But, why not choose a system that has "automatic RS".
In other words, loss of AC power initiates RS.
Then whatever your main disconnect is = RS switch....for ALL arrays.
Stick a label next to it saying "RAPID SHUTDOWN SWITCH". Done.
The OP didn't bring it up storage, but it is one reason why you might need a shutoff means other than shutting off the service in general. In that case, the solar remains energized by design after the service de-energizes, and therefore would need a separate shutoff.
Also consider just how first responders will shut off the AC power of the service as a whole. It can be the service disconnect, but existing/grandfathered situations may not make that easy. The brand new requirement for outside service disconnects on dwellings makes this convenient, but an existing main service disconnect might be deep in the main house's basement. This would mean adding an outdoor initiation device of some form or another, for a system in general, to meet the intent of rapid shutdown. Utilities in my area commonly require an outside-mounted disconnect, which doubles as rapid shutdown initiation, so that is another way to fulfill the need. In concept, a first responder could pull the meter to cut the power to the property, but I wouldn't count on an AHJ approving this as a rapid shutdown initiation method.
On a system with multiple buildings, the desired points of interconnection might be scattered throughout the property, i.e. locally at each building's respective subpanel. It could be appealing to give each building its own rapid shutdown initiation device without connecting anything between buildings, had the NEC not required them to be grouped. Requiring them to be grouped could mean the need to bring the systems all the way back to the main house, rather than interconnecting locally within the building that hosts the array. One way to economize this, is to only bring a control circuit back to the grouped E-stop switches on the main house, that activate shunt-trip breakers in the detached buildings.
