Please Help me to understand FLA battery.

[paulcheung]

Hi guys,

I am try to understand how the flood lead acid battery works. I read some of the materials about the battery and some phases which I don't understand, I hope some one can explain to me so I can get more understand how these batteries work and try to prolong their usable life. Thank you in advance.

I understand most of the batteries are died from Sulfations, Also grid corrosion is another cause. I understand how sulfation kills the batteries but I don't quite understand how grid corrosion kill the batteries.

What is grid corrosion? is the lead plates dissovle in the acid? or something else?

How is the batteries deteriorates in perfect working condition? is the plates been dissovle in the acid from charge and discharges?

How to determine the capacity of the batteries? is the surface area of the plates by the size and numbers of the plates? has the thickness any thing to do with the capacity? or just last longer because it is thicker?

Thanks

Paul Cheung from Cloudy Mandeville in Sunny Jamaica.

[Sunking]

I understand how sulfication kills the batteries but I don't quite understand how grid corrosion kill the batteries.

What is grid corrosion? is the lead plates dissovle in the acid? or something else?

Well you can start by looking up the definition of the word CORROSION. But yes DISOLVE is one way to look at it. In batteries it is called Lead Shedding. Like sulfation, corrosion of the grid plates is going to happen. All you can do is to minimize the corrosion. The biggest offender is over charging. Here is a link that might help.

[QUOTE=paulcheung;110933]How is the batteries deteriorates in perfect working condition? is the plates been dissovle in the acid from charge and discharges? Corrosion happens during the charge cycle, sulfation occurs during the discharge cycle or being left discharge. As I said both are going to happen. If it did not happen then batteries would last forever. All you can do is try to slow down the process, but it will happen no matter what you do.

How to determine the capacity of the batteries? is the surface area of the plates by the size and numbers of the plates? has the thickness any thing to do with the capacity? or just last longer because it is thicker?

It is determined by the amount of lead in it, how much electrolyte there is, and surface area of the plates.

To measure capacity is not something you can do accurately but the basic concept is very easy. Amp Hours = Amps x Hours. So to measure that you connect a constant current load onto the battery after it has been fully charged up, and measure the time it takes for the cell voltage to reach 1.75 volts DC. So if you put a 10 amp load on a battery and it takes 5 hours to discharge you have 50 AH. However it is not something a DIY can do accurately. The reason is you cannot get your hands on a constant current load source. Example lets say you have a 12 volt battery rated at 100 AH @ the 20 hours discharge rate or 5 amps. Well you might think all you need is a 2.4 Ohm power resistor. Well that works at 12 volts but drops to 10.5 end voltage which only resorts in 4.3 amps.

There are load boxes out there to measure AH, but extremely expensive.

OK with that said you can make a James Bond Terster by simply using car headlights and a few switches. One more catch is you have to account for Peukert Law.

[paulcheung]

Thank you Dereck, now I understand the corrosion in the battery, the other question about capacity is really try to determine the cost of ownership of the Rolls batteries. The ones in question is the 6CS25P and the S-550 batteries. The S-550 has 2/7 years Warranty 428 amps hour at 20 hours rate and the 6CS25P has 3/10 years Warranty 820 amp hours at 20 hours rate. The 6CS25P is cost almost 4 times the S-550 yet it doesn't have 4 time amount lead but the cycle curve is about 2.5 times more. 5000 cycles at 20%DOD compare to 2000 cycle at 20%DOD.

Is there other factors why the 6CS25P cost almost 4 times the S-550? I am try to see if it is justify the 4 times cost when I need to replace my two banks of 4000 series Rolls. I need about 800amp hours at 48 volts.

Thank you.

[mapmaker]

Also grid corrosion is another cause. I understand how sulfation kills the batteries but I don't quite understand how grid corrosion kill the batteries.

Here's some pictures of NEGATIVE plate corrosion from an old Sandia report. The link I used to download it is now broken

fig2.jpg
fig3.jpg

--mapmaker

[ChrisOlson]

Thank you Dereck, now I understand the corrosion in the battery, the other question about capacity is really try to determine the cost of ownership of the Rolls batteries. The ones in question is the 6CS25P and the S-550 batteries. The S-550 has 2/7 years Warranty 428 amps hour at 20 hours rate and the 6CS25P has 3/10 years Warranty 820 amp hours at 20 hours rate. The 6CS25P is cost almost 4 times the S-550 yet it doesn't have 4 time amount lead but the cycle curve is about 2.5 times more. 5000 cycles at 20%DOD compare to 2000 cycle at 20%DOD.

Is there other factors why the 6CS25P cost almost 4 times the S-550?

The 6CS25P has deeper sumps, thicker plates, more electrolyte reserve capacity over the top of the plates, plus individually replaceable cells. The advantage of the 6CS25P, and why we use them here instead of the cheaper S-530 (now S-550) is because the 5000-series batteries will run as many cycles at 80% DoD as the 4000-series will at 20% DoD.

The 5000-series are not designed for 20% DoD cycling and they will go "limp" within six months on that kind of duty. They must be cycled to at least 50% DoD on a regular basis, and 80% DoD at least once a month. Because they are designed for deeper cycling you get higher charging efficiency and more kWh of usable storage over the battery's life - AND you do not need as many amp-hours of capacity to do the same job as with the 4000-series. The cost of your off-grid batteries is not how much they cost up front - it is how many dollars/kWh they cost. The 5000-series wins hands down in cost/kWh of storage over the battery's life, even though they are more expensive up-front.

So basically, look at it like this - the S-550 is a "casual" battery that will work well for part-time off-grid cabins, grid battery backup systems, or smaller full-time off-grid homes.

The 6CS25P is a heavy duty off-grid battery that will take virtually anything you can throw at it, work the living snot out of it, and it still comes back for more. It is best suited to serious off-grid installations where you do not want to be replacing batteries every 7 years, and have the option of replacing an individual cell (instead of an entire battery) if one goes tits up at some point. Because you can cycle it deeper on long PSOC cycles, it achieves much higher efficiency and lower cost/kWh than the 4000-series.

[Sunking]

the other question about capacity is really try to determine the cost of ownership of the Rolls batteries.

Paul I have gone over this with you a couple of times and probable 100 times here on the forum. You have to build a cost analysis model to determine estimated cost. First and most important is to base the model on no more than 20% DOD on any given day, and never take the battery below 50%, or leave it in a discharged state for more than 24 to 36 hours. Lets use Rolls product line up. Rolls has 3 series of batteries of 4000, 4500, and 5000. I am not familiar with the 4500 line up and have no historical data. However I have quite a bit on the 4000 and 5000 series. Next a battery is considered end of life when it fails to hold 75% of its rated capacity. Second the Cycle Life vs DOD is not real. It is a lab test result under ideal condition on a accelerated test platform that puts a battery through several cycles in a day

OK if you give a battery TLC and follow the rules of DOD for the 4000 series you can expect a 3 to 5 year product and 5 to 7 for a 5000 series. So lets look at Rolls S-550. In the USA the lowest price I can find is $460 delivered with all sales tax. It is a 6 volt 428 AH @ 20 hour rate. The battery capacity is 6 volts x 428 AH = 2.57 Kwh which makes the $/Kwh investment = $179. So if we look at the upper life span of 5 years is 1825 days. Sticking to the 20% DOD rule is 2.57 Kwh / 5 = .514 Kwh per day from the battery. Over 5 years the battery will deliver 1825 days x .514 Kwh = 928 Kwh. That means in battery cost alone you paid $460 / 928 Kwh = $0.495 per Kwh or lets just call it 50-cents per Kwh

Now in Jamaica you cannot get the S-550 delivered to you for $460. I suspect more like $1000 USD or 111,050 JMD. That would put your Kwh cost at roughly $1.07 USD or $119.66 JMD per Kwh.

So now I will let you crunch the real numbers for your area. What i am certain yo are going to learn even though Jamaica power rates are high, off-grid is still way more expensive.

[paulcheung]

The S-550 is not available in Jamaica yet, I believe it is new. We get the S-530 which is 400 amp hours for $40,000 Ja. Dollars delivered, (I have to pick it up 5 minute from where I live on my pickup so no big deal) which is $387 to $400 US dollars, Thank God it is tax and duty free as it is solar system. I believe the S530 and the S550 are the same battery just re-branded as they have the same size and same amount of plates and same thickness.

What I need to know is in my off grid working condition, would it be better to buy one set of the 6CS25P one bank or two banks of the S-550 and two sets in the life span of the 6CS25P. The cost of the 6CS25P in Jamaica is around $145,000 to $165,000 depend on who I get them from.

I have another question about the charging rate. I know it is best to charge the batteries at C8 to C12 rates. but sometime the condition change and I wonder if it is ok for the charge current reach to c6 to c7 for a few minutes, for example this morning the weather is overcast, I start the generator to supply the house and charge the batteries a little so bring it back to over the 80%SOC. The sun peek out and the combination current from the PV and the generator go over 60 amps for the 400 amp hour battery bank for a minute or so. Should I be worry? what is exactly the damage to the battery when over the C8 rate charge current for a short period time occasionally?

Thank you.

[paulcheung]

The 6CS25P has deeper sumps, thicker plates, more electrolyte reserve capacity over the top of the plates, plus individually replaceable cells. The advantage of the 6CS25P, and why we use them here instead of the cheaper S-530 (now S-550) is because the 5000-series batteries will run as many cycles at 80% DoD as the 4000-series will at 20% DoD.

The 5000-series are not designed for 20% DoD cycling and they will go "limp" within six months on that kind of duty. They must be cycled to at least 50% DoD on a regular basis, and 80% DoD at least once a month. Because they are designed for deeper cycling you get higher charging efficiency and more kWh of usable storage over the battery's life - AND you do not need as many amp-hours of capacity to do the same job as with the 4000-series. The cost of your off-grid batteries is not how much they cost up front - it is how many dollars/kWh they cost. The 5000-series wins hands down in cost/kWh of storage over the battery's life, even though they are more expensive up-front.

So basically, look at it like this - the S-550 is a "casual" battery that will work well for part-time off-grid cabins, grid battery backup systems, or smaller full-time off-grid homes.

The 6CS25P is a heavy duty off-grid battery that will take virtually anything you can throw at it, work the living snot out of it, and it still comes back for more. It is best suited to serious off-grid installations where you do not want to be replacing batteries every 7 years, and have the option of replacing an individual cell (instead of an entire battery) if one goes tits up at some point. Because you can cycle it deeper on long PSOC cycles, it achieves much higher efficiency and lower cost/kWh than the 4000-series.

Hi Chris,

I understand what you are saying, just that to me the BOM (bill of Material) in the 5000 series does not come to around 4 times compare to the 4000 series. The plates are thicker but not double and more plates but not 2 times so why the cost about 3.7 times the cost? I wonder if there is any other factors in it.

Thanks.

[ChrisOlson]

OK if you give a battery TLC and follow the rules of DOD for the 4000 series you can expect a 3 to 5 year product and 5 to 7 for a 5000 series. So lets look at Rolls S-550. In the USA the lowest price I can find is $460 delivered with all sales tax. It is a 6 volt 428 AH @ 20 hour rate. The battery capacity is 6 volts x 428 AH = 2.57 Kwh which makes the $/Kwh investment = $179. So if we look at the upper life span of 5 years is 1825 days. Sticking to the 20% DOD rule is 2.57 Kwh / 5 = .514 Kwh per day from the battery. Over 5 years the battery will deliver 1825 days x .514 Kwh = 928 Kwh. That means in battery cost alone you paid $460 / 928 Kwh = $0.495 per Kwh or lets just call it 50-cents per Kwh

Sunking, those batteries last way longer than that. Ours reach their 7th anniversary tomorrow and still deliver new rated capacity on a 65% DoD cycle, as measured by our TriMetrics. Our neighbor 5 miles to the east of us on the lakeshore has a set of 12 year old 5000 Surrettes that are still running strong.

Batteries on off-grid service in a full-time off-grid home don't get cycled every day like that. Maximum is 260 cycles/year on most off-grid systems I've worked with and helped set up. And some, like us, cycle our batteries only 60-70 times per year. At noon here our bank is at 79% SOC and it is charging at a little over 20 amps:





But our bank has not been ABOVE 85% SOC for 11 days (TriMetric keeps track of this) as I type this post. Only a wet-behind-the-ears off-grid beginner is going to set a system up for 20% DoD cycling and have them burned out within 7 years. If you set up for 20% DoD cycling you got WAY too much lead setting in your battery room and the natural aging process gets them before they are worn out. 90% or better of us experienced off-gridders don't do that. The batteries are about $1,200 each and a string of 8 of them is 20 kWh storage for $9,600. Here they get cycled at an average rate of 14.1 kWh/day in and 13.3 kWh out, for about 4.8 MWh/year. This data is logged by our Conext ComBox, and even though our daily power consumption is 25-30 kWh/day, only roughly half of it gets cycled thru the batteries because we are running on solar or wind, or sometimes generator, for the balance. And the batteries only get used when there is no incoming power from other sources.

So in a real off-grid installation where these batteries will run 3300 cycles on PSOC cycling like this, the real cost is about 20 cents/kWh for every kWh you get out of the batteries over a 10 year period. At 10 years they are down to 75% original capacity usually, but they are still usable if your cycling pattern does not need more than that amount of capacity. So the end result is that some of us manage to get 12 years from them, some have gone as long as 15 years.

Now, I know this real-world stuff doesn't always agree with theory. But it's been said that in theory there is no difference between practice and theory, but in practice there is.

[ChrisOlson]

I understand what you are saying, just that to me the BOM (bill of Material) in the 5000 series does not come to around 4 times compare to the 4000 series. The plates are thicker but not double and more plates but not 2 times so why the cost about 3.7 times the cost? I wonder if there is any other factors in it.

Quite a bit of it is manufacturing cost and not just materials. The 5000-series are dual container, which is higher manufacturing cost with stainless steel bolted cell connections when you pop the lid off the outside container to get to the "jars". And different separator and positive plate treatment in the 5000-series that makes them more durable, but costs a lot more. And part of it is volume too. There are lots more of the 4000-series sold than there is 5000-series, and with the 5000-series being more labor intensive to build, that adds cost.

If you intend to live off-grid full time, the 5000-series will cost you less money over the long term than 4000's. You do not need to have the weight in lead with 5000's that you need for 4000's, because they can be cycled deeper and run long PSOC cycles with no adverse effects. The 5000-series batteries were used in fishing trawlers and sailing yachts long before they started marketing them for off-grid systems. And the bulk of Rolls' sales for 5000's is still in the marine world. But if you saw a 6CS25P sitting alongside a S-530 or S-550 you'd see immediately why it is a $1,200 battery and the S-530/550 is a $400 battery. They are in two different worlds sort of like comparing a gasoline engine to a comparable heavy-duty diesel for doing the same job.

[paulcheung]

Chris I see what you say. Still I don't think that justify the 350% cost than the 4000 series, I guess the max production on the 4000 series help carry the price down. Do you notice every item in the solar PV system cost less in the past ten years except the batteries.

[ChrisOlson]

Chris I see what you say. Still I don't think that justify the 350% cost than the 4000 series, I guess the max production on the 4000 series help carry the price down. Do you notice every item in the solar PV system cost less in the past ten years except the batteries.

Yes, not batteries. They have gone up significantly in price in the last 10 years. Environmental regulations combined with one of the most successful recycling programs ever devised has increased their price.

The 5000's are not 350% of the price of the 4000's. Let's look at batteries from one supplier so we're not looking at a difference in markup. And say you need a 20 kWh 48V battery. I am selecting this place:

http://www.batterystuff.com/all-products-by-brand/rolls-surrette-battery/

The 400ah S-530's (basically the same as the newer 550) are $340. The 820ah 6CS25P's are $1,050. You need 8 of the 5000-series for a cost of $8,400 for your battery bank. You need 16 of the S-530's for a cost of $5,440. So the 5000's cost roughly 50% more than the 4000's up front.

But when you look at how many kWh you can get before the battery is worn out, the price of the 5000's becomes cheaper.

Let's say you cycle 180x/year (once every 2 days on rough average). The length of the pro rata warranty on these batteries was not arrived at by accident. It happens to coincide with when Rolls has determined that the battery reaches 75% of original capacity based on 260 cycles/year to 50% DoD. If it didn't, Rolls would be paying out pro rata money on battery replacements all the time. And to actually get that warranty you have to provide Roll's with logs from when the battery was new, and those logs even have to have amount of water added to each cell at service time, and what the SG is on each cell at service time. If you can't provide those logs your warranty is zero after the full replacement time expires. And even during the full replacement time it is like pulling hen's teeth to get warranty from Rolls on a battery.

The 4000-series are going to be at 75% original capacity in 7 years (15 kWh useable). And during that time you will have at least one battery out of the 16 fail. If you have your system set up with battery monitors on each string like we got here, and you are really damn good, you will catch this failed battery before it wrecks an entire string. 90% of cases don't and end up with a destroyed string because of one battery that went south. But remember you need a 20 kWh (useable capacity) battery? You are down to 15 kWh in 7 years, meaning that your battery capacity is grossly short starting at 5 years when they begin to rapidly deteriorate to that 75% OEM capacity level. So you spend 2 years fighting with batteries that are going south, even if you end up replacing one due to a failure.

The 5000-series are going to be at 75% OEM capacity in 10 years @ 260 cycles/year. However, they can be cycled deeper than the 4000's. 820ah @ 48V is actually a 39 kWh battery and you have only been using 50% of this capacity for 10 years. Now let me make this clear by bold text: the 5000-series batteries will do more cycles at 80% DoD than the 4000-series will at 50% DoD and equal them at 20% DoD. Even though they have lost 25% of their original capacity in 10 years, they still have the ability to deliver your 20 kWh/day that you need without excessive voltage "sag" and without replacing them.

The bottom line? The 5000-series end up being useful for at LEAST twice as many cycles as the 4000-series for only 50% more money. And you never have a battery go bad in a 5000-series. You can lose a cell and replace it just like any other industrial battery with 2V "jars" in it. So I'll let you do the math on it - twice the kWh over the useful life for only 50% more upfront money and less maintenance cost over the life of the bank. The 5000-series wins hands down if you want to spend the least amount of money on your off-grid system over the long term. Too many people with no experience only look at upfront cost and end up taking it in the shorts.

[paulcheung]

OK understood, two questions though.

1. I know you have a very complex setup and use a lot of equipment to monitor your battery system and don't cycle the battery daily, but for folks like me are using the battery every night down to 20 to 35%DOD sometime even 50% occasionally. how the 260 cycles per year coming? isn't that 365 cycles per year? Can you explain?

2. One battery fail on the 4000 series didn't get caught and kill the whole string, so the 5000 series doesn't do that? they have different structure that prevent that happen? I know you can replace one cell but if it didn't get caught in time then what happen?

Thank you.

[mapmaker]

2. One battery fail on the 4000 series didn't get caught and kill the whole string, so the 5000 series doesn't do that? they have different structure that prevent that happen? I know you can replace one cell but if it didn't get caught in time then what happen?

It's a matter of serial vs parallel. When you have a bad cell in a parallel bank, the good string(s) can mask the problems in the bad string. Meanwhile, real damage is being done to the the good string(s).

With a single series string, a cell can go bad, but you'll know it right away.

--mapmaker

[ChrisOlson]

1. I know you have a very complex setup and use a lot of equipment to monitor your battery system and don't cycle the battery daily, but for forks like me are using the battery every night down to 20 to 35%DOD sometime even 50% occasionally. how the 260 cycles per year coming? isn't that 365 cycles per year? Can you explain?

Our battery is sized to use roughly 13 kWh of its 39 kWh capacity on a daily basis. This amounts to 33% of its capacity. Assuming we would fully charge every day we would discharge our battery to about 67% SOC every day. However, we don't do that. We use opportunity loads in the form of electric water heating to use up our solar capacity for that instead of charging batteries every day. We have a device called a Morningstar RD-1 Relay Driver:



That RD-1 is a programmable logic controller and it controls our water heating system and limits battery charging. It turns on progressively more water heating load as voltage tries to rise to Absorb V by operating SSR's. This sends the solar power to the water heater instead of batteries, and the RD-1 constantly adjusts how much load is on the system to match incoming RE power with loads to keep the voltage below Absorb V and "float charge" the battery instead of absorbing it. Once every week to 10 days or so, historically we get an exceptional RE day where the water heaters kick out due to the thermostats shutting off the elements and the batteries get absorbed and back to 100% SOC.

The reason we do this is because batteries do not live their lives based on the sun rising and setting like humans do. So quit trying to associate the solar cycle, and your daily cycle, with a battery cycle. Example: you discharge a fully charged battery at the 100hr rate, how long does it take to discharge it? 4 days. Then you spend a day charging it. This is a five day cycle. This is what we do here, and have been doing it for many years. Although in perfect conditions we will cycle our battery from about 50% SOC to 85% SOC on a daily basis for many days, using the RD-1 to control it (I have used many methods, including Waste Not in Classics, but the RD-1 is the latest method because it has way more flexible programming than a Classic does).

The reasons I do this are many. But in a nutshell we achieve very high cycle efficiency with our battery bank here. And our batteries run nice and cool for many days at a time, never exceeding 25C temp even in very hot weather. Batteries that are cycled to only 80% SOC, then recharged every day are being cycled on the most inefficient part of their discharge/charge curve and they run hot because of it. Running hot shortens the battery's life drastically from over-charging it (or charging it when it doesn't need to be charged).

This goes into quite a bit more detail, as I have spent years tweaking and tuning this system to get maximum kWh return from our battery investment, and I use one of the most sophisticated logging systems in the RE business to track it. But it is a different topic - the above is just in a nutshell.

2. One battery fail on the 4000 series didn't get caught and kill the whole string, so the 5000 series doesn't do that? they have different structure that prevent that happen? I know you can replace one cell but if it didn't get caught in time then what happen?

People that spend the money on 5000-series batteries are usually not going to have a low-end RE system. That means you will have battery monitors on the individual strings, do your battery service on a regular basis with logs, and you know what you are doing. You will catch a bad cell long before it becomes a problem and replace it.

People that tend to buy the lower-end batteries are usually not going to take care of them properly. They just buy them and hope for the best based on they read on forums (where they usually get bad information from people that don't have the experience to be providing the information). Off-grid systems are a whole different world than telecom battery backup systems, or grid-tie battery backup. There aren't many of us that live off-grid. And fewer yet that have been at it enough years to know what to do, and how much it really costs. Until you been there done it, you don't realize the implications of buying this new place you just bought that is miles from any utility lines and now you have to figure out how to survive and live a somewhat "normal" lifestyle. That's the position I found myself in many years ago, with a wife that was not quite sure about the whole thing. I've made my share of mistakes, but overall we've done pretty well here and would not give up our off-grid lifestyle even if ALGOR donated one of his mansions to us.