We have a site with a substantial solar array that is owned by the building owner.  The LEED Credit form requires uploaded supporting documentation as follows: "upload confirmation of renewable attribute ownership if the on-site renewable energy system is owned by the building owner"

Will a simple letter from the owner suffice?  Proving a PPA or contractual arrangement seems easier to confirm, but it is unclear exactly what is being asked for here. Yes, the REC's are owned, but how do we need to prove it?  Is there a way to establish ownership of the REC's without any additional cost?  The system hasn't been commissioned yet and isn't generating any energy, but this is a construction credit so I cant imagine having to prove generation quite yet.  Designed output is already available.  Any input would be greatly appreciated!