Hello. I just bought a Bluetti SP200S solar panel. I have two of the old SP200 solar panels. Would appreciate if someone would tell me if this SP200S will be compatible with the old SP200 panels?
Nobody will be able to give you a specific answer. There are too many factors involved and every use case is different. Just try it out for yourself and let us know the result. 
Hi @QuirkyQuest the panels need to be identical to work properly the panels have different ocv and amps so either go with the single or but another pv200 or pv200s.
They’re not really compatible to mix, even though both are 200W they have slightly different voltage/current specs so combining them can reduce performance. Best to use matching panels together or run them separately instead of mixing.