I have a saved search and I want to store the results at the end of each day... rather than an email being sent everyday and having to use that, is there a way to automatically store the details of this within documents and files as an excel or csv file?

As long as you can store your Excel file on OneDrive or SharePoint Celigo's CloudExtend Excel Analytics for NetSuite will let you put that search on a schedule directly from a Microsoft add-in that resides in Excel. You could set the schedule to run once a day (or more) so your file will always be up to date without you ever having to touch it again.

Scheduled script + save the file in the file cabinet

Schedule script load the search result greater than 0, load the file and append the new data to it. Beware of 10 MB limitation if data is huge.