Within the qvw, write a macro that will export charts to excel. Configure a document trigger that will fire the macro OnPostReload. Reload the document using a batch file (not the server scheduler). The batch file would have a line similar to this: c:\program files\qlikview\qv.exe -R d:\application.qvw
the batch file can then be scheduled to run via windows task scheduler.
when reloading using qlikview server or publisher, macro execution is ignored.. that's why you have to reload using batch mode.