If I can butt in here, my understanding is the charge controller only controls the amps coming from the panel. It does not make more amps on its own to deliver to the battery, just helps control the flow so batteries are charged in the best and most efficient way possible (instead of hooking the panels directly to the batteries). In most cases a folding panel, or 100 or 120 watt rooftop panel, will realistically only produce around 7amps optimum (meaning when aimed for maximum exposure to the sun in a clear sky), so a 10 or 15 amp PWM charge controller is enough.
IF you think you're going to have a larger array of panels, or add more panels later and a lot more amps being delivered to the charge controller, then getting a 20 or 30 amp controller will prevent having to get a larger amp controller later to handle the larger input. When you go even bigger, then an MPPT controller is worthwhile, as it tweaks more from your panels.
That's my understanding of it all, at least.
Here's a piece I wrote about folding vs mounted panels that may be helpful, in the thread:
On Trail Camp Solar Power
and a piece on solar set-ups and how they're wired in the thread:
Let's See Your Solar Setups for Camping
You can read more about charge controller types here:
Which solar charge controller: PWM or MPPT?
Let us know what you end up doing, as the info may be helpful to others.
I don't pretend to be an end-all expert, but I love experimenting with off-grid and self-sustainable set-ups, so if there's anything I can help shed more light on, ask away. If it's beyond my experience or knowledge, I'll be the first to admit it.
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