Solar Battery Setup is draining faster and faster

hmong2017

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)

Photowhit

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.

...and yes a battery can read high voltage, but have very minimal capacity!

Estragon

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.

littleharbor2

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.

westbranch

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....

hmong2017

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.

...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.

Estragon

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.

Photowhit

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.

Raj174

 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

BB.

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