LiFePO4 - The future for off-grid battery banks?

[Sunking]

THIS is what can make the up-front cost reasonable, when you look at the overall life-cycle of the product itself, the things that it powers, and the operational freedom that pays off in the end.

PN therein lies my main issue with LFP. You know the history of Chi-Com Prismatic LFP as well as I do starting with Thundersky just 8 or 9 short years ago. It is not a success story. From the start wildly exaggerated cycle life claims of 1000 to 2000 cycles. Two bankruptcies, and 5 product revisions later today and they still claim 1000 to 2000 cycles to 80% DOD. To this day I know of no documented Lithium any type that has a proven track record of 1000 to 2000 cycles. It is one thing to claim 2000 cycles with no proof or evidence vs say FLA with a 50 year history and proven track record of exceeding 1000 to 2000 cycle. 2000 cycles is about 6 to 8 years.

For EV especially DIY EV there is no other choice using Chi-Com Prismatic. It is the only game in town unless you get a chance at a salvaged EV pack. Otherwise price, availability, and thermal management are just out of reach$ of DIY. Solar you have 2 choices. Either proven Pb that is less expensive and last longer, or a gamble on Chi-Com. As of now we are still 6 to 10 years from knowing if LFP works or not as claimed.

[jedics]

Just saw on FB that telsa sets are supposed to be avail in Australia by the end of the year.

As far as I am aware these will be a grid tied only solution unfortunately.

Although Im sure competing companies will be offering it and will sure to bring the price down.

[Bala]

As far as I am aware these will be a grid tied only solution unfortunately.

Although Im sure competing companies will be offering it and will sure to bring the price down.

As with a lot of grid connect solar systems, people will ignore logical consideration of ROI and buy it because the sales pitch says it will save them money.

[donald]

As with a lot of grid connect solar systems, people will ignore logical consideration of ROI and buy it because the sales pitch says it will save them money.

The ROI will theoretically work based on many years of useful service by the battery.

Early adopters may not come out ahead financially, but they are needed to get the market moving.

[PNjunction]

Notice how all discussions seems to revolve back to commercial EV's as the only source of experience?

All discussions rapidly get out of context of OUR application of relatively low voltage / low current, something these cells laugh at, unless you have purposely used an insanely small bank to begin with, drawn to the promise of 80% DOD leaving you with no autonomy. Mistake #1.

Something not mentioned either is that in a fixed installation, these cells aren't going to be subject to physical stress / vibration etc. They are just going to sit there and laugh at the load your inverter places upon them - again of course assuming you were duly diligent in sizing your bank in the first place.

If ANYONE is going to get the rated cycles out of them, it would be US - the "Sub-C" application users.

The cycle testing HAS been done by the manufacturers, but as Prof Jeffrey Dahn has pointed out, that is just sausage-factory rapid hammer cycling. BUT, this is done typically at .3C to .5C from 10 or so to 100% SOC. WE aren't going to do that, operating PSOC, and limiting our cycle extremes. So the outlook is very good. But few consider our sub-c niche, especially coming from the so-called "lead acid mentality".

Look guys, I never said LiFepo4 was for everybody. In fact, I purposely use lead as my standby/backup because in that instance, I want to go from 100% SOC downwards, something you needn't do with LFP, nor is it recommended. To purposely have LFP sitting at 75% or so in standby means a hugely expensive bank, and just sitting there is definitely not taking advantage of it's capabilities for sure - unless you were a commercial grid supplier. That I can understand easily. My lifepo4 is used for daily cycling, and frequently leaving it in a major state of discharge without worry until I come back to it.

Thing is, there really is no point in discussing LFP, because we always get sidetracked with non-solar housebank applications, be they 48v or lowly 12v. And quite frankly, 99% of the comments come from those who will never use it, but just want to fan the flames for entertainment, and not education.

At over 72,000 reads of this thread as of this writing, there certainly is a LOT of interest. But getting to the gold amongst the dross is nearly impossible with all the sidetracks, politics, personal agendas, disgruntled CFO's, trash-hackers, and whatnot.

[Living Large]

Thing is, there really is no point in discussing LFP, because we always get sidetracked with non-solar housebank applications, be they 48v or lowly 12v. And quite frankly, 99% of the comments come from those who will never use it, but just want to fan the flames for entertainment, and not education.

I lurked here for education from the start. With a low insolation, cold environment and shading after 2:30PM, I desired fast charging for periods where the genny is needed. I also was looking for low toxicity and high energy density. I was willing to pay a premium to take advantage of multiple characteristics of LFP after considering other options.

However, what happened is I realized at some point late that I was not willing to rely on a solar system for a year round house in the boondocks in the mountains. If I can't get POCO because my HOA will not permit where I want to run it, I will be selling my cabin. It's partially a matter of principle, but there was definitely a shift away from the enthusiasm I had for the idea in the first place. The irony is that the conditions that made LFP attractive to me have convinced me I shouldn't go solar.

There certainly are a number of comments related to politics, trolling, etc, but there is wheat within the chaff. I suppose it is a fair question how many will get something they can use.

[lkruper]

I lurked here for education from the start. With a low insolation, cold environment and shading after 2:30PM, I desired fast charging for periods where the genny is needed. I also was looking for low toxicity and high energy density. I was willing to pay a premium to take advantage of multiple characteristics of LFP after considering other options.

However, what happened is I realized at some point late that I was not willing to rely on a solar system for a year round house in the boondocks in the mountains. If I can't get POCO because my HOA will not permit where I want to run it, I will be selling my cabin. It's partially a matter of principle, but there was definitely a shift away from the enthusiasm I had for the idea in the first place. The irony is that the conditions that made LFP attractive to me have convinced me I shouldn't go solar.

There certainly are a number of comments related to politics, trolling, etc, but there is wheat within the chaff. I suppose it is a fair question how many will get something they can use.

Sorry to hear you would sell your cabin. Perhaps if it comes to that you could supply a well-thought out plan for solar that could help sell the cabin.

[Sunking]

Notice how all discussions seems to revolve back to commercial EV's as the only source of experience?

All discussions rapidly get out of context of OUR application of relatively low voltage / low current, something these cells laugh at, unless you have purposely used an insanely small bank to begin with, drawn to the promise of 80% DOD leaving you with no autonomy. Mistake #1.

I agree to some extent, but there is over lap, especially when you compare a pure EV like a long range Tesla. Do that, you now are comparing Apples to Apples charge and discharge rates, and loose any debate about Sub C-Rates when they are similar. Another point in the Sub C-Rate debate in most cases Solar is charging at a higher C-Rate than an EV. Solar is in excess of C/6 and can go as high as C/2 if you live in areas with low Insolation. So on the Charge side there is no Sub C-Rate debate, Solar is charged faster. On the discharge side, Sub C-Rate comes into play. You are much higher risk of over discharging a cell in an EV with short burst of acceleration using high C-Rate than with Solar. That just means you need more automation on an EV with Respect to LVD.

Last is capacity. No meat on this bone. A Solar LFP battery can be smaller, equal, or larger in size. No C-Rate issue here.

Something not mentioned either is that in a fixed installation, these cells aren't going to be subject to physical stress / vibration etc. They are just going to sit there and laugh at the load your inverter places upon them - again of course assuming you were duly diligent in sizing your bank in the first place.

This is really the only major difference between Solar and EV. In Solar you do not need a very constrictive box, that is insulated thermally, and uses Thermal Management. You do not need much if any thermal management with Solar assuming the batteries have ventilation above 32 and below 100.

Technically the only difference between an EV and Solar System application is an EV must have Thermal Management, Active LVD, and Automated systems to watch over because the user cannot do that while driving. In Solar some think you must you the high level of Automation that is used in an EV which is False. EV's do not charge to 100% SOC normally, and do not allow the customer to access full capacity of the battery. You can do the same thing without a high degree of automation or special equipment if you know what you are doing. Otherwise, then you should use a high level of automation, but tune it so it limits the amount of SOC to less than 100% and never allow you to go below 10 to 20%. .

[karrak]

Cost of power from LFP battery

You can buy and operate a FLA battery for 5 and a few up to 10 years. There are a couple out there. A really good FLA cost around $200 to $250 per Kwh. If it last say 5 years means just in battery cost alone you paid $1250 / 1825 days = 69-cents per Kwh just for the batteries. You want AGM or LFP? They cost twice as much and last half as long. That means $2500 / 913 days = $2.74 cents per Kwh or 4 times more than FLA.

Are you saying that AGM and LFP batteries only last 2.5 years (913/365)? My LFP battery is two and a half years old and shows no signs of any variation from its initial specifications, still has same storage capacity and same internal impedance(resistance). Unless you can give me proof to the contrary I can't see any reason why an LFP battery will not last around ten years or more in off-grid applications. If you use the ten year figure you end up with the same price as good quality FLA batteries. This was the conclusion I came to before I purchased the LFP battery and the reason I purchased the LFP battery.

Here are some figures from the real world. My Winston battery made up of thirty two 90Ah cells which equates to a nominal storage capacity of around 9.5kWh cost AU$4213.44 or AU$443.52 per kWh in April 2013.

From power usage information logged via my BMS, for the year to date I have drawn 18374.54 Ah from the battery which equates to around 1.8kWh per day. This equates to around 6500 kWh over a ten year period. If we divide by the cost of the battery we get a cost of around $0.65 cents per kWh. For the past couple of years we have not been living at home full time. If we were I would expect our use from the battery to be around 3kWh per day so would bring the cost down to around $0.40 cents per kWh.

There are also other savings from using an LFP battery. I can have a smaller solar array and solar charge controller due to the high efficiency of the battery and not having to keep the battery charged as close to 100% as possible to stop sulphation. From data logged by my BMS, the overall efficiency of my battery over the past few months is around 94%-95%. I have no need of a generator as I can comfortably keep the battery at a PSOC (partial state of charge) i.e. not full.

Simon

[karrak]

Charge Rates from solar

I agree to some extent, but there is over lap, especially when you compare a pure EV like a long range Tesla. Do that, you now are comparing Apples to Apples charge and discharge rates, and loose any debate about Sub C-Rates when they are similar. Another point in the Sub C-Rate debate in most cases Solar is charging at a higher C-Rate than an EV. Solar is in excess of C/6 and can go as high as C/2 if you live in areas with low Insolation. So on the Charge side there is no Sub C-Rate debate, Solar is charged faster. On the discharge side, Sub C-Rate comes into play. You are much higher risk of over discharging a cell in an EV with short burst of acceleration using high C-Rate than with Solar. That just means you need more automation on an EV with Respect to LVD.

I find the charge rates you say puzzling, in my case my maximum charge rate is a little over C/10, most other people I know with off-grid systems with LFP batteries charge at less than C/5. Your design criteria that the battery should have three days storage implies you only need an average charge of C/3 per day. Even if you spread this over only a few hours you end up with a maximum charge rate of C/6. If high charge rates do cut down the life of an LFP battery and I had an oversize solar array I would look at limiting the charge rate into the battery to say less than C/5.

Last is capacity. No meat on this bone. A Solar LFP battery can be smaller, equal, or larger in size. No C-Rate issue here.

Due to the much smaller internal impedance(resistance) of LFP batteries you can use a much smaller battery than you would need to with an FLA battery if you need to run large loads. In my case I can draw over 6kWs from a 9.5kWh LFP battery (~0.6C) with less that a 10% voltage drop. Try doing that with an FLA battery, especially if it is a few years old.

Simon

[SunEagle]

Are you saying that AGM and LFP batteries only last 2.5 years (913/365)? My LFP battery is two and a half years old and shows no signs of any variation from its initial specifications, still has same storage capacity and same internal impedance(resistance). Unless you can give me proof to the contrary I can't see any reason why an LFP battery will not last around ten years or more in off-grid applications. If you use the ten year figure you end up with the same price as good quality FLA batteries. This was the conclusion I came to before I purchased the LFP battery and the reason I purchased the LFP battery.

Here are some figures from the real world. My Winston battery made up of thirty two 90Ah cells which equates to a nominal storage capacity of around 9.5kWh cost AU$4213.44 or AU$443.52 per kWh in April 2013.

From power usage information logged via my BMS, for the year to date I have drawn 18374.54 Ah from the battery which equates to around 1.8kWh per day. This equates to around 6500 kWh over a ten year period. If we divide by the cost of the battery we get a cost of around $0.65 cents per kWh. For the past couple of years we have not been living at home full time. If we were I would expect our use from the battery to be around 3kWh per day so would bring the cost down to around $0.40 cents per kWh.

There are also other savings from using an LFP battery. I can have a smaller solar array and solar charge controller due to the high efficiency of the battery and not having to keep the battery charged as close to 100% as possible to stop sulphation. From data logged by my BMS, the overall efficiency of my battery over the past few months is around 94%-95%. I have no need of a generator as I can comfortably keep the battery at a PSOC (partial state of charge) i.e. not full.

Simon

Depending on the manufacturer and actually duty cycle of the battery an AGM or LFP lifespan can exceed 2.5 years. But based on the history the average usage of those type batteries rarely have lasted beyond 3 years.

To say that a battery has been deemed to last 10 years because of accelerated testing is misleading because based on how they are used in a real life situation the lifespan could be much shorter.

If you have gotten 2.5 years out of your batteries they may go for another 2.5 years or just rapidly fall off the curve of their rated output. So to be safe you really can't say that all LFP batteries will perform that same as yours or if "any" will last 10 years without better "real life" testing.

I hope yours last long although there isn't any solid history to say all LFP will last long. I am just being realistic. No one ever stakes their reputation on a single data point.

[Sunking]

Due to the much smaller internal impedance(resistance) of LFP batteries you can use a much smaller battery than you would need to with an FLA battery if you need to run large loads. In my case I can draw over 6kWs from a 9.5kWh LFP battery (~0.6C) with less that a 10% voltage drop. Try doing that with an FLA battery, especially if it is a few years old.

Simon

Hey one-trick pony go get some more help, your all wrong again. . Not even talking about FLA. It was in reference to EV and Solar capacity size.

[reed cundiff]

??

"... comparing Apples to Apples charge and discharge rate..." Is this not the way to properly compare? Or am I missing some artifact in reasoning?

[PNjunction]

I agree to some extent, but there is over lap, especially when you compare a pure EV like a long range Tesla.

That's the thing - I don't care what Tesla is doing for the following reasons:

1) They aren't using LiFepo4, but another chemistry that is higher up the scale in unnecessary energy density and less stability. LFP at the bottom end of the rung, is already far more than sufficient for our needs and basically the safest. Longest life is when run at no more than .5C, and while they can take 1C or even more in bursts, most of us will never achieve that, nor do we NEED that, unless you are running a very high powered genny.

2) They are using non-lfp non-prismatic cells which adds to the complexity of the overall system - frequently requiring the use of proprietary or walled-garden support electronics. With large prismatics like Winston, CALB, GBS, etc, one can diy it like you would with lead, as long as you follow basic safety and operational rules. These non-lfp cylindrical cells have even higher performance characteristics than the large prismatics, so all that performance is wasted in our application - unless one is trying to make a ridiculously small battery bank.

3) While the price of these non-lfp, cylindrical cells is coming down, the safety and complexity issues remain. Even if they came down to 10-cents a cell, for us, we should only by paying about a penny due to the waste of performance. We are also back to the safety, stability, and complexity even at a penny a piece. No thanks.

This is what I mean about EV use when applied to solar-housebanks. Unfortunately, all roads seem to lead back to Tesla, and everyone forgets the basics about why LFP in large prismatic form was chosen for our application in the first place.

[inetdog]

If they used LFP, I doubt they would have been able to deliver the 1500 amp currents required for their Insane and Ludicrous Mode acceleration figures.
Maybe not a requirement for a useful EV, but definitely a marketing point for their high end buyers.