Our off grid solar system is ready to go online. This video shows how we sized our battery bank to meet our needs. We used the Rolls s-1450 batteries for our system.
Here is the formula to calculate the proper size for the system. Our goal was to not notice a huge difference in available power when the house is built. We wanted to not have to always worry about power.
This formula is based on using 28kW a day. (We use about 21kW to 24kW)
28kW per day (about 840kW per month)
DC input voltage = 48v
28000 / 48 = 583 amp h/day
583 * 1.25 (for inverter loss and battery efficiency) = 728 AH/day
728 amp hr/day * 1 day of autonomy = 1456 amp hr
1456/0.8 (battery discharge) = 1820 amp hr
1820*1.59 lead acid battery temperature multiplier = 2894 optimum battery size in amp/hours
2894/1124 amp/hours (for the S-1450s) = 2.6
2 (number of parallel strings required)* 24 (2v*24=48v)= 48 x S-1450
Here is a link to the batteries: http://www.rollsbattery.com/wp-content/uploads/batteries/S-1450.pdf