In Power BI for Office 365, you can schedule the data in the Excel data model (Power Pivot) to be refreshed daily or weekly. This is one of the additional pieces of functionality available when the Excel workbook has been uploaded to your Power BI App in Office 365.
However, as of this writing (February 2014), scheduled data refresh for data loaded to Power Pivot via Power Query is not yet supported. It will be supported - it just didn't make it in time for the initial release.
If you see an error such as this...
The following system error occurred: Class not registered. The provider 'Microsoft Mashup.OleDb.1' is not registered.
...that tells you that Power Query is present in the Excel file and so data refresh cannot yet be scheduled.
More information about which data sources can be refreshed automatically can be found here: