Comparing current FLA to any future LFP

[MikeGoodman59]

FLA vs LFP thought.

Have Interstate 2X strings 420AH batteries, 48V in parallel through SMA SI5048. Again: 2x8 (6V) twice.

My first set of Trojans lasted 10 years. On my second set of batteries. Replaced 2 years ago, $6,400, cycling more frequently this time.

Mine is grid tie, battery backup. Discharge and check specific gravities about every quarter. Typically go down to 40% SOC, 60% DOD. ... Can hold essential loads @120V 4 days spring/fall, 2 days in winter, 3 days summer (zero AC). ... No concern keeping heat down to 62F in winter to reduce air handler load.

48 VOLTS, 840 AMP HOURS.
40,320 WH ... At typical 50% DOD, would have to compare to 20,160 WH LiFePo4. (Hoping the math is right). That means I would need 4X 48V 100AH LFP batteries. (4.2?)

$6,400 2 YEARS AGO on the 16 FLAs.
$1500x4 SigSol for LiFePo4 (12/23)

Does that make it a wash?
Granted they're different animals.
Granted I still currently maintain Sp. Gr.

The above is in my primary residence, can maintain daily. As compared to my off-grid cabin, 1 hr north. Any possible concerns have to do with how often I could visit, how well they would maintain without frequent oversight.

Would require weekly visits? Central North Carolina down to min possible ~15F outside?

Is lithium iron phosphate simply a brain dead choice any more?

Use lithium iron phosphate with heaters?

As an aside, should I cycle my FLA more frequently? Deeper?

 

[time2roll]

The LFP will simply out perform the FLA in every aspect. Yes there would need to be some prep for 15F same as the FLA should not be allowed to over discharge and freeze.

 

[yodamota]

My neighbor who works in the industry said every other component the same, only the batteries being changed. the LFP made his system 25% more efficient.

 

[Skypower]

Battery backup only? Holding a high state of charge and only needing the batteries for when the grid fails? How often does the power go out? The batteries are only 2 years old, are they still performing at expected levels? Still some factors to consider before switching over.

 

[chrisski]

the LFP made his system 25% more efficient

How Is it more efficient? Is it because he can by less watt hours because LFP can tolerate 80 DOD versus lead acid batteries at 50% DOD?

 

[OffGridForGood]

The above is in my primary residence, can maintain daily. As compared to my off-grid cabin, 1 hr north. Any possible concerns have to do with how often I could visit, how well they would maintain without frequent oversight.

Would require weekly visits? Central North Carolina down to min possible ~15F outside?

Is lithium iron phosphate simply a brain dead choice any more?

Use lithium iron phosphate with heaters?

Do you mean the new LFP are for the cabin? - ie since your FLA are only two years old and are in your primary residence. (I think this is what you are getting at: what batteries to use at the cabin, knowing the LFP and FLA are 'about the same cost per useable Wh'
Questions:
does the cabin have grid tie?
does the cabin have heat when you are not there?
does the cabin have internet connection available? (to allow you to remote monitor)
does the cabin site have open area suitable for PV solar input - how about during winter?

You can get LFP with heaters built in, with controls that will cycle the heaters off and on.
Not too hard to build an insulated battery box, as long as there is enough available solar coming in to not drain the batteries running the heating pads.

 

[Checkthisout]

Lipo4 is a brain dead choice, yes.

EXCEPT

When freezing temps are involved. You need enough solar juice or generator to keep the batteries or room they are in above freezing.

 

[OffGridForGood]

Lipo4 is a brain dead choice, yes.

EXCEPT

When freezing temps are involved. You need enough solar juice or generator to keep the batteries or room they are in above freezing.

If the LFP batteries are being charged, they need to be above freezing temp.
The LFP could sit in a cabin un-used (storage) below freezing without damage.
In long term storage the cells should be left about 50% SOC.

 

[rhino]

How Is it more efficient? Is it because he can by less watt hours because LFP can tolerate 80 DOD versus lead acid batteries at 50% DOD?

Charge efficiency for LiFePO4 is around 99% compared to 95% or less for lead acid. The Peukert exponent (affect of battery capacity based on how fast it is being discharged) for LiFePO4 is normally set around 1.05 or less whereas lead acid around 1.25.

 

[time2roll]

How Is it more efficient? Is it because he can by less watt hours because LFP can tolerate 80 DOD versus lead acid batteries at 50% DOD?

LFP absorbs 100% of the solar pretty much right to 100% charged. FLA otoh will be tapering current as it approaches 100% and could run out of sun before it finishes. Especially if going down to 40%. Then how to squeeze in a 60 minute equalization once a week?

If the LFP does not make 100% it is no issue. FLA that charges to 90% will start sulfating and need even deeper discharges that could put them in a death loop.

 

[Crowz]

I don't look at the cold weather part being as bad in some situations since the extra dod the lfp can do would handle heating the batteries to protect against the cold. This of course is within "reason" since it can cause problems if the charge amount isn't enough to make up for the drain from the heating. But if its not being used during these times I would hope solar would be able to put the fairly small draw of the heating pads power usage back each day.

 

[MikeGoodman59]

Thank you for your response. I will try to address all of your thoughtful questions, in some sensible order.

Any new system would be for my off-grid cabin. My home is doing fine as is. Almost wish I'd had the nerve to pull the trigger on LFPs back in 2021 but I have a forklift maintenance shop owner friend. More traditional FLA.

Cabin has power/telephone 300 ft away. Energy company has agreed to drop secondary, 240V underground as needed. Trying to avoid, trying to stay away from the system. Definitely not a purist on that.

Was my power out math right about LFP versus FLA? $6400 for FLAs. vs $6000 4X 48Vx100AH LFP?

Is the new technology proven compared to the work involved in maintaining lead acid?

Would gel or AGM be a better alternative if not present every day?

Cabin could have heat if one of those solar heat pumps will serve the purpose. Will has done a good job demonstrating. Don't yet understand the tie in to the batteries when sun is down. Money is not the primary consideration. Reliability in those systems is. Believe that that could provide minimalist heat as needed when not present, 50F as target. Only 1 hour away, could manage it somehow.

Internet connection can be done through mobile provider, T-Mobile wireless unit. There is remarkably very good service despite its remote location.

Cabin has 10 acres of open, 100% solar exposure at Central North Carolina latitude.

Insulated battery box with heaters would do the job.

Need not be a one size fits all. Could have one large system, several small systems, one of them on a hand truck. Very impressed with what Will did with the 120 hand truck system, yellow EG4. Like the TROPHY battery over the EG4 battery because of the terminals.

Pictures show my land, Google Earth doesn't show building yet, seen from small road corner shot. ... Would likely do ground Mount or put up another carport wall.

Do you mean the new LFP are for the cabin? - ie since your FLA are only two years old and are in your primary residence. (I think this is what you are getting at: what batteries to use at the cabin, knowing the LFP and FLA are 'about the same cost per useable Wh'
Questions:
does the cabin have grid tie?
does the cabin have heat when you are not there?
does the cabin have internet connection available? (to allow you to remote monitor)
does the cabin site have open area suitable for PV solar input - how about during winter?

You can get LFP with heaters built in, with controls that will cycle the heaters off and on.
Not too hard to build an insulated battery box, as long as there is enough available solar coming in to not drain the batteries running the heating pads.

 

[MikeGoodman59]

Battery backup only? Holding a high state of charge and only needing the batteries for when the grid fails? How often does the power go out? The batteries are only 2 years old, are they still performing at expected levels? Still some factors to consider before switching over.

I hope I am answering all of your well thought out concerns.

No, my system is grid tie/battery backup as needed, meaning I can sell or consume. Power very rarely goes out. Run tests every 2 to 3 months.

The batteries are performing well, perhaps the only concern being the accuracy of a float bulb hydrometer. But consistent readings, charted every time, pre discharge, post discharge, post charge.

Other factors about what to pick involve:

a) sustainability in potentially unheated space
b) I am thinking about bringing power from a local power pole, 300 ft away, 240V secondary
c) it would be available through one of Will Prowse's suggestions about off-grid DC heat pumps

 

[MikeGoodman59]

Shifting gears from type of battery, presuming LFP, choice then becomes DIY (hand truck type system? Semi-permanent?) or portable power station.

The Hysolis Apollo seems to be the clear winner over the Eco-Flow Delta Flo. ... Reasons include my moving my 12x235 panels up to the land, where there is better solar exposure, and the 500 volts, 5000 (4400?) watts of solar power intake. ... My REC panels have a VOC of 37.4

AND I CAN TIE THEM INTO A DOUBLE APOLLO, TWO EXPANSION BATTERY SYSTEM. (All caps because I am really trying to nail this down.)

I am an engineer and can handle the DIY, but thinking the "double-double" Apollo with an additional DIY hand truck. ... I am in a good place with money so that's a good thing at my age.

 

[MikeGoodman59]

Do you mean the new LFP are for the cabin? - ie since your FLA are only two years old and are in your primary residence. (I think this is what you are getting at: what batteries to use at the cabin, knowing the LFP and FLA are 'about the same cost per useable Wh'
Questions:
does the cabin have grid tie?
does the cabin have heat when you are not there?
does the cabin have internet connection available? (to allow you to remote monitor)
does the cabin site have open area suitable for PV solar input - how about during winter?

You can get LFP with heaters built in, with controls that will cycle the heaters off and on.
Not too hard to build an insulated battery box, as long as there is enough available solar coming in to not drain the batteries running the heating pads.

Trying not to miss anything. My home system doesn't really get much solar exposure, basically running it as a gen-bat system, likely to move my 12x235 rec panels up there, 12 years old, might as well get life out of them. ... Thinking of keeping the home system without the panels, running the eg4 genverter. ... Entering my third day of off-grid test at home, have the Honda triple fuel 12000 w generator tied into my system. Also have portable Honda 2200 inverter generator.

 

[MikeGoodman59]

LFP absorbs 100% of the solar pretty much right to 100% charged. FLA otoh will be tapering current as it approaches 100% and could run out of sun before it finishes. Especially if going down to 40%. Then how to squeeze in a 60 minute equalization once a week?

If the LFP does not make 100% it is no issue. FLA that charges to 90% will start sulfating and need even deeper discharges that could put them in a death loop.

Your comments make me look outside on an overcast day in Central North Carolina. WAY BETTER exposure on my land, COMPLETELY CLEAR 180° TO THE SUN but generally down to about 2 KW-HR at my home on a day like today.

Suspect it would be presumably closer to 4-6 KW-HR with better solar exposure. 2800W system, so not that impressive. Panels have been out on the sun since 2011 so some degradation.

Thinking of getting 2X Apollo "double-double" systems, main unit plus one extension battery two times. Old panels on one, new panels on the other.

The trick will be to get the T-Mobile internet device, set up a different phone, keep track of it through the app.

 

[time2roll]

For 20+ kWh consider a DIY battery for lower cost and better control.
Can add more as time, money and need is determined without worry of combining with an aged battery.

 

[Horsefly]

Lipo4 is a brain dead choice, yes.

EXCEPT

When freezing temps are involved. You need enough solar juice or generator to keep the batteries or room they are in above freezing.

For my two 230Ah 24V LiFePO4 batteries I used two 12V 12W heating pads (in series for 24V), and with outside temps between 20°F and 0°F (IIRC) I am able to keep the battery (inside its insulated box) between 50°F and 60°F with only around 3-4Ah per 24 hour period. That means that if I get no solar for four weeks the battery would only go down from 100% SoC to 50% SoC. In my case (9,000 ft elevation in Colorado) there will never be straight weeks with no solar.

So I think a good DIY battery design with heating pads and an insulated box is a no-brainer for even cold winters.

Edit to add: I had to go search for it myself, but here's the thread where I describe my battery box build and tests. The graphs of the temperature tests is on the next-to-last page of the thread.

https://diysolarforum.com/threads/horseflys-cabin-solar-lifepo4-upgrade.27472/

 

[KITROBASKIN]

Wonderful for you to have these options and possibilities.

How much would it cost to get grid power to your cabin? Might that money be better served using it to maintain independence from the utility with its service charges and add-ons?

Perhaps get those flooded lead acid batteries and (mature but functioning fine) solar panels to where the sun is shinier and build something with LFP’s at your home. Seems like the FLA will last longer if they don’t get so deeply discharged.

It is hard for us to get the complete picture of what you would like to accomplish. How much time do you anticipate actually being at your cabin? What time of year? What will you be powering and how much of the time? What would you like in the future?

 

[glandpuck]

I just replaced Trojan FLA bank with LFP.
Gone is my distilled water.
Gone is my specific gravity tester.
Gone is my use of Kopr Kote on the terminals.
Gone is my wire brush to clean off acid build-up.
Gone is my checking battery acid levels monthly.
Gone is my venting of hydrogen from the boil off gassing inside my garage.
Now, my batteries are connected from battery can bus to inverter input. Loop communication. Minimal settings to set and forget. No maintenance to explain to anyone else.

I think for first time users of FLA for solar, there is a learning curve. To get the optimum life expectancy, they need to be exercised, given proper absorb voltages and times, equalized periodically too and more. As well as making sure they are not over discharged. That can be a task that takes a while to get comfortable doing.

Hoping for 15 years of useful life.