newbie looking for reassurance!

rednosepitrednosepit Registered Users Posts: 11 ✭✭
Hello, group! Ive been reading and learning from these forums for quite some time and I'm excited to make my first post!
I've been off grid for 3 1/2 years and I've successfully killed my first battery bank, hopefully through no fault of my own.
Heres my specs first.
location: Southern middle Tennessee
pv array: (6) 100 watt renogy monocrystalline panels, Wired in series
charge controller: Renogy mppt tracer (20 amp)
existing battery bank: (6) duracell ultra agm 12 volt 155 ah batteries wired in 3 parallel strings to get 465 ah @ 24v (these batteries are considerd U.P.S. batteries)
inverter: go-power pure sine wave 24v inverter (1500 watts)
My consumption average is 1 kilowatt hour per day.

I noticed my battery voltage had been looking a little on the low side several months ago. Checking individual batteries with a volt meter I originally found 2 dead batteries in the string. So I simply removed those two batteries from the bank and reduced my energy consumption substancially as well. Fast forward 2 months and I found myself in the same predicament with 2 more dead batteries in the bank. Again, I removed them from the bank and left one 155 ah 2 battery connection in place, and turned the inverter off. One week later after I checked on the set up and with minimal load at night (13 watt led light on) the voltage dropped low enough to trigger the lvd on the inverter and it shut down. So  now all 6 of my batteries are junk.
My charge controller display averages 50-60 volts  at 10 amps input from my array during the day so I feel comfortable that my system is working properly. And I also understand that I have effectively achieved over 1200 cycles from my battery bank.
My questions are: Does my setup look correct as in does anything stand out as a battery killer?
Am I correct that agm batteries do not have the cycle life as traditional flooded batteries?
Is 3.5 years too short of a lifespan on this battery bank?

I'm considering purchasing 8 trojan t105 batteries as my replacement bank which will be wired in two strings of 4 giving me 450 ah @ 24v.
 I will build a housing for them that will vent outdoors as they will be kept indoors.
All variables aside, what would the average cycle count of these t105s be compared to the previous batteries?
Is there anything I should be doing differently to help keep my bank alive?
I'm excited to read the responses from the pros!!!!!!
Thank you so much in advance!

Comments

  • BB.BB. Super Moderators, Administrators Posts: 28,773 admin
    Welcome to the forum RedNose!

    3.5 years from a UPS rated battery (rated more for float charging and using when a power failure occurses)is probably not that bad, especially if they have been kept on the warm side (75F or warmer).

    I always like to start with your loads and design a "balanced system" that will give you good life and meet your expectations.

    So, lets say your needs are 1 kWH per day. That is not a large load (generally lighting, cell phone charging, RV water pump, Laptop Computer for a cabin). The typical "optimum" battery bank would be 2 days of storage (bad weather/no sun) and 50% maximum discharge. I am going to start this as a 12 volt battery bank design, because I think your are better off with with a low power/high efficiency 12 volt 300 Watt AC inverter vs a larger inverter (which uses more power just to turn on... Typically 6 Watts for a smaller inverter, closer to 10-20 Watts just to run your larger inverter). 24 volt would be OK too if you need a larger inverter for short/heavy loads (Microwave, power tools, etc.)...
    • 1,000 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/12 volt battery bank = 392 AH @ 12 volt battery bank
    2x 6 volt batteries @ 200 AH in series (12 volts @ 200 AH) times 2 parallel strings for a 12 volt @ 400 AH battery bank and 6x golf cart batteries (~$400 worth of batteries).

    Next, sizing the solar array. Two sets of calculations, the first based on the size of the battery bank. Larger battery banks, need more charging current. 5% rate of charge is good for weekend/summer usage. 10%-13%+ is better for full time off grid.
    • 400 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 377 Watt array minimum
    • 400 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 753 Watt array nominal
    • 400 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 979 Watt array typical "cost effective" maximum
    Your ~600 Watt array is a bit on the small side for a daily use system and a 24 volt @ 465 AH battery bank. A full time 10% rate of charge would have been:
    • 465 AH * 29.0 volts charging * 1/0.77 panel+controller derate * 0.10 rate of charge = 1,751 Watt array nominal
    This is an issue with "too large" of battery bank. You need a large solar array for optimum (10%) rate of charge. In the olden days, people where told to add batteries to increase the output of their system. Back then batteries where cheap and solar panels were expensive. It is now solar panels that are cheap and batteries that are expensive... And the better way to "up size" an off grid solar system is to add solar panels (which are actually generating electricity, not adding to storage).

    And then sizing the array based on your loads and location... 1 kWH load, fixed array facing, best average harvest angle year round:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Murfreesboro
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 54° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    3.20
     
    3.65
     
    4.54
     
    5.00
     
    5.08
     
    5.13
     
    JulAugSepOctNovDec
    5.21
     
    5.11
     
    5.14
     
    4.81
     
    3.68
     
    3.09
     
    Let's say you use system year round, and use a genset in the winter when needed:
    • 1,000 WattHours per day * 1/0.52 off grid system eff * 1/3.09 (Dec average) = 622 Watt array "break even" December
    So, your 600 Watt array is just about the smallest you would want (based on load). If your AC inverter drew 15 watts "just being turned on" and was left running 24 hours per day (15w*24h=) is 360 WH per day just for the inverter...

    Anyway, using a MorningStar 300 Watt PSW AC inverter would draw 6 watts, and if you use the auto sleep mode (inverter sleeps unless there is >6 Watt AC load), and you would use a fraction of this.

    Lots of guesswork here. Energy usage is a highly personal set of choices. For example, if you need a minimum of 1,000 WH per day in winter and don't want to use a genset, you might want 2x larger solar array (1,244 Watt array) (better than adding batteries).

    https://www.solar-electric.com/morningstar-si-300-115v-ul-inverter.html

    Then there is the sizing of the Charge Controller... Generally, you like a higher voltage battery bank because you get "extra capacity" for your charge controller "for free":
    • 20 amps * 14.5 volt charging * 1/0.77 array+controller derating = 377 Watt "maximum MPPT" array @ 12 volt batt bus
    • 20 amps * 29.0 volt charging * 1/0.77 array+controller derating = 753 Watt "maximum MPPT" array @ 24 volt batt bus
    So, here I am suggesting that you go with a lower voltage battery bank to get a "more optimal" AC inverter for your smaller loads. But, the problem is that you need a much larger MPPT solar charger (and more expensive) to output that much current into a 12 volt bank:
    • 1,244 Watt array * 0.77 panel+controller deratign * 1/14.5 volts charging = 66 Amp minimum rated MPPT charge controller
    I will stop typing here, because you probably have lots of questions and corrections for me/us.

    The above is just some starting points for discussions. None of the above is the "only correct answer". Lots of things to play with here.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 3,413 ✭✭✭✭✭
    IMHO, 3.5yrs/1200 cycles isn't terrible for AGMs designed for standby(UPS) use.

    600w of panels likely produces ~450w in decent sun, which should cover your 1kwh/day load (if no shading issues), but may be a bit low for catching up after a run of gloomy weather.  Do you have a generator or other means of charging?

    At 50%  SOC, a 450ah bank is down 450x24x0.5=5400wh.  In winter, average daily insolation (used Nashville) is ~3hrs, so the array might produce 1500wh/day on average.  With a 1000wh load, that only leaves ~500wh to catch up with the 5400wh deficit.  Absent a generator to help, this could leave the bank in a low SOC for longer than it really should.

    For a full-time off-grid system, something on the order of a 10% rate of charge capacity is reasonable, so for a 10800wh bank, that would be 1080 ÷.75(panel derate) = 1440w array.

    For a weekend cabin type use, where the pv can catch up with no loads, 600w could work ok, but for more full-time I'd want generator to supplement charging and/or more solar.

    A reasonable life expectancy for T105s would be ~5yrs, but would be much shorter with problems like chronic undercharging or leaving at <70% SOC for many days at a time.
    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
  • rednosepitrednosepit Registered Users Posts: 11 ✭✭
    Wow! Thank you so much for the information packed reply! I will have to read it several times to absorb it all!

    I now must add that I do in fact have 2 additional 100 watt panels in storage that i can add to my array that will bring it to 800w.

    My charge controller is an mppt controller. the maximum allowable input is 20 amps and 100 volts. I think i conveyed that incorrectly originally. I purchased the 2 extra panels as a "just in case" measure for future upgrades which I now see I will need to utilize.

    I just looked up the specs on my 24v inverter.
    no load current draw is .65 amps and power saving mode is .05 amps.
    So if I'm calculating correctly that would bring my daily consumption from the inverter to 15.6 amps times 24 volts which brings me to 374 watt hours per day!! wow!

    You are spot on with my loads being led lighting, an rv water pump, cell phone and laptop charging, etc. My only other major load is a converted deep freezer which I've averaged with a kill-a-watt meter to consume 250 watt hours per day. My on demand water pump pulls 120 watts while running and the freezer pulls 110 watts with a good spike upon start up. I sized my inverter for the use of the extremely occasional power tool use and 1000 watt microwave use.

    I'm a little foggy about the down sizing of my bank voltage to 12 volt. I was under the impression that the higher bank voltage was more efficient.  I do understand i could effectively get my needed ah with less batteries at 12 volts but at the trade off of having to purchase another extremely expensive inverter.

  • rednosepitrednosepit Registered Users Posts: 11 ✭✭
    Having read your reply a few more times I understand further what you are saying about down sizing my inverter for more efficiency.
    I will have to re read my manual for my charge controller, but i seem to remember that the capabilities were cut basically in half when used on a 12 volt setup vs. 24 volt and I think that is why I ultimately decided on 24 volt when I built the system.
    Again, thank you so much for your insight! I cant wait for more info!!!!!
  • EstragonEstragon Registered Users Posts: 3,413 ✭✭✭✭✭
    With fridge and pump loads, I'd stay with 24v.  The 300w 12v inverter Bill mentioned is nice (I use one), but won't likely start the fridge, and maybe not the pump.  With your existing inverter you can likely save a fair bit by unplugging chargers etc at night so it can use the search/power saver mode.

    To use the extra pair of panels, you'll need get a second charge controller.

    You might consider a single string bank for [email protected] = 5400wh.  Using 1000wh/day and min 50% that gives you a couple days no sun.  Use the cash saved on the second string towards a small inverter generator?
    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
  • rednosepitrednosepit Registered Users Posts: 11 ✭✭
    thanks estragon! I do in fact have a standby generator and an automatic 24v charger for "just in case"
    As far as adding the extra charge controller. I was under the impression that adding the 2 additional panels would still keep me under the 100 volt, 20 amp threshhold that my charge controller is rated for. I would have to re- crunch those numbers but i seem to remember the tech support at renogy telling me that in 24 volt mode the charge controller would accept 800 watts of pv.
    I will also mention that this cabin is in fact mostly a weekend cabin. since it is vacant all day and only utilized for a couple hours at night maybe 3 days a week. The only constant draw is the freezer and the inverter itself.
    Another question... My inverter does in fact have a power save mode. Would it be harmful to put it in power save mode constantly? That way it would only come on when the freezer kicks on?
    I'm loving all the knowledgeable input!!!!


  • EstragonEstragon Registered Users Posts: 3,413 ✭✭✭✭✭
    A 20a controller might "accept" 800w of panel, in the sense that it can be overpanelled to that extent.  800w ÷24v charging = 33a, or ~50% more than the controller rating.  Realistically, 800w rated pv could put out 600w (25a) or so in "normal" operating conditions, but the controller is limited as a 20a load, so the last potential 5a won't be drawn by the controller.  Depending on ambient temps etc, the controller may cut current drawn further as it heats up.

    We sometimes overpanel because pv is pretty cheap, and overpanelling lets us get some useful charge in overcast conditions.  There's a limit to how far you can go with that though, which is where the 800w "accept" number comes in.

    In your case, you're underpanelled, so you want all the amps you can get.  Adding a second 20a controller would split the 800w into two 400w arrays, with each outputting ~400x.75÷24= ~12a each.  If a cloud goes by and there's more power to be had, you get it.

    Putting the inverter into search mode shouldn't normally be a problem, although a couple of things to watch for. 

    A microwave led etc that doesn't draw enough power to bring the inverter out of search mode, but gets enough power from the search probe to light will flash at the search probe rate (typically a few seconds).  Best to unplug or switch off such things.  At best, they're annoying.

    The other is things like fridge electronics, which can sometimes get messed up with stuff like defrost cycles.  I have a simple fridge that does fine with inverter search, but some of the more complicated ones can have issues.
    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
  • rednosepitrednosepit Registered Users Posts: 11 ✭✭
    great insight!!! everything is normally unplugged accept for the freezer.. which is a standard deep freezer with the thermostat played with to run fridge temps. I'm going to play with some numbers tonight. Thank you both for your help so far.Please keep it coming!!!!
  • mike95490mike95490 Solar Expert Posts: 8,194 ✭✭✭✭✭
    I'd suggest checking the voltage label of the panels and when you add panels, split them into 2 strings of 4 - IF the Voc of 4 in series, is less than 100Vdc  You use the Voc for your voltage limit, and generally add 20% of the voltage for cold weather, since cold panels produce higher voltage.

    I concur with keeping the system at 24V, the fridge needs the benefit of a higher voltage on the DC side of the inverter.   Try looking for a high effiecency inverter in the 800 -1200W range - you need some good surge capability for starting the AC motors.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 28,773 admin
    If you can run your inverter in search mode/power save with the freezer/refrigerator--Then you should be fine. Just run the inverter full on when you are there.

    If you are running the freezer/fridge while you are not there, then having a larger battery bank and solar array is a good thing. More or less, the weakness of off grid solar power systems is that if you do not have enough sun (bad weather) or something else goes wrong (somebody forgot to turn everything off when you left, something "broke", etc.), the battery bank is the major item "at risk".

    Lead acid batteries (and most rechargeable batteries) do not like to be taken to zero volts (and hate "reverse charging"). Winter weather and unattended loads are frequently good ways of "murdering" your battery bank (and losing the food in the fridge).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rednosepitrednosepit Registered Users Posts: 11 ✭✭
    Lots of great insight here again! Thank you all so much! If I remember correctly I do think I would have had to wire 2 strings  of 4 panels in parallel to utilize the full 800 watt capacity of my charge controller. I just hot home for the evening so I'm going to dig up my paper work. I must say I'm absolutely blown away by the wealth of knowledge you fine folks are flooding me with!. And I honestly feel lucky to have been living off grid for this long without a hiccup until now! Looking forward to conversing more!
  • littleharbor2littleharbor2 Solar Expert Posts: 1,231 ✭✭✭✭
    Considering the cost of a new set of batteries you really ought to consider the minor additional cost of a 40 - 45 amp MPPT charge controller. Your controller is actually limited to 20 amps, OUTPUT.  You need higher current to keep your battery bank happy and healthy.

    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.

  • rednosepitrednosepit Registered Users Posts: 11 ✭✭
    i believe the collective suggestion is definitely a charge controller upgrade, along with additional panels which fortunately I have 2 of on stash. What do you, fine professionals, suggest as far as brand?
    As far as the battery bank is concerned... Am I still making a sound decision by purchasing 8 trojan t-105s for a 450 ah 24v bank?

  • rednosepitrednosepit Registered Users Posts: 11 ✭✭
  • EstragonEstragon Registered Users Posts: 3,413 ✭✭✭✭✭
    If trojans are available locally at a reasonable price, they'd be a good choice IMHO.  Decent T105 (GC sized) batteries are widely avaikable though, so if the trojans are a sunstantial premium or need to be shipped in, I'd consider going with a local alternative.

    In general, GC type batteries can work well.  Being flooded, you can (and should) monitor SG, which is much better than voltage alone for catching impending problems.

    The Renogy controllers seem to work for those using them, and there's a lot to be said for going with a controller brand you're already familiar with.
    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
  • rednosepitrednosepit Registered Users Posts: 11 ✭✭
    Good morning, experts! Did a bunch of spec reading and number crunching last night! To my pleasant surprise, my current charge controller is in fact a 40 amp and not a 20 amp charger!!!!  I apparently forgot that over the course of 3 years.  Lucky me!
     I plan to keep my current mppt charge controller in place, add 2 more 100 watt panels to my array.. 2 parallel strings of 4 panels each,  bringing my voc to 90 volts max and 800 watts, and I will also leave my inverter in power save mode while I'm away. 
    The Trojan t-105 batteries are available to me locally for 125 dollars a piece. I'm going to call the place today and see if their are any alternatives in stock. I like the idea of using the Trojans based on their reputation. I also have a wholesale account through interstate batteries. Their gc2 equivalent is 129 my cost a piece.. but I noticed they offer a 2300 series golf cart battery that boasts 240 ah for 10 dollars more. That would bring my bank up to 480 ah. Am I pushing the limits bringing my ah up any higher than my original  465 ah? I'm a little concerned with dropping down to 450 ah from 465ah. I know it's only 15 ah but that's 365 wh!!! That's basically what my inverter was consuming in a day. What do you, fine folks think?
  • EstragonEstragon Registered Users Posts: 3,413 ✭✭✭✭✭
    Local Trojans at $125 sounds pretty reasonable to me.  IIRC, some Trojans want a bit higher charging voltages than other flooded, but this isn't likely an issue for your application.  It's mainly if the bank is cool/cold and/or the controller isn't adjustable.  

    Whichever you decide on, I'd check voltage in case they've sat around without a periodic top-up charge.  A good dealer shouldn't let that happen, but...

    A <10% capacity difference isn't really material, as identical batteries could vary by about that anyway.
    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
  • BB.BB. Super Moderators, Administrators Posts: 28,773 admin
    Note that 4x Vmp~18 volt panels is getting a bit high for Voc-cold... If you have cool winters, Voc-array-cold may exceed the 100 vdc maximum input voltage for your controller (very hard freezes could get upwards of 108 VDC)...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rednosepitrednosepit Registered Users Posts: 11 ✭✭
    BB. said:
    Note that 4x Vmp~18 volt panels is getting a bit high for Voc-cold... If you have cool winters, Voc-array-cold may exceed the 100 vdc maximum input voltage for your controller (very hard freezes could get upwards of 108 VDC)...

    -Bill

    my panels are actually 12 volt panels. The voc listed on them says 22.5 volts. Is it possible that on freezing days the panels could go over their rated open circuit voltage?
  • EstragonEstragon Registered Users Posts: 3,413 ✭✭✭✭✭
    A string of 4 would be ~90v, but that's at ~room temp.  In freezing temps, that may be getting too close for comfort on a 100v max controller.

    What happens is on a cold morning (lows are often right around dawn) the voltage rises in the weak morning light, and peaks before the sun hits the panels to warm them.  Even with little current in the weak light, the controller can be damaged with the overvoltage, and many controllers will log the event to void warranty.

    To check, find the record low ever recorded at your location, and the voltage-temperature adjustment coefficient for your panels.  If too high, a smaller string size or higher voltage controller will be needed.
    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
  • BB.BB. Super Moderators, Administrators Posts: 28,773 admin
    Oh yes...

    Voc-std is at ~77F. Anything below 77F increases the output voltage (Voc, Vmp

    Panels run "hot" when under direct sunlight. However, first thing in the morning, freezing temps, and clear sky, the cells will start out at ambient temperature (or even a bit lower) until they get heated by the sun.

    The switching transistors in the charge controller only care about "overvoltage", even if the there is hardly even any direct sun on the panels.

    Using the Midnite tool (kind of "busy" for answering this question).... Voc=22.5 volts, 4x in series, 10 degrees F, get 101.2 Volts calculated for Voc-array-10F operation.

    http://www.midnitesolar.com/sizingTool/index.php

    Some controllers will log the maximum array voltage and if it exceeds the rated input, they will invalidate the warranty.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rednosepitrednosepit Registered Users Posts: 11 ✭✭
    Man, They sure make it hard to get the "advertised" 1000 watts @ 24v capability of that charge controller lol
  • mountainmanmountainman Registered Users Posts: 166 ✭✭
    Yes with 100 watt panels it is. You have to either do 2 in series and 5 in parallel with a combiner box and or fuses. Or buy 1 panel and do 3s 3p again with a combiner. Imo 100 watt panels and a 100 volt cc works better with smaller like rv 12 volt 450 amp hour 600 watt systems. For 1000 watt arrays 4 250 watt panels work best with 100 volt cc.Trogen recommend normal 10 to 13% 20% max charge rate. 45 amps at 10% with your 450 @24 bank up to 90 amps max. As estragon said your way under paneled. 450×29÷.77×.10=1694 watts at 10% charge rate.
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 [email protected] volts 300 watt psw inverter. 2 kw genny. Iota 45.
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