Hey, Noob here, pls help :)

velo27

I have recently bought a reasonable little off grid system. 24v - 2x340w panels, 30a charge controller, 1700w inverter with 2x270ah batteries AGM...

 I went from in summer the batteries being 100% charged by 10am, running deep freeze 24/7, washing machine a couple of times a day and the water pump and barely moving the SOC till the sun went down, then the deep freeze would maybe use 10-15% soc overnight.

After running the batteries very low one night (thought the charge controllers job was to prevent this), got awaken by inverter beeping, I'm now getting very erratic readings from the charge controller, soc dropping and rising 40-50% within the space of an hour.

I'm confused as to whether the charge controller is giving false data, seems unrealistic, the batteries are stuffed or this is normal for autumn? 
>
The contoller is set GEL and I have AGM, but don't see a setting for AGM, the guy who i bought them off, says the controller was preset and no need to change anything...

Any help appreciated 

mcgivor

Welcome to the forum 

The controller SOC  indications are voltage based, thus merely an indication of something they cannot accurately measure.
The deep discharge will likely take many hours to recover the lost capacity, this needs to be done ASAP to prevent the lost capacity becoming permanent through sulfation, even if it requires disconnecting all loads to do so.

mike95490

Are you in the southern hemisphere and moving into winter ?   Shorter charging days, longer nights to drain the batteries.

But you MUST get the batteries charged back up before they fail.

Charge controllers control charging.   LVD ( Low Voltage Disconnects ) are often built into the inverter to protect it.   Some charge controllers have "LOAD" terminals for small lighting loads

BB.

You probably simply pulled more power/energy from the solar+battery bank than it could supply over time... You may have had enough sun in summer to squeak by--But now going into winter, not so much.

For example (guessing), you freezer probably draws ~1,000 WattHours per day. And maybe another 500-1,000 WH per day for washer (again pure guess).

You can use an AC power meter to measure your Watt*Hours per day energy usage... I think this is the type you want:

https://www.amazon.com.au/Digital-Wattmeter-Analyzer-Electronic-Automatic/dp/B07PH8RD5Y

Now--Look at your system... First the battery bank... Normally for Lead Acid batteries, suggest using 25% of battery capacity per day and for 50% max discharge (longer battery life):

• 540 AH * 12 volt battery bank * 0.85 AC inverter eff * 1/2 days storage * 0.50 max planned discharge = 1,377 WH per day (over night) from battery bank

Say you want to draw 2,000 WH per day from your system (~1,000 WH "over night" and cloudy weather. And another 1,000 WH for washing clothes during the day).  Fixed array facing north around Auckland NZ:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Auckland
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 53° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
5.80	5.54	5.10	4.27	3.47	3.14
Jul	Aug	Sep	Oct	Nov	Dec
3.39	3.82	4.63	4.92	5.41	5.57

• 2,000 WH per day * 1/0.52 off grid AC system eff * 1/4.27 hours of sun per day (April) = 901 Watt "break even" array for April
• 2,000 WH per day * 1/0.52 off grid AC system eff * 1/680 Watt array = 5.66 hours of sun per day, minimum "break even" usage with existing array

Using the (pure guess) numbers, you can see how the model shows that if you run 2,000 WH per day loads (freezer+washer+pump) could work during summer--But as you head into fall/winter/spring, your system does not have enough solar panels to keep up with your loads.

Normally--Break the loads into two types... First is your "base loads"--Those loads you need to run every day (freezer+lights). The second are your optional loads--Only run when it is sunny (washing clothes). For base loads, highly suggest that you have ~2x more solar array than daily usage to ensure that you don't need to run the genset very often, and/or have your food thaw.

For example

• 1,000 WH per day freezer * 2 base load fudge factor * 1/0.52 off grid system eff  * 1/3.14 hours June sun (dead of winter) = 1,225 Watt array suggested nominal size
  

Lots of guesses and suggestions...  But it does look like your system is simply under sized... And without "real" energy usage numbers, it could be worst (1,500 WH per day for freezer, or even more power for washer+water pump). (I guessed you have a DC Water pump for a caravan--They do not use very much energy typically).

-Bill

Photowhit

You have received good information already!

I'd suggest you are just new to living off solar electric systems.

So you already understand that you ran the storage down one night, so you will/should be looking to shift that load to a sunny day with the system fully charged. Looks like every thing worked properly! A charge controller can sometimes be used to disconnect small DC loads when they are drawing your system down, but an inverter should ALWAYS be connected directly to the battery bank.

As others have said, you should be looking to returning your battery bank to fully charged quickly. Does your inverter incorporate a charger? If it does you could run a generator to bring the system back up. You don't want to remain low for too long as this will cause sulfating. Do you know the age of your AGM batteries? Batteries lose capacity later in life.

Doing a few loads of laundry a day sounds like you have a large family. Family can be load themselves...lol. Lots of little loads, phones, laptops can add up. Since you acquired the system have you added to the loads? brought a desktop computer, or additional fans. These all need to be accounted for...