If the battery is driving a load and there isn't solar to
charge and the battery works for several days without getting
a charge due to the local storm or snow on the array or heavy over cast.
I got less than 4 kWh for 4 days - 2 were in the 1kWh out of my 6.5KWP
array. On good days I'm 20 to 35 KWH per day. And if off the grid, (I'm
not), I'm running lights, computer and Air controls. And a monster
fish tank with several pumps, heater, cooler, and fan-pumps.
Therefore at night I draw from the utility and many days as well.
I can make for 50-70 % on really hot summer days and buy 50-30% power
from the grid.
Martin