Hello friends,
Once upon a time I was talking with someone knowledgeable, I don't remember who, about sizing the system for our bus. They said I should have 1 amp-hour of batteries for each 1 watt of solar panels. Thats what I did. I have 1580 amp-hours of batteries and 1580 watts of solar panels. Giving me 790 usable amp-hours of batteries. I have been using this system for about 6 years. On a perfect day the batteries are full at about 1:30. On a cloudy day they are full by about 4:00. On dark rainy days I can last a week or two by cutting back on usage. Then I have to run my 120 amp charger. Thats a 10cf electric refrigerator, doing a load of laundry, baking bread (bread machine), Computers, tv, killer music, ham radio, satellite internet, electric coffee maker, toaster, etc, etc. In the afternoon when the batteries are full I use my electrical tools, skill saw, drills, grinders, etc. and other heavy loads without touching the batteries. I spent many years with too few panels so My goal here was not to have to think about electricity if the sun was shinning. So far so good. We also have a 400 watt Air-X.
I'm not sure if there is a correct formula. BUT, the weak link is always the ability to recharge. So get as many panels as you can afford. I wouldn't worry about ending up with too many panels. They cost way too much for that to happen.
Good Luck
Jerry
'75 Crown Coach
Edited DamonHD amp --> amp-hour