Battery sizer http://www.wholesalesolar.com/solar-information/battery-bank-sizing
Example:
60watt light for 4 hours , 20watt radio for 2 hours, 100watt laptop for 1 hour
To get a very rough idea of the real value with system loses, multiply by 1.5. This will help account for decreasing performance when temperature increases.
Use the formula total daily energy usage is (60Wx4h)+(20Wx2h)+(100Wx1h) = (620*1.5)= 930 Watt-hours
Batteries are used in 12volts , 24volts, 48volts
Take the 930Watthours/ 12 or 24 or 48 = 930/12= 78AH Battery