Wiring 12V nominal panels in series and using a PWM controller with a 24V battery bank may be more efficient than a parallel wiring scheme.
When wiring in series, shade on one panel will limit the harvest current to the lowest of the multiple panels. When wiring in parallel, shade on one panel will limit the harvest current to the aggregate of the multiple panels.
Controller efficiencies and power handling differ. While one controller may accept and efficiently deliver the most current with higher voltage, another may produce less power with higher voltage, comparatively. In the most general terms, smaller RV sized controllers will gain in heat with higher voltages. Higher heat means lost power and may effect longevity.
For expandability, sizing a controller to handle the higher voltages of the initial system wired in series, may require a controller replacement if controller input voltage is exceeded by the addition of more panels wired in series.
IMO, wire sizing is a non-issue for nearly all RV solar installations. If the difference in size is based on cost, an owner could change to a lesser quality toilet tissue and recover the cost difference between barely adequate wire and larger cable within a month. YTPMMV.
For residential installations where series mounted strings are typical, there is a lot of sense in using micro inverters like the
Enphase system.
Since the system will operate without the current drop when a module is lost//shaded/malfunctioning, it makes for good sustainability. I'm reading that the durability of some micro inverters is in question and replacement costs are significant.
