Material you will find on powerpivot will tell you that powerpivot is specifically designed to be used in conjunction with a data base for maximum efficiency. Access is a database and powerpivot is not. Power pivot that exists in Excel was for sure not designed for use as a database. In fact excel and access were designed to be buddies but access did not take off in popularity the way excel did. I do believe that powerpivot will be more popular than access this is likely even now.