at or below 46.0 for 2 hours. There's also two other triggers, one that starts the Cat if the voltage is at or below 44.8 for 30 minutes, and another one that starts the Cat if the voltage is 44.0 or below for 15 seconds.