I have an RV with 3 100w Renogy solar panels in parallel, connected to a 100/20 victron charge controller. Wanted to add 3 additional 100w Renogy panels this summer. Planned on rewiring the existing 3 panels from parallel to series, then adding 3 new panels (also in series), upgrading to a 100/50 charge controller, to make a series/parallel configuration. However, rewiring existing 3 panels to series would be a major PITA (connectors are under panels, lifting panels, cleaning up permabond, tape, brackets, etc…). Would it make more sense to just buy an additional 100/20 charge controller, put the 3 new panels on the new controller, and connect both the old and the new charge controller to the same battery bank (2x100Ah Battleborn Batteries)?
On a good day, you should get at least 1.5kWh of charge from a 300w array. It would make sense to add a second array that will allow you to charge the 200Ah which would be approx 2.8kWh from 0%.
The parallel array will perform better with shading. If you series connect them a tiny amount of shade on one panel will drop the entire output to the current that one panel can produce.
Keeping them in parallel should be fine you might only be around 5A ea so a total of 15A into the controller.
If shading is not an issue you can make the decision to series connect or parallel the new panels.
The 100/20 is small compared to the 150/100. 2 of them will not take much room and also give you better performance monitoring and redundancy.