Replacing Off-Grid FLA’s with ?

Anawa

I jumped in on the tail-end of another discussion about battery bank replacement last week, but y’all had already gone on and the thread stopped. Looking for advice from the sage cadre that monitor this forum. 

Let me begin by saying the advice I received at this forum over 9 years ago was, and remains, invaluable. I have directed many people here that want to “know more about or how to do solar”. In addition to being a sound source of advice, it’s relieved me personally from a lot of nonsensical questions and having to listen to a bunch of climate change virtue signaling and hysterical ranting! For the record, my decision to install an off-grid solar system was for very pragmatic reasons… it’s was cheaper! I live over a mile off the so-called “paved road” in dense trees and around here, they don’t install power lines for free.

Here’s some starting info. My 800Ah forklift batteries are on their last leg. Don’t want to waste y’all’s valuable time lamenting how they won’t charge like they used to, nor how fast they discharge, etc. They’re kaput, finished, toast, history, etc. The only redeeming thought on this is, I followed the advice of one of the forum’s member (Photowit) over 9 years ago when he advised that if this was my first off-grid experience with batteries, then I might consider using the cheapest FLA battery (forklift) as my “training wheels”. Yep, I learned how-to and not-to take care of my batts and at the time, it only cost $5,000! 

Well boys, it ain’t $5,000 anymore. Right now I’m looking at $8,000 plus for about the same setup. If I stick to FLA’s, I would like to upgrade to RE grade, Surrette’s, etc. I’ll get into that down below.

The reason I’m asking for y’all’s advice is because it’s not ALL about the cost. For me, there are many moving parts that I need to consider. To begin with, I’m 80 years old. Right now I’m in good health, but at this point in life that could change in an instant. I have a lot of land to tend, a sizeable garden to maintain, 2 miles of roads to maintain, Boy Scouts, Girl Scouts, church and other groups visiting on a frequent basis. Yes, tending the FLA’s did get lost in the daily shuffle, the price was paid and the time devoted to such solar activity will not increase as I get older.

Although I have family nearby, they do not live with my wife and I. After I’m gone, I do not want my wife worrying about tending the batteries and wondering what’s going-on with all that buzzing, lights blinking, and other crap in the Inverter Room. I have someone available for equipment malfunctions, but the batteries are another issue.

It’s obvious that my ultimate upgrade for my system would be LFP’s. I believe my next choice would be the RE grade FLA’s. I’m open to other considerations, I not sure what they would be. 

Here’s some considerations: PV array 6.1kw put into service 2015; inverter and CC’s equipment 9 years old; baseline daily 6kwh; summer time AC load add another 6.5kwh; mini-splits primarily for AC; wood burning stove primary heat source; and water supply on another system.

Money is not the primary factor, but is a concern. Needless to say, both my wife and I are retired and although it does not cost a lot to live where we do, our savings ain’t like they used to be thanks to our political ruling class. 

I’ll need to go shopping and looking for guidance on battery bank size and configurations for the LFP and FLA’s. Will I need to upgrade any components of my current equipment? Also, your recommendations on product selection?

Thanks in Advance

Paul
In Georgia 

Dave Angelini

I see what you mean here Paul. That is a super complicated number of systems. I like just one offgrid, with crucial spares !

Having 12V in the house is pretty much not code and definitely not insurable, if I am reading this right. Looks like you need to be able to monitor this with optics if you stay with Outback. I am pretty much a rep for Schneider and I still think they are the best out there. They are not perfect but they do push the state of the art really well. Closing the charge and discharge loop with LFP since 2017.

Definatly think of the other person offgrid.  You do not want to hear my stories on that !  In 500 plus clients, there are about  20 that never cared about what would happen if they did not show up one day.

Below is Insight Cloud. It allows Schneider or Outback Optics to look at your system. it also allows someone like me to troubleshoot and maintain the system. It is on a smart phone for anyone you want to see the power system. Each of these systems has a ton of detail when you dial in. Pretty cool that you can see site weather, Soc, Gen, alarms, and solar production. Peace of mind is as good as Melatonin, sometimes😊

Good Luck and see what others say. Take your time but winter is coming😉

Anawa

Dave, as always good advice! Glad you’re still around. 

Paul

Anawa

Dave, we’ll talk more about the monitoring system after I get this problem taken care of. Melatonin is good, but a good smooth single malt is hard to beat. 

Paul

BB.

I am a bit more than a decade behind you in age... And we have run across this issue with the surviving spouse (or the getting too old to maintain the system spouse).

LFP (LiFePO4) batteries are today's pretty close to ideal batteries. Maintenance free (no water), ideal charging (faster than Lead Acid, more efficient). With limitations/complication (Lithium rechargeable batteries do not like running much below 40F, and should not be recharged/heavy discharged at freezing and below) so you end up with needing to keep the batteries warm in winter. And they should last you 10+ years (good quality) of daily solar usage. The complexity of the BMS (battery management system hardware and possible communications back to the Solar Charge Controller/off grid system) means balancing the brand model of batteries/BMS/Off Grid solar system (if you go full "integration" between BMS and Charging System--The ideal setup for best battery life/monitoring).

You could go with AGM batteries... Sub freezing operations are just fine (yes, there is less battery capacity when cold/freezing) for AGM and FLA. AGMs don't need water. Probably are a bit more forgiving than LiFePO4 batteries to an over/undercharging event. And good quality AGMs can last you 5-7+ years.

Some years down the line--What happens next. Is your wife (or you) going to be cable to maintain the system? With Dave's suggestion of a Schneider system with integrated BMS support of the batteries--You do have the remote support via Internet to be able to debug the system (you do have an Internet connection?). But what do you do if you do need service (repairing/replacing of a heavy inverter? Cleaning of cable connections, replacing the next battery bank, etc.)? I suggest that batteries typically last 5-10 years. And the electronics will last 10+ years if they are doing well. And typically parts/repairs become problematic after 5-10 years for the "old inverters/charge controllers/etc.). It is just the nature of the electronics industry (old components are no longer made, manufacturer no longer has repair/support program, no software support available, etc.).

Do you work with a local (to you) designer/installer so that you can have onsite support if needed? Will the person/company be around in 10+ years? Will he (or you) document the system for the "daily maintenance" by the next user and have information on the system design for debugging support (if/when needed next)?

Another question to ask--Is there utility power available in your area these days? Sometimes the grid slowly extends to more remote areas--On the other hand, there is "rural de-electrification" going on these days where utilities are looking to shed the remote customers and/or jacking up connection fees/power prices to continue to make money? And the costs of running a new utility connection can be cost prohibitive too (thousands of $$$ per mile).

The positive of a utility connection can increase the value of your property--Whereas I humbly suggest a solar power system (even a well designed and functioning system) usually adds little, if anything, to the property value for a buyer.

More questions than answers at this point.

-Bill

Anawa

Thanks Bill, sage advice as usual!  The omission of anything FLA’s in your response is noted. 

Would you help me determine the replacement size of both the AGM and LFP battery banks and what would be the estimated costs? I’m shopping as we speak. I do not want to stray too far off the trail and waste vendor’s time. I’m assuming the AGM would be about the same as FLA’s, but what about the LFP’s? And, is my current solar array a decent size? 

Thanks

Paul 
In Georgia 

BB.

Here is sort of a short an sweet (yea--Short for me) very quick solar power design that addresses the first level sizing tasks....

It it is not a detailed/complete set of design questions/answers (such as max surge power for power tools) and such. But it does give you a quick way to size a workable solar power system. And to show how depending on you specific needs and asumptions will affect the system design.

Using or rules of thumbs, I would suggest that lead acid batteries should plan on using about 25% of capacity per day to 50% of total capacity (2 days of normal storage).

This allows for the fact that lead acid batteries take longer times to charge (sun is up only x hours per day) and discharging 50-20% state of charge gives longer battery life (usage during bad weather) and upwards of 20% lots of capacity due to aging.

For lithium ion batteries, they are very efficient at charging. 98+% vs 80% or so for lead acid (AGM batteries are probably 90+% efficient). And with enough solar panels, you can charge most lithium batteries at 20% or faster (i.e. 40% capacity recharge in 2 hours vs 9+hours for lead acid).

I suggest sizing lithium batteries to:

Capacity * 60% usage (80% full - 20% empty) = 60% of capacity (conservative)
Capacity * 80% usage (100% full - 20% empty) = 80% of capacity (less conservative)
Capacity * 95% usage (100% full - 5% empty) = 95% of capacity (using all energy, no buffer/safety margin)

The 100% vs 80% full charge--People that know more than I have offered that Li Ion batteries run just fine to 100% full cycling. The "conservative" usage has been to 80% (or some other fraction full).

Batteries do wear from aging and cycling... Bottom usage to 20% of capacity leaves some margin for bad weather and 20% loss of capacity due to aging.

Also, with Lithium Ion batteries, since they charge a lot faster/more efficiently vs Lead Acid--You could size your system for ~1 day of storage (maybe with a bit of buffer) and the second day--you may have 10-20% harvest (cloudy weather) and the solar can mostly keep  up with daily usage (and still charge battery bank for over night).

Just to use an example for math... Say you want 3.3 kWH per day of energy (enough for a "near normal" electrical existence with lots of conservation). Some examples of the math may look like (this is assuming a refrigerator at 1,000-1,500 WH per day plus efficient well pump, LED lighting, laptop computer, cell phone charging, washing machine couple times a week):

3,300 WH per day * 1/0.85 off grid AC inverter eff * 2 days of storage * 1/0.50 max planned discharge * 1/48 volt battery bank = 324 AH @ 48 volt battery bank FLA conservative

Note the above FLA battery is to 50% nominal/daily discharge and you can discharge to 20% (battery bank in good condition) or another 30% of capacity--Or better than 1 day of additional storage for those poor weather/broken genset days.

For Lithium Ion, the same 48 VDC design may look like one of these:

3,300 WH per day * 1/0.85 AC inverter eff * 2 days of storage * 1/0.60 capacity * 1/48 volts = 270 AH @ 48 volt lithium bank relatively conservative design
3,300 WH per day * 1/0.85 AC inverter eff * 2 days of storage * 1/0.80 capacity * 1/48 volts = 202 AH @ 48 volt lithium bank less conservative design
3,300 WH per day * 1/0.85 AC inverter eff * 1 days of storage * 1/0.95 capacity * 1/48 volts = 85 AH @ 48 volt lithium bank 1 day aggressive design

These assumptions also affect solar array design... For example, a typical FLA design would look like (typical is 10-13% minimum off grid array):

3,300 WH loads * 1/0.85 AC inverter eff * 2 days of storage * 1/0.50 max planned discharge * 1/48 volt battery = 324 AH @ 48 volt battery bank
324 AH * 58 volt charging * 0.10 rate of charge * 1/0.77 solar panel+controller deratings = 2,441 Watt array 10% minimum rate of charge for FLA
 
But we also need to look at your solar harvest.... Fixed array, 34 degree angle, facing south, Lincolnton Georgia, 48% off grid losses using PVWatts:
https://pvwatts.nrel.gov/pvwatts.php

Month	Solar Radiation ( kWh / m2 / day )	AC Energy ( kWh per 1,000 Watt solar array per month )
January	4.53	127
February	4.81	119
March	5.26	141
April	6.18	157
May	5.84	152
June	5.82	142
July	5.75	145
August	5.74	145
September	5.83	144
October	5.30	140
November	4.85	128
December	3.63	103
Annual	5.30	1,643

Say you want "break even" month of December (probably need to use genset during bad weather):

3,300 WH per day * 1/0.52 off grid FLA system eff * 1/3.63 December Average hours of sun = 1,748 Watt array Dec break even

If you do not want to use a genset in an emergency, then you want only use 50% to 65% of "predicted solar harvest" account for bad weather:

1,748 Watt array * 1/0.65 solar fudge factor = 2,690 Watt array (conservative FLA array for December)

As you can see there are a lot of variables here that depend on your needs (use more power in summer for fans/fridge/irrigation vs winter cool weather). You need to "model" your needs--I cannot give you an "exact answer" not knowing your usage.

Overall system efficiency/deratings (from solar panel => charge controller => battery bank => AC inverter => AC output. For AGM, the overall efficiency is around 0.62 vs 0.52 for FLA. You can use 0.68 for overall system efficiency for the Li Ion+AC inverter system.

Doing the same math in Li Ion Battery bank.... There is no minimum rat e of charge needed for Li batteries... So all we need is to replace the energy used per day from solar:

3,300 WH per day loads * 1/0.68 Lithium off grid system eff * 1/3.63 December ave = 1,693 Watt array "December break even"
1,693 Watt array * 1/0.65 solar fudge factor = 2,605 Watt array with 65% production usage fudge factor

I am going to stop here--This is a lot of information and probably a bit confusing as written... Please feel free to ask questions.

I did 3.3 kWH per day system as a suggestion of what you can aim for in terms of conservation... Or you can take my above examples and (6,000 kWH per day / 3,300 kWH per day example= ) x1.82 larger battery bank and array....

It sounds like your present system (800 AH @ 48 volts FLA + solar panels) was sized pretty well for your needs. 

-Bill

Wheelman55

Paul. Here’s some real world comments…no math here:)

Some years ago Dave helped us put together our system. I think we just squeezed into his first 100 or so clients😀

We are in a sunnier area than you at the 29th parallel and use Discover lithium batteries in a closed loop. Schneider gear, 5.2kw array, 390 ah battery bank. 

Everything works tremendously well. 

Note that the Discover batteries have a built in buffer of 10% or so. Meaning that the bms keeps something “in the tank” even when taken down to zero. 

In fact Dave had me run the batt down to zero to make sure that the system would restart the next morning. Worked as it should. 

We occasionally have three to four days in a row with minimal production. The 390 ah bank holds up fine. 

The batts will take pretty much any level of charging that you can give them…either high or low. 

The batts were expensive, however the peace of mind is high. 

We run a modern house: fridge, freezer, mini splits, router, range hood, fans, lights and a Vitamix:)

You won’t be sorry if you go lithium and closed loop. 

Best of luck with your decisions. 

Anawa

Wheelie, thanks for the encouragement! As I consider the factors, I’m definitely leaning to LFP’s. I’m the kind of guy that will consult with the “Big Guy” (and I don’t mean that idiot in the WH) on matters like this and this is where He seems to be guiding me. 

We’ve got a lot of moving parts here, especially when folks show up and want to stay 3-4 days and we open up the guest house. That additional load can not always be absorbed with our current system capacity. I’m even considering increasing the LFP battery capacity a bit to save on the propane when guests arrive. 

I’m not sure what you mean by a “closed loop”? Not familiar with the term in a solar sense. 

Paul
In Georgia

Dave Angelini

Open loop is what you are doing now to charge. You adjust set-points based on voltage. This is what you will do with LFP unless you close the loop. 

A closed loop system uses the BMS to adjust set points dynamically based on the BMS state charge internally. This can save 30% of fuel if you use a genset. It also can charge faster on bad solar days. Most all of the DIY LFP batteries are open loop and it does involve you much more in learning and monitoring.

Closing the loop is much easier, precise, and costly as your electronics need to be capable. Outback has not been a leader in closed loop BTW.

Anawa

Okay Dave, I’m listening!  As usual, anything to do with off-grid solar is like the proverbial tar baby story. Hope I’m not cancelled and banned from the forum for using that that analogy, but it just seems right with this open vs closed loopie stuff.

Dave, you’re a great asset to everyone visiting this site and I do not want to hijack all your time and resources. If you would be willing to guide me a bit more (until we hit another TB) I would appreciate it. There may be others out there that could benefit also. 

Simply, you can see my equipment set-up in my profile. What’s your most cost effective suggestion? 

Paul

Dave Angelini

Well drop me an email below Paul. You are getting into my business expertise. General Info is here.
Specific info I have a $500 fee that is refundable for a year.