Here is a simple flow chart.
Budget-->Energy Audit-->Battery bank size-->number of watts-->PWM or MPPT. What ever type of controller is chosen, make sure it has adjustable set points and a temperature probe that is on the battery.
One rule of thumb is between 60 and 150 watts of panels per 100 amp-hours of storage. The smaller the battery bank the higher the wattage needed (per 100 amp-hours). Here is a link to the rather special spreadsheet which includes an energy audit, that N8GS has created to help size solar battery charging systems!
Solar Spread Sheet N8GSFor a nice explanation of solar, try this link:
Golden rules of solarThis is what is balanced and best for twin twelve volt batteries.
As it often doesn't cost a dime more to do this, I think it is worth the trouble.
If you wish to understand the "why" surf here:
correctly interconnecting multiple twelve volt batteriesOthers may say it doesn't matter--but unless there is a compelling reason to not optimize charging and discharging why not do it the best possible way?
Here is a video of 3 twelve volt batteries that have been wired in an unbalanced manner for 2 years. They have been equalized. The test shows how CCA has been adversely affected.
unbalanced for 2 years