What is the difference between 30a and 10a solar controller

Compare if there is any difference in how the controller treats the battery. Is the more expensive one more adjustable? An unadjustable controller is as clever as a car that goes one speed.

The only mistake I made was maxing out my controller. Now upgrading will cost a bundle.

I wouldn't think one was more efficient than the other but one may have more features than the other.

For PWM controllers, you get your "expected amps" from the array and then multiply the amps by 1.25 and get the nearest sized controller to that, going higher if practical.

What is my "expected amps"? Take the rated Isc (do NOT use the lower Imp figure!) off the panel labels and add them up if in parallel. You will get Isc in full sun at times and even more sometimes so that is what the 1.25 allows for.

EG, you have two 130w panels with Isc of 8.2a each in parallel, so your "expected amps" is 16.4a times 1.25 = 20.5a So in this case you could get a 20a controller. If the answer came to say 23a IMO get a 25 or 30a to stay above the margin of 1.25 times. (US NEC guide for that 1.25)

If you have MPPT, then your controller likely will clip the amps at its rating so you can ignore the 1.25 part. Also the new Bogart PWM has an amp limiter ISTR, but that is an exception for PWMs AFAIK.

Assuming the 10a is adequate for the panels provided... the 30a allows for system expansion where the 10a probably not. All other things equal that is all there is.

I was just wondering the same thing. Zamp Solar (for example) has two "kits," one with a 10a and one a 30a with the same wattage panels (150 I think). I thought it was strange to offer the same panels with different controllers.

Assuming the 10A controller is appropriate for the setup being sold and these are both for the same voltage batteries, the main advantage of the larger controller would be that you could add additional panels in the future without having to upgrade the controller. One or the other might also be a better/nicer/more efficient controller, but of course there's no way to tell if that's true or not without further details.