Solar Battery Setup is draining faster and faster

hmong2017
hmong2017 Registered Users Posts: 39 ✭✭
in Solar Beginners Corner #1
I've had this setup for a little over half a year now. Just three days ago I realize that the batteries aren't lasting me like every other normal nights. I use the exactly same electronics which is a Medium Size energy Star Saver Freezer Chest  and 4 LED light bulbs plus a plastic Fan that runs all night.

Now the batteries will be drained from 80% down to 30% 2 or 3 hours before sunrise. It usually lasted me all night until sunrise. 

Setup Description:
- 8 of 260 WATT 24V Solar panels connected in parallel
- Combine box with breakers  
- MPPT 80A Charge Controller 
- 8 of 200Ah 12V Deep Cycle Batteries (Mighty Max Brand) two into one to get 24V-200Ah thereafter parallel to get 800Ah
- 24V Power Inverter Modified Sine Waves 5000Watt 

What I've tried so far:
- Reduce my energy consumption by unplugging the fan and turn off the lights at night. 
- Check all breakers in the combine box
- run battery tests (all good)


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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #2
    How are you determining the State of Charge 80%, 30%...? I'm guessing AGM batteries since that's what popped up when I searched.

    What array size and what has your weather been like?

    Is your chest freezer using more power because it's in hot ambient temperatures?

    They appear to be AGM batteries, When you say you've tested them, How was that done? Just checking for voltage? ...or did you load test them? Load testing is applying a large load say 100 amp and see if the batteries hold voltage. (They will, of course drop, but then hold a voltage bad batteries will just keep dropping) They make testers just for this purpose, you want the battery disconnected from the system when testing.
    Image result for battery load tester
    ...and yes a battery can read high voltage, but have very minimal capacity!




    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.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #3
    260w panels may not work well in parallel charging a 24v bank, especially in warm/hot weather. You may be a bit underpanelled for an 800ah bank to begin with, and too-low input voltage may be making it worse.

    You may want to check the actual voltage at the controller input terminals in good sun - if it's much under high 30s, this could be part of the problem. Mppt controllers need some headroom above absorb charging voltage (~28v?) from the panels, typically about 30% higher, so 36ish volts at the input terminals. If it's less, putting the panels in series strings of 2 panels may help.
    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
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,095 ✭✭✭✭✭
    #4
    4 strings of batteries is not optimal, How are they wired?  (picture?) AGM batteries have very low resistance. Wired poorly, in parallel will add varied resistance causing premature failure of some, at first, then all batteries in the end.

    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,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #5
    Please post the  make, model, etc of the PV's... I am suspicious of their output not being high enough especially in a hot summer.as they may be GT Panels and may need to be series oriented....

     
    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
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  • hmong2017
    hmong2017 Registered Users Posts: 39 ✭✭
    #6
    Photowhit said:
    How are you determining the State of Charge 80%, 30%...? I'm guessing AGM batteries since that's what popped up when I searched.

    What array size and what has your weather been like?

    Is your chest freezer using more power because it's in hot ambient temperatures?

    They appear to be AGM batteries, When you say you've tested them, How was that done? Just checking for voltage? ...or did you load test them? Load testing is applying a large load say 100 amp and see if the batteries hold voltage. (They will, of course drop, but then hold a voltage bad batteries will just keep dropping) They make testers just for this purpose, you want the battery disconnected from the system when testing.
    Image result for battery load tester
    ...and yes a battery can read high voltage, but have very minimal capacity!




    I used that kind of battery tester. It's been really hot over 103F and the sun is in direct to the panels all day about 12 hours.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #7
    In that heat, you could be losing a couple of volts Vmp. Assuming 60cell panels in parallel, which are marginal for mppt charging a 24v nominal bank, the controller may not be able to charge properly even with long daylight hours.
    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
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #8
    Estragon said:
    In that heat, you could be losing a couple of volts Vmp. Assuming 60cell panels in parallel, which are marginal for mppt charging a 24v nominal bank, the controller may not be able to charge properly even with long daylight hours.
    Nice catch, even 72 in parallel is not a good setup for an MPPT type charge controller.

    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.
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    edited July 2018 #9
     Several forum members have expressed concern that the 60 cell panels wired in parallel will not charge your 24 volt battery properly, I also agree and suggest rewiring them two in series by 4 in parallel. 

    Rick
    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,599 admin
    #10
    By the way, I don't think we know which brand/model of MPPT 80 Amp Solar Charge controller you have... Just make sure that Vpanel input is higher than Voc-array-cold (maximum array voltage).

    2series x 2parallel would be (roughly) Voc-cold-array ~ 96 volts (in sub freezing climate).

    Want to ensure you do not damage your electronics/charge controller. Most (US brand) 80 Amp charge controllers should be able manage Vpanel~140-150 VDC minimum.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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