A new section added to the 2014 edition of NFPA 58 are Automated Cylinder Exchange Stations. These stations are unmanned, automatic computer controlled cabinets that allow individuals to purchase and exchange propane cylinders. This new added benefit allows stores to make sales throughout the day when their store is not otherwise occupied. I have not had the opportunity to see any of them in practice yet, but I have been able to see demo's of them in various locations. Below this post is a picture from the NFPA 58 Handbook of one of these installations.
-Eric Nette, P.E.