Charging time from solar looks straightforward until weather and efficiency enter the picture. The simple version is battery capacity divided by effective solar wattage, but that only works if you define effective wattage realistically.
A 200W panel is not a 200W panel all day. Sun angle, cloud cover, wiring losses and battery charging behavior all reduce practical output. That is why most field-ready estimates are built around peak sun hours and system efficiency rather than nameplate wattage alone.
This is also why daily production often matters more than one continuous charging-time number. In real trips, you are almost always charging in blocks across a day, not in one perfect uninterrupted session.