"Daily AC load" is usually in Kilo watt hours.

Other than that it showed the same results I got
for sizing my system by hand, so seems to work OK.
Could use a few more inputs & outputs. Maybe estimated
array size in watts? Maybe hours of light per day?
Once you start, you can't stop :-)

Once you get to the calculator, go on to the bottom of the first page and click the Study It button, then scroll to the bottom of the second page and click the first Calculate It button.

At the top of that page, enter the total watt hours per day. Not kilowatt hours! This is actual watt hours.

The calculator will calculate the number of batteries required, but keep in mind, it is set up so that you never pull the battery bank below 80% (80% full, not 80% used) so as to keep them healthy for a long time. I adjusted it one time to do 50%, but that is a pretty deep discharge. I set it back to 80% and that will cover the few extreme situations that happen. For example, if you have your bank sized for a 2-no-sun-day size and you get 3 no-sun days once in a while. You're still ok, long as it don't happen a whole lot.

It also calculates the number of solar panels it would require to keep thos batteries charged and supply all the power needed.

Charging losses, inverter losses, temparature correction losses and etc. are all calculated in.

To try out the calculator, go to:
http://dsjscrd.gotdns.com/calc

Enjoy!

Otherwise you will need a back up generator and my advice would be to use that daily at your peak usage time, usually evening load. This is because you gain the most from your Re at lower battery volts (arguable I know) but if you are runing a generator let it run to meet a load without further loadng the batteries.

The further you run you batteries down the greater the harm for a given period of time, now it is all a compromise but......