Panels are rated in amps and volts which is bettery way to view their output. A MPPT controller will take 100% of the output from the panel and not simply clip the voltage down to a level the battery can take (14.5v). I balanced the amp hours consumed per day with the amps per hour produced by the panel(s).
If you consume 40 AH per night and want to replace it during the day and have two 5-amp panels you get 10 amps per hour and it will take about 4 hours of full sunlight to recharge the battery or battery bank.
I used 5 hours as the average amount of daylight available throughout the year to decide on the capacity needed to charge for my system. This allows for sub optimum conditions like clouds, angle of the sun, winter, dirt on the panels, etc.
A good place to start is with a charge monitor like the TriMetric to determine accurately how much charge you are consuming and can calculate what will be needed to restore the batteries to 100%.
