Here’s the deal with solar. The panel wattage needed depends on battery capacity. Battery capacity needed depends on power usage. Most TTS leave the dealer with a single 75 or 80 amp hour marine battery, which is the minimal battery needed for emergency braking. It’s the cheapest choice possible.
That battery can be well supplied by 100 watts of solar assuming full sunshine and that you use no more than the 40 amp hours the battery can supply without causing premature damage. Frankly, most of us would be better served with 2 such batteries, or better yet, a 100 amp hour lithium battery. These would call for 200 watts of solar, and better yet even more to allow for cloudy days or shady campsites.
As with everything else, YMMV. Just like with computer RAM and towing horsepower, more is better, limited mostly by cost. I am in the process of going solar myself, with 200 watts of panel and a single 75 AH battery (37.5 AH usable). By the start of camping season, I’m planning to have 400 watts and at least 100 AH usable battery.
