This calculator I got off the web for free. Credit to the author.
It starts by allowing you to capture your watts per item and how long you want the device/s to be on at night. This is rather crucial to know.
Then taking into account factors daylight hours for your area, losses, age of batteries, DOD, how many days backup you need, it calculates your battery bank requirements, gives you the minimum inverter size you need, as well as how many panels you would, depending on your preferred make and model, need.
It is good to then sit and change values like system volts, and see the impact.
It is a good guideline.