LiFePO4 - The future for off-grid battery banks?

[Sunking]

Most people don't want the criticism and ridicule from the posters that inhabit the site. Potential Advertisers / Sponsors would see it as a net loss to be on here.

Especially a shyster like Iron Bran. Username alone is a rip-off and plagiarism

Meet the real and only Iron Byron.

[jedics]

new but keen

Hi all, I came across this thread while researching an off grid system to go on a 12 meter refrigerated semi trailer. After reading about AGM batteries and how long they take to charge to 100% together with the fact they shouldnt be discharged bellow 50% I quickly started to prefer lithium.

Ive been in contact with a seller installer briefly(lithium batteries Australia site), he likes the victron stuff and has a 3 year warranty on his batteries but my rough calculations say it will take me about 5 years to break even on the batteries alone. eg. approx 400ah of LifePO4 will be 6 to 7 grand and my bills are currently about $1200 a year.

Im still getting a handle on the basics and I was hoping to get an overview firstly of what size system makes sense, Im in South Australia, if my bills average $1200 a year with the appliances I have currently, would a 400ah system with say 6x 250watt panels and a 3000watt inverter and being sensible be enough for me to live off grid?

I dont have easy access to my exact billing (long story) to give exact usage but I am only after estimations atm just to start getting an idea of the costs involved and maybe some directions on kits people may have bought.

cheers.

[PNjunction]

I dont have easy access to my exact billing (long story) to give exact usage but I am only after estimations atm just to start getting an idea of the costs involved and maybe some directions on kits people may have bought.

Estimations are costly. You don't want to "wing it" with solar, no matter what chemistry you choose.

Winging it with LiFePo4's additional up-front cost makes it even harder for the wallet to swallow. Don't get me wrong, I use and LOVE LiFePo4, but if you walk into a sales-office or forum without knowing your actual power needs - you become an easy target.

What I'd do in this case is in fact go ahead and use high-quality pure-lead AGM's, armed with the knowledge that most people UNDERcharge them, and take steps not to do that. Accept the fact that in solar, we will never get it perfect due to the variable power supply in the sky, and just do the best we can.

The most important thing now beyond chemistry, is to get an accurate measurement of your real power needs. You just might find that a high-quality agm that can be found 10-minutes away fits the bill.

[jedics]

Estimations are costly. You don't want to "wing it" with solar, no matter what chemistry you choose.

but if you walk into a sales-office or forum without knowing your actual power needs - you become an easy target.
Thats why Im on the net researching and learning

What I'd do in this case is in fact go ahead and use high-quality pure-lead AGM's, armed with the knowledge that most people UNDERcharge them.
What has my knowledge have to do with which technology I go with? Its not as if I need to buy them tmrw, I can learn, as for not undercharging AGM, most people under charge because it take so long to get them up to their last 20% of charge which means they arent full the next day giving you only about 30% of their capacity if you dont drain them under 50%, which is the whole reason Im considering lithium, 1/4 of the time to recharge them.

The most important thing now beyond chemistry, is to get an accurate measurement of your real power needs. You just might find that a high-quality agm that can be found 10-minutes away fits the bill.

Im sure I can get a hold of a power bill, but if I toss out my electric heater for a gas one, build an evap aircon instead of using an electric Im going to be heading to the vicinity of 400ah surely? Yes Im sure I can get some AGM's near by but with the kind of money Im going to be spending for my long term home Im wondering how I might feel about them in 3 years time when they dont hold a charge like they used to.

By the way how long have you had yours? Have they lost any capacity in 'that' time?

[Living Large]

The whole reason Im considering lithium, 1/4 of the time to recharge them.

This was a big factor in my choosing LFP. My location has poor insolation, and I didn't want to have excessive gen run time and the maintenance that comes with it to fully charge my batteries. I believe the run time difference in my case was a factor of two to three to one.

[Sunking]

After reading about AGM batteries and how long they take to charge to 100% together with the fact they shouldnt be discharged bellow 50% I quickly started to prefer lithium.

The whole reason Im considering lithium, 1/4 of the time to recharge them.

OK no one has caught this, but your assumptions are false. AGM can easily be charged at C/4 or less, just as fast as Lithium. Secondly it would be very doubtful you need batteries that conditions dictate a fast charge from an Over Sized Panel Wattage. So if your justification of going to the expense and complexity to use Lithium because AGM cannot be charged as fast is 100% Completely False.

As for AGM discharge depth is not the same as Flooded, they can easily go to 80% DOD. However if you have a proper design of say 3 full usable days between charges, LFP requires the exact same number of Amp Hours. Example if you need 30 Ah per day, you need a 120 AH battery. Makes no difference if it is AGM or LFP. With AGM has the same usable range of 80% as LFP.

[lkruper]

OK no one has caught this, but your assumptions are false. AGM can easily be charged at C/4 or less, just as fast as Lithium. Secondly it would be very doubtful you need batteries that conditions dictate a fast charge from an Over Sized Panel Wattage. So if your justification of going to the expense and complexity to use Lithium because AGM cannot be charged as fast is 100% Completely False.

As for AGM discharge depth is not the same as Flooded, they can easily go to 80% DOD. However if you have a proper design of say 3 full usable days between charges, LFP requires the exact same number of Amp Hours. Example if you need 30 Ah per day, you need a 120 AH battery. Makes no difference if it is AGM or LFP. With AGM has the same usable range of 80% as LFP.

Concorde Lifeline says they can be charged up to 5C.

[Sunking]

Concorde Lifeline says they can be charged up to 5C.

Yes I know, some AGM's can be charged in excess 1C as you pointed out with Concorde be able to charge at 5C. I use C/4 because it is a SAFE number and some numb nut may run with it and do no harm. In other words it is the lowest C-Rate which is limited by the slowest charging AGM's out there. I can sleep at night with recommending C/4. If you want to know the real upper limit check your battery manufacturers O&M manual. I will say at least a minor Majority are 1C or higher.

I just wanted to let the OP know he is making a purchase and technology decision based on false data and assumptions. .

[PNjunction]

Yes Im sure I can get some AGM's near by but with the kind of money Im going to be spending for my long term home Im wondering how I might feel about them in 3 years time when they dont hold a charge like they used to.

By the way how long have you had yours? Have they lost any capacity in 'that' time?

5 years on an old Odyssey. Not enough to be consequential in my relatively low-current non-sli applications. I baseline with a West Mountain Radio CBA-IV, and now followup with additional IR check with an iCharger 306B on my 6 other pure-lead's. Not lab equipment to be sure, but good enough for consumer use. Pure-lead only please.

The key is to not undercharge them, which is easy to do with solar if one follows the typical "canned" presets, which are conservative by design, and really intended for float/standby use. "Read CYA".

Yes, you need to do more research. The reason we don't take batteries below 50% DOD is that provides the most reasonable minimum amount of cycle life. HOWEVER, with lifepo4, you don't think in terms like you do with lead, such as from 0-50% DOD scale. It is a sliding window of PSOC operations, and typically for best results one uses a 10-80% DOD scale window.

EVEN THEN, as a wise solar-user, you don't cut yourself short on autonomy, no matter how good the lifepo4 is! Beware of any sales-droid foaming at the mouth talking about taking your bank down to 80% on a *regular* basis. If you do, that means your bank is in fact too small from a day-to-day liveable solar standpoint. One or two days of no autonomy and you are done - unless you want to start burning genny fuel.

Take it easy man - perhaps turn off the argumentative bolding - we're trying to save you money in the long run by not jumping headlong into some foregone conclusions.

My smaller 20 and 40ah lifepo4 banks made from GBS cells are doing GREAT - just to show you that I'm no chemistry bigot. As great as I think they are, lifepo4 such as those from GBS or even Victron, have not reached even a 10 years worth of experience since the large format prismatics got into general public consumption - circa about 2008 or so.

[PNjunction]

Concorde Lifeline says they can be charged up to 5C.

Yes, but Mr. Puekert is still hanging around in bulk. While getting up to the absorb point very quickly is a good idea, now your absorb will be longer. At least thats what I have observed when having fun like this.

So there is also a practical point to consider when doing super fast charging with pure-leads. For a solar housebank of reasonable financial proportions, you aren't going to be hitting even 0.3C anyway. Genny - sure possibly.

But as Sunking points out - for the neophyte that doesn't know what temp-comp, hot-spots, thermal runaway is, or using the agm pulled from the depths of the garage and hitting it with 5C, NOT a good idea.

[jedics]

This was a big factor in my choosing LFP. My location has poor insolation, and I didn't want to have excessive gen run time and the maintenance that comes with it to fully charge my batteries. I believe the run time difference in my case was a factor of two to three to one.

I noticed there isnt much of people posting what components they are actually using in their system here, is that because moderators dont want the site turning into a sales place?

I'd of thought it would be the best way to see what results in efficiency versus cost is the best solution, Id really like for people to chime in on this as I know batteries and inverters are not created equal but price is a factor of course

[inetdog]

I noticed there isnt much of people posting what components they are actually using in their system here, is that because moderators dont want the site turning into a sales place?

I'd of thought it would be the best way to see what results in efficiency versus cost is the best solution, Id really like for people to chime in on this as I know batteries and inverters are not created equal but price is a factor of course

There is no policy against describing or specifying in as much detail as the poster wants the equipment they are using or are evaluating.
What the Forum does not generally allow is clickable links to those components on a retail site or FleaBay. Links to the manufacturer's site are usually just fine.

Take a look as multiple members signatures that describe the exact components they are using.
Other members give detailed lists of proposed components from quotes received.
If members do not list specific components it is more likely because they were not asked.

And please take it easy on the bold. If you are visually challenged, you can just increase the font size in the formatting tools bar.

[Living Large]

I noticed there isnt much of people posting what components they are actually using in their system here, is that because moderators dont want the site turning into a sales place?

I'd of thought it would be the best way to see what results in efficiency versus cost is the best solution, Id really like for people to chime in on this as I know batteries and inverters are not created equal but price is a factor of course

Will you please not post in bold? See how much easier it is to read your post when it is not in bold? You're hurting people's eyes - not the same as upper case, but just as annoying.

I was not assuming I could use 80% of AGM's capacity the same as LFP, as Sunking mentioned above. I also wanted a battery with no out-gassing, so maybe that was the chief criteria that caused me to move to LFP. I do recall my gen run time was going to be longer, for whatever the reason. It may have had to do with float or having to equalize on occasion.

[Willy T]

I noticed there isnt much of people posting what components they are actually using in their system here, is that because moderators dont want the site turning into a sales place?

It's because most of the posters here do not have a functioning PV system using LFP batteries, unless you count a golf cart or a couple bench top battery packs. The people that do have a functioning system don't seem to stay long and are not interested in arguing about gnats on pinheads.

In real life the efficiency is not all that great with a normal PV to battery capacity ratio. Those that data log find the I/O is about 94-96 % efficient and the charging time is almost the same using a 3% ending amps in the saturation phase as FLA. The cost is 3 times as much as FLA, so unless you have a weight issue or storing them inside they do not seem to be worth it.

[PNjunction]

I'd of thought it would be the best way to see what results in efficiency versus cost is the best solution, Id really like for people to chime in on this as I know batteries and inverters are not created equal but price is a factor of course

I turned off the bold for you. Thanks.

Without knowing your actual power needs, all this leads to is endless speculation for a proposed system that may never see the light of day. In some circles, that would be seen as a trolling maneuver.

In addition to knowing your actual power needs, you should also provide your location - at least geographically close. There is the issue of solar-insolation to be taken into account. Solar insolation hours are far different than just sunrise-to-sunset and are critical unless one wants to wing it.

Thus, a proposed system might work in Arizona, but be a total pipe-dream and waste of time and money in the pacific northwest, unless you have an unlimited wallet. You know that going off-grid with batteries is about 10-times the cost of your local poco on average right?

For a place you intend to live in, you have to take it seriously. We can get away with winging it with camping and so forth, but for permanent living quarters it is a different story.

These two requirements - your power needs and your solar insolation - stated up front, are what makes the difference between just throwing things at the wall and seeing what sticks, to doing it right.