Kw/h in vs Kw/h out of batteries

CALLD
CALLD Solar Expert Posts: 230 ✭✭
Ok so since getting my small off grid system live a few months ago I've totally obsessed about the batteries as

I'm sure many others with off grid systems have done in the beginning.


One of the things that really bugs me other than the impossible task of trying to determine the real SOC of sealed

batteries is the battery efficiency.



Many sites and handbooks say lead acid can achieve 85% efficiency. BS!!!
I cannot see how this is possible without

keeping your batteries in a permanent state of partial charge, say between 40 & 80%, and still I doubt more than

70% efficiency is attainable.

Firstly I'm talking about actual energy efficiency "joule for joule" and not AH

efficiency (coulomb for coulomb).
It doesn't help much if you have to put each AH into the battery at a much higher voltage than you're going to get

it back out at. There already is a huge waste!

I'll give you a real world results of the efficiency I'm getting

and how much it's pissing me off.

On a sunny day this time of year I'm getting a total of 180AH from my panels

going into my 24V batteries at an average voltage of 28.5V throughout the day. It starts from roughly 24.5v in the

morning and climbs to my maximum set point of 30V where it stays for 2 hours before dropping to 28V for float

charge until the PV output fades into night. The total kw/h thus produced is over 5. What I'm getting back out of

the batteries at night rarely exceeds 150AH at an average voltage of 24v, but that's the best case scenario, on

average its only about 140AH at 24v. The battery voltage starts out at 25.8v, drops rapidly to 24v and then drops

gradually to 23.4v just after dawn. This translates into an average power return from the batteries of just

3.36kw/h from 5.13kw/h put in. That's only 65% energy efficiency!

Surely there has to be a better way of doing things? I could maybe get about 10 to 20% more out of my batteries if

I didn't insist on them reaching a full state of charge every day and maybe allowed them to go to a lower SOC and

only charge to say 80 - 90%. Then just to be good I could bring them to a full SOC once a week or so. Is that safe

to do or will I destroy my batteries in the process?

Comments

  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries

    What does your system look like? Panels, Charge controller, Inverter?

    What are you measuring with? A battery monitor that measures across a shunt, going into your battery?

    Do you understand other system losses?
    ...I don't know if your using the solar panels wattage as your production number, solar panels typically produce around 75-80% of their panel rating in full sun, you can start by knowing your panels NOCT value(Normal Operating Cell Temperature).

    Where are you measuring output? Do you understand that an inverter is only 85-90% efficient?

    You do appear to understand that battery charging does taper off between 80-85% full to 100%.

    If your measuring your battery capacity and usage from a voltage number when batteries have not been at rest for a few hours then you don't have a good idea of what State of Charge they are in....
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Grinnin
    Grinnin Solar Expert Posts: 39
    Re: Kw/h in vs Kw/h out of batteries

    I think I understand what you're saying. It is true that batteries are inefficient. My system also puts a lot more kWh into the batteries than I get out.

    I don't understand why you would focus on efficiency. There may be more efficient batteries but they certainly cost more than lead/acid. The storage technology is an imperfect part of an imperfect system. The efficiency of the solar panels is far worse, below 20%.

    The entire system is there for me to change "free" sunlight into electricity. The inefficiencies of everything from wires to voltage conversion circuits and batteries are included in the calculations. For storage efficiency, supercapacitors would probably be more efficient, but they would be pretty expensive and big.
    CALLD wrote: »
    I could maybe get about 10 to 20% more out of my batteries if

    I didn't insist on them reaching a full state of charge every day and maybe allowed them to go to a lower SOC and

    only charge to say 80 - 90%. Then just to be good I could bring them to a full SOC once a week or so. Is that safe

    to do or will I destroy my batteries in the process?
    You may be able to increase the numerical efficiency of your storage. Will that let you use more of the sunshine hitting your panels? For my system, the batteries float for much of the afternoon in summer. The kWh going in are "free" since I have only a few "discretionary" loads like charging portable battries.

    You CAN charge to 90% most of the time and then charge to 100% once a week. Your batteries may lose a little lifespan but probably not much. Batteries are not permanent even in the best systems.

    AFTERTHOUGHT: I wrote the above while thinking of an all-solar, no generator system. I can understand that if you use a generator often then inefficiency could be an irritant. I'd say use the generator less often.
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries

    Sounds like a case of expectations being a long way from reality and that divide is causing a lot of stress.
    Off grid systems are often a never ending learning process, but if the personal stress involved is too much, it can seriously affect health.
    If grid power is available, it might be a good idea to connect, then write off the present system as an educational experience.
  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    Re: Kw/h in vs Kw/h out of batteries

    Thanks Grinnin, yes that's what I wanted to know. I did think it's hardly feasible to get batteries to 100% SOC every single day due to periodic cloudy weather anyway unless you charged them from the grid or generator on such days. I could happily forgoe lets say 10 to 20% of my battery life in exchange for relaxing daily charging requirements a bit. Charging to a minimum of 80% daily is an easy enough target for me to reach (unless we get a week of overcast weather, which fortunately is near impossible here in sunny SA!).

    In response to Photowit, these are actual Ampere Hour logs taken at the charge controller which is a few feet from the battery. I have over the course of 4 months painstakingly logged the AH's going into the battery from day-to-day. For Yesterday it was as follows:

    Time V A-in Sol
    06:00 23.5 0
    07:00 23.4 1
    08:00 24.2 7
    09:00 25 15
    10:00 25.5 22
    11:00 25.8 25
    12:00 26.5 24.9
    13:00 28 24
    14:00 30 22.5
    15:00 30 20
    16:00 28 16
    17:00 26 2
    18:00 25.8 0.3

    For the Amps going out it was a bit of a guess, but I have tested my inverter's current draw across a range of loads using the charge controller's load terminals up until the maximum load the charge controller could take before it would have shut off the load to protect itself. This was at just under 30 amps yielding 692watts at the AC side measured by an AC watt meter. I've determined that the inverter efficiency is over 90% for most loads under 700watts. The load on my batteries is on average, less than 400watts throughout any evening. Under normal circumstances the inverter connects directly to the battery. I boil my 2000watt kettle every morning before sunrise to "load test" the partially discharged batteries and check the voltage sag to monitor there state of health so that I can pick-up any deterioration in the battery. The kettle drags the (already lovoltage down from 23.5v to 22.6 over the duration of the boil and the bounce-back is to 23.3v. It's pretty much been like that since I started checking...
  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    Re: Kw/h in vs Kw/h out of batteries
    Sounds like a case of expectations being a long way from reality and that divide is causing a lot of stress.
    Off grid systems are often a never ending learning process, but if the personal stress involved is too much, it can seriously affect health.
    If grid power is available, it might be a good idea to connect, then write off the present system as an educational experience.

    You're so right it is really stressful, and perhaps expectations were too high. Wish I could go off grid-tied here but firstly our power utility doesn't do buy-back, and most of my demand is at night so I need batteries. Hopefully one day they will allow me to sell to the grid, then I will get a GTI and just keep some batteries for emergency power for blackouts...
  • mryimmers
    mryimmers Solar Expert Posts: 117 ✭✭✭
    Re: Kw/h in vs Kw/h out of batteries

    Ever since I installed my Trimetric battery monitor, I do a lot less stewing and fretting as to what is going on.:D
    Definitely worth installing on any battery based system!
    510 watt pv, TS-MPPT 60, Exeltech XP1100, XP600 & XP250 @ 24V, 4x Trojan 105RE, Trimetric 2030, Yamaha EF2400i gen.
  • Grinnin
    Grinnin Solar Expert Posts: 39
    Re: Kw/h in vs Kw/h out of batteries
    CALLD wrote: »
    I could happily forgoe lets say 10 to 20% of my battery life in exchange for relaxing daily charging requirements a bit. Charging to a minimum of 80% daily is an easy enough target for me to reach
    I'm much farther north than you are south which means that I get shorter days in winter than you do. During a cloudy week in winter I can easily go a week without a full charge, dropping toward 60% SOC. Every few years it goes on even longer and the batteries will drop to 50%. Still my first set of batteries lasted 8 or 8.5 years and I went to a smaller set for these past 5 or so years. (I really forget when the first set had a shorted cell.)

    A friend does something similar to what you contemplate, only his is for electric vehicles. This is an engineer who converted a pickup and motorcycle to lead/acid but now has Li car and motorcycles (plural). The house has many kW of solar and is grid-tied but with battery backup. My point is that he studies this and has lots of experience with different charging and battery systems. ANYWAY his focus is on watt-hours per mile, and in order to get the most distance for the energy, he charges his vehicles to 90% for several cycles then only occasionally tops them up. This is not a problem at all for his current Li vehicles, but I believe he also would short-charge his previous vehicles.

    I also had neighbors who would use their batteries until the LVD disconnected the inverter. Then they'd hook up a generator until they had electricity again. Where I use the "top" of the battery capacity they were constantly using the "bottom" of it. Batteries never lasted very long and concluded that off-grid solar doesn't really work.

    There's a big difference between not getting 100% daily and using only the bottom of the battery.

    Good luck.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries

    Do you understand the problem with your numbers?

    They only measure the amps coming and going at your Charge Controller(CC) so any loads including the inverters idle, are NOT included in your efficiency rating. You are NOT reading the amps going into your battery, you are reading the amps coming out of your CC. So if your inverter is using 30 watts or 300 watts this is not going to your battery.

    "mryimmers" spoke of his trimetric, the trimetric measures the current passing through a shunt going to the battery so it takes into account the power/wattage being used. There are others available...

    I would also strongly recommend getting and using a hydrometer, voltage at 23.5 in the morning might be 60% capacity, if you have a good sized load, or it could be 30% with no load for a while.

    What type of batteries are you using with a absorption at 30 volts and a float at 28V? it would appear that your never seeing a reduction of amps going to your batteries, and your CC just set for 2 hours at max? Without knowing your loads while this is going on we are kinda shooting in the dark.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • nsaspook
    nsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Kw/h in vs Kw/h out of batteries
    CALLD wrote: »
    Ok so since getting my small off grid system live a few months ago I've totally obsessed about the batteries as
    I'm sure many others with off grid systems have done in the beginning.
    One of the things that really bugs me other than the impossible task of trying to determine the real SOC of sealed
    batteries is the battery efficiency.

    If you want to understand what a mess it is to model batteries then look at this link.
    http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1046&context=elecengtheses

    Efficiency loss in batteries is like death and taxes. You can only do so much.
  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    Re: Kw/h in vs Kw/h out of batteries
    Photowhit wrote: »
    Do you understand the problem with your numbers?

    They only measure the amps coming and going at your Charge Controller(CC) so any loads including the inverters idle, are NOT included in your efficiency rating. You are NOT reading the amps going into your battery, you are reading the amps coming out of your CC. So if your inverter is using 30 watts or 300 watts this is not going to your battery.
    .

    Yes you are right that is not the current flowing into the batteries, there is a 3 amp load from the inverter (yes I've measured it) while it's powering my house alarm and a few other things on standby during the day. The total kw/h out I've been measuring is over a 24 hour period so I figured I'd taken everything into account.
    Photowhit wrote: »
    Do you understand the problem with your numbers?

    I would also strongly recommend getting and using a hydrometer, voltage at 23.5 in the morning might be 60% capacity, if you have a good sized load, or it could be 30% with no load for a while.

    Wish I could, but they are sealed batteries, silver calcium type with very bad polarisation losses hence the low voltage readings in the morning and the very high charging voltages.
    Photowhit wrote: »
    What type of batteries are you using with a absorption at 30 volts and a float at 28V? it would appear that your never seeing a reduction of amps going to your batteries, and your CC just set for 2 hours at max? Without knowing your loads while this is going on we are kinda shooting in the dark.

    As said they are silver calcium SLA batteries. The current would taper off until it was only at about 8 amps at 30v after 2 hours at absorbtion if I switched off the inverter, however the day I took those readings I was gradually adding loads to the inverter as the current was tapering off because I was trying to squeeze every drop I could out of the PV (I know it sounds obsessive but it was for the purposes of gathering data on the system's performance). The 2 hour absorb stage a factory set parameter on my charge controller, can't change it, however I can change the voltage set points which is why I purposefully set them high. As the 400AH battery is quite large for the max average peak PV current of 25A the charging is quite gentle anyway, takes a decent amount of time to get to absorb phase anyway, hardly ever before 14:00, most of the sun's power is gone after 16:00 this time of year.
  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    Re: Kw/h in vs Kw/h out of batteries

    Thanks guys, what I gathered from this thread is that batteries just aren't that efficient and its a fact of life. One can try various things like running at a slightly lower than full state of charge some of the time to help but there is only so much you can do without destroying batteries. Maybe when LiFePo4 batteries become more mainstream and affordable things will improve a bit. Otherwise one has to try and shift as much of the load to daylight hours as possible and use less at night although this is not easy.

    It seems the only thing to do if you want to be totally off-grid is to get a massively over-sized system (money no object) so you can just sit back and forget about it. For me with a daily demand of 25kw/h that would be a 10kw array, 3000AH/48v battery and a 12kw inverter. Serious money, not likely to ever pay for itself - but the independence it would bring may just be enough to help me sleep better at night...
  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries

    I remember long ago when I started reading about batteries, the first thing on the list was that my battery would need 110 - 120% of the Ahrs used put back in to do a complete charge. I'm surprised nobody has mentioned that in this thread...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries
    CALLD wrote: »
    Thanks guys, what I gathered from this thread is that batteries just aren't that efficient and its a fact of life.

    I dont know anything about silver calcium, and the voltages do sound very high for a sealed pack. But in a nutshell, AGM batterys are said to be more efficient than FLA for one reason, lower internal resistance. During bulk charge, amps in amps out coulomb efficiency is approx 100%. Where you lose watts at this point is from voltage drop from the batterys resistance. During absorb amps in amps out effciency drops to something like 80%, caused by electrolysis. (as well as the voltage drop from int resist, although the IR does reduce some as it charges.)
    One can try various things like running at a slightly lower than full state of charge some of the time to help but there is only so much you can do without destroying batteries.

    If you are interested in this stuff, you need better data. I recomend midnite gear, as it enables you to accurately measure and log every day/minute/second watts in/ watts out of the battery to a excell sheet. The Classic and some other controllers have the ability to restrict the number of days that full aborsb cycles occur. It is generally considered that so long as the battery fully charges once a week, that is sufficient to prevent sulphation. However the key is ensuring a true 100% charge, and again classic handles this with a proper end amps regime, and then top is off with good float period.
    Maybe when LiFePo4 batteries become more mainstream and affordable things will improve a bit. Otherwise one has to try and shift as much of the load to daylight hours as possible and use less at night although this is not easy.

    Youre only obsessing about battery efficiency because you already have a cheaper power option, (grid) at your disposal. At the presetn time youll be hard pressed to beat grid pricing, so you brought that particular angst upon yourself.

    LiFePo4, does have a higher overall charge efficiency, you are right. Far from being expensivem my calculations show that LiFePo4 is already economic, costing about the same per kWh delivered for large prismatic cells, and thats not even factoring improved charge efficiency, psoc and other management advantages.
    It seems the only thing to do if you want to be totally off-grid is to get a massively over-sized system (money no object) so you can just sit back and forget about it. For me with a daily demand of 25kw/h that would be a 10kw array, 3000AH/48v battery and a 12kw inverter. Serious money, not likely to ever pay for itself - but the independence it would bring may just be enough to help me sleep better at night...

    The only thing you can do, is what all off gridders do. Learn to conserve. At 25 units a day you have huge potential to reduce your consumption. A dollar spent the money on insulation, water and energy efficient appliances gets a way way better ROI than a dollar spent on RE gear. After thats done, then design and build a well engineered system, and sit back and enjoy.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries
    zoneblue wrote: »
    The only thing you can do, is what all off gridders do. Learn to conserve. At 25 units a day you have huge potential to reduce your consumption. A dollar spent the money on insulation, water and energy efficient appliances gets a way way better ROI than a dollar spent on RE gear. After that's done, then design and build a well engineered system, and sit back and enjoy.

    Well said! and THIS is something WELL WORTH obsessing about! The payback can be awesome! Not kidding!
    BTW, in my early years I had read and took as fact, was that 130% of Amp Hours used had to be returned to the battery to bring it back to full charge. So "knowing" that in advance, even if it was inflated, gave me the heads up I needed to not get stressed over battery efficiency losses. just accepted that it is what it is.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries
    CALLD wrote: »
    As said they are silver calcium SLA batteries.

    So I had not heard of silver calcium batteries, so I googled it quickly and fist listing stated "The benefits or silver calcium batteries are improved CCA performance " While I don't know if it hurts it's deep cycle performance, this is not a feature you look for in a deep cycle battery.
    CALLD wrote: »
    The 2 hour absorb stage a factory set parameter on my charge controller, can't change it, however I can change the voltage set points which is why I purposefully set them high. As the 400AH battery is quite large for the max average peak PV current of 25A the charging is quite gentle anyway, takes a decent amount of time to get to absorb phase anyway, hardly ever before 14:00, most of the sun's power is gone after 16:00 this time of year.

    This is improper thinking, so long as the voltage is ahead of what the battery needs it should absorb fine, typically AGM batteries don't want voltage that high! Have you checked your manufacturers recommendations? High voltage may damage your AGM batteries. Once they out gas they can lose much or all of their capacity. I suspect 30volts will be higher than your manufacture recommends.
    CALLD wrote: »
    Thanks guys, what I gathered from this thread is that batteries just aren't that efficient and its a fact of life. One can try various things like running at a slightly lower than full state of charge some of the time to help but there is only so much you can do without destroying batteries.

    Not sure how long you've been at it, but you might do some of the other suggestions, like picking up a shunt based battery monitor.

    You sound like you have been checking things out, just to be sure we're on the same page;

    You have 4 - 12v 100ah AGM batteries set up as 2 strings of 4?(or something equivalent).

    When you say your measuring a 3 amp load, this would be DC into the inverter while charging? so @80watts?
    CALLD wrote: »
    It seems the only thing to do if you want to be totally off-grid is to get a massively over-sized system (money no object) so you can just sit back and forget about it. For me with a daily demand of 25kw/h that would be a 10kw array, 3000AH/48v battery and a 12kw inverter. Serious money, not likely to ever pay for itself - but the independence it would bring may just be enough to help me sleep better at night...
    At this point to Off Grid Solar is not likely to pay for it's self unless your grid electric costs more than 50-70 cents a Kwh. Even in my near ideal situation, heating with wood, greatest demand for solar in the summer, and silly cheap costs/bargain hunting, I figure some where around 26 cents a kwh, + needing to monitor the system, check water levels, cut fire wood...

    I would be cheaper at least for now paying the @20 cents a kwh for electric.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    Re: Kw/h in vs Kw/h out of batteries

    Thanks guys for all the replies, there is a wealth of information to be found here!

    I'm still learning so much about off grid systems and it appears the learning will never stop.

    There seems to be so many different strategies out there when it comes to charging. The equalization charge really makes my head hurt when I think about it. I've now been told 30v is too high for my batteries, but then at the same time people elsewhere talk about periodically charging to 32 or even 34 volts to equalize the battery. I have never ever done that because I fear I may just cook them to death. I once took them to 31volts after a very deep discharge. In the beginning I used to have it set at 29.2 volts which is the recommended voltage for calcium batteries. Two things I subsequently learnt made me up the voltage to 30v. The first thing was temperature, my battery room is quite cold at this time of year and the temperature sensor on my charge controller doesn't help much because it just warms up to the temperature of the charge controller and not the battery so I disabled it. The second is that generally cycling voltages should be higher than once-off recharge voltages especially when the time for recharging is short as is the case in winter. I maybe guessing a bit here but what can I do when everyone has a slightly different opinion? I have noticed though that on cloudier days when the voltage doesn't quite reach 30v, perhaps only 28 that the capacity of the battery isn't really that much different. So I will heed the warnings about 30v and set it back lower, maybe to 29.6v. I do know that they need to gas to mix the electrolyte, under 29v not much gassing happens with these batteries. Even that day when I pushed them to 31v there was no venting, and the temperature had only barely climbed high enough for me to notice with the back of my hand against the battery...
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries
    CALLD wrote: »
    There seems to be so many different strategies out there when it comes to charging. The equalization charge really makes my head hurt when I think about it. I've now been told 30v is too high for my batteries, but then at the same time people elsewhere talk about periodically charging to 32 or even 34 volts to equalize the battery. I have never ever done that because I fear I may just cook them to death. I once took them to 31volts after a very deep discharge. In the beginning I used to have it set at 29.2 volts which is the recommended voltage for calcium batteries. Two things I subsequently learnt made me up the voltage to 30v. The first thing was temperature, my battery room is quite cold at this time of year and the temperature sensor on my charge controller doesn't help much because it just warms up to the temperature of the charge controller and not the battery so I disabled it. The second is that generally cycling voltages should be higher than once-off recharge voltages especially when the time for recharging is short as is the case in winter. I maybe guessing a bit here but what can I do when everyone has a slightly different opinion? I have noticed though that on cloudier days when the voltage doesn't quite reach 30v, perhaps only 28 that the capacity of the battery isn't really that much different. So I will heed the warnings about 30v and set it back lower, maybe to 29.6v. I do know that they need to gas to mix the electrolyte, under 29v not much gassing happens with these batteries. Even that day when I pushed them to 31v there was no venting, and the temperature had only barely climbed high enough for me to notice with the back of my hand against the battery...

    I actually don't know if AGM batteries need to mix electrolyte, since it is 'held in place' in the absorbed glass mat. Most AGM batteries are not meant to be Equalized. A few with specific instructions are, I think Concord lifeline(?) are... Might check with your manufacturer. Some have very specific instruction for equalizing, very controller amount of current, Might not be appropriate for a standard charge controller.

    BTW - very cold temps effect the capacity of batteries, I don't know about AGM's but flooded batteries loss 30% of their capacity around 0 degrees Fahrenheit.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Kw/h in vs Kw/h out of batteries

    Typically--"Equalization" if AGM is just to hold the Absorb Voltage for XX extra minutes (no elevated charging voltage).

    Concorde/Lifeline does allow elevated corrective equalization voltage--But it is (as I understand) only used if you think you have sulfation/low capacity issues ("fix" a failing battery).

    questions about conditioning/equalizing charge for AGM sun extender battery.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Kw/h in vs Kw/h out of batteries

    AGM's do not suffer from any noticeable stratification effects but they are affected by cold because it's the same chemical process and the lower temperatures slow it down.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries
    AGM's do not suffer from any noticeable stratification effects

    Not so: http://forum.solar-electric.com/showthread.php?p=137202#post137202

    In many large AGM installations, the AGM batteries, if tall, are their sides (usually on racks) to mitigate the effects of stratification.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Kw/h in vs Kw/h out of batteries
    vtmaps wrote: »
    Not so: http://forum.solar-electric.com/showthread.php?p=137202#post137202

    In many large AGM installations, the AGM batteries, if tall, are their sides (usually on racks) to mitigate the effects of stratification.

    --vtMaps

    Yes, so.
    Read my post properly and understand it in context.
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries
    CALLD wrote: »
    There seems to be so many different strategies out there when it comes to charging.

    Each bank does differ but at the core of it, there are only a few real chemistry variations, and more or less an established three stage constant voltage regime for each. It just takes a bit of homework to determine these values for your bank. If you are lucky and you have a switched on manufacturer they will provide charge specs for RE use. If not its usually a matter of taking what specs they do provide and merging them with the chemistry defaults. For AGM something like 28.4 - 28.8 are usual absorb, and for float, 27.0- 27.4. The silver is a bit of a curve ball, but all AGM batterys (except TPPL) use calcium as an additive as opposed to anitmony in FLA. Like i and others said your setpoints seem high. You do want to charge a battery, but you also dont want to errode the grids, or burn up excessive recombinant catylyst from too high a setpoints.
    The equalization charge really makes my head hurt when I think about it. I've now been told 30v is too high for my batteries, but then at the same time people elsewhere talk about periodically charging to 32 or even 34 volts to equalize the battery.

    I doubt it. The only packs that require those sort of voltages are flooded cells with thick plates, eg surrette. Do that to an AGM and youll get thermal runaway and popped vents.
    I have never ever done that because I fear I may just cook them to death. I once took them to 31volts after a very deep discharge. In the beginning I used to have it set at 29.2 volts which is the recommended voltage for calcium batteries. Two things I subsequently learnt made me up the voltage to 30v. The first thing was temperature, my battery room is quite cold at this time of year and the temperature sensor on my charge controller doesn't help much because it just warms up to the temperature of the charge controller and not the battery so I disabled it.

    If your primary charging source, (and your backup) doesnt properly temp compensate, then you have rubbish, and should put it in the appropriate container. This requires an external battery sensor and ALL decent controllers have one, and the ability to program the correct coefficient for your bank. FOr AGMs its usually a bit lower than for FLA, around 3 or 4 mV per *C off 25*C.
    The second is that generally cycling voltages should be higher than once-off recharge voltages especially when the time for recharging is short as is the case in winter. I maybe guessing a bit here but what can I do when everyone has a slightly different opinion? I have noticed though that on cloudier days when the voltage doesn't quite reach 30v, perhaps only 28 that the capacity of the battery isn't really that much different.

    See above, RE use is a bit of a mixture of cycle and standby, but its closer to cycle in nature in my view. In winter i do daily absorbs for the reason you state, and in summer only every 5 days. In winter there isnt the hours in the day to be charging at float voltage, and you are right it takes longer at lower setpoint. But this isnt a reason to hammer your bank.
    So I will heed the warnings about 30v and set it back lower, maybe to 29.6v. I do know that they need to gas to mix the electrolyte, under 29v not much gassing happens with these batteries. Even that day when I pushed them to 31v there was no venting, and the temperature had only barely climbed high enough for me to notice with the back of my hand against the battery...

    The only way to detect venting, is to weigh the batterys before and after.

    The easiest way to keep things stirred up in AGMs is to keep the charge rates up. Its the view here that the oft recomended 5-13% of C(20) charge rate is too low for AGMs, which will happily accept 20%. A particular trap there is larger arrays, small packs, which often are charged by mid morning and never see the full charge rate. Been there done that.

    BTW, its more common to find AGM cells in 2v, and hence its easy to detect cell imbalanced cell voltages. Once a quarter log cell voltages at rest. Anything outside 50mV or so might be cause for an extended absorb. Long floats while hard on teh pack do tend to keep these balances in check.

    Good luck, AGMs do make you scratch your head at times thats for sure, too much too little etc. See you at the lithium store for the next pack... maybe.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Alaska Man
    Alaska Man Solar Expert Posts: 252 ✭✭
    Re: Kw/h in vs Kw/h out of batteries

    25 Kwh!?!?!......... that's huge for off grid.

    anything over 4Kwh is to big in my opinion. saving energy and increasing efficiency of my appliances is at the top of my list.

    You could Bulk Charge with your genny and let the solar array top them off. I make sure my bank is charged 100% once a week.Most of the time we run between 75% and 95% as read by the Trimetric. That means if I have to run my genny it's only for a few hours in the morning and then only on cloudy days. If your battery is fairly new I have found that my bank has gotten better performance at two years old than when it was new.

    Of course my loads a 1/8th of yours. If I used 3Kwh in a 24 hour period I'd be b!tching at someone.
  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    Re: Kw/h in vs Kw/h out of batteries
    Alaska Man wrote: »
    25 Kwh!?!?!......... that's huge for off grid.

    anything over 4Kwh is to big in my opinion. saving energy and increasing efficiency of my appliances is at the top of my list.

    You could Bulk Charge with your genny and let the solar array top them off. I make sure my bank is charged 100% once a week.Most of the time we run between 75% and 95% as read by the Trimetric. That means if I have to run my genny it's only for a few hours in the morning and then only on cloudy days. If your battery is fairly new I have found that my bank has gotten better performance at two years old than when it was new.

    Of course my loads a 1/8th of yours. If I used 3Kwh in a 24 hour period I'd be b!tching at someone.

    I suppose that is matter of opinion, like how long a piece of string is. It comes down to ambition though. Why do we need solar panels? The grid is always cheaper than an off grid system. Even if you don't have a grid, a generator is always a cheaper option. I have never seen a remote construction contractor opting to use solar panels instead of a big diesel generator, even when it's a big project likely to take several years to completion. We use solar for a number of reasons in places that don't offer rebates like they do in the USA. In my instance it's because I don't want the noise of a generator. I have access to reliable and affordable grid power, but wanted to have insurance against possible blackouts at first so I bought a big UPS and some batteries. I then realized that the expensive. UPS setup was just sitting there most of the time doing absolutely nothing waiting for a power cut that may never occur. The obvious thing was to add PV and make some use of it. It's also a case of "Doing our bit to cut the carbon footprint". Wanting a 25kw/h per day system is an ambitious dream, but one day when I win the lottery it will be done! By then my demand for power will have increased substantially too, so all efforts to become more efficient will likely be offset by expansion. Perhaps this should have been in the other thread called "why we live off grid"
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Kw/h in vs Kw/h out of batteries
    Alaska Man wrote: »
    25 Kwh!?!?!......... that's huge for off grid.
    Anything over 4Kwh is to big in my opinion.
    That's very true in the typical off-grid world. The vast majority of us cannot begin to imagine a 25 Kwh/day off-grid consumption rate.
    But I guess if someone has the money and wants to do it, it can be done, no matter how expensive and impractical it may be, or appear to be.
  • jcheil
    jcheil Solar Expert Posts: 722 ✭✭✭
    Re: Kw/h in vs Kw/h out of batteries
    That's very true in the typical off-grid world. The vast majority of us cannot begin to imagine a 25 Kwh/day off-grid consumption rate.
    But I guess if someone has the money and wants to do it, it can be done, no matter how expensive and impractical it may be, or appear to be.

    You are correct in that statement, it all depends on the person and their lifestyle.

    I for example, LOVE being off-grid mostly because I like the country, the isolation and the "peace". However, I am still a working man (software developer) so I "need" a significant amount of computer devices, routers, servers, etc to be here with me all which consume more than the average amount of power. That may seem "impracticable" for many people but a necessity for me in order to stay employed.

    I also I ENJOY all the little "extras" I have in life (which I "could" do without but "choose" to have) such as a swimming pool, central AC (mini-splits), 7.1 Surround Sound in my living room and a 60" TV. So that is why I decided to bite the bullet (a $30k bullet) and install a much larger system than most. I just wish I had listed to people (many from here) many years ago and just did it all at once instead of "re-buying" stuff 3 times. It would have saved me a ton of money in the end.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html