End of Battery Life Replacement Strategy

richardimorserichardimorse Registered Users Posts: 60 ✭✭
I have a 10 year old Dual Outback 80 configuration (32 degrees) so it is time to replace the batteries, currently using 24 * 12V 230AH batteries gel VRLA, so now comes reality instead of theory, everything on the internet is theory on this subject aimed at people starting out in their journey with solar power, I have been doing it for 10 years already.

So what to choose I am thinking higher capacity batteries to reduce the number of "real" 2V cells in the configuration from 144 to something lower more like 72 at 460AH or 48 at 690AH or just replace like with like

2nd Question . . . what to do with my near end of life batteries, here I am not having problems right now, so they probably just operate normally as 180AH batteries due to degradation over the years, what do you think I should do with them, one option is to look at having 2 battery banks to reduce the cost of upgrade, could be an option to split everything, currently the everything is split apart from the battery bank, I could just get a second battery bank the existing one has 66,000 Watt Hours lets assume that has degraded to 50,000 Watt Hours

If I add a second battery bank sized at 40,000 watt hours brand new would that be a good approach, no advice anywhere on these strategies
currently have 9 strings of 3 panels 175W each split in a ratio of 5:4 between the two MPPT charge controllers

Or is it better to take the old batteries to my second home as a new installation for grid resilience.

What to do when your battery bank costs USD 15,000

Comments

  • mcgivormcgivor Solar Expert Posts: 2,423 ✭✭✭✭✭
    edited September 16 #2
    Welcome to the forum 
    What is the 32 degrees reference to? Currently 24*12 V would be 288 cells no? Just trying to understand, I've a few thoughts just need some clarification.


    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • littleharbor2littleharbor2 Solar Expert Posts: 1,112 ✭✭✭✭
    Still waiting for the coffee myself but me thinks 144 cells.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • mcgivormcgivor Solar Expert Posts: 2,423 ✭✭✭✭✭
    edited September 16 #4
    Perhaps thinking about a different chemistry is an alternative, LFP for example, given the current bank is not dead but dying, this would afford some time to study options. There are two approaches, a manufactured system or DIY, the latter dose involve more time the former more $$, the DIY is not as complicated in practice as it is in theroy, with assistance it's less so. Naturally I've no idea of your knowledge base so this may, or may not, be beyond your skill set. Based on price alone 15K $ could buy a very similar Ah capacity LFP battery with the advantage of being able to use a much greater depth of discharge without premature degredation associated with lead acid. This would allow a smaller Ah capacity to do the work of a larger lead acid bank, bearing  in mind even LFP's life expectancy is decreased the harder they're used, operating between 95% and 20% SOC is preferable, 75% capacity versus 50% at best,  to get 10 years with LA your DOD must have been less, one would assume. So without rambling on too much, have you ever considered a change?
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • mcgivormcgivor Solar Expert Posts: 2,423 ✭✭✭✭✭
    Still waiting for the coffee myself but me thinks 144 cells.
    24×6 not 24×12, good catch. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • EstragonEstragon Registered Users Posts: 3,039 ✭✭✭✭✭
    If I was to replace my bank, I'd consider Lifepo, but in the end might stay with LA based mainly on cost, but also on complications around low temp charging.

    Staying with LA, I'd definitely go with 2v individual cells sized for my needs (~500ah in my case) if available at reasonable cost. For me, the extra cost for VRLA isn't worth it, but it might be for some applications.

    As for what to do with the existing, at 10 years old, the bank is near end-of-life. Although it's only showing its age with capacity loss for now, there's a decent chance one or more cells will suffer a more catastrophic failure. I wouldn't size a new bank on the assumption the old one will stay in service long term as when it ultimately fails, you might not want to add new batteries to the now-older new bank. Keeping it in service in a separate application where if it fails and it takes time to replace it's not an issue might be an option. If you had an application where a 12v bank would work might be able to keep it going for some time by swapping out batteries as they fail.

    Personally, I'd probably just consider them near EOL, and use the luxury of having a serviceable (for now) bank to take my time looking for replacement, and apply the savage value of the old bank to offset the cost of the new one.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • softdownsoftdown Solar Expert Posts: 1,928 ✭✭✭✭
    What does "(32 degrees)" communicate? 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Marc KurthMarc Kurth Solar Expert Posts: 448 ✭✭✭✭
    edited September 16 #8
    I have a 10 year old Dual Outback 80 configuration (32 degrees) so it is time to replace the batteries, currently using 24 * 12V 230AH batteries gel VRLA, so now comes reality instead of theory, everything on the internet is theory on this subject aimed at people starting out in their journey with solar power, I have been doing it for 10 years already.

    So what to choose I am thinking higher capacity batteries to reduce the number of "real" 2V cells in the configuration from 144 to something lower more like 72 at 460AH or 48 at 690AH or just replace like with like

    2nd Question . . . what to do with my near end of life batteries, here I am not having problems right now, so they probably just operate normally as 180AH batteries due to degradation over the years, what do you think I should do with them, one option is to look at having 2 battery banks to reduce the cost of upgrade, could be an option to split everything, currently the everything is split apart from the battery bank, I could just get a second battery bank the existing one has 66,000 Watt Hours lets assume that has degraded to 50,000 Watt Hours

    If I add a second battery bank sized at 40,000 watt hours brand new would that be a good approach, no advice anywhere on these strategies
    currently have 9 strings of 3 panels 175W each split in a ratio of 5:4 between the two MPPT charge controllers

    Or is it better to take the old batteries to my second home as a new installation for grid resilience.

    What to do when your battery bank costs USD 15,000

    You said that you are not having any problems now. My approach would be to continue to use your existing battery bank until it becomes unusable. I often suggest that as capacity falls off, simply discharge them a bit deeper as needed to serve your loads. you may have another 3-5 years of usable life. Because you are exploring other uses for these batteries, I suspect that you feel that there is more life in them.
    With six parallel strings of VRLA's running for 10 years, my experience makes me assume that your battery bank is shallow cycled and spends a lot of time in float.
    Whether you replace them with fewer, larger cells or changing chemistry - will come down to economics.
    If you lose an individual battery, you can bypass that string and continue on with that 16% missing. Then you could use the three other batteries from that string as replacements for another failure.
    Marc

    I always have more questions than answers. That's the nature of life.
  • BB.BB. Super Moderators, Administrators Posts: 28,184 admin
    I believe the original poster is somewhere near the very southern portion of South Africa (32 degrees south).

    Getting 10 years on a set of VRLA in daily use--You are doing something right (or possibly, you have been shallow cycling your battery bank and you really do not need as large of battery bank (i.e., your battery bank near 50% capacity, but still more storage than you need?).

    You might go through your battery bank and see how the individual batteries are doing (check voltage across batteries, check specific gravity--if possible with your VRLA). If you have access to a DC Current Clamp DMM (digital multimeter)--You could make sure that each string is carrying (roughly) its share of current. Weed out the battery(ies) that are not carrying their share of the load.

    Your present array of:
    • 9p * 3s * 175 Watt panels * 0.77 panel+controller deratings * 1/68 volts charging = ~63 Amps
    Normally we suggest 5% to 13% rate of charge for a lead acid battery bank... 10%+ is good for full time off grid usage.

    That would suggest around a 630 AH @ 48 volt battery bank would be very happy with your present array.

    I certainly like your idea to get the number of parallel battery strings down... I suggest that 1-2 parallel strings is "optimum", and would suggest not going over 3 parallel strings if you can (you may have limitations on what large AH batteries/cells you can purchase in your region). Also, the physical size/weight of batteries may be an issue (24 volt forklift batteries can weigh over 1,000 kg... Need lift gate on delivery truck, hard/flat surface to move around, issue with stairs...???).

    Why do you think you need new batteries? Are these still supporting your needs presently?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • richardimorserichardimorse Registered Users Posts: 60 ✭✭
    softdown said:
    What does "(32 degrees)" communicate? 
    Thats the temperature in centigrade, the batteries are in Mozambique in an outbuilding that is not cooled, the outside temperature is 32 degrees in peak season and drops to a freezing cold 25 in July 
  • richardimorserichardimorse Registered Users Posts: 60 ✭✭
    mcgivor said:
    Welcome to the forum 
    What is the 32 degrees reference to? Currently 24*12 V would be 288 cells no? Just trying to understand, I've a few thoughts just need some clarification.


    mcgivor said:
    Welcome to the forum 
    What is the 32 degrees reference to? Currently 24*12 V would be 288 cells no? Just trying to understand, I've a few thoughts just need some clarification.


    mcgivor said:
    Perhaps thinking about a different chemistry is an alternative, LFP for example, given the current bank is not dead but dying, this would afford some time to study options. There are two approaches, a manufactured system or DIY, the latter dose involve more time the former more $$, the DIY is not as complicated in practice as it is in theroy, with assistance it's less so. Naturally I've no idea of your knowledge base so this may, or may not, be beyond your skill set. Based on price alone 15K $ could buy a very similar Ah capacity LFP battery with the advantage of being able to use a much greater depth of discharge without premature degredation associated with lead acid. This would allow a smaller Ah capacity to do the work of a larger lead acid bank, bearing  in mind even LFP's life expectancy is decreased the harder they're used, operating between 95% and 20% SOC is preferable, 75% capacity versus 50% at best,  to get 10 years with LA your DOD must have been less, one would assume. So without rambling on too much, have you ever considered a change?
    mcgivor said:
    Perhaps thinking about a different chemistry is an alternative, LFP for example, given the current bank is not dead but dying, this would afford some time to study options. There are two approaches, a manufactured system or DIY, the latter dose involve more time the former more $$, the DIY is not as complicated in practice as it is in theroy, with assistance it's less so. Naturally I've no idea of your knowledge base so this may, or may not, be beyond your skill set. Based on price alone 15K $ could buy a very similar Ah capacity LFP battery with the advantage of being able to use a much greater depth of discharge without premature degredation associated with lead acid. This would allow a smaller Ah capacity to do the work of a larger lead acid bank, bearing  in mind even LFP's life expectancy is decreased the harder they're used, operating between 95% and 20% SOC is preferable, 75% capacity versus 50% at best,  to get 10 years with LA your DOD must have been less, one would assume. So without rambling on too much, have you ever considered a change?
    Estragon said:
    If I was to replace my bank, I'd consider Lifepo, but in the end might stay with LA based mainly on cost, but also on complications around low temp charging.

    Staying with LA, I'd definitely go with 2v individual cells sized for my needs (~500ah in my case) if available at reasonable cost. For me, the extra cost for VRLA isn't worth it, but it might be for some applications.

    As for what to do with the existing, at 10 years old, the bank is near end-of-life. Although it's only showing its age with capacity loss for now, there's a decent chance one or more cells will suffer a more catastrophic failure. I wouldn't size a new bank on the assumption the old one will stay in service long term as when it ultimately fails, you might not want to add new batteries to the now-older new bank. Keeping it in service in a separate application where if it fails and it takes time to replace it's not an issue might be an option. If you had an application where a 12v bank would work might be able to keep it going for some time by swapping out batteries as they fail.

    Personally, I'd probably just consider them near EOL, and use the luxury of having a serviceable (for now) bank to take my time looking for replacement, and apply the savage value of the old bank to offset the cost of the new one.
    Estragon said:
    If I was to replace my bank, I'd consider Lifepo, but in the end might stay with LA based mainly on cost, but also on complications around low temp charging.

    Staying with LA, I'd definitely go with 2v individual cells sized for my needs (~500ah in my case) if available at reasonable cost. For me, the extra cost for VRLA isn't worth it, but it might be for some applications.

    As for what to do with the existing, at 10 years old, the bank is near end-of-life. Although it's only showing its age with capacity loss for now, there's a decent chance one or more cells will suffer a more catastrophic failure. I wouldn't size a new bank on the assumption the old one will stay in service long term as when it ultimately fails, you might not want to add new batteries to the now-older new bank. Keeping it in service in a separate application where if it fails and it takes time to replace it's not an issue might be an option. If you had an application where a 12v bank would work might be able to keep it going for some time by swapping out batteries as they fail.

    Personally, I'd probably just consider them near EOL, and use the luxury of having a serviceable (for now) bank to take my time looking for replacement, and apply the savage value of the old bank to offset the cost of the new one.
    Estragon said:
    If I was to replace my bank, I'd consider Lifepo, but in the end might stay with LA based mainly on cost, but also on complications around low temp charging.

    Staying with LA, I'd definitely go with 2v individual cells sized for my needs (~500ah in my case) if available at reasonable cost. For me, the extra cost for VRLA isn't worth it, but it might be for some applications.

    As for what to do with the existing, at 10 years old, the bank is near end-of-life. Although it's only showing its age with capacity loss for now, there's a decent chance one or more cells will suffer a more catastrophic failure. I wouldn't size a new bank on the assumption the old one will stay in service long term as when it ultimately fails, you might not want to add new batteries to the now-older new bank. Keeping it in service in a separate application where if it fails and it takes time to replace it's not an issue might be an option. If you had an application where a 12v bank would work might be able to keep it going for some time by swapping out batteries as they fail.

    Personally, I'd probably just consider them near EOL, and use the luxury of having a serviceable (for now) bank to take my time looking for replacement, and apply the savage value of the old bank to offset the cost of the new one.
    Given the track record of the Gell VRLA doing anything other than replacing like with like is going to raise eyebrows, particularly given the temperature in this building is 30 during the day and 25 during the night. 

    Option 1: Split the 50,000 Watt Hour battery bank into 2 banks using the existing 5:4 split ratio for the panels, ending up with two systems as follows:

    a) 5 Panel Strings on the old Batteries with 50,000 Watt Hours (an increase from original design of 36,666) and let them fail and be taken out of service as required, starting by reducing the battery strings from 6 to 5 after weeding out the 3 worst batteries and having spares for replacement making the battery bank 41,666 Watt Hours against a design spec of 36,666
    b) 4 panel Strings on the new batteries using more powerful batteries meeting a design spec of 20,000 Watt Hours plus a reserve say 24,000 Watt Hours with as few batteries as possible say 24 * 500AH batteries

    Option 2: Go for a replacement option of 3 strings of 460AH or 2 strings of 690AH batteries and truck the rest of the batteries home for my own solar system or for battery backup for the mains or look at their salvage value
  • richardimorserichardimorse Registered Users Posts: 60 ✭✭

    Taking option 1 would then require a 2nd replacement later on, say in 5 years if we get lucky, which does not sound like a bad option, I know it detracts from the single batter bank idea, but sweating the assets on half the battery bank sounds like a feasible strategy, right now they are working fine, I haven't done an in depth analysis on the batteries, including shutting down the recharge for 2 days.

    We just took over the management of the resort, so there is funding available, trying out new battery technology is going to raise eyebrows.
    even a new rack with new battery types is going to be looked at suspiciously, you replace the batteries with something 1/2 the size and they will think it has half the capability.

    Currently it only draws between 0.3KW and 3.2KW load depending on the time of day
  • richardimorserichardimorse Registered Users Posts: 60 ✭✭
    I have a 10 year old Dual Outback 80 configuration (32 degrees) so it is time to replace the batteries, currently using 24 * 12V 230AH batteries gel VRLA, so now comes reality instead of theory, everything on the internet is theory on this subject aimed at people starting out in their journey with solar power, I have been doing it for 10 years already.

    So what to choose I am thinking higher capacity batteries to reduce the number of "real" 2V cells in the configuration from 144 to something lower more like 72 at 460AH or 48 at 690AH or just replace like with like

    2nd Question . . . what to do with my near end of life batteries, here I am not having problems right now, so they probably just operate normally as 180AH batteries due to degradation over the years, what do you think I should do with them, one option is to look at having 2 battery banks to reduce the cost of upgrade, could be an option to split everything, currently the everything is split apart from the battery bank, I could just get a second battery bank the existing one has 66,000 Watt Hours lets assume that has degraded to 50,000 Watt Hours

    If I add a second battery bank sized at 40,000 watt hours brand new would that be a good approach, no advice anywhere on these strategies
    currently have 9 strings of 3 panels 175W each split in a ratio of 5:4 between the two MPPT charge controllers

    Or is it better to take the old batteries to my second home as a new installation for grid resilience.

    What to do when your battery bank costs USD 15,000

    You said that you are not having any problems now. My approach would be to continue to use your existing battery bank until it becomes unusable. I often suggest that as capacity falls off, simply discharge them a bit deeper as needed to serve your loads. you may have another 3-5 years of usable life. Because you are exploring other uses for these batteries, I suspect that you feel that there is more life in them.
    With six parallel strings of VRLA's running for 10 years, my experience makes me assume that your battery bank is shallow cycled and spends a lot of time in float.
    Whether you replace them with fewer, larger cells or changing chemistry - will come down to economics.
    If you lose an individual battery, you can bypass that string and continue on with that 16% missing. Then you could use the three other batteries from that string as replacements for another failure.
    Marc

    I didn't think of adjusting the DoD settings, in either case, when the inverter shuts down we put the system on a generator as it is 100% off grid, no mains supply whatsoever, so it is a matter of when we start the generator, something to look into when I test the battery bank.
  • richardimorserichardimorse Registered Users Posts: 60 ✭✭
    BB. said:
    I believe the original poster is somewhere near the very southern portion of South Africa (32 degrees south).

    Getting 10 years on a set of VRLA in daily use--You are doing something right (or possibly, you have been shallow cycling your battery bank and you really do not need as large of battery bank (i.e., your battery bank near 50% capacity, but still more storage than you need?).

    You might go through your battery bank and see how the individual batteries are doing (check voltage across batteries, check specific gravity--if possible with your VRLA). If you have access to a DC Current Clamp DMM (digital multimeter)--You could make sure that each string is carrying (roughly) its share of current. Weed out the battery(ies) that are not carrying their share of the load.

    Your present array of:
    • 9p * 3s * 175 Watt panels * 0.77 panel+controller deratings * 1/68 volts charging = ~63 Amps
    Normally we suggest 5% to 13% rate of charge for a lead acid battery bank... 10%+ is good for full time off grid usage.

    That would suggest around a 630 AH @ 48 volt battery bank would be very happy with your present array.

    I certainly like your idea to get the number of parallel battery strings down... I suggest that 1-2 parallel strings is "optimum", and would suggest not going over 3 parallel strings if you can (you may have limitations on what large AH batteries/cells you can purchase in your region). Also, the physical size/weight of batteries may be an issue (24 volt forklift batteries can weigh over 1,000 kg... Need lift gate on delivery truck, hard/flat surface to move around, issue with stairs...???).

    Why do you think you need new batteries? Are these still supporting your needs presently?

    -Bill
    Yes, but we know they are not going to last for much longer, this is the least researched area of solar, what to do as your battery bank reaches end of life, in this case it is 100% off grid so it reverts to generator under failure conditions, and is so remote, that getting out to fix it by road costs 0.5 new battery cost battery each time and 16 hours driving, unless we fly in which is the cost of 2 batteries.  Also there are no parts and these have to be flown or driven in the same distance.  Taking in batteries has to be done by road, so Wet LA is out of the question due to terrain and temperature, hence the reason sealed gel was used originally.

    The thinking was to leave the 24 * 12V 230AH in place on 5 out of 9 panel strings and triage them for 5 years, while 24 new higher capacity 360 AH 4V batteries or an alternative are installed now for 4 out of 9 panels (this is the existing split on the outback 80's) the owner thinks he is eating a second set of 24 batteries so everything looks the same to him and the old batteries can remove a string of 4 batteries under failure conditions and then a second string of 4 batteries swapping over the battery banks so 4 panels are on the 16 old batteries until they then need replacing with the same solution 5 years down the road.

    So the cycle is 

    Buy new 12V Year 0 (i)
    Buy 50% 4V Year 10 (ii)
    Buy 50% 4V Year 15 (iii)

    ...

    Maybe it is simpler to just replace all of them now for $15,000 instead of half of them for $7,500
  • richardimorserichardimorse Registered Users Posts: 60 ✭✭
    softdown said:
    What does "(32 degrees)" communicate? 
    Thats the temperature in centigrade, the batteries are in Mozambique in an outbuilding that is not cooled, the outside temperature is 32 degrees in peak season and drops to a freezing cold 25 in July 
    This is centigrade so 32 is 90 F during the day and 25 is 77 F at night in the summer (Nov-April)
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,137 ✭✭✭✭✭
    I would buy one $ 7.5K group and see how you do. Then within a year buy the second group if you need them. If you can still get them.

    Also look into the 2V 1,100 AH cells. They are at my cost about $500 each so even more money. Two strings of the 400AH would be OK, if you can get them. Maybe just one 400AH string and use the old as bank 2.

    It looks like you are shallow cycling to get that kind of life and your virtual tracked solar is a big reason also that you got this kind of life.
    Tracking is the best way offgrid to make a battery last. Good Luck
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • richardimorserichardimorse Registered Users Posts: 60 ✭✭
    I would buy one $ 7.5K group and see how you do. Then within a year buy the second group if you need them. If you can still get them.

    Also look into the 2V 1,100 AH cells. They are at my cost about $500 each so even more money. Two strings of the 400AH would be OK, if you can get them. Maybe just one 400AH string and use the old as bank 2.

    It looks like you are shallow cycling to get that kind of life and your virtual tracked solar is a big reason also that you got this kind of life.
    Tracking is the best way offgrid to make a battery last. Good Luck
    Not many people would have noticed the virtual tracking using additional panels on a wide arc, or perhaps we can attribute that to the local labor being creative when building the solar panel support stands out of fence posts.

    24 * 2V batteries seems the way to go this time.  What are your thoughts on getting 25 and rotating one out every 2 months.


  • richardimorserichardimorse Registered Users Posts: 60 ✭✭

    I guess the first step is to do a proper battery test on the existing battery bank, to identify the weakest and strongest batteries and to perform a discharge and recharge test to determine the Watt Hours left in the bank as a whole, what are your thoughts on the weakest batteries of the 24 existing batteries:

    1. Retire one of the 6 strings when you install the new bank (rearrange the strings so that you retire the 4 weakest batteries),
        (a) bring one battery home for the camper van, leave the other 3 as spares on trickle charge
        (b) leave all 4 on trickle charge
        (c) no need to leave them on a trickle charge, just charge them up every 3 months the you do a battery inspection visit
    2. Identify the weakest 6 and strongest 6 batteries and distribute them one each on the 6 battery strings.
  • richardimorserichardimorse Registered Users Posts: 60 ✭✭
    I would buy one $ 7.5K group and see how you do. Then within a year buy the second group if you need them. If you can still get them.

    Also look into the 2V 1,100 AH cells. They are at my cost about $500 each so even more money. Two strings of the 400AH would be OK, if you can get them. Maybe just one 400AH string and use the old as bank 2.

    It looks like you are shallow cycling to get that kind of life and your virtual tracked solar is a big reason also that you got this kind of life.
    Tracking is the best way offgrid to make a battery last. Good Luck
    Not many people would have noticed the virtual tracking using additional panels on a wide arc, or perhaps we can attribute that to the local labor being creative when building the solar panel support stands out of fence posts.

    24 * 2V batteries seems the way to go this time.  What are your thoughts on getting 25 and rotating one out every 2 months.


    They were made from fence posts to stop theft, nice shiny metal brackets can be resold for scrap or stolen for the local indigent population to use in their homes, having a solar panel on their roof is a dead give away, so they are less likely to be stolen than the support stands
  • BB.BB. Super Moderators, Administrators Posts: 28,184 admin
    In series strings, the "weakest battery" is usually what limits the AH capacity of the string. So "match" the batteries in a string (weak batteries with with batteries; strong batteries with strong batteries in each series string). The "strong string" will provide/sink more Amp*Hours and the weak string will provide less during discharging/charging.

    "Open batteries" (failed open) batteries will stop current flow through a string (and the other batteries will not see any charge/discharge current) (high resistance batteries will certainly limit current flow).

    "Shorted cell batteries" will drop the voltage of a string by ~2 volts per shorted cell--That will limit or prevent that string from providing load currents, and will sink way more current during charging. Obviously, not a good thing (open cell, the rest of the batteries in the string just sit there and slowly self discharge--With a shorted cell, that string gets way more than its share of charging current and usually will over charge the rest of the batteries, and discharge the rest of the bank at night).

    Generally, AGM and GEL batteries have very low self discharge and can go 6 months between charging cycles (~24 hour charging cycle). However, in hot climates/storage conditions, self discharge current goes up (typically for every 10C over ~25C, self discharge current goes up by 2x and the batteries will last 1/2 as long (faster aging)). At 30+C, you should probably place them on charge every 3 months (1-3 months between charging cycles). You can check the resting voltage... Ideally, you do not want the batteries to be spending any time "resting" below 75% state of charge (sulfation happens much faster below ~75% SoC).

    Yes, rotating batteries sounds good--But I am not fan of doing that. Lots of work and wear&tear on the cables/batteries/your back. Get a spare battery and setup a nice float charger/charge once every 1-3 months...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,137 ✭✭✭✭✭
    I noticed because I have been doing forms of tracking for close to 30 years offgrid.
    As for 24, the real advantage of this system is you can lose a battery and lower the charge control and inverter LBCO by 2V and still have normal system. Just a slight loss of capacity until you replace it. The key for you is being able to get a reliable replacement down the road.
    Good Luck!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • richardimorserichardimorse Registered Users Posts: 60 ✭✭
    BB. said:
    In series strings, the "weakest battery" is usually what limits the AH capacity of the string. So "match" the batteries in a string (weak batteries with with batteries; strong batteries with strong batteries in each series string). The "strong string" will provide/sink more Amp*Hours and the weak string will provide less during discharging/charging.

    "Open batteries" (failed open) batteries will stop current flow through a string (and the other batteries will not see any charge/discharge current) (high resistance batteries will certainly limit current flow).

    "Shorted cell batteries" will drop the voltage of a string by ~2 volts per shorted cell--That will limit or prevent that string from providing load currents, and will sink way more current during charging. Obviously, not a good thing (open cell, the rest of the batteries in the string just sit there and slowly self discharge--With a shorted cell, that string gets way more than its share of charging current and usually will over charge the rest of the batteries, and discharge the rest of the bank at night).

    Generally, AGM and GEL batteries have very low self discharge and can go 6 months between charging cycles (~24 hour charging cycle). However, in hot climates/storage conditions, self discharge current goes up (typically for every 10C over ~25C, self discharge current goes up by 2x and the batteries will last 1/2 as long (faster aging)). At 30+C, you should probably place them on charge every 3 months (1-3 months between charging cycles). You can check the resting voltage... Ideally, you do not want the batteries to be spending any time "resting" below 75% state of charge (sulfation happens much faster below ~75% SoC).

    Yes, rotating batteries sounds good--But I am not fan of doing that. Lots of work and wear&tear on the cables/batteries/your back. Get a spare battery and setup a nice float charger/charge once every 1-3 months...

    -Bill
    I think the current batteries are gel+agm hybrid, they have a 12 year float life at 25 deg and 10 year at 30 deg so lets assume we get 11 years, also at a 20% DoD cycle the 12 years drops to 10 years, so lets call that 9 years due to temperature, at 30% DoD thats 7 years hence my worry that they are at end of life, however if they were only 6 years old, a do nothing strategy might suffice for now.

    So if they are 6 years old, and they want more power, a good strategy might be to add three more panel strings = 9 panels at 175W

    Lets assume original sizing is good, so 27 panels feed 66,000 Watt Hours, lets assume a 33% battery bank degradation to 44,000 Watt Hours so 18 panels can manage that same as before, the inverter is going to work harder on this battery bank needs a quick sizing check

    then installing 9 new panels and a 2nd battery bank at 44,000 Watt Hours might sound a good proposition, MPPT/Inverter redundancy is 50% same as before, but they might want that increasing with more power to 75% with a four of each perhaps using outback 60's, well for the sake of sameness that could just as well be two more of the 80's give or take a few hundred dollars. Better not to change any of that to keep costs down on the electrical work and the ease of upgrade.

    So we could double their power usage and cover the battery end of life story with the same upgrade just by adding 9 more panels


  • richardimorserichardimorse Registered Users Posts: 60 ✭✭
    BB. said:
    In series strings, the "weakest battery" is usually what limits the AH capacity of the string. So "match" the batteries in a string (weak batteries with with batteries; strong batteries with strong batteries in each series string). The "strong string" will provide/sink more Amp*Hours and the weak string will provide less during discharging/charging.

    "Open batteries" (failed open) batteries will stop current flow through a string (and the other batteries will not see any charge/discharge current) (high resistance batteries will certainly limit current flow).

    "Shorted cell batteries" will drop the voltage of a string by ~2 volts per shorted cell--That will limit or prevent that string from providing load currents, and will sink way more current during charging. Obviously, not a good thing (open cell, the rest of the batteries in the string just sit there and slowly self discharge--With a shorted cell, that string gets way more than its share of charging current and usually will over charge the rest of the batteries, and discharge the rest of the bank at night).

    Generally, AGM and GEL batteries have very low self discharge and can go 6 months between charging cycles (~24 hour charging cycle). However, in hot climates/storage conditions, self discharge current goes up (typically for every 10C over ~25C, self discharge current goes up by 2x and the batteries will last 1/2 as long (faster aging)). At 30+C, you should probably place them on charge every 3 months (1-3 months between charging cycles). You can check the resting voltage... Ideally, you do not want the batteries to be spending any time "resting" below 75% state of charge (sulfation happens much faster below ~75% SoC).

    Yes, rotating batteries sounds good--But I am not fan of doing that. Lots of work and wear&tear on the cables/batteries/your back. Get a spare battery and setup a nice float charger/charge once every 1-3 months...

    -Bill
    I think the current batteries are gel+agm hybrid, they have a 12 year float life at 25 deg and 10 year at 30 deg so lets assume we get 11 years, also at a 20% DoD cycle the 12 years drops to 10 years, so lets call that 9 years due to temperature, at 30% DoD thats 7 years hence my worry that they are at end of life, however if they were only 6 years old, a do nothing strategy might suffice for now.

    So if they are 6 years old, and they want more power, a good strategy might be to add three more panel strings = 9 panels at 175W

    Lets assume original sizing is good, so 27 panels feed 66,000 Watt Hours, lets assume a 33% battery bank degradation to 44,000 Watt Hours so 18 panels can manage that same as before, the inverter is going to work harder on this battery bank needs a quick sizing check

    then installing 9 new panels and a 2nd battery bank at 44,000 Watt Hours might sound a good proposition, MPPT/Inverter redundancy is 50% same as before, but they might want that increasing with more power to 75% with a four of each perhaps using outback 60's, well for the sake of sameness that could just as well be two more of the 80's give or take a few hundred dollars. Better not to change any of that to keep costs down on the electrical work and the ease of upgrade.

    So we could double their power usage and cover the battery end of life story with the same upgrade just by adding 9 more panels


    On the other hand, it might just be a good idea to get a 2nd pre integrated Dual outback 60 config complete with breakers and attach it to the second battery bank rather than mess with the electrics and just do our work in the combiner boxes to have 4 * 9 panel feeds to the Outback MPPT controllers, more expensive but easier to install with loads of capacity, they did indicate that they might want more power, but doesn't everyone say that, would need to sit them down and see if they really want the extra power, money is not an issue here as they are in the BUNDU or OUTBACK if you are Australian
  • BB.BB. Super Moderators, Administrators Posts: 28,184 admin
    Check the maximum charging current for your present & proposed battery bank.

    In the US, GEL batteries are generally used for standby power systems and have something likea C/20 (5%) rate of charge (100 ah battery, 5 amp charge rate).

    Generally, for a full time off grid system, a 10% to 13% rate of charge for solar charging makes life easier.

    And most deep cycle lead acid flooded cell and AGM types have a recommended 10% minimum rate of charge.

    Your system at 5% rate of charge (and shallow cycling) is probably helping your present bank and its long life so far.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • richardimorserichardimorse Registered Users Posts: 60 ✭✭
    BB. said:
    Check the maximum charging current for your present & proposed battery bank.

    In the US, GEL batteries are generally used for standby power systems and have something likea C/20 (5%) rate of charge (100 ah battery, 5 amp charge rate).

    Generally, for a full time off grid system, a 10% to 13% rate of charge for solar charging makes life easier.

    And most deep cycle lead acid flooded cell and AGM types have a recommended 10% minimum rate of charge.

    Your system at 5% rate of charge (and shallow cycling) is probably helping your present bank and its long life so far.

    Bill
    Hi Bill,

    So we have fixed the problems resulted in a system with 5 parallel strings of 48V each at 230Ah (1 decommissioned) = 55,200 Wh design power, since it is now 7 years old on RA12-230 DG Rittar Gel batteries, it is at end of life, so lets assume 35,000 Wh from the 20 batteries

    The lightning strike worked out well, because it highlighted the need to re-invest in the solar system, here is what we have permission for:

    New requirements:

    1) Laundry (cold wash cycles no dryers)
    2) TV systems all new technology 100W max

    Savings:

    1) Replace 5 B or C efficiency chest freezers (500Watt each) fridges with A grade equipment
    2) Replace all cfl bulbs with LED

    1) Replace very old 4.5kVA generator with 7.5kVA system with AGS for main system, keep old generator for old system/other
    2) Add 3rd VFX3048E Inverter to bring max power up to 9000 Watts with steady power of 5,000 Watts and add 3rd Flexmax 80 if required
        configure generator for must start daily if required, power contribution if over 9000 watts and low battery conditions
    3) Add solar panels as required to meet charging load, reuse decommissioned 2 * tracking systems with very small wind footprint e.g. max 4m tall x2m wide, (they were decommissioned due to wind when wind footprint was 4m x 4.8m)
    4) Add new battery bank using 24 * 2 Volt 1150Ah AGM batteries to get a 55,200 Watt Hour design life
    5) Use the 35,000Wh batteries on the laundry and triage them out over the next 5 years after which we will replace with a 2nd 55,200Wh battery bank by which time number of resort suites will have increased and total power in the two battery banks dropped to 100,000Wh
    6) use generator to support batteries as required, and work out total panels to support 90,000 Wh batteries using new 365W panels
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