High voltage Low Amps-Watts

I should add... The charge controller will only draw current if the batteries need charging and/or you have DC loads turned on when the sun is up. I am sure you are comfortable with running solar charge controller(s). It was working as you expected before "it failed".

And--The "classic reset". Disconnect solar panels, disconnect battery bank. Wait 5 minutes. Connect battery bank first, then connect solar panels.

The other "digital" issue--You can try clearing memory/reset to factory defaults. Rebooting, then set to your needs. Sometimes digital memory gets corrupted and the controller will get confused. Reseting memory and programming again can clear these faults.

-Bill "just to cover the bases" B.

Solar panels are usually thought of as a "solar battery"--A battery being a device that supplies (for example) constant voltage @ 12 VDC regardless of load (or 10.5 to 15.0 volts roughly).

In reality, solar panels are a current source. They supply (for example 100 watts / 17.5 Volts Vmp = ) 5.7 Amps (under full noon time sun) from zero volts to ~Vmp*0.8 (17.5v*0.8 temperature derating= ) 14 volts, declining to zero amps @ Voc (voltage open circuit).

Vmp and Voc are temperature dependent. The Voc/Vmp specs are at 25C/77F under factory test conditions (a few seconds of "artificial sunlight). In "real life", the cells are something closer to 60C/140F under full Texas sun on a hot/windless day. At hot temperatures, Vmp and Voc fall. Conversely, under cold temperatures Voc and Vmp rise.

Note: Imp and Isc are also temperature dependent--They rise as temperature of the cell increases--However it is something like 1/5 or 1/10 of the amount of fall in Voc/Vmp--So is usually ignored.

A couple of nice graphs on how solar panels "work":

https://forum.solar-electric.com/discussion/comment/359660#Comment_359660

And just to double check the sizing of your system using our rules of thumbs for generic system design:

Suggest battery support 2 days of "no sun" and 50% max planned discharge (for longer life):

• 6.5 Amps * 24 hours per day = 156 AH per day
• 6.5 Amps * 12 volts = 78 Watt load
• 156 AH * 12 VDC = 1,872 Watt*Hours per day (@ 12 VDC)
• 156 AH per day * 2 day storage * 1/0.5 max discharge = 624 AH

So, your 710 AH bank is sized nicely.

Next to size the solar array... Two calculations. One based on battery bank capacity (bigger banks need more solar panels). And the second based on hours of sun per day and size of loads:

Charging, 5% rate of charge can work for weekend/sunny weather systems. 10%-13% rate of charge is recommended for full time off grid systems (most flooded cell lead acid battery mfg. recommend 10% minimim rate of charge). Over 13% rate of charge, recommend a remote battery temperature sensor (hot batteries have reduced charging voltages--Can get thermal run away).

• 710 AH * 14.5 volts charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 669 Watt array minimum
• 710 AH * 14.5 volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 1,337 Watt array nominal
  
• 710 AH * 14.5 volts charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 1,738 Watt array "typical" cost effective maximum

700-800 Watts of solar is on the "low side" for a full time off grid system.

Next, sizing array based on your location (hours of "noon time equivalent" sun per day) and your loads. Guessing that you are near Corpus Christi, Texas. Fixed array, tilted to ~28 degrees from horizontal, facing south:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Corpus Christi
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 62° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.60	4.13	4.84	5.07	5.34	5.59
Jul	Aug	Sep	Oct	Nov	Dec
5.81	5.65	5.32	5.00	4.12	3.54

And that you run the system 12 months a year... That would give us an array of:

• 1,872 WH per day * 1/0.61 off grid DC power system eff * 1/3.54 hours of sun per day = 867 Watt array "break even for December"

The above is based on long term average weather conditions (something like 20 years)... For a system design, suggest only using 65% to 50% for "base loads" (loads that you must run every day)--Especially if you do not have a backup genset and cannot have a loss of power:

• 867 Watt "break even December" array * 1//0.65 base load fudge factor = 1,334 Watt array @ 65% derate
• 867 Watt "break even December" array * 1//0.50 base load fudge factor = 1,734 Watt array @ 50% derate
  

So based on a myriad of SWAGs... I would suggest that you could justify a 1,334 to 1,734 Watt array for a reliable/off grid system with little need for backup power. Note solar numbers are not that "accurate"--Typically any number within 10% is pretty much "the same". Carried "extra" digits so you can follow my math and not to get cumulative roundoff errors.

Suggested MPPT controller sizing:

• 1,334 Watt array * 0.77 panel+controller derating * 1/14.5 volts charging = 71 Amp minimum suggested MPPT controller
• 1,734 Watt array * 0.77 panel+controller derating * 1/14.5 volts charging = 92 Amp minimum suggested MPPT controller

The 77% derating is based on hot solar panels in typical weather conditions. You will rarely have "clipping" events (a few hours a year?) on very cool/clear days. (quality MPPT controllers can safely and reliably "clip" their output current to not exceed their ratings).

And that an 800 Watt array is right on the edge of not working reliably for December.

Note--If you have some version of Lead Acid batteries--Try to keep them cool (shaded, ventilated, ground bunker, etc.). Hot batteries tend to age much faster. The rule of thumb is for every 10C over 25C (or 18F over 77F), the battery aging is 2x faster (or 1/2 life). Lithium Ion (LiFePO4 or similar) would be great for hot climates (Li Ion batteries cannot be charged/discharged if below ~40F--Lead Acid is better in cold/sub freezing climates).

Any corrections or questions?

-Bill

Welcome to the forum Krawczukj and thank you for your kind words.

You are more than welcome to start your own discussion about your system or general questions--Or if you have information, feel free to jump in and help other folks with answers for their systems.

Being that far north--Adding a genset adds costs, freezing weather, and other issues to the mix for winter running. Details matter with solar/electrical systems!

Take care,
-Bill