LiFeP04 Batteries for Solar & BMS

[Living Large]

LL what PN is saying is the less usable range you use, the less important a BMS becomes.

Duh! I missed that totally. I knew there was a big picture I was missing, but I couldn't see it. Thanks!!!

I don't think about the factors such as balancing and LVD we have discussed, because in my mind we resolved how to address them for an off-grid system. Easy for someone with no hardware to do. I appreciate these are very real concerns and affect users of LFP.

[Legit]

Hello SK, have been checking out a few of your posts, really appreciate the time, effort and knowledge you give - I would like to go off the grid and have noted and agree with your comments on the costs involved - would however like do the sums on this as our electricity costs are high due to the politics, in short the Have's support the Have Not's in our country, this senario does warrant a peep at going off the grid - our government does not entertain the grid-tie option at present as they stand to loose revenue.

Would you agree that the storage of energy is a big cost of a Solar System? - on this I would value your thoughts on the link below, not are what to make of this or how the setup works.

http://www.pri.org/stories/2015-04-06/how-do-you-catch-sun-make-electricity-night-german-inventor-has-answer

[Sunking]

Would you agree that the storage of energy is a big cost of a Solar System?

Absolutely, plus inefficiencies and utilization.

- on this I would value your thoughts on the link below, not are what to make of this or how the setup works.

OK it is a Battery Management System or BMS and guessing it is a very expensive system. I take issue when he claims 8 year payback. For one the batteries will not likely last 8 years. Cannot really offer much as the article does not offer any meaningful details. All they give you is it lithium batteries using a BMS.

[Legit]

Many thanks SK, will try to get more info on the system.

[PNjunction]

LL what PN is saying is the less usable range you use, the less important a BMS becomes...

< ..snip .. >

Bottom line or take away here is if you want to go to or near 100% SOC you have to use a BMS to TOP BALANCE and make sacrifices.

I couldn't have said it better! I get tongue-tied in all the logic.

Evaluate your application and choose what works best for you. Some ways are better than others, but may be impractical from your own maintenance capabilities, involve more or less risk etc.

As for cycle life and staying away from the top and bottom knees - again evaluate your application and environment to see how far you want to take it.

In *general* terms, the closest example is your own lithium cellphone battery, which of course is NOT lifepo4, but serves a useful demonstration.

They are charged and shipped somewhere around 50%. Aside from shipping regulations, keeping a lithium based battery fully charged aggravates "lithium plating" secondary reactions. Likewise, fully discharged they chemically decompose quickly. The hope here is that during retail storage stored at 50% or so, you'll get to them before reaching decomposition, and not being shipped and stored fully charged, lithium plating won't be occuring.

Normally you'll only receive around 350 or so "full cycles" of total charge and total discharge. If you operate them conservatively, then they will last far longer because statistically, you are cutting down on the secondary reactions by staying close to the middle, but yes there is also an aging factor like there is with all batteries. The additional life is not just from shallow-cycling, but avoiding secondary reactions the closer you get to the top or bottom over time. Ideally, never fully charge your cellphone battery. But will that be practical? Only you will know the line between useful and obsessive.

I know this is a blatant oversimplification and really don't want to get into cellphone batteries. However it may serve as a convenient example close to nearly everybody. If you are seeking the max cycle life of any lithium-based battery chemistry, being conservative will help get you there if your application allows such a luxury.

[Sunking]

PN not certain what cell phone manufactures do, but some of the EV manufactures underrate battery capacity. Tesla is one of them and Chevy Volt. Not certain on the Tesla other than I know they limit charge and discharge capacity. I know for fact Chevy Volt only charges to 80% SOC, and Cut-Off at 20% SOC so only 60% of the actual capacity is accessible. That can certainly be applied to any application if you can afford it. Example if you want 100 AH per cycle, then use 160 AH cells. What I cannot tell you with any certainty because I have not ran a cost model is if you can justify the extra expense of larger cells to get longer cycle life. We always have to remember lithium and all batteries have a self life that over laps cycle life.

[PNjunction]

This is what I find so attractive about lifepo4 in a solar storage application - that sliding window of SOC / DOD under irregular solar conditions without incurring battery damage long term. But that means de-rating and oversizing your bank a little bit to do so. Once again though, this costs more up front.

Strangely, we're almost back to the 50% capacity rule like with lead, but with far less um, autonomy-anxiety!

Additional capacity to account for unforeseen extra loads, inclement weather, minor mistakes in the power budget, etc. Can't charge it back up to 90% SOC? No problem as long as you design to allow for a sliding window, which ordinarily would damage Pb pretty quickly. Not to mention being able to totally unhook and leave your battery for a year or more as long as you have 40% or so in it and no parasitic loads.

Aside from the fun we're having dealing with top / bottom balance, voltages, etc, I find the practical ability to have sliding windows, and being able to just walk away from a partial discharge for a year or more so liberating. And I'm just a 12v geek - someday I'll be 24 or 48v with some REAL loads. This practical aspect is what excites me so much, even though my wallet might complain in the beginning. But being able to treat my battery poorly if it were lead, (within reason of course) and have lifepo4 just shrug it off and even reward me for doing so is what blows my mind.

[Sunking]

Additional capacity to account for unforeseen extra loads, inclement weather, minor mistakes in the power budget, etc. Can't charge it back up to 90% SOC? No problem as long as you design to allow for a sliding window, which ordinarily would damage Pb pretty quickly. Not to mention being able to totally unhook and leave your battery for a year or more as long as you have 40% or so in it and no parasitic loads.

Well PN the irony of this whole thread and LFP batteries is it is only people like you and I who can work with them because we have the knowledge and skills to pull it off as long as we ignore cost. As for the public cannot be done because they do not have the knowledge or skills, not is there any automated equipment out there to work around that. Only thing out there now is Top Balance and it is expensive and is the root cause of battery failures.

Something else is coming to the surface. Chi-Com LFP batteries are on their 3rd generation, and the 3rd generation has been out now for just over a year now. Each generation claimed 1000 to 2000 cycles. Well many folks with year old 3rd generation LFP cells are now starting to report capacity loss and failures. New package same ole line of crap. Failures are still being traced to over discharge using Top Balance, but capacity loss is a huge disappointment and set back. No matter what the manufactures say or do, calendar life still remains at 2 to 4 years regardless of cycles.

[Legit]

Well PN the irony of this whole thread and LFP batteries is it is only people like you and I who can work with them because we have the knowledge and skills to pull it off as long as we ignore cost. As for the public cannot be done because they do not have the knowledge or skills, not is there any automated equipment out there to work around that. Only thing out there now is Top Balance and it is expensive and is the root cause of battery failures.

Something else is coming to the surface. Chi-Com LFP batteries are on their 3rd generation, and the 3rd generation has been out now for just over a year now. Each generation claimed 1000 to 2000 cycles. Well many folks with year old 3rd generation LFP cells are now starting to report capacity loss and failures. New package same ole line of crap. Failures are still being traced to over discharge using Top Balance, but capacity loss is a huge disappointment and set back. No matter what the manufactures say or do, calendar life still remains at 2 to 4 years regardless of cycles.

That's the info I need,thks, there is this chap in our neck of the woods who converts petrol vehicles to electric www.freedomwon.co.za he seems suitably qualified in the field and uses Sinopoly LifeP04 batteries with a Orion BMS battery monitoring system, says the same setup can be used for a solar system - what do you reckon SunKing? does the Orion BMS also do this "over discharge using Top Balance"

[Living Large]

{snip}

Strangely, we're almost back to the 50% capacity rule like with lead, but with far less um, autonomy-anxiety!

{snip}

Does this mean my plan to use a window of 20%SOC to 90%SOC on a LFP bank, bottom balancing and a BMS, was all wet? We had discussed staying away from the knees. What am I missing, forgot, or never knew? Is my plan to use 70% of the capacity not realistic?

[Sunking]

Does this mean my plan to use a window of 20%SOC to 90%SOC on a LFP bank, bottom balancing and a BMS, was all wet? We had discussed staying away from the knees. What am I missing, forgot, or never knew? Is my plan to use 70% of the capacity not realistic?

No LL everything still applies.

[Sunking]

That's the info I need,thks, there is this chap in our neck of the woods who converts petrol vehicles to electric www.freedomwon.co.za he seems suitably qualified in the field and uses Sinopoly LifeP04 batteries with a Orion BMS battery monitoring system, says the same setup can be used for a solar system - what do you reckon SunKing? does the Orion BMS also do this "over discharge using Top Balance"

Well I use GBS rather than Sinopoly with a Orion Jr as a smart battery monitor in my NEV (neighborhood electric vehicle) my racing golf cart so to speak. CALB, Sinopoly, GBS and a handfull of others are all Chi-Com LFP battery manufactures from the failed Thundersky Batteries. Same crap different package and name.

Orion is a centralized BMS with some smarts, but it does not have to be used as a BMS in the traditional sense. I use it as a battery monitor to turn off my battery charger. I Bottom Balance.

Anyway from an economic POV using Chi-Com LiFeP04 batteries is really the only option because they cost around 40 to 50-cents per watt hour. By a brand like A123, LG, Enerdel and others and you are looking at $2 to $4 per watt hour. Additionally LiFeP04 is really the only choice one has for solar because they do have the longest cycle life. Ironically LiFeP04 is the worse choice for electric vehicles because they have the lowest energy density and lowest charge/discharge rates and thus why no EV manufactures use them. Well A123 cylindrical cells can be used in EV's as they have high charge/discharge rates butt still poor energy density (low range), but they cost $2/wh.

So to answer your question LiFeP04 aka LFP batteries are the only logical selection for solar applications. And Chi-Com large format prismatic cells are about the only option at 45-cents per watt hour. Think what a nightmare and expense of using A123 cylidirical cells would be having say 8000 cells for a 48 volt 200 AH battery. You can do the same thing with 16 Chi-Com 200 AH cells for 1/5 the cost. Even at 45-cents per watt hour is way too much to be feasible when you can get a FLA that last just as long or longer for 15 to 20 cents per watt hour.

Even at 15 cents per watt hour is a looser compared to commercial power. Batter systems are no where close to competing with commercial power.

[Legit]

Well I use GBS rather than Sinopoly with a Orion Jr as a smart battery monitor in my NEV (neighborhood electric vehicle) my racing golf cart so to speak. CALB, Sinopoly, GBS and a handfull of others are all Chi-Com LFP battery manufactures from the failed Thundersky Batteries. Same crap different package and name.

Orion is a centralized BMS with some smarts, but it does not have to be used as a BMS in the traditional sense. I use it as a battery monitor to turn off my battery charger. I Bottom Balance.

Anyway from an economic POV using Chi-Com LiFeP04 batteries is really the only option because they cost around 40 to 50-cents per watt hour. By a brand like A123, LG, Enerdel and others and you are looking at $2 to $4 per watt hour. Additionally LiFeP04 is really the only choice one has for solar because they do have the longest cycle life. Ironically LiFeP04 is the worse choice for electric vehicles because they have the lowest energy density and lowest charge/discharge rates and thus why no EV manufactures use them. Well A123 cylindrical cells can be used in EV's as they have high charge/discharge rates butt still poor energy density (low range), but they cost $2/wh.

So to answer your question LiFeP04 aka LFP batteries are the only logical selection for solar applications. And Chi-Com large format prismatic cells are about the only option at 45-cents per watt hour. Think what a nightmare and expense of using A123 cylidirical cells would be having say 8000 cells for a 48 volt 200 AH battery. You can do the same thing with 16 Chi-Com 200 AH cells for 1/5 the cost. Even at 45-cents per watt hour is way too much to be feasible when you can get a FLA that last just as long or longer for 15 to 20 cents per watt hour.

Even at 15 cents per watt hour is a looser compared to commercial power. Batter systems are no where close to competing with commercial power.

Many this for the detailed reply, my next question is, how much maintance is required on the FLA battery, and what sort of maintance is required to maximise the life cycles out of the FLA battery?

[Living Large]

Many this for the detailed reply, my next question is, how much maintance is required on the FLA battery, and what sort of maintance is required to maximise the life cycles out of the FLA battery?

Equalization periodically, checking the electrolyte level regularly, not discharging beyond a certain depth of discharge (which varies depending on which expert is telling you), charging at the right rate, storing them charged.
Here are a few sources of many on the internet:

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

http://rollsbattery.com/public/docs/user_manual/Rolls_Battery_Manual.pdf

[Living Large]

No LL everything still applies.

Good, I'll go back to sleep now, and rest easy - even though there is a high level conversation the wheels are having about moving windows that are over my head

My best guess is restricting oneself to 50% will extend the number of cycles beyond what could be expected utilizing 70%, but also requires increased cost.