300 watt solar panels and 600ah battery bank only lasting one day?

Ideally, it would be best to measure the Watt*Hours (or kWH) per day with a Kill-a-Watt type meter:

https://www.solar-electric.com/kiacpomome.html

But, using your numbers, we can estimate your needs:

• 77 Watts * 20 minutes * 1/60 minutes per hour * 24 hours per day = 616 WH per day (a bit on the "low side" for typical small fridge)

Warmer days, freezing ice, opening door multiple times per day, putting warm food in to cool, etc. all push the numbers up. For the following, assume 850 WH per day:

• 850 WH per day * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge (for longer battery life) * 1/12 volt battery bank = 333  Amp*Hour @ 12 volt "nominal" battery bank

Note that this is for a refrigerator only load--If you have other loads, then you need to account for them too. Lets say you want 1,850 WH per day, then the battery size would be around:

• 1,850 WH per day * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge (for longer battery life) * 1/12 volt battery bank = 725  Amp*Hour @ 12 volt "nominal" battery bank

Note, for various reasons, I would suggest that no more than ~800 AH battery bank. And that you are close to a good fit for a 24 volt battery bank.

Sizing the solar array... Two calculations. One based on 5% to 13% rate of charge for the battery bank (5% works for weekend/summer cabins. 10%+ works better for full time off grid power system).

• 725 AH * 14.5 volts charging * 1/0.77 panel and charge controller deratings * 0.05 rate of charge = 683 Watt minimum array
• 725 AH * 14.5 volts charging * 1/0.77 panel and charge controller deratings * 0.10 rate of charge = 1,365 Watt array nominal
• 725 AH * 14.5 volts charging * 1/0.77 panel and charge controller deratings * 0.13 rate of charge = 1,774 Watt array "cost effective" maximum

And then there is sizing the array for the daily amount of power you want to use and the amount of sun you will get. Assuming a fixed array:

Tupelo
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 41° angle from vertical:
(Optimal winter settings)

Jan	Feb	Mar	Apr	May	Jun
3.53	3.76	4.48	4.87	4.62	4.54
Jul	Aug	Sep	Oct	Nov	Dec
4.67	4.72	4.98	4.91	3.92	3.40

Assuming you don't use the system much in winter (or use a genset to help), toss the bottom three months. November at 3.92 hours of sun per day for "break even" solar usage (may need to use genset some if bad weather):

• 1,859 WG per day * 1/0.52 AC off grid system eff * 1/3.92 hours of sun per day = 908 Watt array minimum

850 WH per day for refrigerator plus another 1,000 WH for the rest of your loads should be a pretty useful system. If your other loads are not much, you could get down to ~500 WH per day for those other loads and run the calculations again.

Lots of guesswork here--But should give you an idea of what it would take to run your loads and the math if you want to run the numbers again with your assumptions.

-Bill